Tesi: "Root traits and exudation"

1

Guyonnet, Julien. "Effet de la stratégie de gestion des ressources des plantes sur l’investissement dans l’exsudation racinaire, et les conséquences sur les communautés bactériennes." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1008.

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Abstract (sommario):

L'exsudation racinaire est connue pour avoir une influence sur le fonctionnement des communautés microbiennes, en particulier celles impliquées dans le cycle de l'azote (Haichar et al, 2012). Elle est liée à la physiologie de la plante, cette dernière pouvant être évaluée via les traits fonctionnels végétaux, permettant une classification des plantes en fonction de leur performance dans leur environnement. Ainsi, nous pouvons distinguer d'une part les espèces exploitatrices, avec une efficience de la photosynthèse élevée et une acquisition rapide de l'azote dans les sols, et d'autre part les plantes conservatrices, possédant des caractéristiques contraires (Aerts & Chapin, 1999) et des plantes intermédiaires dont les caractéristiques sont intermediaires.L'objectif de ces travaux de thèse est de déterminer l'influence de la stratégie de gestion des ressources de 6 poacées, réparties le long d'un gradient de stratégie de gestion des ressources, allant de stratégies conservatrices (Sesleria caerulea et Festuca paniculata), intermédiaires (Antoxanthum odoratum, Bromus erectus) à des stratégies exploitatrices (Dactylis glomerata et Trisetum flavescens), sur la diversité et le fonctionnement des communautés totales et dénitrifiantes. I) Dans un premier temps nous avons étudié le lien entre la stratégie de gestion de ressources des plantes et la quantité d'exsudats racinaires dans le sol adhérent aux racines (SAR). Nous avons ensuite déterminé l'influence de la quantité d'exsudats racinaire sur les activités microbiennes potentielles des communautés microbiennes du SAR (respiration et dénitrification potentielles), puis par une approche ADN-SIP (Stable Isotope Probing) couplée à du séquençage haut-débit, l'influence de l'exsudation racinaire sur la structure et la diversité des communautés bactérienne colonisant le SAR et le système racinaire. II) Dans un second temps, nous avons étudié le lien entre la stratégie de gestion des ressources des plantes et la nature des exsudats racinaires libérés au niveau du SAR et présents dans les extraits racinaires en analysant les profils des métabolites primaires chez Festuca paniculata, Bromus erectus et Dactylis glomerata, représentant respectivement des stratégies de gestion des ressources conservative, intermédiaire et exploitatrice Root exudation is known to influence microbial communities functioning, in particular those involve in nitrogen cycle. (Haichar et al, 2012). It’s linked to plant physiology, which can be evaluated with functional traits, allowing a plant distribution in function of their performance in their environment. Thus, we can distinguish competitive species, with higher photosynthetic capacity and rapid rates of N acquisition, conservative species with the opposite characteristics (Aerts & Chapin, 1999) and intermediate plants, with intermediate characteristics.The objective of this work is to determinate the influence of nutrient management strategiy of 6 poaceae, along a strategies gradient from conservative strategy (Sesleria caerulea and Festuca paniculata), intermediate (Antoxanthum odoratum and Bromus erectus) to competitive strategy (Dactylis glomerata and Trisetum flavescens), on diversity and functioning of total and denitrifying communities.I) Firstly, we studied the link between the plant nutrient management strategy and the root exudates quantity in the root adhering soil (RAS). Then, we determined the influence of the rate of root exudation on potential microbial activities (respiration and denitrification), and with a DNA-SIP (Stable Isotope Probing) approach coupled to high-throughput sequencing, the influence of root exudation on the bacterial structure and diversity of communities colonizing the RAS and the root system. II) Secondly, we studied the link between the plant nutrient management strategy and the nature of molecules exuded in RAS and present in root extracts by analyzing primary metabolites profile to Festuca paniculata, Bromus erectus and Dactylis glomerata, respectively a conservative, an intermediate and a competitive plant. Then, we determined the influence of primary metabolites profile of each plant on semi-real denitrification of communities colonizing RAS of plants. III) Finally, an mRNA-SIP approach is in progress to determine the influence of exuded metabolites on active bacterial communities functioning and the expression of genes involved in denitrification process in RAS and root system. Our results show an influence of the nutrient management strategy on the rate of carbon exudation, the competitive plants exuding more than conservatives ones

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2

Delamare, Jeremy. "Analyses de deux stratégies d’acclimatation à un stress thermique intense reposant sur une thermo-sensibilisation ou une sensibilisation médiée par des bactéries PGPR chez le colza et la caméline." Electronic Thesis or Diss., Normandie, 2023. http://www.theses.fr/2023NORMC243.

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Abstract (sommario):

Le changement climatique auquel nous sommes confrontés est caractérisé notamment par une modification des profils thermiques en termes d’intensité, de durée et de répétition des vagues de chaleur. Ces vagues de chaleur surviennent lors des stades reproducteurs des plantes qui sont également les plus critiques pour l’élaboration des composantes de rendement et des critères de qualité grainière des grandes cultures. Les oléagineux tels que le colza et la caméline sont des espèces particulièrement impactées par le stress thermique, causant de fortes pertes de rendement et une diminution de la qualité grainière. Ainsi, il est nécessaire d’identifier de nouveaux leviers d’acclimatation, telles que des stratégies reposant sur l’acclimatation des plantes. Le thermopriming consistant à préparer les plantes à répondre de façon plus rapide, efficace, intense et/ou sensible à un stress thermique par une exposition préalable à un stress de même nature pourrait permettre d’acclimater les plantes qui mettraient en place des mécanismes de réponses adaptés. L’inoculation des plantes avec des PGPR est un levier d’acclimatation de plus en plus étudié, qui permet de limiter les impacts du stress thermique. Cependant, bien que ces deux types de stratégies d’acclimatation soient principalement étudiés pour limiter l’impact des stress sur le développement des parties aériennes et sur le rendement, peu d’études se sont intéressées à leurs effets sur la morphologie et les fonctions racinaires comme l’exsudation racinaire. Dans le cadre de cette thèse, nous avons analysé chez le colza et la caméline (i) d’une part les effets d’une augmentation graduelle de température précédant un stress thermique, sur le rendement et la qualité grainière et sur la morphologie et l’exsudation racinaire et (ii) d’autre part les effets de l’inoculation de deux Pseudomonas présentant des activités PGPR afin de limiter les impacts du stress thermique sur le rendement et la qualité grainière. De plus, afin de connaitre l’impact du stress thermique et de l’inoculation de PGPR (combinés ou non) sur la plante et la rhizosphère associée, les effets de ces traitements ont été étudiés sur l’exsudation racinaire, l’allocation de carbone (C) dans le système sol-plante, les traits morphologiques racinaires et les communautés microbiennes du sol. Nos résultats ont montré que le colza et la caméline présentent des stratégies contrastées quant à leur réponse au stress thermique. En effet, la caméline semble réagir au stress en augmentant son investissement dans les parties racinaires, en améliorant qualitativement son exsudation et en stimulant l’activité des communautés microbiennes à l’inverse du colza qui semble plutôt endurer le stress. De plus, ces deux espèces ont réagi différemment aux deux stratégies d’acclimatation appliquées. En effet, chez le colza, le thermopriming a permis de diminuer l’exsudation en C et de maintenir son rendement et sa qualité grainière alors qu’il a eu un impact plus négatif sur l’exsudation et la morphologie racinaire chez la caméline. L’inoculation des PGPR est une stratégie d’acclimatation qui tend à limiter les effets du stress thermique sur le rendement et la qualité grainière chez le colza. Cependant, les PGPR agissent comme un puits supplémentaire chez le colza impactant son développement, son exsudation ainsi que l’activité et la composition des communautés microbienne. A l’inverse, la caméline est peu impactée par l’apport de PGPR et semble par conséquent piloter les interactions plante/bactéries plutôt que les subir. En résumé, ces leviers d’acclimatation semblent démontrer des effets bénéfiques pour les plantes. De plus, il pourrait être intéressant d’intégrer les effets de la sélection variétale sur les stratégies de réponses des plantes face au stress et notamment la variabilité des fonctions racinaires et des interactions avec la rhizosphère, à la lumière de la sélection variétale différentiellement subie par le colza et la caméline The on-going climate changes that we are facing are characterized in particular by modifications of temperature profiles in terms of intensity, duration and repetition of heat waves. These heat waves occur during the reproductive stages of the crops, which are also the most critical for seed yield elaboration and grain quality in crops. Oleaginous species such as rapeseed and camelina, are species particularly impacted by heat stress that cause yield penalties and a lower seed quality. Therefore, to cope with heat stress, it has become necessary to identify new acclimation levers that differ avec genetic and agronomic levers, such as strategies based on plants acclimation. Thermopriming which consist in priming the plants in a way to help them respond more rapidly, effectively, intensively and/or sensitively to heat by a prior exposure of a stress of the same nature could allow the plants to acclimate and develop appropriate response mechanisms. The plant inoculation with Plant Growth Promoting Rhizobacteria (PGPR)-type bacteria is also an acclimation lever increasingly studied, that limit the impacts of abiotic stress such as heat stress. However, although these two types of acclimation levers are mainly studied to limit stress impact on aboveground development and yield, few studies have observed their effects on root morphology and functions such as root exudation. In this thesis we analysed in rapeseed and camelina (i) the effects of a gradual increase in temperature prior a heat stress on yield and grain quality and on root morphology and exudation and (ii) the effects of inoculating two Pseudomonas with PGPR activities in order to limit the impact of heat stress on yield and grain quality. Moreover, in order to understand the impact of heat stress and PGPR inoculation (combined or not) on the plant and associated rhizosphere, the effects of these treatments were studied on root exudation, carbon (C) allocation in the soil-plant system, root morphological traits and soil microbial communities. Our results showed that rapeseed and camelina have contrasting strategies in terms of response to heat stress. Indeed, camelina seems to respond to the stress by increasing its investment to the roots thus improving the quality of exudation and stimulating the activity of microbial communities, unlike rapeseed, which seems to undergo heat stress. In addition, these two species respond differently to the two acclimation strategies applied. In rapeseed, thermopriming reduced C exudation and maintained yield and grain quality, whereas it had a more negative impact on exudation and root morphology in camelina. PGPR inoculation is an acclimation strategy that tends to limit the effects of heat stress on yield and grain quality in rapeseed. However, PGPRs act as an additional sink in rapeseed, impacting its development, exudation and the activity and composition of microbial communities in the rhizosphere. By contrast, camelina is slightly affected by the addition of PGPRs and seems to control the plant/bacteria interactions rather than be affected by them. In short, beneficial effects on plants of these acclimation levers have been evidenced. In addition, it could be interesting to integrate the effects of varietal selection on plant response strategies to stress, and in particular the variability of root functions and interactions with the rhizosphere, in the light of the varietal selection differentially undergone by rapeseed and camelina

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Plum, Sara A. "Manipulation of sources and sinks of grasses : growth, photosynthesis and root exudation." Thesis, Bangor University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389504.

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4

Roworth, Joshua David. "The characterisation of root exudation and colonisation in the rhizosphere of land plants." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:0f21602e-73c7-4470-a598-ec9f16093190.

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Abstract (sommario):

The rhizosphere of land plants is a diverse and complex environment that is critical to the life cycles of plants. Plants release photosynthetically fixed carbon into the rhizosphere that can act to solubilise nutrients, detoxify metals, and modify soil microbial communities. Within these soil microbial communities a diverse range of microbes exist, ranging from the beneficial plant growth promoting rhizobacteria to plant pathogens. These microbes must be able to effectively colonise the rhizosphere and plant rooting systems for their survival. To study root exudation and the bacterial colonisation of the roots two separate techniques were used. To study the spatial and temporal release of exudation in Oryza sativa, Zea mays, Arabidopsis thaliana, and Marchantia polymorpha, luciferase based bioreporters, which respond to plant derived carbon were used. These bioreporters based in Rhizobium leguminosarum allowed for the production of maps showing the spatial nature of exudation from plant roots, alongside changes in exudation temporally. In this work I showed that the release of the C4-Dicarboxylic acids was conserved across all plant species tested. Moreover, the release of these exudates occurred on specific rooting structures, such as lateral roots, and not across the whole rooting system. This work has shown that R. leguminosarum based bioreporters can be flexibly used across a range of different plant species. For studying the genetic basis of Azorhizobium caulinodans colonisation of the O. sativa rhizosphere, a technique known as insertion sequencing was used. This technique highlighted bacterial genes involved in rhizosphere and root colonising growth. Using these data, several interesting gene operons were identified that played a crucial role in rhizosphere growth. One example was a putative propionate catabolism operon, indicating that A. caulinodans is using plant-derived propionate as a carbon source for growth. Insertion sequencing was also used to probe the genetic basis of nitrogen fixation in A. caulinodans, here I showed that insertion sequencing was applicable to this study and could identify a number of genes involved in low nitrogen growth.

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5

Holz, Maire [Verfasser], and Andrea [Akademischer Betreuer] Carminati. "Biophysical factors controlling root exudation and rhizosphere extension / Maire Holz ; Betreuer: Andrea Carminati." Bayreuth : Universität Bayreuth, 2020. http://d-nb.info/1209196565/34.

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6

MUELLER, KEVIN E. "INVESTIGATIONS INTO THE USE OF TREES FOR PHYTOREMEDIATION OF PAH CONTAMINATED SOILS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1123258067.

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7

Rummel, Pauline Sophie [Verfasser]. "Nitrate uptake, root exudation, and litter quality - crop plant effects on denitrification and its product stoichiometry / Pauline Sophie Rummel." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2021. http://d-nb.info/1236401689/34.

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8

De, Lucchi Chiara. "Improving key root traits in sugar beet: Fusarium resistance." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3424410.

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The challenge of the twenty-first century is to produce enough food to meet population demands without extending land or damaging the environment. Combining a maximum number of desirable traits such disease resistance, greater yield, and high quality is a desirable goal for plant breeders. The development of resistant crop genotypes is essential to ensure global food security, make the plant more useful and avoid crop losses. The development of molecular markers linked to the target traits is needed to predict phenotypic variation based on genotype. Marker-Assisted Selection (MAS) can reduce costs and the time required to obtain new cultivars by comparing selection only based on phenotypic evaluation. Single nucleotide polymorphisms (SNPs) are widely used as genetic marker. Sugar beet (Beta vulgaris L.) is the second source of world sugar supply and is grown in all temperate zones. The crop is attacked by many pathogens and among these, the soil-borne fungus Fusarium oxysporum causes severe sugar beet damages. Two different formae speciales have been reported in sugar beet, F. oxysporum f. sp. betae that causes Fusarium yellows, and F. oxysporum f. sp. radicis-betae that causes Fusarium root rot. Disease symptoms are characterized by wilt and yellow leaves that normally die as the disease progresses. Internal symptoms consist of a brown or grey brown vascular discoloration and in the case of root rot, there is a back external rot in the primary root. Sugar beet varieties are susceptible to F. oxysporum, which can cause a lower root yield and reduce sugar quality. No genetic studies have been done up to now, so no genes or quantitative trait loci (QTLs) conferring resistance to F. oxysporum in sugar beet have been reported. The aims of this work were (i) to investigate the response of a wide collection of sugar beet lines to F. oxysporum f. sp. betae, (ii) to identify resistant lines suitable for future breeding efforts and (iii) to discover molecular markers linked to the Fusarium resistance that could be considered for use in marker-assisted selection (MAS) programs. The first part of the thesis is a literature review of sugar beet breeding achievements, including the discovery of monogermity and cytoplasmic-genetic male sterility (CMS) that allowed the release of hybrid varieties. The review also focused on the breeding progresses against diseases obtained with classical and molecular methods using sources of resistance from wild beets. Next-generation sequencing (NGS) technologies with the recent release of the full sugar beet genome sequence are also reported. Incorporation of genomics into conventional sugar beet breeding programs is essential to obtain important yield achievements in sugar beet. The second part was aimed at screening a wide range of sugar beet lines to identify the different effect to F. oxysporum f. sp. betae inoculation and to select resistant and susceptible lines. To achieve this, 29 sugar beet lines were screened under greenhouse conditions with two highly virulent isolates belonging to different genetic sub-groups. The third part regards an experiment conducted to evaluate the response of different sugar beet breeding germplasm to isolates of F. oxysporum f. sp. betae. In the previously tested lines, an unusual root rot was observed, normally reported in cases of infection with F. oxysporum f. sp. radicis-betae. Eight susceptible lines, from USDA-ARS (US) and UNIPD (University of Padova, Italy), were inoculated with three different isolates of F. oxysporum f. sp. betae, the causal agent of Fusarium yellows. All inoculated lines developed disease symptoms, but severe root rot was observed only in the susceptible UNIPD lines inoculated with isolates that had never caused root rot in the USDA germplasm. In this work, an unusual root rot was reported for the first time that seems to be caused not only by the isolates, but is also due to a germplasm effect. The fourth part was aimed to identify molecular SNP markers linked to the Fusarium resistance in sugar beet. A candidate gene approach was used on susceptible and resistant lines to achieve this goal. Five resistant gene analogues were screened by means of a high-resolution melting (HRM) analysis and two allelic variants, within two genes, were significantly associated to Fusarium resistance. Sanger sequencing allowed the discovery of two SNP markers linked to the resistance. These two SNPs were significantly associated with the resistance and were mapped on the exon of Bv7_171470_ojty and Bv2_043450_zhxk, respectively. Il miglioramento genetico delle piante coltivate, basato sull’esplorazione, sull’utilizzo delle risorse genetiche e sulla ricerca genomica avanzata, è prioritario per soddisfare il fabbisogno alimentare di una popolazione mondiale in costante crescita. In particolare, l’introgressione di tratti desiderabili come la resistenza alle malattie e la maggior resa produttiva è fondamentale per garantire la sicurezza alimentare a livello globale. Per accelerare il miglioramento delle piante è essenziale predire le variazioni fenotipiche sviluppando marcatori molecolari legati ai tratti in esame. La selezione assistita da marcatori molecolari può ridurre costi e tempi di ottenimento di nuove varietà rispetto alla selezione basata solo su variazioni fenotipiche. Fra i marcatori molecolari disponibili, le mutazioni di singola base (SNP) sono i più diffusi. La barbabietola da zucchero (Beta vulgaris L.) è la seconda fonte di zucchero al mondo ed è coltivata in tutte le aree temperate. La coltura è colpita da numerosi patogeni e, fra questi, il fungo Fusarium oxysporum causa severi danni. Due differenti forme speciali di Fusarium, Fusarium oxysporum f. sp. betae (Fusarium yellows) e Fusarium oxysporum f. sp. radicis-betae (Fusarium root rot) sono state identificate in barbabietola. La malattia è caratterizzata da avvizzimento e clorosi fogliare con un progressivo deperimento delle foglie, spesso seguito dalla morte dell’intera pianta. I sintomi interni consistono in una discolorazione vascolare con imbrunimento dei fasci vascolari e, nel caso di marciume radicale, è presente un caratteristico annerimento all’esterno della radice principale. Per il controllo del patogeno, l’impiego di fungicidi e le rotazioni colturali non sono efficaci. L’introgressione di geni di resistenza dal germoplasma selvatico è ritenuta la strategia principale per la difesa della coltura. Questo richiede lo sviluppo di marcatori molecolari legati ai geni di resistenza per la selezione assistita degli individui resistenti. Gli obiettivi del lavoro di tesi sono stati i seguenti: (i) valutare la risposta a Fusarium oxysporum f. sp. betae di un’ampia collezione di linee di barbabietola da zucchero (ii) identificare linee resistenti a Fusarium oxysporum da poter utilizzare in futuri programmi di miglioramento genetico e (iii) identificare marcatori molecolari SNP (polimorfismi del DNA a singolo nucleotide) legati alla resistenza a Fusarium da utilizzare in programmi di selezione assistita da marcatori. Il primo contributo del lavoro di tesi descrive lo stato dell’arte dei risultati ottenuti nel miglioramento genetico della barbabietola da zucchero. Il contributo si focalizza sui progressi ottenuti nella resistenza a malattie con metodi di miglioramento genetici classico e con l’impiego di tecniche molecolari utilizzando come fonte di resistenza germoplasma selvatico. E’ stato inoltre considerato il contributo delle nuove tecnologie di sequenziamento e del recente rilascio del genoma di riferimento al miglioramento genetico della barbabietola. Il secondo contributo riguarda la valutazione della risposta a Fusarium oxysporum f. sp. betae di un’ampia collezione di linee di barbabietola da zucchero al fine di identificare linee resistenti e suscettibili. Per raggiungere questo scopo sono state esaminate 29 linee di barbabietola da zucchero. Le piante sono state infettate con due isolati fungini F19 e Fob220a, appartenenti a due gruppi genetici distinti, entrambi altamente patogenici. Dopo l’inoculo, per un periodo di sei settimane, è stato attribuito, per ciascuna pianta, un punteggio da 0 a 5 in base ai vari sintomi di malattia manifestati, quali: avvizzimento fogliare, clorosi e necrosi. Successivamente, le piante sono state raccolte e le radici sono state esaminate per vedere dove era presente marciume radicale, discolorazione e quali piante invece risultavano resistenti al patogeno. Il terzo contributo descrive la risposta di due diverse collezioni di germoplasma di barbabietola da zucchero a isolati di Fusarium oxysporum f. sp. betae. Linee suscettibili, provenienti da USDA-ARS (US) e UNIPD (Università di Padova, Italia), sono state inoculate con tre distinti isolati di Fusarium oxysporum f. sp. betae, l’agente causa di Fusarium yellows. Tutte le linee inoculate hanno sviluppato i sintomi della malattia, ma un grave marciume radicale è stato osservato solo nelle linee provenienti da UNIPD inoculate con isolati che non avevano mai causato marciume radicale nel germoplasma USDA. Il quarto contributo riguarda l’identificazione, su geni candidati, di marcatori molecolari SNPs associati alla resistenza alla malattia. In particolare, sono stati identificati 5 analoghi a geni di resistenza (RGA) dal lavoro di Dohm et al. 2014 e sono stati analizzati tramite analisi High Resolution Melting (HRM) su 96 campioni delle 6 linee più resistenti e più suscettibili a Fusarium. Due varianti, in 2 dei geni testati, sono risultate significativamente associate (p < 0.01) con la resistenza a Fusarium. Le varianti sono state validate attraverso sequenziamento Sanger. Il sequenziamento ha permesso di individuare due marcatori SNPs. L’associazione tra questi due SNPs e la resistenza a Fusarium è stata successivamente validata con il metodo di genotipizzazione Comparative allele-specific PCR (KASPar) su 96 campioni resistenti e 96 campioni suscettibili. La frequenza dell’allele A sia per lo SNP_Bv7_171470 e lo SNP_Bv2_043450 è risultata significativamente più alta negli individui resistenti rispetto a quelli suscettibili. Questi due SNPs potranno essere utilizzati in programmi di selezione genetica al fine di migliorare la resistenza a Fusarium in barbabietola da zucchero.

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Scott, Gavin D. "Root system traits and root longevities in two contrasting cultivars of Trifolium repens (White clover)." Thesis, University of Aberdeen, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.425002.

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This study uses sequential digital imaging of rhizotron grown root systems of white clover (Trifolium repens) to evaluate the developmental differences in the architecture of two cultivars with contrasting above-ground characteristics. Root lengths and leaf areas were correlated in both cultivars, with large leaved Alice producing greater leaf area and greater root length than the small leaved S184. The key architectural difference between the two cultivars was that Alice produced a higher ratio of terminal lateral length to axial length than S184. Lateral roots had lower survival times compared with axial roots in both cultivars. Amongst lateral roots, survival was positively influenced by diameter. A 0.1 mm increase in diameter was calculated to result in between 23% and 42% reduction in the risk of lateral root mortality. Destructive investigations of the root systems were made at intervals during the experiment and roots of known age and order were excised and evaluated for C and N content and tissue density. Axial roots were found to have higher tissue density and higher C and N content than laterals, and, these traits increased with increasing axial root age. The hypothesis that axial roots are invested with additional high C compounds to increase their persistence in the soil was supported by microscopic analysis which shown a build up of lignin in axial roots as they aged. A population dynamics model was constructed showing the estimated flux of C and N from plant to soil due to root mortality. The most dynamic C and N pool was in the lateral roots. Breeding and selection of white clover cultivars should aim to maximise the ephemeral lateral root system component to enhance N flux from plant to soil.

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Patel, Dhaval V. "Dissecting natural variation of root traits in arabidopsis thaliana accessions." Thesis, University of Nottingham, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503910.

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11

Heras, Ambros Paloma. "Barley root traits for improved subsoil exploration and resource capture." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/43532/.

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Subsoil physical characteristics are often limiting to root growth, one of the major reasons being high density soil. However, deeper and more efficient root systems could help to explore a larger soil volume and reduce the input of nitrogen fertilisers if roots make more use of the nitrogen at depth. The first target was to develop a screening method which allowed barley root extension rates to be quantified after four days of growth in loose and compacted soils. Firstly, seed quality (loss of germination ability caused by poor conditions in storage and long storage time) was identified as a potential source of variation for root extension rate in seedlings. The screening showed that roots growing in compacted soil had a slower extension rate than roots growing in loose soil. In addition, there was an interaction between soil conditions and cultivars meaning that not all of them showed the same ability to overcome high soil density. Root architecture was characterized at days eight and 12 after planting for four selected divergent cultivars. Measurements were made using X-ray micro-computed tomography (µCT)-scanning. The differences between the four genotypes in root architecture (number of primary roots, root extension rate, root length, root area, root volume, convex hull, centre of mass, lateral density, lateral length) were significant at eight days after planting but disappeared at 12 days after planting for most of the traits measured (i.e. growth rate of primary roots). Soil density influenced the root system architecture at both two-time points, roots elongated less and explored less soil in the high compaction treatment. A third experiment was conducted to test the hypothesis that the differences in root architecture observed between the genotypes in response to the soil bulk density in the µCT-scanning would lead to different patterns of nutrient uptake from topsoil and subsoil. Layered soil columns of topsoil and subsoil were constructed with different subsoil physical parameters (loose, compacted and compacted with macropores) and a nitrogen tracer to measure nitrogen capture from the subsoil. Root length density and other traits determining root architecture differed between two barley cultivars and oat, but increased root length density in the subsoil did not improve nitrogen uptake from the subsoil. Hence showing that nitrogen uptake from the subsoil was not directly related with a greater presence of roots in the experiment.

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12

Gougherty, Steven W. "Exudation Rates and δ¹³C Signatures of Bottomland Tree Root Soluble Organic Carbon: Relationships to Plant and Environmental Characteristics". The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448818110.

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13

Bergmann, Joana [Verfasser]. "Root traits and their effect in plant-soil interactions / Joana Bergmann." Berlin : Freie Universität Berlin, 2018. http://d-nb.info/1159900531/34.

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14

Griffiths, Marcus. "Identifying wheat root traits and regulatory genes for nitrogen uptake efficiency." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/48611/.

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Abstract (sommario):

Wheat (Triticum spp.) is a particularly important crop for food security, providing 20% of worldwide calorie intake. Food production is not meeting the projected global demand of an increase of 2.4% p.a. Improvement of resource capture in wheat could help meet this demand. Nitrogen (N) is an essential macronutrient for plant growth and development; however, nitrogen use efficiency (NUE) for cereal production is only 33%. Domestication of modern varieties of wheat may have lost potentially beneficial agronomic traits, particularly in the root system. Optimisation of root system architecture could profoundly improve nitrogen uptake efficiency (NUpE) and in turn increase the yield potential of the crop. Using ancestral wheat germplasm and mapping populations, desirable traits may be identified and bred back into commercial wheat varieties to increase yield potential. Using a high-throughput hydroponic root phenotyping system, N-dependent root traits have been identified in wheat mapping populations. Using transcriptomic analyses, the gene expression profile of a candidate N-dependent root QTL has been identified. Using a new root phenotyping system, X-ray micro-computed tomography (μCT), a three-dimensional representation of wheat roots can now be imaged in soil. A selection of the same mapping lines have been used for 3D μCT analysis based on field NUpE parameters to identify promising root traits in both seedlings and mature plants.

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15

Valverde-Barrantes, Oscar Jesus. "A phylogenetic perspective on fine root ecology: assessing the role of root evolution on fine root functional traits and ecological interactions in woody angiosperms." Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1384641579.

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16

Nazemi, Ghasemali <1976&gt. "Genetic basis of variation for root traits and response to heat stress in durum wheat." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7166/1/nazemi_ghasemali_tesi.pdf.

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Durum wheat is the second most important wheat species worldwide and the most important crop in several Mediterranean countries including Italy. Durum wheat is primarily grown under rainfed conditions where episodes of drought and heat stress are major factors limiting grain yield. The research presented in this thesis aimed at the identification of traits and genes that underlie root system architecture (RSA) and tolerance to heat stress in durum wheat, in order to eventually contribute to the genetic improvement of this species. In the first two experiments we aimed at the identification of QTLs for root trait architecture at the seedling level by studying a bi-parental population of 176 recombinant inbred lines (from the cross Meridiano x Claudio) and a collection of 183 durum elite accessions. Forty-eight novel QTLs for RSA traits were identified in each of the two experiments, by means of linkage- and association mapping-based QTL analysis, respectively. Important QTLs controlling the angle of root growth in the seedling were identified. In a third experiment, we investigated the phenotypic variation of root anatomical traits by means of microscope-based analysis of root cross sections in 10 elite durum cultivars. The results showed the presence of sizeable genetic variation in aerenchyma-related traits, prompting for additional studies aimed at mapping the QTLs governing such variation and to test the role of aerenchyma in the adaptive response to abiotic stresses. In the fourth experiment, an association mapping experiment for cell membrane stability at the seedling stage (as a proxy trait for heat tolerance) was carried out by means of association mapping. A total of 34 QTLs (including five major ones), were detected. Our study provides information on QTLs for root architecture and heat tolerance which could potentially be considered in durum wheat breeding programs.

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17

Nazemi, Ghasemali <1976&gt. "Genetic basis of variation for root traits and response to heat stress in durum wheat." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7166/.

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Abstract (sommario):

Durum wheat is the second most important wheat species worldwide and the most important crop in several Mediterranean countries including Italy. Durum wheat is primarily grown under rainfed conditions where episodes of drought and heat stress are major factors limiting grain yield. The research presented in this thesis aimed at the identification of traits and genes that underlie root system architecture (RSA) and tolerance to heat stress in durum wheat, in order to eventually contribute to the genetic improvement of this species. In the first two experiments we aimed at the identification of QTLs for root trait architecture at the seedling level by studying a bi-parental population of 176 recombinant inbred lines (from the cross Meridiano x Claudio) and a collection of 183 durum elite accessions. Forty-eight novel QTLs for RSA traits were identified in each of the two experiments, by means of linkage- and association mapping-based QTL analysis, respectively. Important QTLs controlling the angle of root growth in the seedling were identified. In a third experiment, we investigated the phenotypic variation of root anatomical traits by means of microscope-based analysis of root cross sections in 10 elite durum cultivars. The results showed the presence of sizeable genetic variation in aerenchyma-related traits, prompting for additional studies aimed at mapping the QTLs governing such variation and to test the role of aerenchyma in the adaptive response to abiotic stresses. In the fourth experiment, an association mapping experiment for cell membrane stability at the seedling stage (as a proxy trait for heat tolerance) was carried out by means of association mapping. A total of 34 QTLs (including five major ones), were detected. Our study provides information on QTLs for root architecture and heat tolerance which could potentially be considered in durum wheat breeding programs.

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18

Pogiatzis, Antreas. "Comparative response of six grapevine rootstocks to inoculation with arbuscular mycorrhizal fungi based on root traits." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/61809.

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Arbuscular mycorrhizal fungi are soil fungi that form a symbiotic association with plant roots. The symbiosis is largely nutritional. The fungi depend on the plants for carbon resources, and the plants benefit from increased access to soil nutrients. The magnitude of plant benefit, however, can vary significantly. Understanding the factors that influence plant growth response is important, especially in agroecosystems where high yield is desirable. It has been suggested that root architecture is a key factor that determines plant responsiveness to arbuscular mycorrhizal fungi, and some studies have been conducted and support this notion. However, a major limitation in such studies is the lack of control for phylogenetic constraints among tested plants, making it difficult to control for confounding variables that are not associated with root architecture. In this dissertation, I explored the variation in plant responsiveness among closely related species (all grapevines) and investigated the potential relationship between root architecture and responsiveness to arbuscular mycorrhizal fungi. I found that root colonization by arbuscular mycorrhizal fungi can improve grapevine growth, although the degree of growth responses differed among grapevine cultivars. The magnitude of the benefit (plant growth response to a fungi) can be partially explained by the pre-colonization root architecture, and in particular with branching intensity, which is largely associated with plant nutrient foraging ability. However, root architecture alone is a poor predictor of plant response to arbuscular mycorrhizal fungi and more factors need to be considered to better understand plant nutrient foraging ability. In addition, mycorrhizas can influence the expression of root traits, such as root branching intensity, average root diameter and the root to shoot ratio. Irving K. Barber School of Arts and Sciences (Okanagan) Biology, Department of (Okanagan) Graduate

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19

Yang, Luojin [Verfasser], Klaus [Akademischer Betreuer] [Gutachter] Dittert, Petr [Gutachter] Karlovsky, and Andrea [Gutachter] Carminati. "Root exudation pattern of sugar beet (Beta vulgaris L.) as influenced by light intensity and P deficiency / Luojin Yang. Betreuer: Klaus Dittert. Gutachter: Klaus Dittert ; Petr Karlovsky ; Andrea Carminati." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://d-nb.info/1109046499/34.

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20

Frost, Aaron Desmond James, and n/a. "The Reciprocal Relationship Between Conduct Problems, Callous Unemotional Traits, and Parenting Behaviour." Griffith University. School of Psychology, 2006. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20070109.094343.

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Callous and Unemotional (CU) traits are a relatively recent addition to the existing body of research examining the development of severe behavioural problems in children, and antisocial behaviour in adults. Children who are high in CU traits display shallow emotions, manipulate other children, lie easily, and demonstrate very little remorse or guilt. Additionally, they are more likely to engage in more severe forms of antisocial behaviour, more often, and from a younger age than their peers. Research has found that CU traits moderate the well-established relationship between parenting and conduct problems. That is, children who are high in CU traits seem to display levels of behaviour problems that are unrelated to the quality or type of parenting they receive. This has serious implications when one considers that the most effective psychosocial treatments available for behavioural disorders are based upon improving parenting, and would therefore require significant modification for children high in CU traits. In addition, the research exploring the moderating role of CU traits in the relationship between parenting and conduct problems has not taken a developmental perspective and considered different ages of children. Finally, existing research has not considered the reciprocal relationship that CU traits have upon parenting behaviour, or the direct relationship between parenting and CU traits. The present study has addressed these limitations by utilizing an accelerated longitudinal methodology. The present study recruited 449 grades one, three and five children from six public primary schools. Questionnaires assessing conduct problems, CU traits, and parenting styles were administered to their parents for completion. Additionally, teacher report was also sought on a number of key variables to ensure validity. One year later, all of these children and their families were re-approached to assess the extent to which each of these variables had changed over time. One year later 233 (51.89%) of the original sample completed the same measures allowing examination of the change in these variables over time. Given the relatively short time period, it was expected that one of the best predictors of any of the key variables at time 2, would be baseline scores measured at time 1. For this reason, hierarchical regression was used to control for temporal stability, as well as demographic factors. Additionally, the hypothesis that a different pattern of relationships would emerge for children of different ages was tested by examining the moderating effect of age upon all predictive relationships. This was done by entering the product of age and the predictor variable(s) as the final step of the regression analyses, and then conducting simple slopes analysis on all significant predictive interactions. Three distinct findings emerged from these analyses. Firstly, age moderates the effect of CU traits on the relationship between parenting styles and conduct problems. Behaviour problems in younger children are better predicted by parenting behaviours and by CU traits than in older children. Secondly, both CU traits and conduct problems were predictive of worsening parental behaviour. Once again, this was particularly evident in younger children. Finally, inconsistent parenting, and corporal punishment were found to be predictive of CU traits. These findings are discussed from a developmental perspective in the context of Bronfenbrenner's (1979) ecological model.

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21

Kiran, Aysha [Verfasser]. "Genetic and phenotypic analysis of complex seed and root traits in oilseed rape (Brassica napus L.) / Aysha Kiran." Gießen : Universitätsbibliothek, 2015. http://d-nb.info/1068874821/34.

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22

Herz, Katharina [Verfasser]. "Drivers of intraspecific variation of plant functional traits, plant performance and root exudates in German grasslands / Katharina Herz." Halle, 2017. http://d-nb.info/1142155315/34.

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23

Thomas, C. L. "High throughput phenotyping of root and shoot traits in Brassica to identify novel genetic loci for improved crop nutrition." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/43440/.

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Abstract (sommario):

Despite the success of breeding for high-yielding varieties during and since the ‘Green Revolution’, there are still an ever increasing number of people who suffer from malnutrition, due to both inadequate calorie intake and ‘hidden hunger’ from insufficient essential nutrients. There are also adverse impacts of such high-input, intensive agriculture on the wider environment. It is necessary therefore to focus breeding efforts on improving nutrient uptake and composition of crops, as well as improved yield. Roots have been an under-utilised focus of crop breeding, because of difficulty in observation and accurate measurement. Furthermore, genetic diversity in crop roots may have been lost in commercial varieties because of the focus on above-ground traits and the use of fertilisers. Techniques which can accurately measure phenotypic variation in roots, of a diverse range of germplasm at a high throughput, would increase the potential for identifying novel genetic loci related to improved nutrient uptake and composition. The aim of this PhD was to screen at high throughput in a controlled-environment, the roots of an array of Brassica napus germplasm. The validity of the system to predict field performance, in traits including early vigour, nutrient composition and yield was assessed. Genetic loci underlying variation for the root traits were also investigated. A high throughput screen of the mineral composition of a mutagenised B. rapa population was also conducted, with the aim of identifying mutants with enhanced mineral composition of human essential elements, particularly magnesium. It has been demonstrated that root traits in the high throughput system can predict field performance, particularly primary root length which has the greatest ‘broad-sense heritability’ and relates to early vigour and yield. Lateral root density on the otherhand was found across the studies to relate to mineral composition, particularly of micro-nutrients. Genetic loci underlying root traits, and enhanced magnesium accumulation have been identified, and have potential for use in breeding Brassica with improved mineral nutrition.

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24

Radanielson, Mariot Ando. "Identification de nouveaux traits de sélection pour améliorer la productivité en situation de déficit hydrique chez le tournesol." Thesis, Montpellier, SupAgro, 2011. http://www.theses.fr/2011NSAM0013/document.

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Le développement de variétés productives et adaptées aux conditions de déficit hydrique est toujours au cœur du défi de l'amélioration variétale chez le tournesol. Pour une nouvelle orientation de la sélection, ce travail se propose d'identifier de nouvelles cibles phénotypiques au travers d'une démarche couplant le phénotypage écophysiologique, la modélisation biophysique et la génétique quantitative. Les cibles potentielles ont été identifiées sur la base de leur variabilité génotypique, leur impact sur le rendement, leur héritabilité et leur facilité de mesure. Des paramètres génotypiques du modèle SUNFLO-CLIMATOR relatifs à la phénologie, l'architecture foliaire et l'accès aux réserves hydriques du sol ont été testés. 19 lignées et 125 hybrides ont été phénotypés au champ et sous serre. La structure génétique des populations d'hybrides a permis d'évaluer l'héritabilité des paramètres génotypiques et leur mode de transmission.La date thermique de la floraison a présenté la variabilité génotypique la plus restreinte, mais l'héritabilité la plus élevée (H²=0.78). Ce trait est un bon indicateur de la précocité de la floraison mais peu pertinent pour améliorer la précocité à la maturité. La date de la maturité physiologique a présenté un déterminisme environnemental important et une amélioration de sa représentation dans le modèle est nécessaire. Les traits caractéristiques de l'architecture ont présenté la plus grande variabilité génotypique. Leur héritabilité était par contre peu élevée (0.20 ≤ H² ≤ 0.39). L'interaction des traits architecturaux était plus importante que leur contribution individuelle dans la variabilité de la productivité. Des investigations plus approfondies sur l'interaction des traits d'architecture devraient apporter plus de précision sur la stratégie d'intégration de ces caractères en sélection. L'utilisation du trait, position de la plus grande feuille, A2gen, et surface foliaire de la plus grande feuille, A3gen, en sélection sur valeur propre des lignées, peut cependant déjà permettre une amélioration de l'efficience d'interception des hybrides durant la phase reproductive et particulièrement dans des conditions de déficit hydrique en fin de cycle. Le trait Indice d'extraction de l'eau IEgen caractéristique de la capacité d'extraction de l'eau du sol, constitue le trait le plus prometteur. Il présente une héritabilité élevée (0.77 ≤ H² ≤ 0.83). La réponse du rendement à sa variabilité est linéaire, avec un gain de 0.8 à 1.5 q ha-1 pour une augmentation de 1 % de la teneur en eau minimale d'extraction de l'eau.La recherche de marqueurs moléculaires pour ces paramètres génotypiques d'intérêt peut être faite et dans le but d'une stratégie de sélection assistée par la modélisation biophysique et le marquage moléculaire This work was an attempt to assist sunflower breeding program by crop physiology knowledge to sustain and to improve productivity under water deficit. The approach was based on using SUNFLO-CLIMATOR, a biophysical crop modelling to identify the limiting factors to plant productivity. These factors were considered as potential new traits for breeding program. Their assessment for this objective corresponded to four criteria: genotypic variability, impact on plant productivity, heritability and simplified phenotyping method. Thus, traits related to genotypic parameters of three processes were analysed: phenology, architecture and soil water uptake. Their variability was evaluated on field and greenhouse experiments carried out with 19 inbred lines and 125 hybrids. Sensitivity analysis of plant yield, simulated with SUNFLO-CLIMATOR model, was then done to estimate the impact of the parameter variability among the studied genotypes. Quantitative genetic analyses were used to evaluate their heritability and the combining ability of the parental inbred lines.Large phenotypic variability was observed for each parameter with a significant “genotype” effect. Thermal time for flowering displayed high heritability about H² = 0.78. Thermal time to physiological maturity (M3) displayed high environmental effect on its variability. Its genotypic variability would probably need new way of modelling such as the development of a seed growth module. Architectural traits related to canopy size and shape presented also lower heritability (0.20 ≤ H² ≤ 0.39) and their impact on plant productivity depends on their interaction. However the trait position of the largest leaf A2gen and its leaf area A3gen could be yet used to screen the best inbred lines for improving radiation interception efficiency of the hybrids during the grain-filling phase.Root depth is a relevant trait for deeper soil. Its access remains difficult and time consuming. For shallower or medium depth soil, higher water extraction capacity seemed allow higher plant yield with linear relationship about 0.8 – 1.5 q ha-1 more per 1% decrease of soil water content minimal for water extraction. The index of water extraction (IEgen) displayed high value of heritability (0.77 ≤ H² ≤ 0.83). The genotypic parameters A2gen, A3gen, IEgen were confirmed with genetic resources to enhance plant productivity under water deficit. Research for their molecular marker would be a next step for this work and an issue for a new selection assisted by marker molecular and plant modelling

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25

Mgbeahuruike, Anthony Christian. "A study of the traits associated with the biocontrol activity of Phlebiopsis gigantea /." Uppsala : Dept. of Forest Mycology and Pathology, Swedish University of Agricultural Sciences, 2009. http://epsilon.slu.se/11605615.pdf.

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26

Hecht, Vera Lisa [Verfasser]. "Root and shoot phenotypic traits and their expression in response to sowing density in spring barley (Hordeum vulgare) / Vera Lisa Hecht." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1221669427/34.

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27

Sharma, Sundrish. "Characterization of quantitative loci for morphological and anatomical root traits on the short arm of chromosome 1 of rye in bread wheat." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1899491951&SrchMode=2&sid=1&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269025605&clientId=48051.

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Abstract (sommario):

Thesis (Ph. D.)--University of California, Riverside, 2009. Includes abstract. Title from first page of PDF file (viewed March 18, 2010). Includes bibliographical references. Issued in print and online. Available via ProQuest Digital Dissertations.

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28

Bakhshandeh, Shiva. "Effect of Climate Change and Soil Management on Water and Nutrient Uptake for Sustainable Yield of Wheat Genotypes with Different Root Traits." Thesis, The University of Sydney, 2018. http://hdl.handle.net/2123/18649.

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Drought and heat stress are the most important climate change factors decrease water and nutrient uptake and therefore negatively affect wheat growth. Surface soil drying decreased both water and NH4+ uptake from the top soil. However, increased water availability with bottom watering increased water uptake from the bottom soil layer, but not NH4+ uptake from the bottom soil layer. With surface soil drying, plants grew more and longer roots in the bottom soil layer, shifting water uptake from the top to the bottom soil, while N uptake was reduced in the top soil because of a decrease in root biomass. Drought stress and heat stress decreased the yield of all wheat genotypes, in particular 249, while combined drought and heat stresses had the most pronounced negative effect on plant biomass and grain yield. Decreasing soil water availability decreased plant-derived C to soil organic carbon (SOC) and microbial biomass through rhizodeposition. Wheat genotypes with smaller root/shoot ratios and thinner roots were more efficiently assimilating C to the grain, while genotypes with higher root/shoot ratios and thicker roots allocated more C belowground through rhizodeposition at the expense of producing more yield. Increasing water availability from 15 % to 25% and reducing air temperature 30 to 25 °C increased N uptake by plants thereby reducing overall N loss, and increased transfer of N from vegetative parts to grain. While crop rotation did not affect soil available N and P, AMF colonization in wheat was on average 60% higher after chickpea than after the canola rotation. Wheat yield after chickpea increased for genotype IAW2013, and was positively related to AMF colonization for both genotypes. N and P fertilization reduced AMF colonization and yield, but increased shoot biomass and leaf tissue N and P concentrations. Leaf δ13C decreased with increased yield, suggesting that higher yielding and AMF colonized plants were less water stressed.

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Zamora-Ledezma, Ezequiel. "Evidences for an indirect effect of root functional traits and plant composition on soil microbial activities in Mediterranean rangelands : a spatial and temporal approach." Thesis, Montpellier 2, 2013. http://www.theses.fr/2013MON20176/document.

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Il est de plus en plus admis que pour comprendre le fonctionnement des écosystèmes, une approche aérienne associée à une approche souterraine est nécessaire en raison des rétroactions entre plantes et sol. La structure des communautés végétales peut affecter le fonctionnement du sol en altérant la quantité et la qualité des ressources intégrant le sol. Les contrôles abiotiques des processus microbiens du sol sont largement documentés, mais les potentiels effets de la composition de la communauté végétale et des traits racinaires sont peu connus. L'étude a été menée sur des prairies méditerranéennes du sud de la France. Nous avons sélectionné 12 communautés contrastées le long d'un gradient de disponibilité des ressources du sol principalement lié à la texture du sol. Les objectifs de cette thèse sont d'évaluer i) la réponse de la composition floristique et des traits foliaires et racinaires mesurés au niveau de la communauté le long gradient édaphique et à travers les saisons, et ii) leurs effets sur trois processus microbiens du sol impliqués dans les cycles du carbone (C) et de l'azote (N) : la respiration potentielle (SIR), la nitrification (NEA) et la dénitrification (DEA). Dans les sols sableux (parcelles peu productives), la communauté végétale possède une stratégie de conservation au niveau des feuilles et une stratégie d'acquisition des ressources au niveau des racines suggérant une forte plasticité des traits racinaires en réponse à la limitation des ressources ; les taux de SIR et NEA sont élevés. Un patron opposé est observé dans les sols argileux des milieux productifs. La DEA ne varie pas le long du gradient. Aucun effet de la richesse spécifique, de l'équitabilité ou de la biomasse végétale sur la SIR ou la NEA n'a été trouvé. Cependant, nous avons démontré qu'il y a une forte influence de la composition fonctionnelle des communautés végétales (abondance des graminoïdes), et surtout des traits racinaires. Nos résultats les plus novateurs montrent que la NEA et dans une moindre mesure la SIR sont positivement corrélés à la concentration en N des racines de la communauté et négativement corrélés à leur ratio C/N, tandis que les traits foliaires analogues ont seulement un effet mineur sur les activités microbiennes. Ces résultats suggèrent que la qualité chimique des racines est le principal pilote des activités du sol et que cela est maintenu à travers les saisons. D'importantes variations saisonnières de la composition floristique des communautés, de leurs traits racinaires et des activités microbiennes, excepté la DEA, ont été mises en avant. Les variations saisonnières des traits racinaires sont interprétées comme un changement relatif de la proportion de racines jeunes/vieilles et suggèrent une asynchronie entre la croissance aérienne et souterraine. Pour la première fois, nous montrons qu'en conditions naturelles, les changements saisonniers des traits fonctionnels racinaires peuvent être impliqués dans le pilotage de la NEA et de la SIR. Ce résultat démontre la nécessité d'études plus approfondies pour comprendre le rôle des traits racinaires comme pilote du fonctionnement du sol It is increasingly recognized that the understanding of ecosystem functioning requires a combined above- and belowground approach, because of the importance of feedbacks between plants and soil. Plant community structure may affect soil functioning by altering the quantity and the quality of resources entering the soil. Abiotic controls on soil microbial processes are well documented, but potential effects of plant composition and root traits are poorly understood. The study was conducted in Mediterranean grasslands located in southern France. We selected 12 contrasting communities along a gradient of soil resource availability, which is mainly driven by soil texture. The aims of the thesis were to evaluate: i) the response of plant composition and leaf and root traits measured at the community level along the soil gradient and across seasons, ii) their effect on three soil microbial processes involved in carbon (C) and nitrogen (N) cycling, i.e. substrate-induced respiration (SIR), nitrifying (NEA) and denitrifying enzyme activities (DEA). In sandy soils (unproductive plots) plant communities had a conservation strategy at the leaf level and an acquisitive strategy at the root level suggesting a strong plasticity of root traits in response to resource limitation; rates of SIR and NEA were higher. Opposite pattern was observed in clay productive soils. DEA did not vary along the gradient. We did not find evidence of a species richness, evenness, or plant biomass effect on SIR and NEA. However, we demonstrated that they were strongly influenced by plant functional composition (abundance of graminoids), and particularly by root traits. Our most innovative finding evidences that NEA, and to a lesser extent SIR, were positively correlated with root nitrogen (N) concentration and negatively correlated with C/Ncom, whereas analogous leaf traits have only minor effect on microbial activities. Our results suggested that the chemical quality of roots is the main driver of soil activities and this was confirmed across the seasons. We highlight strong seasonal variations in plant community composition, root traits and soil microbial activity, except DEA. Seasonal variations in root traits were interpreted as a relative change in the proportion of young versus old roots and suggested an asynchrony between above– and belowground growth. We showed for the first time evidences that in natural conditions, seasonal changes in root functional traits could be implicated in driving NEA and SIR. This result demonstrates the need to further develop studies allowing a better understanding of the role of root traits as soil functioning drivers

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Thosago, Setshele Standford. "Response of selected cowpea lines to low soil phosphorus and moisture stress conditions at Ukulima Farm in Limpopo Province." Thesis, University of Limpopo, 2015. http://hdl.handle.net/10386/1585.

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Thesis (M. Sc.(Agronomy)) -- University of Limpopo, 2015 Cowpea (Vigna unguiculata L. Walp) is an important grain legume grown in many parts of the world mostly by smallholder (SH) farmers. Low soil phosphorus (P) and drought stress are major constraints to legume production and threaten food security. Root architecture is a spatial configuration of the root system which is influenced by moisture status and P uptake. A field experiment was conducted at Ukulima farm near Modimolle in Waterberg district during 2012/13 summer growing season. The treatments comprised of two levels each for soil P (low and high) and moisture status (water stress and well-watered); and eight cowpea genotypes (Tvu 4632, Tvu 6365, Tvu 9848, Tvu 15445, Tvu 16408, Tvu 15143, Oloyin and IT00K-1217). The low P level implied the available P in the soil measured in situ, which was less than 8 mg kg-1 while the high P level entailed fertilization at the rate of 40 kg P ha-1 application to achieve approximately 35 mg P kg-1 of soil . The root traits measured included angle of adventitious and basal roots, number of basal roots, tap root diameters at 5, 10, 15 and 20 cm soil depths; lateral branching densities at depth 5,10 and 15 cm, nodule score, deep score, shallowness score, 3rd order branching density, and 1.5 branching densities at 5 and 10 cm depth. Plant parameters measured were plant height, number of pods per plant, number of seeds per pod, length of the pods, unshelled weight, shelled weight and number of primary and secondary branches. Photosynthetic parameters measured were photosynthetic rate, intercellular CO2 concentration, water conductance, transpiration rate, vapour pressure deficits, sample cell CO2, sample cell H2O and relative humidity in the cell. All treatment factors were combined as split-split plot arrangement fitted into randomized complete block design; with four replicates. Results indicate that the lateral root branching density at 5 and 10 cm differed significantly (P≤0.05) across cowpea genotypes. Genotype showed significant effect on taproot diameter at 10 cm. Moisture status and P level exerted significant effect on cowpea genotypes 15 cm. There were significant differences (P≤0.05) for lateral root branching density observed at 5 and 10 cm depth in P rates x genotype interaction. Statistical analysis showed that P levels and cowpea genotypes had significant effects (P≤0.05) on mean plant height, biomass and highly significantly effects (P≤0.01) on number of branches, days to physiological maturity and mean pod length. The interaction between cowpea genotype and moisture stress condition significantly (P≤0.05) affected hundred (100) seed weight. Cowpea genotype Tvu16408 obtained highest grain yield of 3240 kg ha-1 and lowest was by IT00K1217 which obtained grain yield of 1256 kg ha-1. Results showed that photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O, relative humidity in the cell, intercellular CO2 and vapour pressure deficit differed significantly (P≤0.05) across cowpea genotypes. Soil moisture condition and cowpea genotype exerted significant (P≤0.01) effect on photosynthetic rate, water conductance, transpiration rate, sample cell CO2, sample cell H2O and relative humidity in the cell. Variation in P levels had no significant effect on the measured photosynthetic parameters. Oloyin genotype had the highest photosynthetic rate followed by Tvu 4632 while cowpea genotype Tvu 9848 had the least photosynthetic rate. Interaction of moisture stress and cowpea genotype had a significant effect on intercellular CO2 concentration. Water stress reduced the intercellular CO2 concentration of Oloyin, Tvu 6365 and 4632 but resulted in a significant increase in intercellular CO2 concentration in Tvu 9848 genotype. Results showed that variation in soil P level exerted a significant (P≤0.05) effect on grain tissue P content and uptake, and a highly significant (P≤0.01) difference in P content across the various cowpea genotypes. Moisture stress exerted a significant (P≤0.05) difference on P uptake. The results showed that P levels and cowpea genotype variation exerted significant (P≤0.05) effects on P content, P uptake and nitrogen (N) uptake. Moisture status and cowpea genotype variation exerted significant (P≤0.05) effects on total N and N uptake. Cowpea genotype Tvu 9848 obtained more total N content (4.37%), while the lowest total N content was obtained by cowpea genotype Tvu 15445 with 3035 mg kg-1. The interaction between cowpea genotype and moisture status exerted a significant (P≤0.05) effect on N and P uptake of immature green pods harvested. There is a need to conduct more studies to identify cowpea genotypes, their root architecture and agronomic measures that can do well under xvii drought stress and low soil P conditions. Research needs to be conducted to enhance cowpea productivity under both low soil P and drought stress. Keywords: cowpea genotypes; moisture stress; phosphorus fertilisation; root traits

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Romillac, Nicolas. "Effets de l’introduction du pois dans une succession de cultures sur certaines communautés végétales et bactériennes et leurs fonctions écosystémiques associées." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0266/document.

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Les plantes cultivées peuvent modifier la disponibilité en ressources et les perturbations perçues par les communautés d’organismes présentes dans les agroécosystèmes et en conséquence, influencer les fonctions écosystémiques utiles à la production agricole telles que la minéralisation de N et de S ou la compétition culture-adventices. Notre objectif était d’évaluer l’effet du pois (Pisum sativum L.), introduit dans une succession de cultures, sur les communautés d’adventices et les communautés microbiennes impliquées dans la minéralisation de N et S. Pour ce faire, nous avons mené des expérimentations en conditions contrôlées et utilisé les données d’une expérimentation au champ conduite pendant 5 ans. En conditions contrôlées, nous avons montré que le pois influence via ses traits racinaires certaines activités enzymatiques liées à la minéralisation de N. En revanche au champ, les variables climatiques influencent principalement le fonctionnement des communautés microbiennes impliquées dans la minéralisation de N et S. Par ailleurs, nous avons observé que le pois sélectionnait des communautés d’adventices fonctionnellement différentes de celles d’autres cultures, comme le colza, mais cet effet du pois ne persistait pas sous la culture suivante. En conclusion, les effets du pois sur les communautés microbiennes impliquées dans la minéralisation de N et S sont faibles comparés à ceux d’autres facteurs comme les conditions climatiques. En revanche l’effet du pois sur les communautés d’adventices est fort mais limité dans le temps. Ces résultats montrent la nécessité de mener les expérimentations au champ sur plusieurs années afin de prendre en compte la variabilité climatique Crops species modify resources availability and perturbation regimes perceived by the communities of organisms residing in the agroecosystems and, as a consequence, can lead to alteration of ecosystem functions useful to crop production, such as nitrogen and sulfur mineralization or crop-weeds competition, realized by weeds or microorganisms. Our objective was to study the effect of a legume, pea, when introduced in a crop succession, on weed communities and microbial communities involved in protein decomposition and sulfate ester mineralization, which are the main forms of N and S, respectively, in agricultural soils. To do so, we performed experiments in controlled conditions used data from a 5-years field experiment. In controlled conditions, we showed that pea during its development modify through its root functional traits several enzymatic activities involved in N decomposition/mineralization. However, in the field experiment, climatic factors were the main drivers of the microbial communities involved in N and S decomposition/mineralization. Moreover, pea selected weed communities that were functionally different from weed communities growing in other crops such as oilseed rape. However, this effect did not persist under the following crop. As a conclusion, our results suggest that pea modifications of microbial communities are weak compared to other factors such as climatic factors. However, pea effects on weed communities are strong but short lived. Those results highlight the complementarity of microcosm and field experiments, and the necessity of long term field experiments to take into account climate variability

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Sayed, Mohammed Abd El-Aziz Abd El-Haliem [Verfasser]. "QTL Analysis for Drought Tolerance Related to Root and Shoot Traits in Barley (Hordeum vulgare L.) / Mohammed Abd El-Aziz Abd El-Haliem Sayed." Bonn : Universitäts- und Landesbibliothek Bonn, 2011. http://d-nb.info/101624875X/34.

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Fort, Florian. "Stratégies d’acquisition des ressources des plantes prairiales sous contraintes hydrique et minérale - Rôle du système racinaire dans la réponse aux facteurs structurant les communautés." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/10428/1/Fort.pdf.

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A l’heure où l’on cherche à optimiser les services éco-systémiques fournis par les prairies, une meilleure compréhension du fonctionnement des systèmes racinaires apparait comme nécessaire. Nous avons donc décidé de caractériser les stratégies d’espèces issues des familles des Fabaceae et Poaceae prairiales par la mesure de traits fonctionnels racinaires. Le principal résultat de ce travail est la mise en évidence de plusieurs axes majeurs de différentiation des stratégies racinaires et de leurs relations avec les exigences écologiques des espèces. Le plus important est le compromis entre stratégies de capture et de conservation des ressources. Les espèces à stratégie de capture sont mieux adaptées aux milieux peu stressants notamment pour l’eau, mais sont peu impactées par le manque de phosphore, ce sont aussi des compétitrices efficaces. Bien que les plantes à stratégie de conservation soient mieux à même de se développer dans des milieux continentaux, elles sont plus impactées que les autres par la présence de compétiteurs et le manque de phosphore. Le type de relations existant entre les stratégies aériennes et racinaires apparait aussi comme un marqueur de l’adaptation des plantes aux stress. L’étude du système racinaire est donc un moyen efficace de prédire le comportement des espèces de plantes prairiales face à des contraintes abiotiques et biotiques. Cela ouvre des perspectives particulièrement intéressantes notamment pour la construction de mélanges d’espèces mieux adaptées à leurs environnements.

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Groleau-Renaud, Virginie. "Contrainte mécanique et exsudation racinaire du maïs : incidence de la morphologie du système racinaire." Vandoeuvre-les-Nancy, INPL, 1998. http://docnum.univ-lorraine.fr/public/INPL_T_1998_GROLEAU_RENAUD_V.pdf.

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L’amélioration des performances agronomiques (cultures plus économes et moins agressives pour l'environnement) passe par une meilleure compréhension des mécanismes rhizosphériques. La présente étude s'intéresse à l'influence de la contrainte mécanique, liée à la compaction des sols, sur l'exsudation racinaire (exsudats solubles et mucilages). Le propos est d'évaluer la part respective jouée par la contrainte mécanique ainsi que par les modifications morphologiques induites par cette contrainte sur l'exsudation racinaire. Les travaux sont réalisés à partir d'un modèle expérimental constitué par un dispositif de culture hydroponique stérile permettant de cultiver des maïs d'âge croissant (4, 8, 12 et 16 jours) et de récolter leurs exsudats racinaires. Des billes de verre de diamètre variable (1 mm, 4 mm) permettent de simuler et de moduler l'intensité de la contrainte mécanique. Des mesures morphologiques (croissance et développement des plantes) et physiologiques de l'exsudation racinaire (techniques quantitatives et utilisation de radio-isotopes) sont entreprises. En culture hydroponique stérile, la contrainte mécanique agit principalement sur la morphologie du système racinaire, par une réduction de la longueur des racines principales et une prolifération de racines d'ordre 2, avec une biomasse inchangée. Un épaississement racinaire est mis en évidence à l'apex, zone de libération des composés exsudés. La contrainte mécanique augmente l'exsudation racinaire du maïs. D’autre part, une quantité importante de carbone se dépose à la surface des billes de verre. Ces modifications de l'exsudation racinaire peuvent être attribuées à l'effet direct de la contrainte mécanique sur les racines. Une quantification de l'exsudation racinaire du maïs jeune qui prendrait en compte les sucres, les acides aminés ainsi que les acides organiques, serait essentielle pour comprendre la réponse des plantes à la contrainte mécanique. D’autre part, une meilleure connaissance des mécanismes physiologiques (rôle hormonal) consécutifs à la présence de la contrainte mécanique est à privilégier.

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Beyer, Friderike Verfasser], Christoph [Akademischer Betreuer] Leuschner, and Dirk [Akademischer Betreuer] [Hölscher. "Fine root traits, belowground interactions and competition effects on the rhizosphere of Fagus sylvatica and Fraxinus excelsior saplings / Friderike Beyer. Gutachter: Christoph Leuschner ; Dirk Hölscher. Betreuer: Christoph Leuschner." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2013. http://d-nb.info/104430622X/34.

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Hunter, Kirsten, and n/a. "Affective Empathy in Children: Measurement and Correlates." Griffith University. School of Applied Psychology, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20040610.135822.

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Empathy is a construct that plays a pivotal role in the development of interpersonal relationships, and thus ones ability to function socially and often professionally. The development of empathy in children is therefore of particular interest to allow for further understanding of normative and atypical developmental trajectories. This thesis investigated the assessment of affective empathy in children aged 5-12, through the development and comparison of a multimethod assessment approach. Furthermore this thesis evaluated the differential relationships between affective empathy and global behavioural problems in children versus the presence of early psychopathic traits, such as callous-unemotional traits. The first component of this study incorporated; a measure of facial expression of affective empathy, and self-reported experience of affective empathy, as measured by the newly designed Griffith Empathy Measure - Video Observation (GEM-VO) and the Griffith Empathy Measure - Self Report (GEM-SR); the Bryant's Index of Empathy for Children and Adolescents (1982) which is a traditional child self-report measure; and a newly designed parent-report of child affective empathy (Griffith Empathy Measure - Parent Report; GEM-PR). Using a normative community sample of 211 children from grades 1, 3, 5, and 7 (aged 5-6, 7-8, 9-10, & 11-12, respectively), the GEM-PR and the Bryant were found to have moderate to strong internal consistency. As a measure of concurrent validity, strong positive correlations were found between the mother and father reports (GEM-PR) of their child's affective empathy, for grades 5 and 7, and for girls of all age groups. Using a convenience sample of 31 parents and children aged 5 to 12, the GEM-PR and the Bryant demonstrated strong test-retest reliability. The reliability of the GEM-VO and the GEM-SR were assessed using a convenience sample of 20 children aged 5 to 12. These measures involve the assessment of children's facial and verbal responses to emotionally evocative videotape vignettes. Children were unobtrusively videotaped while they watched the vignettes and their facial expressions were coded. Children were then interviewed to determine the emotions they attributed to stimulus persons and to themselves whilst viewing the material. Adequate to strong test-retest reliability was found for both measures. Using 30% from the larger sample of 211 participants (N=60), the GEM-VO also demonstrated robust inter-rater reliability. This multimethod approach to assessing child affective empathy produced differing age and gender trends. Facial affect as reported by the GEM-VO decreased with age. Similarly, the matching of child facial emotion to the vignette protagonist's facial emotion was higher in the younger grades. These findings suggest that measures that assess the matching of facial affect (i.e., GEM-VO) may be more appropriate for younger age groups who have not yet learnt to conceal their facial expression of emotion. Data from the GEM-SR suggests that older children are more verbally expressive of negative emotions then younger children, with older girls found to be the most verbally expressive of feeling the same emotion as the vignette character; a role more complimentary of the female gender socialization pressures. These findings are also indicative of the increase in emotional vocabulary and self-awareness in older children, supporting the validity of child self-report measures (based on observational stimuli) with older children. In comparing data from the GEM-VO and GEM-SR, this study found that for negative emotions the consistency between facial emotions coded and emotions verbally reported increased with age. This consistency across gender and amongst the older age groups provides encouraging concurrent validity, suggesting the results of one measure could be inferred through the exclusive use of the alternate measurement approach. In contrast, affective empathy as measured by the two measures; the accurate matching of the participant and vignette character's facial expression (GEM-VO), and the accurate matching of the self reported and vignette character's emotion (GEM-SR); were not found to converge. This finding is consistent with prior research and questions the assumption that facially expressed and self-appraised indexes of affective empathy are different aspects of a complex unified process. When evaluating the convergence of all four measures of affective empathy, negative correlations were found between the Bryant and the GEM-PR, these two measures were also found to not converge with the GEM-VO and GEM-SR in a consistent and predictable way. These findings pose the question of whether different aspects of the complex phenomena of affective empathy are being assessed. Furthermore, the validity of the exclusive use of a child self report measure such as the Bryant, which is the standard assessment in the literature, is questioned. The possibility that callous-unemotional traits (CU; a unique subgroup identified in the child psychopathy literature) may account for the mixed findings throughout research regarding the assumption that deficiencies in empathy underlie conduct problems in children, was examined using regression analysis. Using the previous sample of 211 children aged 5-12, conduct problems (CP) were measured using the Strengths and Difficulties Questionnaire (SDQ; Goodman, 1999), and the CU subscale was used from the Antisocial Process Screening Device (APSD; Caputo, Frick, & Brodsky, 1999). Affective empathy when measured by the GEM-PR and the Bryant showed differing patterns in the relationship between affective empathy, CU traits and CP. While the GEM-Father reported that neither age, CU traits nor CP accounted for affective empathy variance, the GEM-Mother report supported that affective empathy was no longer associated with CP once CU traits had been partialled out. In contrast, the Bryant reported for girls, that CU traits were not found to have an underlying correlational relationship. It can be argued from the GEM-Mother data only that it was the unmeasured variance of CU traits that was accounting for the relationship between CP and affective empathy found in the literature. Furthermore, the comparison of an altered CU subscale with all possible empathy items removed, suggests that the constructs of CU traits and affective empathy are not synonymous or overlapping in nature, but rather are two independent constructs. This multimethod approach highlights the complexity of this research area, exemplifying the significant influence of the source of the reports, and suggesting that affective empathy consists of multiple components that are assessed to differing degrees by the different measurement approaches.

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Ghestem, Murielle. "Quelles propriétés racinaires et quelles espèces-outils pour la stabilisation des points chauds de dégradation en Chine du Sud ?" Phd thesis, AgroParisTech, 2012. http://pastel.archives-ouvertes.fr/pastel-00855792.

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La Chine est actuellement confrontée à de sérieux problèmes environnementaux et est listée parmi les pays qui contribuent le plus à la pollution et à la destruction de l'environnement mondial. En particulier, la Chine du Sud est une zone naturellement sujette aux glissements de terrain à cause de conditions tectoniques, climatiques et anthropiques particulièrement défavorables. Depuis la fin des années 1990, l'Etat chinois a mis en place des politiques de reforestation de grande envergure. mais il existe des lacunes de connaissances qu'il convient de combler. En particulier, le choix des espèces les plus adaptées n'est pas aisé parce que les processus par lesquels les plantes stabilisent les pentes ont besoin d'être mieux compris.En introduction, afin de mieux préciser les périmètres qui cadrent cette thèse, sont présentées la situation de la Chine du Sud au regard des glissements de terrain, la discipline d'éco-ingénierie et les solutions qu'elle peut apporter. Ainsi, ce travail (i) se concentre sur des espèces végétales locales, (ii) se limite aux glissements de terrain superficiels, et (iii) concerne à la fois les processus mécaniques et hydriques entre le sol et les racines. A l'intérieur de ces cadres, la thèse a pour objectif de répondre à la question scientifique : quels sont les propriétés racinaires qui influencent la stabilisation des pentes ? La réflexion est ensuite appliquée aux plantes de Chine du Sud afin d'identifier les meilleures espèces-outils. Pour répondre à cette question, à la fois les données de terrain (en Chine du Sud), les expériences de laboratoire (en France) et la formulation de concepts sont mobilisées. Les résultats sont organisés en deux chapitres. Le premier pose la question de l'efficacité de la présence de racines pour stabiliser les pentes, tous d'abord sous l'angle des processus mécaniques, puis sous l'angle des processus hydriques. Le deuxième chapitre permet d'identifier un panel de traits pertinents et non redondants évaluant l'efficacité d'une espèce pour la stabilisation des pentes puis s'appuie sur ce panel afin de sélectionner les espèces chinoises les plus efficaces. Enfin, la discussion aborde les limites de ce travail et propose de nouvelles pistes de recherche.Du point de vue mécanique comme du point de vue hydrique, c'est la conjonction des effets des racines de structure et des racines fines qui importe. Les racines de structure sanas racines fines ne sont pas optimales et peuvent même faire apparaître des lignes de fragilité. Plus précisément, les racines de structure sont particulièrement bienvenues vers l'aval de la pente pour des raisons à la fois mécaniques et hydriques. Les racines fines seules ne sont pas optimales non plus, elles peuvent faire apparaître localement des zones de faiblesse qui, si elles sont proches, participeront au déclenchement d'un glissement de terrain. Des ramifications racinaires denses améliorent la stabilité mécanique. Orientées vers l'aval de la pente, elles améliorent la stabilité hydrique. Les autres traits racinaires pertinents pour évaluer l'efficacité des racines à stabiliser le sol sont la contrainte et la déformation maximale en tension, la concentration en azote et la concentration en sucres solubles.

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Grimal, Jean-Yves. "Influence de l'exsudation racinaire de Zea mays L. Sur mobilisation de formes de phosphore difficilement biodisponibles." Vandoeuvre-les-Nancy, INPL, 1994. http://www.theses.fr/1994INPL058N.

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L’influence de l'exsudation racinaire de Zea mays sur la mobilisation de formes de phosphore difficilement disponibles a été étudiée suivant trois niveaux d'approche. L’étude de l'adsorption d'un modèle d'exsudats (apg) et de mucilages racinaires sur une goethite a montré que l'apg et les mucilages diminuent l'adsorption des ions phosphate. L’effet le plus marqué est constaté lorsque les ions phosphate sont apportés sur le complexe mucilages-goethite. Dans ce cas, le mécanisme mis en jeu est de nature physique. L’enrobage de la goethite a probablement diminué le nombre de sites d'adsorption des ions phosphate. Des cultures en conditions hydroponiques stériles ont permis d'examiner le comportement du maïs en présence d'ions phosphate adsorbés sur une goethite. Dans ces conditions expérimentales, la plante est capable de prélever jusqu'à 23% du phosphore initialement adsorbé. La réponse du maïs à cette contrainte se traduit aussi par une modification des flux de phosphore à l'intérieur de la plante. Le rôle des phosphatases racinaires dans l'acquisition du phosphore a été étudié en mettant à la disposition du maïs le glucose-1-phosphate et le myoinositol hexaphosphate. Les activités phosphatasiques ont été détectées à la surface des racines, dans la solution nutritive ainsi qu’à la surface de la goethite. Les possibilités d'action des phosphatases sont liées à l'accessibilité des phosphates organiques et des enzymes, adsorption sur les colloïdes ou précipitation. Ces résultats montrent que les composés diffusibles (mucilages) par leur action physique et les composés carbonés diffusibles (phosphohydrolases notamment) contribuent à augmenter la mobilité du phosphore à partir de sources peu accessibles pour la plante dans la rhizosphère

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Tremblay-Boeuf, Valérie. "Effets des contraintes mécaniques sur l'exsudation racinaire du maïs." Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL079N.

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Ce travail a permis d'évaluer les effets de la contrainte mécanique sur l'exsudation racinaire du maïs (Zea mays l. , variété Dea) et d'examiner l'importance de ces effets en relation avec le stade de développement de la plante. La culture des plantes a été conduite en conditions stérile et hydroponique. La contrainte mécanique a été simulée à deux niveaux d'intensité, à l'aide de billes de verre de 1 et 4 mm de diamètre. Ces traitements ont été comparés à un témoin sans billes. Les résultats ont montré que la croissance de la plante est influencée par la contrainte mécanique. Cette dernière affecte de façon notable la croissance des parties aériennes, aussi bien la surface foliaire que la matière sèche totale, ainsi que la morphologie du système racinaire. L’application de la contrainte mécanique est également responsable de la stimulation de l'exsudation de composés organiques et inorganiques. En outre, la prise en compte du matériel adhérant au support des racines revêt un rôle essentiel dans l'estimation quantitative de l'exsudation racinaire. En effet, des quantités non négligeables de mucilages racinaires ont été déterminées sur les billes de verre. Les résultats obtenus à partir d'analyses biochimiques, appuyés par des études utilisant les méthodes de marquage isotopique du carbone, démontrent que les plantes stressées ont libéré davantage de composés carbones que les plantes témoins. Selon le stade de développement de la plante, les effets de la contrainte mécanique sont d'ampleur différente et semblent s'amplifier avec la durée de culture. La confrontation de ces résultats avec les données obtenues au champ a confirmé ces tendances et les limites du modèle utilisé ont été définies

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Andrade, Bianca Ott. "Interação solo-vegetação campestre:estudos de caso em diferentes escalas ecológicas." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/148772.

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Enquanto em regiões temperadas o conhecimento sobre a relação solo-vegetação é consolidado, nos trópicos e subtrópicos é preliminar. É urgente a necessidade de se determinar os fatores abióticos que controlam padrões vegetacionais visando dar suporte a estudos de recuperação e conservação. O presente estudo analisa a relação entre fatores abióticos e vegetação campestre na forma de três artigos científicos (capítulos I, II e III) e um artigo de revisão (capítulo IV). Nos primeiros três artigos, analisou-se a variância da vegetação em diferentes escalas ecológicas; e no artigo de revisão, discutiu-se de forma aplicada a variância de fatores bióticos e abióticos em resposta à degradação. Dessa forma, a presente tese objetivou responder as seguintes questões: (I) Que diferenças podem ser observadas dentro de uma mesma espécie quanto à funcionalidade e suas estratégias de alocação sob diferentes graus de disponibilidade de recursos?; (II) Quão variáveis são as propriedades físicas e químicas do solo em diferentes escalas espaciais; e existem propriedades dos solos que podem explicar com maior precisão a distribuição das espécies em diferentes escalas espaciais? (III) Que porcentagem de variância da vegetação pode ser explicada por propriedades pedológicas e climáticas; e quais características de solo e clima melhor explicam esses padrões de vegetação? No capítulo IV é apresentado um modelo conceitual sobre degradação dos campos e sua aplicação aos campos do Rio Grande do Sul (RS). Para responder as questões acima usei dados ao nível de espécie de campos calcáreos da Alemanha (capítulo I); dados ao nível de comunidade em seis áreas campestres do Rio Grande do Sul, sul do Brasil (capítulos II e III); e através da revisão de literatura relacionada à degradação, quanto à capacidade de recuperação dos campos do RS (capítulo IV). Os resultados evidenciaram que: (I) dentro de espécies ficaram evidentes duas estratégias frente à limitação de recursos, enquanto a resposta dos atributos aos diferentes tratamentos se mostrou constante; (II) a variação dos parâmetros do solo relaciona-se à escala espacial aplicada e a variância da vegetação geralmente responde a diferentes parâmetros de solo em diferentes escalas; (III) 45% da variância da vegetação entre biomas nos campos do RS foi explicada por características pedológicas e climáticas, sendo em grande parte governada pela precipitação anual e a porcentagem de saturação por alumínio do solo; e (IV) o modelo conceitual apresenta variações ao longo de dois eixos (biótico e abiótico) e poderá servir de suporte a estudos de conservação e recuperação de campos tropicais e suptropicais, bem como facilitar a tomada de decisões quanto ao manejo e conservação. Como conclusão geral, verificou-se que a vegetação campestre responde a variações ambientais em diferentes escalas espaciais e pode adotar diferentes estratégias para sobrepor filtros ambientais e processos de degradação. O entendimento da relação entre a vegetação e o meio abiótico é de grande importância para tomada de decisões quanto ao emprego de formas alternativas de manejo e conservação. Whereas in temperate regions the abiotic-biotic relationship is well-known, in the tropics and subtropics our understanding is still preliminary. There is an urgent need to determine abiotic factors that control vegetation patterns in order to give support to restoration and conservation approaches. The present thesis analyses the relationship between abiotic factors and grassland vegetation in three original research papers (chapters I, II and III) and a review paper (chapter IV). In the first three papers, vegetation variance in response to abiotic factors was analyzed at different ecological scales; and in the fourth, the variance in biotic and abiotic factors in response to degradation process was discussed with a more applied view. Thus in this thesis the aim is to answer the following questions: (I) Which differences can be found in functional plant traits and allocation strategies within species at different levels of water and nutrient availability?; (II) How variable are physical and chemical parameters in different spatial scales; and are there soil parameters that can more accurately explain plant distribution in different spatial scales? (III) How much of RS grassland vegetation variance can be explained by soil and climatic properties; and which climatic and soil properties better explain these vegetation patterns? In chapter IV a conceptual model of grassland degradation is presented and applied to Rio Grande do Sul (RS) grasslands. To address these questions I used species-level data in a calcareous grassland in Germany (chapter I); community-level data in six sites in RS, South Brazilian grasslands (chapter II and III); and a review of literature studies concerning RS grassland degradation and restorability (chapter IV). The results showed that: (I) at a intraspecific level, the study species showed two allocation strategies in relation to resource stress, while the responses of individual traits to the soil treatments were consistent across species; (II) soil parameters variation are related to the measurement scale applied and the vegetation variance often responds to different soil parameters at different scales; (III) climatic and soil properties explained 45% of vegetation variance between biomes in RS grasslands and the main factors controlling its variance are annual precipitation and percent aluminum saturation; and (IV) the conceptual model is displayed as biotic and abiotic changes along the axes and can serve as a general framework to study degradation and restorability of tropical and subtropical grasslands, and further it may facilitate decisions on alternative management and conservation. As a general conclusion, the grassland vegetation responds to changes in the environment in different scales and may use different strategies to overcome environmental selective forces and degradation process. The understanding of this relationship is of high importance to facilitate decisions on alternative management and conservation.

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Demenois, Julien. "Quelle influence des symbioses mycorhiziennes et des traits racinaires sur l'érosion des sols tropicaux ? Application à la restauration écologique des écosystèmes forestiers dégradés de Nouvelle-Calédonie sur Ferralsols développés sur substrats ultramafiques." Thesis, Paris, AgroParisTech, 2017. http://www.theses.fr/2017AGPT0011.

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Les écosystèmes forestiers tropicaux représentent près de la moitié de la superficie forestière mondiale. Ces écosystèmes qui fournissent des services fondamentaux pour le bien-être de nos sociétés (e.g. régulation des flux de matières, maintien des sols) sont particulièrement touchés (perte et dégradation des forêts) par les changements globaux. La Nouvelle‐Calédonie, et ses substrats ultramafiques, ne font pas exception à cette tendance. L’activité minière et les feux sont responsables de la régression, de la fragmentation, de la dégradation des forêts et de l’érosion des sols. L’archipel est classé parmi les points chauds de la biodiversité mondiale et la restauration écologique de ces écosystèmes revêt de forts enjeux. L’objectif appliqué de cette thèse est de contribuer à la restauration écologique des forêts de NouvelleCalédonie afin de limiter l’érosion des sols sur substrats ultramafiques, et s’inscrit dans le champ disciplinaire de l’écologie de la restauration. L’objectif scientifique est d’étudier l’influence des symbioses mycorhiziennes et des traits racinaires sur l’érosion des Ferralsols développés sur substrats ultramafiques à travers une approche multi-échelle. Dans la première partie, nous mettons en évidence les caractéristiques floristiques et structurales de communautés végétales sur substrats ultramafiques. Celles-ci laissent présager une expression accrue des traits racinaires des espèces dominantes dans les forêts monodominantes. La place centrale du feu et des cyclones dans la dynamique de succession végétale est également soulignée, tout comme celle des symbioses mycorhiziennes dans le maintien de la monodominance de Nothofagus aequilateralis. Dans la deuxième partie, notre travail permet de suggérer l’existence d’un seuil biotique entre les maquis lignoherbacés dégradés et les maquis ligno-herbacés. Les feux répétés seraient la cause principale du franchissement de ce seuil. L’augmentation de la biomasse végétale constituerait en effet le facteur-clé contribuant à accroître la stabilité des agrégats entre ces deux stades. Ainsi, la protection contre les feux, associée à la promotion des successions végétales à travers l’utilisation d’espèces potentiellement facilitatrices comme Costularia arundinacea pourrait constituer une stratégie efficiente pour limiter l’érosion des Ferralsols. De plus, l’influence des communautés végétales (e.g. composition floristique) et fongiques (e.g. biomasse) sur la stabilité des agrégats est clairement mise en exergue. La troisième partie vise à évaluer la capacité d’espèces végétales, associées à des champignons mycorhiziens, à accroître la stabilité des agrégats, mais aussi à identifier les traits racinaires et les associations mycorhiziennes contribuant à cet accroissement. Dans cette partie, nous mettons en évidence que la combinaison de valeurs élevées des traits racinaires « Root Mass Density – Root Length Density – pourcentage de racines fines » est efficace pour augmenter la stabilité des agrégats. Par ailleurs, l’efficacité de cette combinaison de traits racinaires est accrue par les symbioses mycorhiziennes. Ainsi, des trois espèces végétales évaluées, Costularia arundinacea serait l’espèce-outil la plus efficace pour accroître la stabilité des agrégats. Ce travail a ainsi permis de mettre en évidence l’influence des traits racinaires et des symbioses mycorhiziennes sur la stabilité des agrégats des Ferralsols sur substrats ultramafiques, que ce soit à l’échelle des espèces ou des communautés végétales. A notre connaissance, ces résultats sont les premiers acquis sur ce type de sol. Ces résultats permettent de formuler des propositions en vue de la restauration écologique des milieux forestiers de Nouvelle-Calédonie afin de limiter l’érosion des sols sur substrats ultramafiques, mais aussi d’esquisser de nouvelles pistes de recherche Tropical forest ecosystems cover nearly half of the world's forest area. These ecosystems provide basic services for the well-being of our societies (e.g. regulation of material flows, soil preservation) are particularly affected (loss and degradation of forests) by global changes. New Caledonia, and its ultramafic substrates, is no exception to this trend. Mining and fires are responsible for forest regression, fragmentation, degradation and soil erosion. The archipelago is ranked among the hotspots of global biodiversity and the ecological restoration of these ecosystems is a major challenge. The objective of this thesis is to contribute to the ecological restoration of the forests of New Caledonia in order to limit the erosion of soils on ultramafic substrates and is part of the disciplinary field of the ecology of restoration. The scientific objective is to study the influence of mycorrhizal symbiosis and root traits on the erosion of Ferralsols developed on ultramafic substrates through a multi-scale approach. In the first part, we highlight the floristic and structural characteristics of plant communities on ultramafic substrates. These suggest an increased expression of the root traits of dominant species in monodominant forests. The central place of fire and cyclones in the dynamics of plant succession is also emphasized, as well as mycorrhizal symbioses in maintaining the monodominance of Nothofagus aequilateralis. In the second part, our work suggests the existence of a biotic threshold between degraded ligno-herbaceous maquis and ligno-herbaceous maquis. Repeated fires would be the main cause of crossing this threshold. The increase in plant biomass would be the key factor contributing to the stability of the aggregates between these two stages. Thus, fire protection combined with the promotion of plant successions through the use of potentially facilitating species such as Costularia arundinacea could be an efficient strategy for limiting erosion of Ferralsols. In addition, the influence of plant (e.g. floristic composition) and fungal communities (e.g. biomass) on the stability of aggregates is clearly highlighted. The third part aims to evaluate the ability of plant species, combined with mycorrhizal fungi, to increase the stability of aggregates, but also to identify root traits and mycorrhizal associations contributing to this increase. In this section, we demonstrate that the combination of high values for “Root Mass Density - Root Length Density – percentage of fine roots” is effective in increasing aggregate stability. Moreover, the efficacy of this combination of root traits is enhanced by mycorrhizal symbiosis. Thus, of the three plant species evaluated, Costularia arundinacea would be the most effective tool species for increasing the stability of aggregates. This work allowed us to highlight the influence of root traits and mycorrhizal symbiosis on the stability of soil aggregates on Ferralsols on ultramafic substrates, at the scale of plant communities or at the level of plant species. To our knowledge, these results are the first to be acquired on this type of soil. These results make it possible to formulate proposals for the ecological restoration of forest ecosystems in New Caledonia in order to limit soil erosion on ultramafic substrates, but also to sketch new avenues of research

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Polania, Perdomo José A. "Morpho-physiological analysis of adaptive responses of common bean (Phaseolus vulgaris L.) to drought stress." Doctoral thesis, Universitat Autònoma de Barcelona, 2016. http://hdl.handle.net/10803/400243.

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El frijol común (Phaseolus vulgaris L.) es la leguminosa alimenticia más importante en los trópicos. Es cultivada por pequeños agricultores y por lo general expuesta a condiciones desfavorables con mínimo uso de insumos. La sequía y la baja fertilidad del suelo, especialmente deficiencias de nitrógeno (N) y fósforo (P), son principales limitaciones para el rendimiento del frijol en los sistemas de pequeños productores. El frijol puede derivar parte de su requerimiento de N de la atmósfera a través de la fijación simbiótica de nitrógeno (SNF). El estrés por sequía limita severamente la capacidad SNF de las plantas. Identificación de rasgos asociados con resistencia a sequía contribuye a mejorar el proceso de generación de genotipos de frijol adaptados a estas condiciones. Se realizaron ensayos de campo en el Centro Internacional de Agricultura Tropical (CIAT), Palmira, Colombia, para determinar la relación entre rendimiento de grano y diferentes parámetros morfo fisiológicos tales como uso efectivo del agua (EUW), biomasa dosel, removilización de fotosintatos (índice de partición vaina, índice de cosecha, índice de cosecha de vaina) y capacidad de SNF en líneas élites seleccionadas por resistencia a sequía durante la última década. También se validó la metodología de abundancia natural de 15N usando tejido de grano para cuantificar diferencias fenotípicas en la capacidad SNF y su aplicación en programas de mejoramiento. Se utilizó discriminación de isótopo de carbono (CID) para la estimación de uso eficiente del agua (WUE) y uso efectivo de agua (EUW). Se evaluaron 36 genotipos de frijol pertenecientes al acervo genético mesoamericano en condiciones de campo con dos niveles de suministro de agua (riego y sequía) en dos temporadas. Adicionalmente, se realizó un estudio en condiciones de invernadero utilizando cilindros de plástico con suelo, para determinar la relación entre rendimiento de grano y diferentes características morfo fisiológicas de raíz tales como la longitud total de raíces, producción de raíces finas y tasa de crecimiento visual de raíces. La resistencia a estrés por sequía se asoció positivamente con EUW, raíces profundas y vigorosas, mejor crecimiento de las plantas, y superior movilización de fotosintatos a la formación de vaina y granos; y negativamente con días a floración y días a madurez fisiológica. Basándose en diferencias fenotípicas obtenidas en CID, conductancia estomática, biomasa del dosel y rendimiento de grano en condiciones de sequía, las líneas evaluadas se clasificaron en dos grupos, los ahorradores y los gastadores de agua. Estos dos grupos también se diferenciaron en sus características de raíces, los gastadores de agua con un vigoroso y profundo sistema de raíces y los ahorradores con un moderado a superficial sistema de raíces con mayor presencia de raíces finas. Se utilizó el método de abundancia natural de 15N para comparar capacidad de SNF estimada convencionalmente usando tejido foliar vs tejido de grano. Los resultados mostraron una correlación positiva y significativa entre el nitrógeno derivado de la atmósfera (Ndfa) calculado utilizando tejido foliar y Ndfa usando el tejido de grano. El método usando grano mostró variabilidad fenotípica en la capacidad de SNF bajo condiciones de riego y sequía, y una reducción significativa en condiciones de sequía. Se recomienda usar este método en programas de mejoramiento de frijol para mejorar la capacidad SNF. Mejor habilidad SNF bajo estrés por sequía fue relacionada con presencia de raíces gruesas. Mayor absorción de nitrógeno del suelo fue asociado con un sistema de raíces fino y profundo. El índice de cosecha vaina, discriminación de isotopo de carbono y Ndfa usando tejido de grano podría ser criterios de selección útiles en los programas de mejoramiento para seleccionar frijol común con resistencia a la sequía. Common bean (Phaseolus vulgaris L.) is the most important food legume in the diet of poor people in the tropics. This legume is cultivated by small farmers and is usually exposed to unfavorable conditions with minimum use of inputs. Drought and low soil fertility, especially phosphorus (P) and nitrogen (N) deficiencies, are major limitations to bean yield in smallholder systems. Beans can derive part of their required N from the atmosphere through symbiotic nitrogen fixation (SNF). Drought stress severely limits SNF ability of plants. Identification of traits associated with drought resistance contributes to improving the process of designing bean genotypes adapted to these conditions. Field studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia to determine the relationship between grain yield and different parameters in elite lines selected for drought resistance over the past decade. The selected traits were effective use of water (EUW), canopy biomass, remobilization of photosynthates to grain (pod partitioning index, harvest index and pod harvest index) and SNF ability. Moreover, in field trials we also validated the use of 15N natural abundance in grain tissue to quantify phenotypic differences in SNF ability for its implementation in breeding programs aiming to improve SNF in common bean. Carbon isotope discrimination (CID) was used for estimation of water use efficiency (WUE) and effective use of water (EUW). A set of 36 bean genotypes belonging to the Middle American gene pool were evaluated under field conditions with two levels of water supply (irrigated and rainfed) over two seasons. Additionally, a greenhouse study was conducted at CIAT using plastic cylinders with soil inserted into PVC pipes, to determine the relationship between grain yield and different root parameters such as total root length, fine root production and visual root growth rate in same group of elite lines under drought stress. Resistance to terminal drought stress was positively associated with EUW combined with a deeper and vigorous root system, better plant growth, and superior mobilization of photosynthates to pod and seed production, but negatively associated with days to flowering and days to physiological maturity. Based on phenotypic differences in CID, leaf stomatal conductance, canopy biomass and grain yield under drought stress, the tested lines were classified into two groups, water savers and water spenders. These groups also differ in their root characteristics, water spenders with a vigorous and deeper root system and water savers genotypes with a moderate to shallow root system and more presence of fine roots. We used 15N natural abundance method to compare SNF ability estimated from shoot tissue sampled at mid-pod filling growth stage vs. grain tissue sampled at harvest. The results showed a significant positive correlation between nitrogen derived from the atmosphere (Ndfa), estimated using shoot tissue at mid-pod filling, and Ndfa estimated using grain tissue at harvest. The method showed phenotypic variability in SNF ability under both drought and irrigated conditions. A significant reduction in SNF ability was observed under drought stress. We suggest that the method of estimating Ndfa using grain tissue (Ndfa-G) can be applied in bean breeding programs to improve SNF ability. Using this method of Ndfa-G, we identified bean lines that combine greater SNF ability with higher grain yield under drought stress. Better SNF ability under drought stress was related with superior presence of thick roots. Superior N uptake from the soil was associated with a large root system with more presence of fine roots. Pod harvest index, grain CID and Ndfa using grain tissue could be a useful selection criterion in breeding programs to select for drought resistance in common bean.

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Zwicke, Marine. "Impacts d'une canicule sécheresse sur le fonctionnement et la structure des communautés végétales de l'écosystème prairial." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-01020033.

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En Europe, les prairies permanentes représentent l'une des principales formes d'utilisation des terres. La durabilité des services rendus par ces écosystèmes est étroitement liée à la structure et au fonctionnement des communautés végétales qui les composent. La stabilité des processus écosystémiques, sous l'impact des fluctuations environnementales, va alors dépendre des mécanismes de résistance et de récupération propres à ces communautés. Les risques d'apparition d'extrêmes climatiques liés à l'évolution du climat, rendent nécessaire une adaptation des agro-écosystèmes à cette fluctuation climatique accrue. Cela implique de mieux comprendre les mécanismes par lesquels la variabilité du climat influe sur le fonctionnement et la structure des communautés végétales, et comment les pratiques agricoles impactent ces réponses. Cette thèse à pour objectif d'évaluer la vulnérabilité des prairies permanentes à un extrême climatique combinant une canicule et une sécheresse, dans un contexte de changement climatique. Afin d'identifier et de caractériser les mécanismes intrinsèques de la résistance à la sécheresse des communautés végétales, une démarche expérimentale mobilisant les concepts de l'écologie fonctionnelle a été développée. Les effets de la variabilité climatique sur la structure (diversité, composition) et le fonctionnement des communautés végétales ont d'abord été analysés in situ pendant 3 ans, après simulation d'une canicule-sécheresse dans les conditions climatiques actuelles et sous climat modifié (réchauffement et réduction des précipitations). Pour évaluer l'influence de la gestion sur la réponse des communautés végétales aux perturbations climatiques, deux fréquences de fauches ont été appliquées. Ce travail présente l'originalité d'avoir étudié conjointement le fonctionnement aérien et souterrain de la végétation. Sont considérées la production de biomasse, la démographie et la durée de vie des racines, afin de déterminer le rôle du système racinaire dans la résistance et la récupération des communautés végétales après une canicule sécheresse. Nous montrons un effet direct de l'extrême climatique sur la sénescence aérienne et la croissance racinaire dans les deux régimes de fauches. En réponse à un déficit hydrique modéré, la stratégie d'évitement au stress par le maintien de la croissance racinaire a été favorisée par des fauches non fréquentes. A l'automne suivant, les précipitations ont permis un reverdissement rapide de la couverture végétale et la production de nouvelles racines. Une baisse significative de la production de biomasse aérienne annuelle sous climat modifié, et suite à l'application de l'extrême climatique, a été observée pendant les 3 années d'expérimentation. En revanche, la production racinaire n'a pas été significativement affectée. Néanmoins une acclimatation de la croissance racinaire a été mise en évidence un an après l'extrême, en particulier dans les communautés de fauches non fréquemment. Ces changements de fonctionnement aériens et souterrains peuvent s'expliquer en partie par des modifications de la composition botanique. De plus, en réponse aux perturbations climatiques, la mortalité racinaire a été interrompue. Ces résultats inattendus ont donc entrainé une augmentation de la durée de vie des racines et suggèrent un effet négatif sur le turnover racinaire et les cycles biogéochimiques. Une expérimentation complémentaire à l'étude in situ a été menée en conditions semicontrôlées pour déterminer les mécanismes intrinsèques de la résistance à la sécheresse de la prairie permanente. Des traits morphologiques et physiologiques, aériens et souterrains, ont été mesurés sur des monocultures de sept populations prairiales en conditions optimales, puis en conditions de sécheresse afin de caractériser leurs stratégies de survie. Les résultats ont mis en évidence le rôle du système racinaire dans la survie des plantes. (...)

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Rossi, Lorenzo Matteo Walter. "Embankment as a carbon sink : a study on carbon sequestration pathways and mechanisms in topsoil and exposed subsoil." Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG083.

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La séquestration du carbone (C) fait l'objet d'une attention scientifique et politique croissante dans le cadre de la réduction des gaz à effet de serre. Les sols géotechniques ont été négligés en raison de leur potentiel de séquestration du carbone, et l'attention étant concentrée sur les sols agricoles et naturels. Nous visons à évaluer le potentiel des talus géotechniques comme puits de carbone et, par l'étude des espèces végétales et des sols présentant des caractéristiques contrastées, à mettre en lumière les mécanismes de séquestration du carbone organique et les rôles des différents acteurs impliqués. Nous visons non seulement à quantifier le C gagné et perdu dans le sol, mais aussi son origine (nouveau C frais et ancien C préexistant) et comment il est réparti dans différents pools de C qui montrent une stabilité du C différente (qualité du C stocké). Tout d'abord, nous avons évalué la séquestration du carbone dans différents pools de carbone sous un sol semé de 12 espèces herbacées différentes sur une période de 10 mois. La caractérisation des différents traits de racine a permis de comprendre l'influence de la stratégie d'alimentation des ressources en racines (représentée par le spectre économique de la racine) sur la séquestration du carbone. Nous avons montré que les espèces dont les caractéristiques racinaires sont associées à une production élevée de C labile entraînent une augmentation plus élevée de C dans le pool stable de SILT+CLAY (<20µm). Les espèces dont les traits de racine sont associés à un faible apport de C récalcitrant favorisent plutôt l'accumulation dans la fraction POM instable. Ensuite, grâce à une expérience de marquage isotopique stable de 183 jours (CO2 constamment enrichi en 13C), nous avons pu étudier la dynamique du C dans différents pools de C sous deux espèces (L. perenne et M. sativa) sur deux sols (terre végétale, profondeur 0-30 cm et sol remonté, profondeur 110-140 cm) aux caractéristiques opposées. Nous avons mis en évidence le grand intérêt de faire le pont entre l'origine du C et les pools de C lors de l'étude des destins du C du sol, ce qui permet de dévoiler des processus que les méthodes plus traditionnelles cachent. Le nouveau C et l'ancien C présentaient une covariation synergique, avec des pertes plus faibles de l'ancien C associées à de nouvelles entrées de C plus élevées. Ceci est conforme à l'hypothèse de l'utilisation préférentielle du substrat. Cette hypothèse a également été validée par l'étude de l’effet d’amorçage et de la respiration du sol. Celle-ci a montré que la teneur en CO2 inhalé était plus élevée lorsque les entrée C de la plante étaient élevées, tout en augmentant la minéralisation de l’ancien C lorsque les entrées de C de la plante étaient faibles, c’est-à-dire dans le sous-sol. De plus, nous avons validé l'hypothèse de réconciliation entre 'l'hypothèse de l'Utilisation Préférentielle des Substrats' et 'l'hypothèse de la Concurrence', cette dernière déterminant le 'priming effect' dans le sous-sol à faible fertilité. Nous avons observé de nouveaux apports significatifs de C d'origine végétale dans la fraction SILT+CLAY (<20µm, très stable) à l'appui de la preuve de l'effet d'ensevelissement in vivo dans l'hypothèse de la pompe à carbone microbienne du sol. L'effet de l'espèce s'est produit principalement sur les entrées de nouveaux C, mais il a été maîtrisé par l'effet du sol, avec un stockage de C plus faible dans un sol de faible qualité (faible activité et biomasse d'azote et microbienne). Les conditions microbiologiques ont été le principal moteur de la nouvelle accumulation de C et de l'ancienne perte de C et ont aidé à expliquer pourquoi aucun effet de la saturation en C du sol - une théorie centrale dans des études récentes sur la séquestration de C - n'a été trouvé dans le carbone protégé. Cette compréhension fondamentale des interactions plantes-sol nous aide à mieux optimiser la gestion des sols et de la végétation des talus des routes Carbon (C) sequestration is receiving increasing scientific and political attention in a framework of greenhouse gasses mitigation. However, geotechnical soils have been neglected for their C sequestration potential, with the global attention focusing on agricultural and natural soils. In the present thesis project we aim to assess the potential of geotechnical embankments as C sink, and, through the study of plant species and soils showing contrasting features, shed light on SOC sequestration mechanisms and the role of the different actor involved. We aim not only to quantify the C gained and lost in soil, but even its origin (fresh new C input or old preexistent C) and how it is partitioned in different C pools characterized by different C stability (quality of stored C). First, we evaluated the C storage in different pools under soil sowed with 12 different herbaceous species in a 10 months experiment. Assessing different root traits allowed understanding the influence of root economic spectrum on C storage. We showed how traits linked to high labile C are linked to a higher C increase in the stable SILT+CLAY pool (<20µm). Root traits related to a low input of recalcitrant, instead, favor accumulation in the unstable POM fraction. Thanks to a 183 days stable isotope labelling experiment (CO2 constantly enriched with 13C) we were able to study the C dynamics in different C pools under two species (L. perenne and M. sativa) sowed on two soil (topsoil, 0-30cm depth and subsoil brought to the surface, 110-140 cm depth) showing contrasting characteristics. We evidenced the great interest of bridging C origin and C pools when studying soil C fates, allowing unveiling processes those more traditional methods would hide. New C and old C showed synergetic covariation, with lower old C losses associated to higher new C inputs. This is in good accordance with the Preferential Substrate Utilization hypothesis (Cheng and Kuzyakov, 2005). The Preferential Substrate Utilization hypothesis was also validated with the study of priming effect and soil respiration, that showed higher plant derived C in respired CO2 when plant C input were high, while increasing old C mineralization when plant C input were low, i.e. in subsoil. We observed significant plant derived new C input in the SILT+CLAY fraction (<20µm, highly stable) supporting evidence of the in vivo entombing effect in the soil Microbial Carbon Pump hypothesis (Liang et al., 2017). The species effect mainly occurred on new C input, but it was overpowered by the soil effect, with lower C storage in low quality soil (low nitrogen and microbial biomass and activity). In general, microbiological conditions were the main driver for new C accumulation and old C loss, and helped to explain why no effect of soil C saturation – a central theory in recent studies on C sequestration - was find in the protected carbon. Such fundamental understanding of plant-soil interactions help us to better optimize soil and vegetation management for road embankment revegetation

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Leyval, Corinne. "Intéractions bactéries-mycorhizes dans la rhizosphère du pin sylvestre et du hêtre : Incidences sur l'exsudation racinaire et l'altération des minéraux." Nancy 1, 1988. http://www.theses.fr/1988NAN10169.

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L'influence de bactéries solubilisant les phosphates (agrobactérium) et de champignons éctomycorhizogènes sur l'altération d'un mica, la phlogopite et de phosphates insolubles, a été étudiée : en cultures liquides, en l'absence de racine ; dans la rhizosphère du pin sylvestre et du hêtre, en relation avec les composés exsudés. Les thizobactéries favorisent la solubilisation des éléments minéraux par production d'acides organiques. Les champignons ectomycorhizogènes solubilisent les phosphates en culture pure, mais, en conditions symbiotiques, ils jouent surtout un rôle par l'augmentation du volume de sol exploré par les racines, donc des surfaces d'échnage et d'adhésion avec les minéraux

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Yang, Luojin. "Root exudation pattern of sugar beet (Beta vulgaris L.) as influenced by light intensity and P deficiency." Thesis, 2016. http://hdl.handle.net/11858/00-1735-0000-0028-87DC-8.

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Henry, Amelia Lynch Jonathan P. "Root traits for sustainable low-input agro-ecosystems." 2008. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-2974/index.html.

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48

Hagerty, Christina H. "Mapping QTL for root rot resistance, root traits, and morphological trait in a common bean recombinant inbred population." Thesis, 2013. http://hdl.handle.net/1957/38263.

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Root rot diseases of bean (Phaseolus vulgaris L.) are a problem wherever they are grown, and are a major constraint to dry edible and snap bean production. Root rot is a primary yield limitation of snap bean production in the US, especially within the top three snap bean producing states of Wisconsin, Oregon and New York. Bean root rot pathogens will be present by the end of the first season even when starting with clean ground. The decline in yield can be relatively slow, so growers might not notice or appreciate the hidden yield cost associated with root rot disease. Traditional methods for disease control such as fungicides, crop rotations, cover crops, seedbed preparations have been proven ineffective (either physically ineffective or economically unviable) against root rot. Therefore, genetic resistance is needed. In order to address the need for genetic resistance to root rot in snap beans, the highly root rot resistant line RR6950, a small seeded black indeterminate type IIIA accession of unknown origin, was crossed with OSU5446, a highly root rot susceptible determinate type I blue lake four-sieve breeding line to produce the RR138 recombinant inbred mapping population. In this study we evaluated the RR138 RI population in the F₆ generation for resistance to Fusarium solani root rot in Oregon and Aphanomyces euteiches root rot in Wisconsin. We also evaluated this population for morphological traits and root structural traits including pod height, pod width, pod length, pod wall thickness, strings, seed color, flower color, tap and basal root diameter, and root angle measurements. The RR138 population was also genotyped on the 10K BeanCAP Illumina Beadchip. The Single Nucleotide Polymorphism (SNP) data was used to assemble a high-density linkage map and Quantitative Trait Loci (QTL) for phenotypic data were evaluated. The linkage map produced from this study contained 1,689 SNPs across 1,196cM. The map was populated with 1 SNP for every 1.4cM, spanning across 11 linkage groups. Three QTL associated with A. euteiches root rot resistance were consistently expressed in 2011 and 2012 trials. A. euteiches QTL were found on Pv02, Pv04, and Pv06 and accounted for 7-17% of total genetic variation. Two QTL associated with F. solani were found in 2011 trial on Pv03 and Pv07, account for 9 and 22% of total genetic variation, respectively. We also found several QTL for morphological traits and root structural traits including QTL for pod fiber and pod height on Pv04, pod length on Pv01, strings on Pv01, taproot diameter on Pv05, and shallow basal root angle on Pv05, accounting for 21, 26, 12, 20, 11, and 19% of total genetic variation, respectively. QTL discovered from Oregon data for F. solani resistance did not cluster with QTL for A. euteiches root rot resistance. "SNP0928_7", was highly associated with F. solani resistance on Pv07 and "SNP0508_2", was highly associated with A. euteiches on Pv02. QTL and markers associated with QTL from this study will be of value to snap bean breeders developing root rot resistant lines with processing traits, and provide more information about targeting the mechanism of resistance. Graduation date: 2013

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Han, Tsung-Han, and 韓宗翰. "Developing A System for Quantifying Root Traits of Rice Seedlings in 3D." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/x5mne5.

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碩士 國立臺灣大學 生物產業機電工程學研究所 105 Roots are important organs of plants. Root system architecture (RSA), the spatial configuration of roots, of rice (Oryza sativa L.) has shown a high degree of diversity. RSA needs to be quantified with high accuracy to understand the relationship between RSA and functionality of rice roots. This study developed a three-dimensional (3D) imaging system to quantify the RSA of rice seedling roots of 15 varieties. In this work, rice seedlings were cultivated in glass tubes filled with transparent jelly culture medium for ten days. The two-dimensional (2D) side-view images of the seedlings were acquired using the imaging system. Silhouettes of rice roots were then identified from the 2D side-view images using image recognition technology. Three-dimensional images of the rice roots were next reconstructed using the silhouettes and space-carving algorithm. A ground truth was used to validate the accuracy of the system. Last, RSA traits of rice seedling root of 15 varieties were quantified.

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Lin, Shih-Hung, and 林士弘. "Quantitative trait loci mapping for rice root traits under salinity stress at seedling stage." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/71038137113645207736.

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碩士 國立臺灣大學 農藝學研究所 102 Rice is one of the major crops in the world. Because human population grows, increasing rice production is necessary to meet human’s need. Salinity is a common abiotic stress to affect crop production, and rice is one of salt sensitive crops, therefore maintaining rice growth vigor under salt condition is an important issue. Root system is a major physical interaction between plants and soil substrates, it affects nutrients and salt absorption. In this research, we used two populations as study materials, one is recombinant inbred lines population derived from a cross between indica and temperate japonica, and a global diversity panel with 196 accessions. We measured root length under normal and salt condition at seedling stage, and found out degree of root growth vigor inhibited by salinity stress differs by root types. We used high density SNP markers to map QTLs controlling shoot and root growth in response to salt stress, many QTLs in RILs and in global diversity panel were mapped in this study. Although there was positive correlation between root and shoot traits under salinity stress, no identical QTLs were mapped. We selected accessions with good performance under salinity stress, these accessions will be good breeding materials to improve root vigor in elite cultivars, and through molecular assisted selection, QTLs with positive effect can be introduced to elite cultivars efficiently.

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