Дисертації: "Soil plant interactions"

1

Kraus, Tamara Esther Caroline. "Tannins and nutrient dynamics in forest soils : plant-litter-soil interactions /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.

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2

Sørensen, L. I. (Louise Ilum). "Grazing, disturbance and plant soil interactions in northern grasslands." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514291395.

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Abstract Plants and soil organisms are closely linked. Plants are the sole source of carbon in the soil and soil organisms are responsible for recycling of nutrients, making them available for plant growth. To understand the function of a system, it is important to understand the interactions between the soil and plants. These interactions have mainly been studied in temperate areas, with few studies in the arctic and subarctic. The aim of this thesis was to investigate the effect of ecological disturbances in sub- and low-arctic grasslands on soil organisms and plant-soil feedback relationships. The effect of removal of vegetation, replanting of a local plant species, and different components of grazing (trampling, defoliation and return of nutrients) on soil decomposer organisms were studied. Whether short term effects of defoliation depended on plant species community was also studied, as well as whether defoliation in the field could create changes in the soil system systems that affect the growth of seedlings. Experiments were conducted under both controlled greenhouse conditions and in field sites. The results showed that physical disturbance (removal of vegetation and trampling) reduced the abundance and diversity of soil biota. Defoliation increased soil decomposer abundance in the short term. Plant species composition did not affect soil biota and only in a few cases did it changes their responses to defoliation. In the long-term, effects of fertilization and defoliation on the soil biota were context-dependent. However, defoliation did create changes in the soil that reduced the growth of seedlings planted into the soil. Furthermore, plant species community and spatial heterogeneity (revealed by blocking) had important effects on the soil communities.

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3

Bonnett, Samuel A. F. "Biogeochemical implications of plant-soil interactions in peatland ecosystems." Thesis, Bangor University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428831.

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4

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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5

Hänninen, Kaarina. "Tree-cover crop interactions : birch growth, competition and soil properties /." Oulu : Oulun Yliopisto, 2002. http://herkules.oulu.fi/isbn9514267184.

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6

Card, Marcella. "Interactions among soil, plants, and endocrine disrupting compounds in livestock agriculture." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1311287470.

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7

Monteil, Oscar Vazquez. "Wastewater irrigation of crops : the influence of nitrogen on soil-plant interactions." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303449.

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8

Macpherson, Stuart Alexander. "Interactions between lead and phosphate : soil chemistry, plant uptake and ecological implications." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294125.

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9

Al-Turki, Ahmad I. "Myrosinase activity in soil and impact of Brassica on plant-microbe interactions /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486394475979013.

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10

Navarro, Patricia D. "Entomopathogenic Nematodes: Their Interactions with Plant Pathogens and Insecticides in the Soil." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/265815.

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Entomopathogenic nematodes (EPNs) in the families Heterorhabditidae and Steinernematidae, and their bacterial symbionts, have been studied intensively because of their role as natural mortality factor for soil-dwelling arthropods, and their potential as biological control agents for belowground insect pests. Moreover, EPN are recognized as key players in regulating soil food webs and triggering trophic cascades. However, most studies of interactions with EPN have been conducted under laboratory setting and simplified conditions, without consider the dynamic of the EPN and their interactions with other soil components in a wider context. In this respect, knowledge of the effect that other soil organisms or human induced factor may have on EPN dynamic and life cycle in the soil may contribute to improve tactics for their implementation and success as natural regulators of herbivores. The present investigation focused on the interactions of EPN with a selection of insecticides, and biotic (saprobic fungus and plant parasitic nematodes) elements that may be present in the soil, and may potentially interact with EPN. Specifically, I investigated how these factors may affect the life cycle (host search behavior, virulence and reproduction) of EPN. Appendix A shows the effect that a group of selected synthetic and biological insecticides have on EPN virulence and reproduction. The results obtained from this study revealed that most combinations of EPN and insecticides under study increased the mortality of the insect host. However, it was also found that some of these combinations reduced the nematode progeny production and emergence of IJs from the insect cadaver. In contrast in Appendix B, when examining the effect of the saprobic fungus Fusarium oxysporum in the life cycle of the EPN Heterorhabditis sonorensis, it was found that this fungus negatively affected the virulence and reproduction of the EPN in the insect host. In the third study of this dissertation (Appendix C) the interactions studied considered the effect of two EPN on an organism of a different trophic guild, the plant parasitic nematode Tylenchulus semipenetrans. This plant parasitic nematode causes serious diseases in citrus plants by infecting their roots and defoliating their branches. Previous studies have shown that some EPN species may negatively affect the life cycle of plant parasitic nematodes by reducing the damage produced by this plant parasite. Results from this study confirm the antagonistic effect between the selected EPN and the citrus nematode. Specifically, it was found that the presence in the soil of both EPN reduced the survival of infective juveniles of the citrus nematode and their penetration to the root. Moreover, the presence of EPN had an antagonistic effect in the production of eggs of T. semipenetrans females.

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11

Prill, Nadine. "Effects of environmental change on plant performance and plant-herbivore interactions." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:c58761e9-666c-4b7d-a78a-d70de7f253d4.

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Global environmental change fundamentally affects plants and their interactions with other species, and this has profound impacts on communities and ultimately ecosystems. In order to understand the mechanisms involved, we need to elaborate on the combined effects of different global change drivers on multiple levels of plant organization, including the biochemical level (production of defence compounds), the whole organism, the population, and the plant-herbivore interaction level. This thesis investigates (1) the combined effects of factors related to climate change and habitat fragmentation on Brassica nigra and (2) the effects of Zn soil pollution on the heavy metal hyperaccumulator Noccaea caerulescens at these different levels. Common garden and greenhouse experiments with B. nigra applied drought stress and elevated CO2 to examine climate change impacts, while crossing treatments (inbreeding and between-population outbreeding) were used to investigate habitat fragmentation effects. Heterosis was lost under drought stress, and there were several interactive effects of the experimental treatments that varied within and among populations. In a greenhouse experiment with N. caerulescens, plants were grown on soil with different amounts of zinc. Plants had greater herbivore resistance when grown on Zn-amended soil, and invested more in herbivore tolerance when grown on soil without added Zn. In general, the results indicate that factors related to global environmental change have complex and interactive effects on different levels of plant organization. The findings are discussed in terms of their implications for ecology, evolution and conservation.

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12

Steer, Jonathan. "Influences of plant growth and root material on soil microbial community dynamics." Thesis, University of East London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298081.

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13

Batten, Katharine Margaret. "Plant invasion and the soil microbial community : interactions and implications for native plant performance and ecosystem function /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2004. http://uclibs.org/PID/11984.

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14

Emam, Taraneh Megan. "The Role of Soil Biota, Abiotic Stress, and Provenance in Plant Interactions and Restoration." Thesis, University of California, Davis, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=3706585.

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In this dissertation, I asked how soil biota, abiotic stress, and plant provenance influence plant communities and interactions between plants. Soil biota can have positive or negative effects on individual plants, and also influence the diversity and productivity of plant communities through their net effects on individuals and by mediating plant-plant interactions. However, the level of abiotic stress experienced by plants is likely to drive plant responses to soil mutualists and antagonists. Additionally, plant provenance (e.g. population origin) can influence responses to abiotic soil conditions as well as to soil organisms. Understanding how these three interacting components shape plant interactions may improve success of restoration and invasive plant management. During restoration, the goal is typically to create conditions conducive to native plant reestablishment. However, amelioration of disturbed areas by reducing abiotic stress or by adding beneficial soil organisms may unintentionally increase colonization and growth of non-native plants. Using the applied context of mine restoration, I examined how soil biota, abiotic stress, and plant provenance affected plant communities and interactions in four studies. In Chapter 1, I found that both a native grass (Bouteloua gracilis ) and an invasive grass (Bromus tectorum) responded positively to soil biota when grown alone in the greenhouse. However, when grown together, the presence of soil biota increased the competitive ability of Bromus, while the removal of soil biota increased competition by Bouteloua. Results supported the hypothesis that invasive species such as Bromus often have positive responses to soil biota in the invaded range, but I also found that Bromus response to soil biota removal varied considerably by site. In Chapters 2 and 3, I examined how methods used during restoration (application of stockpiled soil and inoculation with soil biota) affected native and non-native plant growth in field plots. I found that native plant biomass and non-native plant biomass both tended to increase when soil abiotic stress was ameliorated through the addition of deeper stockpiled soil. In addition, both native and non-native grasses responded positively to the use of local soil an as inoculant, while non-native forbs responded negatively to local soil inoculum. However, native plants only received significant benefits from inoculation when targeted application to native seedling transplants was used. Commercial mycorrhizal fungal inoculum did not affect plant growth. In studies of both stockpiled soil addition and soil inoculation, year was an important factor in determining plant responses. Variation in effects by year may reflect differences in precipitation timing or amount, or changes associated with plant and soil biota growth over time. In Chapter 4, I used a greenhouse experiment to examine how one type of soil biota, arbuscular mycorrhizal fungi (AMF), influenced plant-plant interactions. I also manipulated abiotic stress (soil phosphorus availability) and plant provenance (stress-tolerant ecotype versus competitive ecotype) to assess whether these factors influenced AMF-mediated interactions among plants. I found that allowing or denying AMF hyphal access between neighboring pots altered plant reproduction. Inflorescence production was substantially decreased when hyphal access was allowed between two stress-tolerant plants. In addition, when hyphal access was permitted from a stress-tolerant plant to a competitive plant, the competitive plant flowered slightly sooner, whereas allowing hyphal access between two stress-tolerant plants led to slightly slower flowering. These results did not appear to be driven by abiotic stress or plant nutrition. It is possible that AMF transmission of infochemicals may play a role in regulating plant phenology and reproduction; however, further research in this area is needed.

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15

Dehlin, Helena. "Ecosystem functioning and plant-soil interactions in forests : influences of quality and diversity of resources /." Umeå : Dept. of Forest Vegetation Ecology, Swedish University of Agricultural Sciences, 2006. http://epsilon.slu.se/200679.pdf.

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16

Robinson, Lynne Allison. "Impacts of interactions with soil organisms on the metabolome of ragwort (Senecio jacobaea L.)." Thesis, University of Sussex, 2013. http://sro.sussex.ac.uk/id/eprint/44738/.

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Plants need to defend themselves against their natural enemies without compromising their interactions with beneficial organisms. Chemical mechanisms underpin many of these interactions and changes in plant metabolism are critical to both robust defences against antagonists and effective signals to mutualists. Further, such plant responses can be systemic, so mediating interactions between spatially separated organisms above and below ground. This thesis aimed to characterise the changes in the ragwort (Senecio jacobaea L.) metabolome caused by two different belowground organisms, an antagonistic herbivorous nematode (Pratylenchus penetrans (Cobb, 1917) Filipjev & Schuurmans Stekhoven, 1941) and a mutualist arbuscular mycorrhizal fungus (AMF) (Glomus intraradices Smith & Schenck). Initially, vegetative and reproductive stage ragwort plants were sampled in the field and the chemical composition of leaf and flower tissues was assessed using a metabolomic approach. Techniques for the identification of key ragwort secondary metabolites were trialled and results demonstrated that plants of different ages differed in their allocation of within plant defences such as flavanoids, pyrrolizidine alkaloids (PAs) and chlorogenic acids. Subsequent experiments with nematodes and AMF focussed on the analysis of leaf tissues from vegetative stage plants. Feeding by the nematode species P. penetrans resulted in increased concentrations of metabolites associated with plant defence, including the main class of ragwort defence compounds PAs. In contrast, colonisation of root material by AMF caused increases in the concentrations of metabolites associated with the maintenance of the beneficial interaction between plant and fungi, such as a number of apocarotenoids known as blumenols. The findings of both experimental studies detected unexpected and previously unreported changes in plant metabolism, highlighting the importance of an untargeted approach when examining the chemical ecology of plant interactions.

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17

Ayres, Edward. "Impacts of rising atmospheric COâ‚‚ concentrations on plant-soil-microbial interactions in forest ecosystems." Thesis, Lancaster University, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421605.

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18

Cunha, Felisberta Maria Jesus. "The influence of extracts of Ascophvllum nodosum on plant and soil-borne pathogen interactions." Thesis, University of Plymouth, 2002. http://hdl.handle.net/10026.1/2348.

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This thesis presents an investigation into the responses to extracts of Ascophyllum nodosum (Maxicrop seaweed extracts - MSE) of two different plants species - wheat and strawberry, and their interactions with two soil-borne pathogens, Gaeumannomyces graminis and Phytophthora fragariae respectively, under various environmental conditions. The responses to MSE using hydroponic, glasshouse and field experiments showed that levels of Take-all infection in wheat were reduced by some of the treatments applied. Repeat experiments showed that consistency of results was poor but a positive trend for disease suppression followed MSE treatments. Studies of strawberry infection by Phytophthora fragariae revealed a significantly reduced level of disease severity in plants grown both in hydroponics and in the growth chamber in response to MSE. In vitro studies of the fungus demonstrated that the seaweed extract treatments severely altered mycelial growth, which drastically reduced formation of sporangia and release of zoo spores. Experiments using β-glucan, β-glucanase and laminarin showed that these could not reproduce the effects observed for MSE treatments suggesting that these components were not responsible for the MSE effect. Applications of potassium salts however, did reproduce the responses observed when applied at concentrations similar to the ones found in the seaweed extract. In these investigations, no significant benefits to non-inoculated strawberry plants could be identified as a response to MSE. Measurement of growth of disease infected plants, however clearly demonstrated that they benefited in terms of growth from the MSE amendments probably as a consequence of the disease suppression obtained.

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19

Di, Palo Francesca. "Plant species and soil nutrient interactions along primary successions: the role of ecological stoichiometry." Thesis, Ulster University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.650087.

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A long-standing question in plant ecology remains about what underlying mechanisms are responsible for the distribution of plant species across environmental gradients. Most plant ecologists agree that the answer lies within the concept of 'niche' and thus in the set of driving 'key-resources' for plant growth under specific environmental conditions. Here I examine two key soil resources: nitrogen (N) and phosphorus (P). I ask whether changes in the availability of Nand P in soils may predict changes in critical plant element ratios (i.e. C:N:P stoichiometry). Very few studies have used an 'ecological stoichiometric' approach to address whether changes in soil nutrient availability and content could explain changes in plant C:N:P tissue stoichiometry along strong soil development gradients. I address this question using four ecological successions distributed across Europe where I measured C:N:P stoichiometry of roots, stems and leaves of 72 plant species. If plant nutrient stoichiometry is determined by Nand P uptake in response to local growth conditions (i.e. pioneer vs. advanced soil development stages), I would expect soil and plant N:P ratios positively related along the soil chronosequence. Overall my results show that soil N:P ratios strongly increased along the gradient of soil development from pioneer to advanced successional stages. However, I found that neither changes in soil nutrient availability, nor total soil nutrient content or soil N:P stoichiometry were significantly related to changes in plant nutrient stoichiometry. Instead I found that plant functional group identity (i.e. legumes vs. grasses vs. forbs) has a strong control over changes in plant N:P ratios regardless of the temporal stage of the ecological succession. I have also found that carbon:nutrient ratios (either C:N or C:P) along primary successions are quite variable and are partly related to changes in soil nutrient status, plant functional group identity and plant compmiment (e.g. roots vs. leaves). The lack of any correlation between soil and plant stoichiometry could be attributed to (1) the presence of internal mechanisms of plant nutrient and carbon use efficiency, (2) belowground ecophysiological processes (e.g. root exudation), and (3) plant-microbial interactions (e.g. symbiosis) all which can affect plant nutrients uptake and nutrient reallocation within compmiments. Finally, my study shows that wild-plant species seem to have a high-degree of internal nutrient regulation (i.e. high stoichiometric homeostasis), whose underlying mechanisms need to be better understood because may be key to better understand plant distribution along environmental gradients

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20

Shan, Shan. "The controls of nutrient limitation on resource allocation belowground." Miami University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=miami1580078025127756.

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21

Turnbull, Gillian Anne. "The role of motility in Pseudomonas fluorescens and Pseudomonas putida in soil-plant-microbe interactions." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367105.

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22

Fornara, Dario Arturo. "Ungulate browsing as an ecosystem process browser-plant-soil interactions in a southern African savanna /." Thesis, Connect to this title online, 2005. http://upetd.up.ac.za/thesis/available/etd-02172006-090829.

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23

Murray, Donna. "Interactions of Pseudomonas fluorescens and soil-borne oomycete plant pathogens in a biological control system." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259856.

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24

Richardson, Harriett Rose. "The role of plant-soil interactions in peatland carbon cycling at a Scottish wind farm." Thesis, University of Glasgow, 2014. http://theses.gla.ac.uk/5636/.

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Northern peatlands play an important role in the cycling of carbon (C) globally, and contain up to one third of the world’s soil C despite only covering a small percentage of its land surface (Gorham, 1991). Changes in climate and land use are increasing the vulnerability of these vast C stocks, by altering the conditions favourable for peat accumulation and therefore C sequestration. The establishment of wind farms on peatlands is increasing in the UK, as a result of the growing need for sustainable energy and the suitably high wind speeds that are typical to these upland ecosystems (Smith et al., 2014). There is limited understanding of the impacts of operational wind farms on their host ecosystems, but evidence to suggest that wind farms create microclimate conditions by altering ground-level temperature is increasing (Armstrong et al., 2014a; Baidya Roy and Traiteur, 2010; L. Zhou et al., 2012). The sensitivity of peatland C cycling processes to wind farm-induced microclimatic changes represents a considerable gap in knowledge. Further, the role that aboveground and belowground peatland communities have in mediating the effects of wind farm microclimates on C cycling processes remains unknown. By examining plant-soil interactions across a peatland at Black Law Wind Farm and under a range of microclimate conditions in the laboratory, this thesis aimed to investigate the influence of plant functional type (PFT) and microclimatic conditions on physical, chemical and biological peatland properties, greenhouse gas (GHG) emissions and litter decomposition. Results show that a PFT legacy in peat plays a mediatory role in the response of CO2 and CH4 emissions to microclimatic differences in temperature and water table. Mass loss of litter is primarily driven by PFT differences in litter quality, with interactions between litter types controlling decomposition of litter mixtures via non-additive effects, and interactions between litter types and PFT legacies in peat affecting the likelihood of home-field advantage and disadvantage (HFA and HFD) litter mass loss. This thesis demonstrates that the direct effects of microclimatic changes in temperature and water table are important drivers of peatland C cycling processes; however the indirect effects of microclimate change on plant community composition e.g. the relative proportion of PFTs could influence these processes to a greater extent. Examining the importance of PFTs in C cycling processes at wind farm peatlands is important in improving predictions of peatland C sequestration under future climate change scenarios, and in calculating the C savings achieved by land-based renewable technologies.

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25

Malyshev, Andrey [Verfasser], and Jürgen [Akademischer Betreuer] Kreyling. "Plant growth responses to winter climate change: from amongand within-species variation to plant-soil interactions / Andrey Malyshev. Betreuer: Jürgen Kreyling." Bayreuth : Universität Bayreuth, 2015. http://d-nb.info/1074461851/34.

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26

Miller, Phearen Kit. "Interactions Between Biochar and Compost in Organic Winter Wheat Production and Soil Quality Under Dryland Conditions." DigitalCommons@USU, 2018. https://digitalcommons.usu.edu/etd/7359.

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Organic wheat grown under dryland conditions encounters challenges such as limited nutrients and water. Maintaining organic wheat production requires solutions to these problems in order to retain economic sustainability for the farmers. Research on biochar and compost have been conducted globally. Despite well known benefits of compost on soil and crop production, few organic farmers apply compost to their fields. Research on biochar is still new. Biochar is charcoal created from pyrolyzing agricultural material under conditions of low oxygen and high heat. Many studies claim that biochar is a valuable soil amendment for improving organic production and reducing environmental pollution (such as greenhouse gas emission, water pollution, or nutrient leaching). It may hold more moisture in the soil and retain nutrients. We conducted a study on the interactions between biochar and compost in organic winter wheat production and soil quality under dryland conditions. We analyzed the response to biochar and compost, and investigated individual and combined effects on wheat yield, wheat quality, and soil quality. This study revealed that compost had significant impacts on increasing wheat yield and had slight impacts on soil quality while biochar had none to slight impacts on soil and wheat production. We validated the usefulness of compost for organic wheat production in dryland condition, but found no real benefit for biochar in this first year.

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27

Hammer, Erin L. "Effects of garlic mustard (Alliaria petiolata) on soil nutrient dynamics and microbial community function and structure." Connect to full text in OhioLINK ETD Center, 2009. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=toledo1241126072.

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Thesis (M.S.)--University of Toledo, 2009. Typescript. "Submitted as partial fulfillment of the requirements for The Master of Science Degree in Biology (Ecology-track)." "A thesis entitled"--at head of title. Bibliography: leaves 44-55.

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28

Maisch, Markus [Verfasser]. "Rusty rice - unravelling rice plant and microbial interactions in the paddy soil iron cycle / Markus Maisch." Tübingen : Universitätsbibliothek Tübingen, 2020. http://d-nb.info/1215568983/34.

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29

Reynolds, Amanda Christine. "Geochemical Investigations of Mineral Weathering: Quantifying Weathering Intensity, Silicate versus Carbonate Contributions, and Soil-Plant Interactions." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194448.

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This study is the geochemical examination of mineral weathering and its path from hinterland, through sediment deposition and pedogenesis, to its dissolution and eventual uptake into plants or precipitation as carbonate minerals. The three papers examine the rate and character of carbonate and silicate mineral weathering over a wide range of climatic and tectonic regimes, time periods, and lithologies, and focus on very different questions. Examination of the 87Sr/86Sr ratios of architectural ponderosa pine in Chaco Canyon, New Mexico confirms a societally complex style of timber procurement from the 10th to the 12th centuries. In El Malpais National Monument, New Mexico, we measured the 87Sr/86Sr ratios in local bedrock and soils and compared them to the leaf/wood cellulose of four conifers (Pinus ponderosa, Pinus edulis, Juniperus monosperma, Juniperus scopulorum), a deciduous tree (Populus tremuloides), three shrubs (Chrysothamus nauseosus, Fallugia paradoxa, Rhus trilobata), and an annual grass (Bouteloua gracilis) and a lichen (Xanthoparmelia lineola). We found that plant 87Sr/86Sr ratios covaried with variations in plant physiognomy, life history, and rooting depth. In addition, the proportion of atmospheric dust and bedrock mineral contributions to soil water 87Sr/86Sr ratios varied predictably with landscape age and bedrock lithology. On the Himalayan floodplain, soils and paleosol silicate weathering intensities were measured along a climatic transect and through time. Overall, carbonate weathering dominates floodplain weathering. But, periods of more intense silicate weathering between 9 - 2 Ma, identified in soil profile and in the 87Sr/86Sr ratios of pedogenic carbonates, appear to be driven by changes in tectonic, rather than climatic, regime. All three papers are good examples of how 87Sr/86Sr isotopic tracer studies can shed light on pedogenic formation rates and internal processes. The complexity of each system warns against generalizations based on just one locale, one species or lithology, or a few isotopic ratios.

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30

Nessa, Ashrafun. "Soil nitrogen transformations and soil-plant interactions as influenced by biochar materials and prescribed burning in native forest ecosystems of southeast Queensland." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/414257.

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The nitrogen (N) cycle is one of the key biogeochemical processes in terrestrial ecosystem which is interlinked with some important soil N transformations, notably soil N mineralization, nitrification and denitrification through both biotic and abiotic mechanisms. Global climate change and soil management practices have disrupted the soil N cycling processes. Soil types, plant species and vegetation diversity and management practices are also associated with changing N cycling processes. Prescribed burnings are applied periodically for fuel reduction to reduce the risk of wildfires. Nevertheless, high frequency burning may limit N availability, and make soil more N and water limited. Biochar is a carbon-rich product produced from organic materials using pyrolysis process and has the potential to modify soil N transformations and N retentions by improving soil-plant water relationships and N availability. In the soil-plant system, biochar can recover and retain N by controlling efficient inorganic N use as well as by recycling the N in a balanced manner which determines the flow, direction and availability of soil N and directly influences N use efficiency by plants and controls the productivity of terrestrial ecosystem. However, the effects of biochar on soil N processes are determined by biochar characteristics and soil properties. Biochar pyrolysis temperatures directly influence biochar properties, for example, the surface area and porosity of biochar increase with increasing pyrolysis temperature, leading to enhanced soil N retention and improve water holding capacity (WHC). Additionally, biochar application rate is another factor to consider because large amounts of applied biochar can impact the N cycle by altering soil pH, enhancing N immobilization, leading to changes in N availability. However, the quantitative information about the relationships between biochar pyrolysis temperature and the mechanisms regulating soil N cycling processes as well as biochar application rates and the mechanisms determining whether and how biochar application rates would affect soil N cycling processes have not been well studied especially under field conditions. Therefore, my thesis aimed to examine how biochar application would enhance soil N transformations and N retention by improving soil-plant water relationships and N availability in the N cycling processes in the forest soils of southeast Queensland, Australia. Briefly, in Chapter 2, I assessed how pyrolysis temperature would affect biochar properties and subsequently soil N transformations through a short term laboratory incubation study at two moisture levels. In Chapter 3, I examined how pyrolysis temperature dependent biochar would influence soil labile C and N pools and microbial biomass under the same experimental condition of Chapter 2. To evaluate the interactions between soil N transformations and soil- plant-biochar systems under field conditions, in Chapter 4, I investigated the soil-plant-biochar relationships by examining how biochar and understorey Acacia species would affect the biological N fixation (BNF) and water use efficiency (WUE) of understorey Acacia species as well as soil C and N pools 15 months after biochar application post fire (nearly 3 years after controlled prescribe burning) in suburban native forest of subtropical Australia. Finally, in Chapter 5, I set up a laboratory incubation study to assess the effects of biochar application rates and understorey Acacia species (Acacia leiocalyx and Acacia disparrima) on soil N pools and transformations post fire soil following a 5-day laboratory incubation at two moisture levels (i.e. 60% and 90% WHC). In Chapter 2, I set up a laboratory incubation for 5-days with pine wood (Pinus radiata) biochar at a rate of 5% (w/w) which was produced under six pyrolysis temperatures (e.g. 500, 600, 650, 45 700, 750 and 850°C). I used 15N natural abundance (δ15N) of inorganic N (NH4+-N and NO3--N) to assess the potential of biochar materials in facilitating forest soil N transformations at two soil moisture levels of 50% and 65% WHC. This study revealed that pyrolysis temperature had significant effects on biochar total N and δ15N. Cumulative nitrification and N mineralization were significantly lower in the biochar amended soils than those of the control soil, with significantly lower δ15N of NH4+-N and δ15N of NO3--N in the biochar amended soil. In this 51 study, nitrification was the key driver of soil N mineralization. Additionally, cumulative nitrification and N mineralization responded non-linearly to the increase in pyrolysis temperature. In this study, an optimum pyrolysis temperature range of 600-700°C was identified for improving soil nitrification and N mineralization under the laboratory incubation conditions whereas the greater cumulative nitrification and N mineralization were found at the 65% WHC compared with those at 50% WHC. In Chapter 3, I measured water extractable organic C (WEOC) and total N (WETN), hot water extractable organic C (HWEOC) and total N (HWETN), microbial biomass C (MBC) and N (MBN) as well as mineral N (NH4+-N, NO3--N) to understand the key mechanisms and identify the main indicators of soil quality which can determine soil labile C and N pools through a 5- day laboratory study using different pyrolysis temperature dependent biochar (500-850°C) at two moisture levels of 50% and 65% WHC. This study showed that WETN was significantly lower in the biochar amended soils compared with those of the control soil. WETN was the most sensitive indicators for determining the changes in soil labile C and N pools and had a significant positive correlation with soil MBN, suggesting that microbial biomass would be able to use water extractable N as energy sources for metabolism purposes. Biochar application significantly reduced soil NO3--N and increased N retention in Yarraman soil by enhancing N immobilization due to increased C input from biochar. The 65% WHC had generally greater soil labile C and N pools compared with those of the 50% WHC. In Chapter 4, I used the soil and foliar samples from a suburban forest where pine wood biochar (600°C) was applied at the rate of 0, 5 and 10 t ha-1, 20 months after prescribed burning. I collected the samples months after biochar application. I used N and C isotope compositions (δ15N and δ13C) to assess the BNF and WUE of two understorey Acacia species (A. leiocalyx and A. disparrima). I also examined soil C and N pools and their stable isotope compositions (δ15N and δ13C). This study revealed that biochar did not affect the BNF and WUE 15 months after biochar application. However, BNF varied significantly between the Acacia species and were significantly greater for A. leiocalyx compared with those of A. disparrima; suggesting that understorey A. leiocalyx was more effective in improving N recovery after prescribed burning via BNF as reflected in more N availability in the soil compared with that of A. disparrima in the suburban native forest of subtropical Australia. Soil NH4+-N was significantly lower in the biochar amended soils compared with that of the control soil due to the surface adsorption and N immobilization. The significant positive relationship between soil δ15N (10-83 20 cm) and foliar δ15N highlights that the mechanisms influencing soil δ15N also influence plant δ15N through N uptake. In Chapter 5, I collected soil from a depth of 0-5 cm from biochar treated forest soil 15 months after biochar application and conducted a 5-day laboratory incubation study. I used δ15N approaches to assess and measure the soil N pools and N transformations. Biochar application at the rate of 10 t ha-1 had lower soil NH4+-N and lower cumulative ammonification in the soil which would help improve N availability by reducing mineral N losses. Day 5 NH4+-N was significantly greater at 90% WHC compared with that of 60% WHC whereas Day 5 δ15N of NH4+-N showed an opposite result, indicating a negative liner relationship between NH4+-N and δ15N of NH4+-N . These results demonstrated that at the greater soil moisture level of 90% WHC, N availability in the form of NH4+-N was greater due to greater N mineralization of organic N with lower δ15N, leading to lower δ15N of NH4+-N. Hence, δ15N of organic and inorganic N in the forest soil could be a useful tool for distinguishing the contributions of different processes such as BNF from soil N transformations as well as N loss mechanisms in the soil N cycle. Thesis (PhD Doctorate) Doctor of Philosophy (PhD) School of Environment and Sc Science, Environment, Engineering and Technology Full Text

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31

Popp, Alexander, Niels Blaum, Stephanie Domptail, et al. "From satellite imagery to soil-plant interactions : integrating disciplines and scales in process based simulation models ; [Poster]." Universität Potsdam, 2006. http://www.uni-potsdam.de/imaf/events/ge_work0602.html.

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Decisions for the conservation of biodiversity and sustainable management of natural resources are typically related to large scales, i.e. the landscape level. However, understanding and predicting the effects of land use and climate change on scales relevant for decision-making requires to include both, large scale vegetation dynamics and small scale processes, such as soil-plant interactions. Integrating the results of multiple BIOTA subprojects enabled us to include necessary data of soil science, botany, socio-economics and remote sensing into a high resolution, process-based and spatially-explicit model. Using an example from a sustainably-used research farm and a communally used and degraded farming area in semiarid southern Namibia we show the power of simulation models as a tool to integrate processes across disciplines and scales. <hr> Interdisziplinäres Zentrum für Musterdynamik und Angewandte Fernerkundung Workshop vom 9. - 10. Februar 2006.

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32

Van, Zyl Albertus J. "Assessment of the possible interactions between soil and plant water status in a Vitis vinifera cv. Merlot vineyard." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/96088.

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Thesis (MScAgric)--Stellenbosch University, 2014. ENGLISH ABSTRACT: Irrigation scheduling decisions are based either on the direct measurement of soil water status (SWS) or on physiological measurements like plant water status (PWS). Soil based measurements are quick and easily automated, but the plant response for a particular quantity of soil moisture varies as a complex function of evaporative demand. A plant-based approach measures the plant stress response directly, but is an integration of environmental effects as well. In contrary to soil-based methods, plant based measurements can indicate when to irrigate, but not the quantity. Pre-dawn leaf water potential (ΨPD) is determined mostly by the soil moisture level, and can serve as a measure of static water stress in plants and an index of bulk soil water availability or even as an estimate of soil water potential at the root surface. Therefore it should be possible to establish a link between SWS and PWS, but it is largely unknown how stable the link in a heterogeneous vineyard would be, and how the grapevine vegetative and reproductive response relates to this link. Plant water status plays a large role in determining vigour and yield of the plant. The levels of PWS are influenced by irrigation, but it was mostly affected by the season and vine location in the vineyard. More negative plant water potentials reduced vigour, but had a less pronounced effect on yield, while also reducing overall wine quality. Vigour variability in the vineyard was largely attributed to soil heterogeneity, which seemed to have a strong effect on SWS. SWS measurements were calibrated according to the observed variability, increasing the accuracy of measurements significantly. Soil water content values were used to establish a link between SWS and PWS. This link was determined over time using nine plots, consisting of rain-fed and irrigated regimes, in variable vigour areas. A non-linear relationship was found between ΨPD and percentage extraction of plant available water for rain-fed plots. When irrigation was applied, no correlation could be found. In this study, for Merlot in the Stellenbosch region, PWS differences affected vigour, and to a lesser extent yield, as well as wine quality. More negative plant water potentials reduced vigour more in high vigour areas than in lower vigour areas, which in turn led to unbalanced vegetative: reproductive ratios. This disturbed vine balance may have had a bigger impact on wine quality than PWS levels. Therefore a well-managed and balanced vine is able to withstand more stress, with less detrimental effects. This study also highlights the danger of limiting the assessment of soil and plant water status conditions to point measurements in vineyards with high levels of vigour variability. AFRIKAANSE OPSOMMING: Besluite rakende die skedulering van besproeiing word gewoonlik gebaseer op die direkte meting van grondwaterstatus (GWS), of op fisiologiese metings soos byvoorbeeld plantwaterstatus (PWS). Grond gebaseerde metings is relatief vinnig en maklik om te outomatiseer, maar die plantrespons vir ŉ spesifieke grondwaterinhoud varieer as ŉ komplekse funksie van dampdruktekorte. ‘n Plantgebaseerde benadering meet die plantstresreaksie direk, maar is ŉ integrasie van omgewingstoestande. In teenstelling met grondgebaseerde metodes, kan plantgebaseerde metodes aandui wanneer om te besproei, maar nie die hoeveelhede wat besproei moet word nie. Voorsonsopkoms blaarwaterpotensiaal (ΨPD) word grootliks deur die grondwaterinhoud bepaal, en kan as ŉ maatstaf van statiese waterspanning in plante en as ŉ indeks van bulk grondwaterbeskikbaarheid dien, of selfs as ŉ benadering van die grondwaterpotensiaal by die worteloppervlak. Dit behoort dus moontlik te wees om ŉ verwantskap te bepaal tussen GWS en PWS, maar dit is grootliks onbekend hoe stabiel hierdie verwantskap sal wees in ŉ heterogene wingerd, asook hoe die wingerdstok se vegetatiewe en reproduktiewe reaksie die verwantskap kan beïnvloed. Plantwaterstatus speel ŉ groot rol in die bepaling van groeikrag en opbrengs in die wingerdstok. Die vlakke van plantwaterstatus word deur besproeiing beïnvloed, maar word skynbaar meesal deur die seisoen en wingerdstok se ligging in die wingerd bepaal. Meer negatiewe plantwaterpotensiaalvlakke het gelei tot laer groeikrag, maar het ŉ minder uitgesproke effek gehad op opbrengs, terwyl dit in die algemeen wynkwaliteit verswak het. Groeikrag variasie in die wingerd kon grootliks aan grond heterogeniteit toegeskryf word, wat skynbaar ŉ sterk invloed op grondwaterstatus gehad het. Grondwaterstatus metings is gekalibreer volgens die variasie wat waargeneem is, wat die akkuraatheid van metings beduidend verhoog het. Grondwaterinhoud waardes is gebruik om ŉ verwantskap aan te dui tussen SWS en PWS. Hierdie verwantskap is oor tyd bepaal vir nege persele, wat bestaan het uit droëland asook besproeide persele, in areas waarvan die groeikrag verskil het. ŉ Nie-liniêre verband is gevind tussen ΨPD en die persentasie onttrekking van plantbeskikbare water vir die droëland persele. Waar besproei was, kon geen verband gevind word nie. In hierdie studie, vir Merlot in die Stellenbosch area, het PWS vlakke groeikrag en tot ŉ mindere mate opbrengs en wynkwaliteit beïnvloed. Meer negatiewe plantwaterpotensiaal vlakke het groeikrag meer beïnvloed in hoër groeikrag areas as in die laer groeikrag areas, wat ook gelei het tot ongebalanseerde vegetatiewe:reproduktiewe verhoudings. Hierdie versteurde balans in die wingerdstokke kon dalk ŉ groter impak op wynkwaliteit gehad het as PWS vlakke. Daar moet dus gepoog word om goed bestuurde en gebalanseerde wingerdstokke te hê, sodat strestoestande beter weerstaan kan word met minder nadelige gevolge. Die studie beklemtoon ook die gevaar verbonde daaraan om die bepaling van grond- en plantwaterstatus te beperk tot puntmetings in wingerde met groot variasie in groeikrag.

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33

Kervroëdan, Léa. "Plant traits and functional diversity effects on runoff and sediment retention : application to soil erosion control in temperate agricultural catchments." Thesis, Amiens, 2018. http://www.theses.fr/2018AMIE0031/document.

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Au sein des communautés végétales, les traits fonctionnels dirigent et influencent les processus sol-plantes. Le ruissellement et l'érosion concentrés, causes principales de la dégradation des sols, peuvent être contrôlés par des végétations herbacées qui créent une rugosité hydraulique induisant la réduction de la vitesse des flux de ruissellement et la rétention des sédiments. L'approche des traits, plutôt que taxonomique, permet de comprendre et caractériser les effets directs de la végétation sur le ruissellement et la rétention des sédiments. Ce projet de recherche vise à approfondir les connaissances vis-à-vis des effets (i) des traits fonctionnels (Chapitre 1), (ii) de la complémentarité des traits (Chapitre 2), et (iii) de la diversité fonctionnelle (Chapitre 3) sur les écoulements concentrés et la rétention des sédiments afin d'évaluer l'efficacité et le design de haies herbacées pour réduire les impacts de l'érosion des sols dans les bassins versants limoneux d'Europe. Parmi les combinaisons de traits principaux identifiées comme augmentant la rugosité hydraulique (densité et diamètre des tiges, et densité et surface foliaire), certains traits sont négativement corrélés. Un meilleur effet pourrait donc être atteint au sein d'assemblage d'espèces par un effet complémentaire des traits. Cependant, des effets non-additifs des diversités en espèces et fonctionnelle ont été trouvés, chacun généré par un effet dominant des traits dans les communautés testées. Ces effets des traits et de la diversité fonctionnelle sur la rugosité hydraulique et la rétention des sédiments constituent une nouvelle avancée dans la compréhension des effets de l'assemblage des traits sur les processus d'écoulement et d'érosion des sols ainsi qu'une base pour le design et la modélisation des haies herbacées pour le contrôle du ruissellement et de l'érosion Plant-soil processes are driven and influenced by plant functional traits in vegetation communities. Concentrated runoff and erosion constitute the main cause of soil degradation and can be managed by herbaceous vegetation creating hydraulic roughness that induces flow velocity reduction and sediment retention. Using plant trait-based approach, unlike taxonomical approach, allows to understand and characterise the direct effects of the vegetation on runoff and sediment retention. This research project aims to deepen the knowledge regarding the effects of (i) plant functional traits (chapter 1), (ii) traits' complementarity (chapter 2) and (iii) functional diversity (chapter 3) on concentrated runoff and sediment retention processes, in order to evaluate the efficiency and design of herbaceous hedges to reduce the impacts of soil erosion in loamy European agricultural catchments. The identification of the main efficient traits and traits' combinations towards hydraulic roughness increase (stem density, diameter, leaf area and density) highlighted negatively correlated traits, suggesting that a trade-off could be reached within a plant species assemblage through a complementarity effect of the traits. However, non-additive effects of plant species diversity and functional diversity were found, both driven by dominant traits in the community. The effects of traits and functional diversity on the hydraulic roughness and sediment retention constitute a new advance in the understanding of plant trait assemblage on runoff and soil erosion processes and a baseline for the design and modelling of herbaceous hedges for runoff and erosion control

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34

Scott, Drew Austin. "ENVIRONMENTAL HETEROGENEITY EFFECTS ON DIVERSITY AND NITROUS OXIDE EMISSIONS FROM SOIL IN RESTORED PRAIRIE." OpenSIUC, 2019. https://opensiuc.lib.siu.edu/dissertations/1683.

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Ecological theory predicts that high environmental heterogeneity causes high biodiversity. Theory further predicts that more biodiversity results in greater ecosystem functioning. These theoretical predictions were evaluated in three studies using grassland restorations from agriculture.

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35

Hicks, Lettice Cricket. "Controls on carbon cycling in tropical soils from the Amazon to the Andes : the influence of climate, plant inputs, nutrients and soil organisms." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23477.

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Tropical soils are a globally important store of terrestrial carbon (C) and source of atmospheric carbon dioxide (CO2), regulated by the activity of soil microorganisms, through the mineralisation of plant residues and soil organic matter (SOM). Climatic warming will influence microbial activity, and this may accelerate the rate of C release from soils as CO2, contributing to alterations in current atmospheric composition, and generating feedbacks to climate change. Yet the magnitude of C loss from tropical soils remains uncertain, partly because we do not fully understand how non-climatic factors – including the chemistry of plant inputs, the availability of soil nutrients and the composition of the decomposer community – will interact to determine the response to changes in temperature. This thesis examines how these factors together regulate the rate of C cycling in contrasting soils across a 3400 m tropical elevation gradient in the Peruvian Andes, spanning a 20 ºC range (6.5 – 26.4 ºC) in mean annual temperature. Large-scale field-based manipulation experiments, translocating leaves and soil-cores across the elevation gradient (to impose an in-situ experimental warming treatment), were combined with controlled laboratory studies to examine the microbial-scale mechanisms which underlie the processes of decomposition and soil respiration observed in-situ. Results show that, across the gradient, rates of leaf-decomposition were determined principally by temperature and foliar chemical traits, while soil fertility had no significant influence. The effect of temperature was, however, stronger across higher-elevation sites, suggesting a greater vulnerability of the C-rich soils in montane systems to increased C loss under climatic warming. In lowland forests, the presence of invertebrate macrofauna also accelerated rates of decomposition, but leaf chemistry explained the greatest proportion of the observed variance, with a strong role for leaf chemical traits also identified under controlled conditions. Despite marked differences in microbial abundance and community composition among soils, these metrics were not associated with observed rates of decomposition. These results suggest that climate-related changes to plant species distributions (with associated changes to the chemistry of leaf-inputs), and upslope extension of macrofaunal ranges, could strongly influence future rates of leaf decomposition, independently of the direct response to warming. From the soil translocation study, root-soil interactions stimulated substantial net C loss from montane soils following translocation downslope (experimental warming treatment), indicating that warming-related changes to root productivity, exudation and/or species-composition could represent an important mode of future C loss from these soils. To examine more closely how inputs of plant-derived C influence the turnover of pre-existing SOM, and whether soil nutrient availability modulates the response, soils were amended with simple and complex 13C-labelled substrates in combination with inorganic nutrient treatments. Isotopic partitioning was used to determine the degree to which C and nutrient inputs accelerated (positive priming) or retarded (negative priming) the decomposition of SOM. Amendment of upper montane forest and montane grassland soils with nitrogen (N; alone and in combination with C) substantially retarded the decomposition of SOM, suggesting that microbial demand for N strongly regulates the turnover of organic matter in these soils. In contrast, amendment of lower montane and lowland forest soils with C stimulated positive priming of SOM, which was strongest in response to the simple C substrate and was not influenced by nutrient treatments, suggesting that microorganisms in these soils are primarily constrained by availability of labile C. Functional differences among microbial groups were also evident, with gram-negative bacteria and fungi using more labile sources of C while gram-positive bacteria used more complex C. Together, results from these studies considerably advance our understanding of soil C dynamics across lowland and montane systems, painting a rich picture of interacting processes which will determine the future soil C balance in tropical ecosystems. They show that the influence of temperature on the rate of soil C cycling is strongly affected by the nature and composition of plant-derived and atmospheric inputs, the principal additional constraints varying with elevation, leading to both opposing and reinforcing effects on rates of decomposition. The greater observed temperature sensitivity of decomposition at higher elevations is coupled with high microbial demand for N which regulates the turnover of SOM, whereas at lower elevations leaf decomposition is accelerated by active macrofaunal breakdown, while microbial decomposition of SOM is constrained by the availability of labile C. Under a global change scenario of increased temperature and N deposition, results therefore suggest that: (i) modified chemistry of plant inputs will influence rates of decomposition, independently of climate; (ii) increased availability of labile C will lead to more rapid decomposition of SOM at lower elevations; (iii) greater root productivity (associated with warming and plant-community shifts) will stimulate soil C loss across montane regions; but (iv) at higher elevations, a possible countervailing effect may be imposed on rapid warming-accelerated decomposition if increased N availability reduces microbial mineralisation of SOM. The net effect on the ecosystem C budget will depend on the balance of C gain from primary productivity and C loss from soils. Overall, however, the results presented here suggest that the large soil C stores in higher-elevation montane regions are particularly vulnerable to substantial reductions under exposure to short- and medium-term climatic warming.

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36

Moller, Leandra. "Soil yeasts, mycorrhizal fungi and biochar: their interactions and effect on wheat (Triticum aestivum L.) growth and nutrition." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20417.

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Thesis (MSc)--Stellenbosch University, 2012. ENGLISH ABSTRACT: In order to test the effect of different plant growth-promoting strategies on Triticum aestivum L. (wheat), we investigated the ability of biochar and a grain-associated soil yeast, to improve the growth of this crop. Our first goal was to study the effect of biochar amendments to sandy soil on the growth and nutrition of wheat in the presence of mycorrhizal fungi. This was accomplished by amending soil with 0%, 1%, 2.5%, 5% and 10% (w/w) biochar and cultivating wheat plants in these soil-biochar mixtures. After harvesting, plant growth and mycorrhizal colonization of roots were measured. In addition, we studied the nutritional physiology of these plants with regards to nitrogen (N), phosphorous (P) and potassium (K) concentrations, as well as the growth efficiencies and uptake rates of these nutrients. We found that wheat growth was improved by biochar amendments to soil, probably as a result of elevated K levels in the plant tissues supplied by the biochar amendments. The second goal of this study was to obtain a soil yeast from the rhizosphere of another monocot in the family Poaceae, i.e. Themeda triandra Forssk. (red grass), and then evaluate this isolate for its ability to improve wheat performance. Three different Cryptococcus species were isolated from the rhizosphere of wild grass, i.e. Cryptococcus zeae, Cryptococcus luteolus and Cryptococcus rajasthanensis. Since C. zeae was previously isolated from maize, an isolate representing this species was selected to be used in further experimentation. With the ultimate goal of testing the ability of this yeast to improve wheat growth, its effect on wheat germination was investigated and compared to that of two other soil yeasts, i.e. Cryptococcus podzolicus CAB 978 and Rhodotorula mucilaginosa CAB 826. These three yeasts were subsequently tested for their ability to improve wheat growth in pot cultures in a greenhouse. After one and two months of growth, the culturable yeasts present in the rhizosphere and bulk soil were enumerated. The effects of these yeasts were elucidated by measuring wheat growth in terms of dry weight, as well as root and shoot relative growth rates (RGR). Changes in wheat nutrition were evaluated by determining the concentrations, growth efficiencies and uptake rates for P, K, zinc (Zn) and iron (Fe). During this study, it was found that only C. zeae CAB 1119 and C. podzolicus CAB 978 were able to enhance seed germination. Similarly, it was shown that C. zeae CAB 1119 was able to improve wheat growth during the first and second month of cultivation, whereas C. podzolicus CAB 978 only improved growth during the first month, and R. mucilaginosa CAB 826 had no effect on growth. This improved growth could be attributed to C. zeae CAB 1119 improving the P, K, Zn and Fe growth efficiency of wheat, which positively influenced the root and shoot RGR, and subsequently wheat growth. Our final goal was to test whether C. zeae CAB 1119 could affect wheat growth and nutrition when cultivated in sandy soil, which contained natural microbial consortia and 10% (w/w) biochar. Plants treated with viable or autoclaved cells of C. zeae CAB 1119, were subsequently cultivated in soil only or soil amended with biochar. After one month, plants were harvested and growth was measured with regards to dry weight, root RGR and shoot RGR. In addition, the concentrations of P, K, Zn and Fe were analyzed for these plants, where after the growth efficiencies and uptake rates were calculated for these four nutrients. Results indicated that plants growing in soil amended with biochar, and treated with viable C. zeae CAB 1119, showed the best growth. The increased root and shoot RGR witnessed in these plants was probably due to increased concentrations of P and K in the plants. This study opens new avenues of research with regards to the bio-fertilizers of wheat. AFRIKAANSE OPSOMMING: Die uiteindelike doel van die studie was om die effek van verskillende plantgroei bevorderende metodes op die groei van Triticum aestivum L. (koring) te ondersoek. Dus het ons die vermoë van houtskool en ‘n graan-geassosieerde grondgis getoets om die groei van dié plant te bevorder. Die eerste doel van die studie was om die effek van houtskool toedienings tot sanderige grond te evalueer. Dit is bewerkstellig deur 0%, 1%, 2.5%, 5% en 10% (w/w) van die houtskool by die sand toe te voeg en koring in die houtskool-sand mengsels te kweek. Na die verlangde groei tydperk is die koring geoes en die mikorrizale kolonisasie op en in die koring wortels bepaal. Gedurende hierdie studie is die effek van bogenoemde toedienings op die fisiologie van die plante ondersoek deur die konsentrasies, opname tempo’s, en groei ekonomie van die plante vir stikstof (N), fosfaat (P) en kalium (K) te bepaal. Ons het gevind dat die groei van koring deur die toediening van houtskool bevorder is en dit blyk dat dié effek weens die teenwoordigheid van hoë K vlakke in die plantweefsel is. Die tweede doel van ons studie was om ‘n gis vanuit die risosfeer van ‘n monokotiel wat aan die familie Poacea behoort, naamlik Themeda triandra Forssk. (rooigras) te isoleer. Die vermoë van die isolaat om die groei van koring te bevorder was daarna getoets. Drie verskillende Cryptococcus spesies was vanuit die risosfeer van rooigras geïsoleer, nl. Cryptococcus zeae, Cryptococcus luteolus en Cryptococcus rajasthanensis. Omdat C. zeae in ‘n vorige studie vanaf mielies geisoleer was, is ‘n isolaat van hierdie spesie gebruik in verdere eksperimente. Met die doel om te bepaal of dié gisspesie koringgroei kan bevorder, was die effek van C. zeae op die ontkieming van koring bestudeer en vergelyk met dié van twee ander grond giste, nl. Cryptococcus podzolicus CAB 978 en Rhodotorula mucilaginosa CAB 826. Hierdie drie giste is ook ondersoek om die groei van koring in ‘n glashuis te bevorder. Na een en twee maande se groei was die getalle van giste teenwoordig in die risosfeer en grond verder weg van die wortels bepaal. Die effek van dié giste op die groei van koring is bepaal in terme van droë gewig asook die relatiewe wortel en halm groei tempos. Veranderinge in die nutrient status van koring is ondersoek deur die konsentrasies, groei-ekonomie en tempo van opname vir P, K, sink (Zn) en yster (Fe) te bepaal. Ons het gedurende dié studie gevind dat C. zeae CAB 1119 en C. podzolicus CAB 978 die ontkieming van koring kon verbeter. Ons het ook gevind dat C. zeae CAB 1119 die groei van koring gedurende die eerste en tweede maand van groei kon bevorder, terwyl C. podzolicus CAB 978 dit net gedurende die eerste maand kon vermag en R. mucilaginosa CAB 826 geen effek gehad het nie. Die verbeterde groei kon aan C. zeae CAB 1119, wat die P, K, Zn en Fe groei effektiwiteit van die plante verbeter het, toegeskryf word. Die verbetering van groei effektiwiteit het ‘n positiewe invloed op die relatiewe groeisnelheid van die wortels en halms gehad, en dus op koringgroei. Die laaste doel van die studie was om te bepaal of C. zeae CAB 1119 die groei van koring kon bevorder wanneer die koring in sand wat natuurlike mikrobiese populasies bevat en met houtskool aangevul is, gekweek word. Plante is met lewensvatbare of nielewensvatbare selle van C. zeae CAB 1119 behandel en gekweek in sanderige grond, en/of grond waarby 10% (w/w) houtskool toegevoeg is. Die plante is na een maand geoes en die groei bepaal in terme van droë massa en die relatiewe wortel en halm groei tempos. Die konsentrasies van P, K, Zn en Fe in die plante, asook die fisiologie van die plante, nl. groei ekonomie en tempo van opname, met betrekking tot P, K, Zn en Fe is bepaal, Ons het gevind dat plante wat in die houtskool-grond mengsel gekweek is en met lewensvatbare selle van C. zeae CAB 1119 behandel is die beste groei getoon het. Die verbeterde relatiewe groei tempos van die wortels en halms was mees waarskynlik die gevolg van verhoogde P en K konsentrasies in die plante. Hierdie studie toon nuwe resultate in verband met die gebruik van biologiese alternatiewes tot kunsmis.

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37

Barthelemy, Hélène. "Herbivores influence nutrient cycling and plant nutrient uptake : insights from tundra ecosystems." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-120191.

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Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

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Eskelinen, A. (Anu). "Plant community dynamics in tundra: propagule availability, biotic and environmental control." Doctoral thesis, University of Oulu, 2009. http://urn.fi/urn:isbn:9789514293139.

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Abstract Plant community composition and diversity are determined by the balance between rates of immigration and extinction. Processes of immigration to a local community, i.e. propagule availability and dispersal of propagules between and within habitats, set the upper limit for the pool of species potentially capable of coexisting in a community, while local biotic interactions, i.e., competition, facilitation, herbivory and interactions with below-ground ecosystem components, and environmental factors control colonisation and establishment, and determine the persistence and dynamics of already existing species. In this thesis, I studied (1) the interactions between propagule availability, biotic and environmental constraints on colonisation, and (2) the interdependence between biotic and environmental factors regulating community processes in already established resident vegetation. First, I found that both propagule availability and competition with adult plants limited the rates of colonisation and total community diversity in a relatively low-productive tundra ecosystem. Long-term exclusion of mammalian herbivores and alleviation of nutrient limitation by fertilization increased the intensity of competition with established vegetation, and diminished immigration rates. In addition, I also found that community openness to colonization depended on the initial community properties, i.e., the functional composition and the traits of dominant plants in resident vegetation, which mediate the effects of nutrient addition and biomass removal on immigration rates. Second, adult plants in the resident vegetation experienced an increased extent of neighbourhood competition and herbivory in nutrient enriched conditions and in naturally more fertile habitats. However, the effects were also species-specific. On a community level, release from heavy grazing favoured lichens over graminoids and increased species richness. Furthermore, I also showed that plant community composition was strongly linked with soil organic matter quality and microbial community composition, and that these vegetation-soil-microbe interactions varied along a gradient of soil pH. Overall, my results emphasise that propagule availability, biotic and environmental control over community processes are strongly interconnected in tundra ecosystems. Especially, my findings highlight the role of plant competition and herbivory and their dependence on soil nutrient availability in governing colonisation and resident community dynamics. My results also indicate that plant functional composition and traits of dominant plants are of great importance in channelling community responses to external alterations and dictating plant-soil interactions.

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39

Heckenroth, Alma. "Evaluation des méthodes de phytostabilisation adaptées à la restauration écologique d'une friche industrielle incluse dans une zone protégée : cas de l’usine de l’Escalette dans la zone coeur du parc national des Calanques." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0001.

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Sur le site de la friche industrielle de l'Escalette dans le parc national des Calanques (Marseille), une réflexion alliant écologie de la restauration et phytoremédiation est menée dans le but d'optimiser les fonctions écosystémiques qui limitent les transferts d'éléments traces métalliques et métalloïdes (ETMM) des sols. Une caractérisation in situ de la composition et la structure des communautés végétales natives et spontanées a été menée sur des sites fortement contaminés, permettant de sélectionner des plantes tolérantes. La réponse de deux espèces pérennes natives à l'hétérogénéité de la contamination des sols en ETMM a été évaluée in situ, notamment via l'analyse des interactions sol-plantes microorganismes de la zone rhizosphérique. Enfin, des essais de restauration écologique des communautés végétales natives, basés sur la capacité de plantes natives tolérantes à stabiliser les ETMM et les dynamiques de résilience des communautés végétales, ont été menés sur une zone fortement contaminée. Les résultats indiquent qu'un siècle de contamination en ETMM a affecté de façon significative les communautés végétales en terme de composition, diversité et structure. Ils mettent en évidence une tolérance des plantes natives impliquant des microorganismes symbiotiques. Les résultats préliminaires des essais de restauration écologique confirment le choix d'espèces natives pour relancer une dynamique de végétation sur sols très contaminés et l’importance de créer des microsites favorables dans des milieux (semi-)arides hétérogènes. Ils apportent une contribution au développement d'écotechnologies pour la restauration des sols contaminés dans un contexte méditerranéen On the Escalette brownfield, included in the area of the Calanques National Park (Marseille, southeastern France), a research project combining restoration ecology and phytoremediation is carried out, in order to optimize the ecosystem functions which limit the transfers of metals and metalloids (MM) and to restore the functions of the contaminated soils. We developed an in situ characterization approach of the composition and structure of plant communities that grow on MM contaminated sites. This enabled the selection of native plants, tolerant to high concentrations of MM. In a second step, the response of two native perennial species to surface and depth heterogeneity of MM soil contamination was evaluated in-situ, regarding the soil-plant-microorganism interactions at the rhizosphere level. Finally, ecological restoration trials of native plant communities were carried out in a polluted hotspot, based on the ability of native plants to stabilize MM and the resilience dynamics of plant communities.The results indicated that a century of MM pollution pressure produced a significant correlation with plant community dynamics in terms of composition, diversity and structure. They showed that the tolerance of native plants involves symbiotic microorganism interactions. Preliminary results from ecological restoration trials confirmed the method for native plants species selection to recover a vegetation dynamic on highly polluted soils and the importance of creating favorable microsites in heterogeneous (semi-)arid environments. They contribute to the development of ecotechnologies for the restoration of contaminated soils in a Mediterranean context

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40

Kumar, Amit [Verfasser], and Johanna [Akademischer Betreuer] Pausch. "Plant-microbial interactions in the rhizosphere : root mediated changes in microbial activity and soil organic matter turnover / Amit Kumar ; Betreuer: Johanna Pausch." Bayreuth : Universität Bayreuth, 2018. http://d-nb.info/1160301956/34.

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41

Condron, Leo M. "Chemical nature and plant availability of phosphorus present in soils under long-term fertilised irrigated pastures in Canterbury, New Zealand." Lincoln College, University of Canterbury, 1986. http://hdl.handle.net/10182/1875.

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Soil P fractionation was used to examine changes in soil inorganic and organic P under grazed irrigated pasture in a long-term field trial at Winchmore in Mid-Canterbury. The soil P fractionation scheme used involved sequential extractions of soil with O.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH I P), 1M HCl (HCl P) and 0.1M NaOH (NaOH II P). The Winchmore trial comprised 5 treatments: control (no P since 1952), 376R (376 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since), 564R (564 kg superphosphate ha⁻¹ yr⁻¹ 1952-1957, none since) 188PA (188 kg superphosphate ha⁻¹ yr⁻¹ since 1952) and 376PA (376 kg superphosphate ha⁻¹ yr⁻¹ since 1952: Topsoil (0-7.5cm) samples taken from the different treatments in 1958, 1961, 1965, 1968, 1971, 1974 and 1977 were used in this study. Changes in soil P with time showed that significant increases in soil inorganic P occurred in the annually fertilised treatments (l88PA, 376PA). As expected, the overall increase in total soil inorganic P between 1958 and 1977 was greater in the 376PA treatment (159 µg P g⁻¹) than that in the 188PA treatment (37 µg P g⁻¹). However, the chemical forms of inorganic P which accumulated in the annually fertilised treatments changed with time. Between 1958 and 1971 most of the increases in soil inorganic P in these treatments occurred in the NaHCO₃ and NaOH I P fractions. On the other hand, increases in soil inorganic P in the annually fertilised treatments between 1971 and 1977 were found mainly in the HCl and NaOH II P fractions. These changes in soil P forms were attributed to the combined effects of lime addition in 1972 and increased amounts of sparingly soluble apatite P and iron-aluminium P in the single superphosphate applied during the 1970's. In the residual fertiliser treatments (376R, 564R) significant decreases in all of the soil inorganic P fractions (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p) occurred between 1958 and 1977 following the cessation of P fertiliser inputs in 1957. This was attributed to continued plant uptake of P accumulated in the soil from earlier P fertiliser additions. However, levels of inorganic P in the different soil P fractions in the residual fertiliser treatments did not decline to those in the control which indicated that some of the inorganic P accumulated in the soil from P fertiliser applied between 1952 and 1957 was present in very stable forms. In all treatments, significant increases in soil organic P occurred between 1958 and 1971. The overall increases in total soil organic P were greater in the annually fertilised treatments (70-86 µg P g⁻¹) than those in the residual fertiliser (55-64 µg P g⁻¹) and control (34 µg P g⁻¹) treatments which reflected the respective levels of pasture production in the different treatments. These increases in soil organic P were attributed to the biological conversion of native and fertiliser inorganic P to organic P in the soil via plant, animal and microbial residues. The results also showed that annual rates of soil organic P accumulation between 1958 and 1971 decreased with time which indicated that steady-state conditions with regard to net 'organic P accumulation were being reached. In the residual fertiliser treatments, soil organic P continued to increase between 1958 and 1971 while levels of soil inorganic P and pasture production declined. This indicated that organic P which accumulated in soil from P fertiliser additions was more stable and less available to plants than inorganic forms of soil P. Between 1971 and 1974 small (10-38 µg P g⁻¹) but significant decreases in total soil organic P occurred in all treatments. This was attributed to increased mineralisation of soil organic P as a result of lime (4 t ha⁻¹) applied to the trial in 1972 and also to the observed cessation of further net soil organic P accumulation after 1971. Liming also appeared to affect the chemical nature of soil organic P as shown by the large decreases in NaOH I organic P(78-88 µg P g⁻¹) and concomitant smaller increases in NaOH II organic P (53-65 µg P g⁻¹) which occurred in all treatments between 1971 and 1974. The chemical nature of soil organic P in the Winchmore long-term trial was also investigated using 31p nuclear magnetic resonance (NMR) spectroscopy and gel filtration chromatography. This involved quantitative extraction of organic P from the soil by sequential extraction with 0.1M NaOH, 0.2M aqueous acetylacetone (pH 8.3) and 0.5M NaOH following which the extracts were concentrated by ultrafiltration. Soils (0-7.5cm) taken from the control and 376PA annually fertilised treatments in 1958, 1971 and 1983 were used in this study. 31p NMR analysis showed that most (88-94%) of the organic P in the Winchmore soils was present as orthophosphate monoester P while the remainder was found as orthophosphate diester and pyrophosphate P. Orthophosphate monoester P also made up almost all of the soil organic P which accumulated in the 376PA treatment between 1958 and 1971. This indicated that soil organic P in the 376PA and control treatments was very stable. The gel filtration studies using Sephadex G-100 showed that most (61-83%) of the soil organic P in the control and 376PA treatments was present in the low molecular weight forms (<100,000 MW), although the proportion of soil organic P in high molecular weight forms (>100,000 MW) increased from 17-19% in 1958 to 38-39% in 1983. The latter was attributed to the microbial humification of organic P and indicated a shift toward more complex and possibly more stable forms of organic P in the soil with time. Assuming that the difference in soil organic P between the control and 376PA soils sampled in 1971 and 1983 represented the organic P derived from P fertiliser additions, results showed that this soil organic P was evenly distributed between the high and low molecular weight fractions. An exhaustive pot trial was used to examine the relative availability to plants of different forms of soil inorganic and organic P in long-term fertilised pasture soils. This involved growing 3 successive crops of perennial ryegrass (Lolium perenne) in 3 Lismore silt loam (Udic Ustochrept) soils which had received different amounts of P fertiliser for many years. Two of the soils were taken from the annually fertilised treatments in the Winchmore long term trial (188PA, 376PA) and the third (Fairton) was taken from a pasture which had been irrigated with meatworks effluent for over 80 years (65 kg P ha⁻¹ yr⁻¹). Each soil was subjected to 3 treatments, namely control (no nutrients added), N100 and N200. The latter treatments involved adding complete nutrient solutions with different quantities of N at rates of 100kg N ha⁻¹ (N100) and 200kg N ha⁻¹ (N200) on an area basis. The soil P fractionation scheme used was the same as that used in the Winchmore long-term trial study (i.e. NaHCO₃ P, NaOH I P, HCl P, NaOH II p). Results obtained showed that the availability to plants of different extracted inorganic P fractions, as measured by decreases in P fractions before and after 3 successive crops, followed the order: NaHCO₃ P > NaOH I P > HCl P = NaOH II P. Overall decreases in the NaHCO₃ and NaOH I inorganic P fractions were 34% and 16% respectively, while corresponding decreases in the HCl and NaOH II inorganic P fractions were small «10%) and not significant. However, a significant decrease in HCl P (16%) was observed in one soil (Fairton-N200 treatment) which was attributed to the significant decrease in soil pH (from 6.2 to 5.1) which occurred after successive cropping. Successive cropping had little or no effect on the levels of P in the different soil organic P fractions. This indicated that net soil organic P mineralisation did not contribute significantly to plant P uptake over the short-term. A short-term field experiment was also conducted to examine the effects of different soil management practices on the availability of different forms of P to plants in the long-term fertilised pasture soils. The trial was sited on selected plots of the existing annually fertilised treatments in the Winchmore long-term trial (188PA, 376PA) and comprised 5 treatments: control, 2 rates of lime (2 and 4 t ha⁻¹ ) , urea fertiliser (400kg N ha⁻¹ ) and mechanical cultivation. The above ground herbage in the uncultivated treatments was harvested on 11 occasions over a 2 year period and at each harvest topsoil (0-7.5 cm) samples were taken from all of the treatments for P analysis. The soil P fractionation scheme used in this particular trial involved sequential extractions with 0.5M NaHCO₃ @ pH 8.5 (NaHCO₃ P), 0.1M NaOH (NaOH P), ultrasonification with 0.1M NaOH (sonicate-NaOH p) and 1M HCl (HCl P). In addition, amounts of microbial P in the soils were determined. The results showed that liming resulted in small (10-21 µg P g⁻¹) though significant decreases in the NaOH soil organic P fraction in the 188PA and 376PA plots. Levels of soil microbial P were also found to be greater in the limed treatments compared with those in the controls. These results indicated that liming increased the microbial mineralisation of soil organic P in the Winchmore soils. However, pasture dry matter yields and P uptake were not significantly affected. Although urea significantly increased dry matter yields and P uptake, it did not appear to significantly affect amounts of P in the different soil P fractions. Mechanical cultivation and the subsequent fallow period (18 months) resulted in significant increases in amounts of P in the NaHCO₃ and NaOH inorganic P fractions. This was attributed to P released from the microbial decomposition of plant residues, although the absence of plants significantly reduced levels of microbial P in the cultivated soils. Practical implications of the results obtained in the present study were presented and discussed.

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Soti, Pushpa Gautam. "Influence of Soil Biogeochemical Properties on the Invasiveness of Old World Climbing Fern (Lygodium microphyllum)." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/960.

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The state of Florida has one of the most severe exotic species invasion problems in the United States, but little is known about their influence on soil biogeochemistry. My dissertation research includes a cross-continental field study in Australia, Florida, and greenhouse and growth chamber experiments, focused on the soil-plant interactions of one of the most problematic weeds introduced in south Florida, Lygodium microphyllum (Old World climbing fern). Analysis of field samples from the ferns introduced and their native range indicate that L microphyllum is highly dependent on arbuscular mycorrhizal fungi (AMF) for phosphorus uptake and biomass accumulation. Relationship with AMF is stronger in relatively dry conditions, which are commonly found in some Florida sites, compared to more common wet sites where the fern is found in its native Australia. In the field, L. microphyllum is found to thrive in a wide range of soil pH, texture, and nutrient conditions, with strongly acidic soils in Australia and slightly acidic soils in Florida. Soils with pH 5.5 - 6.5 provide the most optimal growth conditions for L. microphyllum, and the growth declines significantly at soil pH 8.0, indicating that further reduction could happen in more alkaline soils. Comparison of invaded and uninvaded soil characteristics demonstrates that L. microphyllum can change the belowground soil environment, with more conspicuous impact on nutrient-poor sandy soils, to its own benefit by enhancing the soil nutrient status. Additionally, the nitrogen concentration in the leaves, which has a significant influence in the relative growth rate and photosynthesis, was significantly higher in Florida plants compared to Australian plants. Given that L. microphyllum allocates up to 40% of the total biomass to rhizomes, which aid in rapid regeneration after burning, cutting or chemical spray, hence management techniques targeting the rhizomes look promising. Over all, my results reveal for the first time that soil pH, texture, and AMF are major factors facilitating the invasive success of L. mcirophyllum. Finally, herbicide treatments targeting rhizomes will most likely become the widely used technique to control invasiveness of L. microphyllum in the future. However, a complete understanding of the soil ecosystem is necessary before adding any chemicals to the soil to achieve a successful long-term invasive species management strategy.

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Xi, Nian-Xun. "Effects of patchy nitrogen inputs and soil nitrogen heterogeneity on grassland structure and function." Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22542/document.

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A l’échelle mondiale, les prairies fournissent une grande variété de services écosystémiques et sont le support économique de nombreux systèmes d’élevage. Dans un contexte global éminemment changeant, une meilleure compréhension de la structure et du fonctionnement des prairies est incontournable pour proposer à la fois des gestions plus durables des ressources et promouvoir la fourniture de services écosystémiques diversifiés par ces écosystèmes. Les prairies étant des écosystèmes dynamiques et hétérogènes, notre capacité à prédire leur fonctionnement et leurs trajectoires de réponse à un facteur environnemental (climat, gestion) reste un défi scientifique important. Ainsi, dans des prairies pâturées, l’activité de grands herbivores va être facteur d’hétérogénéité des nutriments du sol via l'excrétion. Cependant les effets de ces apports nutritifs en « patchs » et de l'hétérogénéité spatiale du sol sur la structure et les propriétés de la prairie restent peu connus. L’objectif de cette thèse est d’examiner les effets de l'hétérogénéité spatiale de l'azote (N) dans le sol sur l’écosystème prairial, en portant une attention particulière sur les réponses des communautés végétales. Notre démarche a combiné des approches expérimentales et de modélisation pour analyser les impacts d'un certain nombre d'attributs de « patch » (différentes formes d’N, taille et contraste du patch), et leurs interactions possibles avec le régime de pluviométrie ou encore la date des apports en N. Nous montrons que des apports hétérogènes en N augmentent la production des plantes et la variabilité de la biomasse intra-parcelle quel que soit la forme d’N, mais qu’ils ne modifient pas, à court terme, la production à l’échelle de la parcelle prise dans son entier. Néanmoins, des apports hétérogènes d’N-organique favorisent l’asynchronie spatiale et temporelle entre les compartiments plante - sol, avec des implications pour le fonctionnement de la prairie à plus long terme. Contrairement à la production, la structure de la communauté végétale répond significativement à l’hétérogénéité en N, avec une dominance accrue de certaines espèces et un changement dans le rang des espèces subalternes. Contre toute attente, dans cette étude, la quantité de pluie ne modifie pas les effets de l'hétérogénéité sur la production et la structure de la communauté végétale. Des simulations réalisées avec un modèle spatialisé montrent que les effets de l'hétérogénéité sur la production à l’échelle de la parcelle varient selon la taille et le niveau de contraste du patch. Pour un même apport total en N, la production répond positivement à la taille de patch, mais elle diminue dans des conditions de fort contraste en comparaison à des conditions de faible contraste. Nous n’avons pas relevé d’interactions entre la taille de patch, le niveau de contraste de patch ou la date des apports en N sur la production de prairie. D’une manière générale, nos résultats soulignent l'importance de l’hétérogénéité en N pour les processus plante-sol à différentes échelles spatiales et montrent que les effets de l'hétérogénéité varient en fonction des attributs des patchs. Les interactions biotiques (ici la compétition) semblent jouer un rôle relativement plus important que les facteurs abiotiques (ici changements chroniques de pluviométrie) pour les effets d'hétérogénéité. Nous concluons que les impacts de l'hétérogénéité en N sur les processus plante-sol peuvent avoir des conséquences sur les rétroactions plante-sol impliquées dans la régulation des cycles biogéochimiques, et sont à même de fournir des informations utiles pour le développement de pratiques de gestion efficientes dans l’utilisation de l’N Grasslands provide a variety of important ecological and economic services worldwide. Improved understanding of grassland structure and function is necessary for the development of sustainable management and maintaining the provision of multiple ecosystem services in a changing environment. However, predicting grassland structure and function is a challenge because grasslands are dynamic, heterogeneous systems. In grazed grasslands, large herbivore activities promote heterogeneity in soil nutrients via excretion, but the effects of patchy nutrient inputs and soil spatial heterogeneity on grassland structure and function remain unclear. This thesis addresses effects of spatial heterogeneity in soil nitrogen (N) for grassland ecosystem structure and function, with particular emphasis on community responses. A combination of experimental and modelling approaches are used to study impacts of a number of different patch attributes (N form, patch size, patch contrast), as well as possible interactions with rainfall regime and timing of N inputs. We find that patchy N inputs enhance within plot-plant production and biomass variability irrespective of N form, but do not modify whole-plot plant production in the short term. Nevertheless, patchy organic N promotes spatial and temporal asynchrony in plant-soil responses, with implications for longer-term grassland function. Unlike plant production, community structure responds significantly to patchy N inputs, with increased community dominance and a shift in the rank of subordinate species. Contrary to expectations, rainfall quantity does not modify heterogeneity effects on either plant production or community structure. Modelling work shows that heterogeneity effects on field-scale production vary depending on patch size and patch contrast. For a fixed total N input, field-scale grassland production responds positively to patch size, but decreases in high- versus low-patch contrast conditions. Patch size does not interact with patch contrast or timing of N inputs on grassland production. Overall, our results highlight the importance of N heterogeneity for plant and soil processes at different spatial scales, and demonstrate that heterogeneity effects vary depending on patch attributes. Biotic interactions (competition) appear to play a relatively greater role than abiotic factors (chronic rainfall changes) for heterogeneity effects. Impacts of N heterogeneity on plant and soil processes may have significant implications on plant-soil feedbacks involved with the regulation of biogeochemical cycling, and provide useful information for the development of efficient N management strategies

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44

Wahbi, Sanâa. "Influence des cultures associées fève/blé sur le potentiel mycorhizien des sols et la structure de la microflore mycorhizosphérique : conséquences sur la productivité des agrosystèmes au Maroc." Thesis, Montpellier, 2016. http://www.theses.fr/2016MONTS031.

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L’avenir d’une agriculture durable, repose sur une gestion optimale de la fertilité des sols et de leurs propriétés physiques et biologiques. Il s’agit de déterminer des pratiques culturales mimant certains processus écologiques (facilitation, complémentarité, effet « plant-soil-feedback) contribuant au maintien de la fertilité des sols. Ces concepts ont longtemps été valorisés de façon empirique dans des pratiques culturales associant simultanément différentes plantes. L’une des pratiques culturales la plus communément rencontrée en milieu méditerranéen associe des légumineuses à des céréales en rotation ou en culture intercalaire. Toutefois, et afin d’optimiser l’impact de ces itinéraires culturaux sur la productivité et la stabilité des agrosystèmes, les mécanismes biologiques mis en jeu doivent être élucidés. Cette étude a pour ambition principale d’améliorer nos connaissances sur les mécanismes mis en jeu au niveau de la microflore du sol et plus particulièrement sur l’importance de la symbiose mycorhizienne dans ces interactions biotiques et abiotiques. En réalisant des expériences en serre et in situ, associant la fêve et le blé en culture intercalaire ou en rotation, les résultats montrent que cette pratique stimule la croissance du blé ainsi que sa nutrition minérale (N et P). Nous avons également montré que cette association induisait des modifications importantes sur la diversité fonctionnelle de la microflore du sol et des bactéries du groupe des Pseudomonas fluorescents ainsi que sur la structure des communautés de champignons mycorhiziens à arbuscules (CMA). Par ailleurs et afin d’optimiser l’impact de la composition de la couverture végétale dans une culture intercalaire, nous avons démontré qu’une augmentation de la diversité de légumineuses améliorait significativement les bénéfices attendus sur la croissance du blé et de sa mycorhization. Ces résultats soulignent la nécessité de développer ce type de pratiques culturales dans les agro-écosystèmes, afin de valoriser les services écologiques rendus par les légumineuses, et d’envisager la gestion des communautés de CMA dans les stratégies agro-écologiques comme une composante majeure de la productivité des cultures durable The future of sustainable agriculture is based on an optimal management of the soil fertility and the soil physical and biological properties. The present study focused on identifying cultural practices that mimic some ecological processes (facilitation, complementarity, "plant-soil-feedback” effect) contributing to the maintenance of the soil fertility. These concepts have been empirically used in farming practices mixing plant species in cropping systems. One of the most commonly Mediterranean cropping system associates legumes to cereal in rotation or intercropping (i.e. Faba bean/ Durum wheat association). However, in order to optimize the impact of crop management on the productivity and stability of agro-ecosystems, the biological mechanisms involved must be clarified. The aim of this study is to improve our understanding of the mechanisms involved in the soil microflora plant interactions and especially the importance of mycorrhizal symbiosis in these biotic and abiotic processes. By conducting experiments in controlled and in situ conditions, our results show that intercropping stimulates the wheat growth and its mineral nutrition (N and P). We also showed that this cultural practice induces significant changes on the soil microbial functional diversity, on the fluorescent Pseudomonas functionalities, and also on the arbuscular mycorrhizal (AM) community structures. Furthermore, and in order to optimize the impact of the composition of the plant cover in intercropping, we have shown that increasing the diversity of legumes significantly improved the expected benefits on wheat growth and its mycorrhizal status. These results highlight the need to manage crop diversity in agroecosystems, in order to enhance the ecological services provided by legumes, and to consider the management of AM fungal communities in agro-ecological strategies as major component to maintain crop productivity

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45

Jewell, Mark. "Diversité des arbres, interactions aériennes et souterraines et décomposition des feuilles mortes." Mémoire, Université de Sherbrooke, 2013. http://savoirs.usherbrooke.ca/handle/11143/75.

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Résumé : La décomposition des litières végétales a été décrite comme étant la deuxième plus importante fonction écosystémique sur terre, après la productivité primaire. Alors que la photosynthèse fournit les apports énergétiques à la plupart des chaînes alimentaires, la décomposition recycle les nutriments, permet leur utilisation future par d’autres organismes et relargue dans l’atmosphère le carbone fixé photosynthétiquement. Dans un contexte de changement climatique, un grand intérêt est porté sur la décomposition des litières, car il s’agit, à l’échelle globale, de la plus grande source d’émission de CO[indice inférieur 2] dans l’atmosphère. Les taux de décomposition des litières sont principalement déterminés par trois facteurs: les variables climatiques, la structure des communautés de décomposeurs et les propriétés chimiques et physiques de la litière. La structure de la communauté végétale hôte dans laquelle se produit la décomposition et d’où provient la litière peut influencer l’ensemble de ces trois facteurs. Des changements dans la structure de la communauté végétale pourraient donc affecter les futurs taux de décomposition et modifier significativement les dynamiques globales du carbone. Malgré cela, la communauté hôte est rarement prise en compte dans les études sur la décomposition des litières. Des expériences enlèvent souvent la litière de son environnment naturel de décomposition, mesurant la décomposition des litières à partir de monolithes ou de microcosmes en laboratoire, afin de contrôler les variations indésirables des propriétés du sol. Dans ce mémoire, j’étudie les effets de plusieurs propriétés fonctionnelles de la communauté végétale hôte sur les taux de décomposition des litières et leur contribution à la respiration du sol. En utilisant une plantation expérimentale d’arbres qui permet de manipuler la structure de leur communauté, je teste l’effet de l’identité fonctionnelle des arbres, des espèces et de la diversité fonctionnelle, ainsi que des interactions entre décomposeurs et arbres sur ces processus écosystémiques. La décomposition des litières et la respiration du sol sont liées aux propriétés fonctionnelles des plantes. La décomposition des litières est bien prédite par les valeurs moyennes de traits fonctionnels des litières, mais plus faiblement corrélée à la diversité spécifique. D’après mes résultats, le nombre d’espèces en mélange de litières ne constitue pas un facteur important pour la décomposition, à cause des interactions globalement idiosyncratiques entre types de litières. Cependant, l’augmentation conjointe de la diversité fonctionnelle des mélanges d’espèces en litières et de la communauté d’arbres-hôtes accélère les taux de décomposition et la respiration du sol. Les premières phases de décomposition de litières en surface ne sont que faiblement affectées par la diversité des plantes, alors que pour la respiration du sol, qui prend en compte les dernières phases de décomposition de litière et de matière organique du sol, la diversité est la propriété fonctionnelle de plantes qui fournit le meilleur pouvoir de prédiction. De plus, j’ai trouvé que les apports spécifiques de litières à long terme pouvaient créer des conditions qui favorisent la décomposition des litières native et pouvaient modifier l’effet de la diversité des arbres sur la décomposition. J’attribue cet effet aux rétroactions entre la litière et les organismes décomposeurs du sol. Ce travail de recherche fournit une nouvelle perspective sur les effets des changements de structure de communauté forestière sur les processus de décomposition. La compréhension de ces effets est nécessaire pour prédire les taux de décomposition de litières et les dynamiques globales du carbone. // Abstract : The decomposition of plant litter has been described as the second most important ecosystem function for sustaining life on earth, after primary productivity. Whereas photosynthesis provides the energy input for most food chains, decomposition recycles nutrients for future use by other organisms and returns photosynthetically fixed carbon back to the atmosphere. In the context of climate change, litter decomposition is of specific interest because it represents one of the largest sources of CO[subscript 2] to the atmosphere globally. Rates of litter decomposition are largely determined by three factors: climatic variables, the structure of the decomposer community, and the chemical and physical properties of the litter. The structure of the host plant community under which decomposition takes place and from which the litter is derived can influence all three of these factors. Therefore, any systematic changes in plant community structure could affect future decomposition rates and significantly alter global carbon dynamics. Despite this, the host plant community is rarely considered in litter decomposition studies. Experiments often remove litter from its natural decomposition environment, instead measuring decomposition of litter in common garden settings and laboratory microcosms to control for unwanted variation in soil properties. In this thesis I investigate the effect of several functional properties of the host plant community on rates of litter decomposition and its contribution to soil respiration. Using an experimental tree plantation that manipulates tree community structure, I test the effect of tree functional identity, species and functional diversity, and tree-decomposer interactions on these ecosystem processes. Both litter decomposition and soil respiration were related to plant functional properties. Litter decomposition was best predicted by average-values of litter functional traits and was poorly related to species diversity. The number of species in a litter mixture does not seem to be important for decomposition, as interactions between litter types were idiosyncratic. However increasing the functional diversity both of mixed-species litter and of the host tree community accelerated rates of litter decomposition and soil respiration. Early stages of surface litter decomposition were only marginally affected by plant diversity. In contrast, diversity was the best predictor of soil respiration, which includes latter stages of litter and soil organic matter decomposition. Furthermore, I found that specific repeated litter input to the soil can result in conditions that favour the decomposition of the long-term litter type and can mediate the effect of tree diversity on decomposition. I attribute this effect to feedbacks between the litter and soil decomposer organisms. This research provides insight into the effect of changing forest community structure on decomposition processes. Such an understanding is necessary to predict future rates of litter decomposition and global carbon dynamics.

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46

Guigues, Stéphanie. "Caractérisation des interactions physico-chimiques entre le cuivre et les racines comme base de développement d'un modèle d'évaluation de la phytodisponibilité des éléments traces." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4307.

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Cette étude a été dédiée au développement d’une nouvelle approche de modélisation de la phytodisponibilité des éléments traces. Cette approche a été employée pour prédire l’adsorption du cuivre (Cu) sur des racines de blé et de tomate. Plusieurs techniques analytiques (titrages acido-basiques, résonance magnétique nucléaire, spectroscopie d’absorption X) ont été employées et croisées avec des résultats de modélisation. Dans un premier temps, la réactivité des racines a été caractérisée. Les racines étant constituées de parois apoplasmiques et de membranes plasmiques, la contribution respective de ces deux compartiments végétaux aux propriétés de complexation des racines a été évaluée. L’étude a ensuite été focalisée sur la complexation du Cu au sein des racines et sur l’évolution de cette complexation en fonction des conditions physico-chimiques du milieu. Grâce aux résultats obtenus sur la caractérisation des racines et à l’acquisition d’un jeu varié de données expérimentales sur la complexation du Cu, le modèle a pu être paramétré. Il a été montré que les propriétés de complexation des racines de blé et de tomate proviennent conjointement des membranes plasmiques et des parois apoplasmiques. La spéciation du Cu au sein des racines était partagée entre les composés pectiques des parois apoplasmiques et les protéines enchâssées à la fois dans les parois apoplasmiques et les membranes plasmiques. Un modèle propre aux racines a pu être développé sur la base d’un modèle existant dédié à la réactivité des substances humiques. Le modèle WHAM-THP, présenté dans cette étude, est un premier pas vers un nouvel outil d’évaluation de la phytodisponibilité des éléments traces This study has been dedicated to the development of a new modeling approach of trace element phytoavailability, focusing on binding reactions between trace element and plant roots. This approach was used to predict copper (Cu) adsorption on wheat and tomato roots. Several analytical techniques (acid-base titrations, nuclear magnetic resonance of carbon 13, X-ray absorption spectroscopy) were used and crossed with modeling results. At first, plant root reactivity was characterized. Because plant roots are consist of cell walls and plasma membranes, the relative contribution of these two compartments in root binding properties was evaluated. The study was then focused on Cu binding reactions on roots and the effects of physico-chemical conditions (pH, ionic strength, presence of cations) on copper binding. The model has been set thanks to results on root characterization obtained and the acquisition of a set of experimental data on Cu binding. It has been shown that binding properties of wheat and tomato roots came from both cell walls and plasma membranes. Copper speciation in roots was shared, almost evenly, between cell wall pectic compounds and proteins embedded in cell walls and plasma membranes. A model, specific to plant roots, has been developed on the basis of a current model dedicated to the humic substances reactivity. The WHAM-Terrestrial Higher Plants model presented in this study is a first step towards a new tool for assessing the availability of trace elements for plants

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47

Abgrall, Corentin. "Réponse de la flore, de la faune du sol et de leur substrat à l'introduction d'espèces exotiques envahissantes végétales." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMR056/document.

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Les espèces exotiques envahissantes végétales sont des plantes introduites et naturalisées hors de leur aire de répartition native et capables de maintenir et d’accroitre leur population. Certaines sont considérées comme transformatrices de par leur effet sur les écosystèmes : leur structure, leur fonctionnement ainsi que leur communauté végétale et animale. Ces transformations peuvent rendre certaines de ces espèces nuisibles de par leurs impacts écologiques et économiques important. Les travaux réalisés dans le cadre de cette thèse et présentés ici ont pour objectif d’approfondir les connaissances sur l’impact des invasions biologiques. La faune du sol, la végétation native et leur substrat ainsi que son fonctionnement ont été étudiés à différentes échelles spatiales. Deux espèces exotiques, envahissantes en Europe, ont été considérées comme modèles pour ces travaux : le robinier faux-acacia (Robinia pseudoacacia) et la renouée du japon (Reynoutria japonica). Premièrement, une méta-analyse globale a permis de démontrer l’effet positif des invasions biologiques végétales sur l’abondance de certains groupes de la faune du sol, notamment les consommateurs primaires, en fonction de la structure de l’habitat (ouvert ou fermé). Ensuite, une étude à large échelle sur le robinier faux-acacia a permis d’illustrer les différences qui peuvent exister dans la réponse des écosystèmes forestiers aux invasions le long d’un gradient latitudinal. Ce gradient, composé de quatre régions distinctes en Europe de l’Ouest présente des différences de climat et de végétation dominante, ces différences modifiant l’impact du robinier faux-acacia. Une étude approfondie sur le robinier faux-acacia en Normandie a permis de mieux comprendre l’effet du robinier faux-acacia sur les communautés animales et végétales ainsi que sur le fonctionnement des écosystèmes par comparaison avec deux essences natives dominantes. Finalement, une manipulation expérimentale en laboratoire a démontré l’impact des composés allélopathiques de la renouée du Japon sur une partie de la faune du sol. Cette étude a montré que certaines espèces exotiques envahissantes sont susceptibles d’influencer la faune, et les réseaux trophiques, du sol par leur métabolisme secondaire. Ces travaux illustrent l’intérêt, dans le contexte des invasions biologiques végétales, de l’étude simultanée des compartiments aériens et souterrains à différentes échelles spatiales Invasive alien plants are species introduced and naturalized outside of their native distribution range and which have the capacity to maintain and expand their population. Some of these species are considered to be ecosystem transformers by altering their structure, functioning as well as resident animal and plant communities. These induced alterations make some of these species undesirable through their ecological and economical impacts. The work presented in this thesis aimed at a better understanding of the impact of biological invasions by alien plants. The soil fauna, native vegetation and their substrate, as well as ecosystem functioning, were studied at different spatial scales. Two exotic alien species, invasive in Europe, were considered as biological models for this work: the black locust (Robinia pseudoacacia) and the Japanese knotweed (Reynoutria japonica). Firstly, a global meta-analysis demonstrated the positive impact that plant invasions can exert on the abundance of some groups within the soil fauna, notably primary consumers, within different types of habitats (open or closed). Then, a large-scale study on the black locust revealed the differences that can can occur in the response of forest ecosystems to invasions along a latitudinal gradient. Study sites along this gradient, distributed amog four distinct regions in western Europe, exhibit differences in climate and dominant native vegetation which can alter the impact of the black locust. A detailed study on black locust impact in Normandy demonstrated the impact of R. pseudoacacia on native plant and soil fauna communities, as well as some ecosystem functions, in comparison to two native tree species. Finally, a laboraty experiment demonstrated the impact that allelopathic compounds extracted from Japanese knotweed rhizomes can have on some organisms within the soil fauna. This study showed that some invasive alient plants can influence the soil fauna, and soil food webs, through their secondary metabolism. This thesis illustrates that simultaneous study of both aboveground and belowground ecosystem compartments at different spatial scales is of interest in the context of biological invasions

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48

Juice, Stephanie. "The Environmental Microbiome In A Changing World: Microbial Processes And Biogeochemistry." ScholarWorks @ UVM, 2020. https://scholarworks.uvm.edu/graddis/1181.

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Climate change can alter ecosystem processes and organismal phenology through both long-term, gradual changes and alteration of disturbance regimes. Because microbes mediate decomposition, and therefore the initial stages of nutrient cycling, soil biogeochemical responses to climate change will be driven by microbial responses to changes in temperature, precipitation, and pulsed climatic events. Improving projections of soil ecological and biogeochemical responses to climate change effects therefore requires greater knowledge of microbial contributions to decomposition. This dissertation examines soil microbial and biogeochemical responses to the long-term and punctuated effects of climate change, as well as improvement to decomposition models following addition of microbial parameters. First, through a climate change mesocosm experiment on two soils, I determined that biogeochemical losses due to warming and snow reduction vary across soil types. Additionally, the length of time with soil microbial activity during plant dormancy increased under warming, and in some cases decreased following snow reduction. Asynchrony length was positively related to carbon and nitrogen loss. Next, I examined soil enzyme activity, carbon and nitrogen biodegradability, and fungal abundance in response to ice storms, an extreme event projected to occur more frequently under climate change in the northeastern United States. Enzyme activity response to ice storm treatments varied by both target nutrient and, for nitrogen, soil horizon. Soil horizons often experienced opposite response of enzyme activity to ice storm treatments, and increasing ice storm frequency also altered the direction of the microbial response. Mid-levels of ice storm treatment additionally increased fungal hyphal abundance. Finally, I added explicit microbial parameters to a global decomposition model that previously incorporated climate and litter quality. The best mass loss model simply added microbial flows between litter quality pools, and addition of a microbial biomass and products pool also improved model performance compared to the traditional implicit microbial model. Collectively, these results illustrate the importance of soil characteristics to the biogeochemical and microbial response to both gradual climate change effects and extreme events. Furthermore, they show that large-scale decomposition models can be improved by adding microbial parameters. This information is relevant to the effects of climate change and microbial activity on biogeochemical cycles.

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49

Jewell, Mark. "Diversit?? des arbres, interactions a??riennes et souterraines et d??composition des feuilles mortes." Mémoire, Universit?? de Sherbrooke, 2013. http://savoirs.usherbrooke.ca/handle/11143/75.

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R??sum?? : La d??composition des liti??res v??g??tales a ??t?? d??crite comme ??tant la deuxi??me plus importante fonction ??cosyst??mique sur terre, apr??s la productivit?? primaire. Alors que la photosynth??se fournit les apports ??nerg??tiques ?? la plupart des cha??nes alimentaires, la d??composition recycle les nutriments, permet leur utilisation future par d???autres organismes et relargue dans l???atmosph??re le carbone fix?? photosynth??tiquement. Dans un contexte de changement climatique, un grand int??r??t est port?? sur la d??composition des liti??res, car il s???agit, ?? l?????chelle globale, de la plus grande source d?????mission de CO[indice inf??rieur 2] dans l???atmosph??re. Les taux de d??composition des liti??res sont principalement d??termin??s par trois facteurs: les variables climatiques, la structure des communaut??s de d??composeurs et les propri??t??s chimiques et physiques de la liti??re. La structure de la communaut?? v??g??tale h??te dans laquelle se produit la d??composition et d???o?? provient la liti??re peut influencer l???ensemble de ces trois facteurs. Des changements dans la structure de la communaut?? v??g??tale pourraient donc affecter les futurs taux de d??composition et modifier significativement les dynamiques globales du carbone. Malgr?? cela, la communaut?? h??te est rarement prise en compte dans les ??tudes sur la d??composition des liti??res. Des exp??riences enl??vent souvent la liti??re de son environnment naturel de d??composition, mesurant la d??composition des liti??res ?? partir de monolithes ou de microcosmes en laboratoire, afin de contr??ler les variations ind??sirables des propri??t??s du sol. Dans ce m??moire, j?????tudie les effets de plusieurs propri??t??s fonctionnelles de la communaut?? v??g??tale h??te sur les taux de d??composition des liti??res et leur contribution ?? la respiration du sol. En utilisant une plantation exp??rimentale d???arbres qui permet de manipuler la structure de leur communaut??, je teste l???effet de l???identit?? fonctionnelle des arbres, des esp??ces et de la diversit?? fonctionnelle, ainsi que des interactions entre d??composeurs et arbres sur ces processus ??cosyst??miques. La d??composition des liti??res et la respiration du sol sont li??es aux propri??t??s fonctionnelles des plantes. La d??composition des liti??res est bien pr??dite par les valeurs moyennes de traits fonctionnels des liti??res, mais plus faiblement corr??l??e ?? la diversit?? sp??cifique. D???apr??s mes r??sultats, le nombre d???esp??ces en m??lange de liti??res ne constitue pas un facteur important pour la d??composition, ?? cause des interactions globalement idiosyncratiques entre types de liti??res. Cependant, l???augmentation conjointe de la diversit?? fonctionnelle des m??langes d???esp??ces en liti??res et de la communaut?? d???arbres-h??tes acc??l??re les taux de d??composition et la respiration du sol. Les premi??res phases de d??composition de liti??res en surface ne sont que faiblement affect??es par la diversit?? des plantes, alors que pour la respiration du sol, qui prend en compte les derni??res phases de d??composition de liti??re et de mati??re organique du sol, la diversit?? est la propri??t?? fonctionnelle de plantes qui fournit le meilleur pouvoir de pr??diction. De plus, j???ai trouv?? que les apports sp??cifiques de liti??res ?? long terme pouvaient cr??er des conditions qui favorisent la d??composition des liti??res native et pouvaient modifier l???effet de la diversit?? des arbres sur la d??composition. J???attribue cet effet aux r??troactions entre la liti??re et les organismes d??composeurs du sol. Ce travail de recherche fournit une nouvelle perspective sur les effets des changements de structure de communaut?? foresti??re sur les processus de d??composition. La compr??hension de ces effets est n??cessaire pour pr??dire les taux de d??composition de liti??res et les dynamiques globales du carbone. // Abstract : The decomposition of plant litter has been described as the second most important ecosystem function for sustaining life on earth, after primary productivity. Whereas photosynthesis provides the energy input for most food chains, decomposition recycles nutrients for future use by other organisms and returns photosynthetically fixed carbon back to the atmosphere. In the context of climate change, litter decomposition is of specific interest because it represents one of the largest sources of CO[subscript 2] to the atmosphere globally. Rates of litter decomposition are largely determined by three factors: climatic variables, the structure of the decomposer community, and the chemical and physical properties of the litter. The structure of the host plant community under which decomposition takes place and from which the litter is derived can influence all three of these factors. Therefore, any systematic changes in plant community structure could affect future decomposition rates and significantly alter global carbon dynamics. Despite this, the host plant community is rarely considered in litter decomposition studies. Experiments often remove litter from its natural decomposition environment, instead measuring decomposition of litter in common garden settings and laboratory microcosms to control for unwanted variation in soil properties. In this thesis I investigate the effect of several functional properties of the host plant community on rates of litter decomposition and its contribution to soil respiration. Using an experimental tree plantation that manipulates tree community structure, I test the effect of tree functional identity, species and functional diversity, and tree-decomposer interactions on these ecosystem processes. Both litter decomposition and soil respiration were related to plant functional properties. Litter decomposition was best predicted by average-values of litter functional traits and was poorly related to species diversity. The number of species in a litter mixture does not seem to be important for decomposition, as interactions between litter types were idiosyncratic. However increasing the functional diversity both of mixed-species litter and of the host tree community accelerated rates of litter decomposition and soil respiration. Early stages of surface litter decomposition were only marginally affected by plant diversity. In contrast, diversity was the best predictor of soil respiration, which includes latter stages of litter and soil organic matter decomposition. Furthermore, I found that specific repeated litter input to the soil can result in conditions that favour the decomposition of the long-term litter type and can mediate the effect of tree diversity on decomposition. I attribute this effect to feedbacks between the litter and soil decomposer organisms. This research provides insight into the effect of changing forest community structure on decomposition processes. Such an understanding is necessary to predict future rates of litter decomposition and global carbon dynamics.

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50

Egelkraut, Dagmar D. "Long-lasting ecological legacies of reindeer on tundra vegetation." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-142131.

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Reindeer can have strong effects on the plant species composition and functioning of tundra ecosystems, and often promote a transition towards a graminoid-dominated vegetation type. As a result, they influence many ecological processes, such as nutrient dynamics, soil biotic composition and functioning, and carbon storage. Several studies suggest that the effect of reindeer on vegetation may follow predictable patterns and could induce an alternative stable vegetation state. However, little empirical data on the long-term stability of reindeer effects on vegetation exist, as it is inherently challenging to study these ecological processes experimentally on a sufficiently long timescale. The main objective of this thesis was therefore to gain a better understanding of the long-term ecological processes following reindeer-induced vegetation shifts. In order to gain a more mechanistic insight in what initially drives this transition, I used a field-based grazing simulation experiment in which I separated defoliation, trampling, moss removal and the addition of feces. This allowed me to test the relative contribution of reindeer-related activities to initiating the shift from moss and heath- dominated tundra towards a graminoid-dominated vegetation state. Additionally, I studied the long-term ecological stability following such a vegetation shift. I did this by addressing historical milking grounds (HMGs): sites where high reindeer concentrations associated with historical traditional reindeer herding practices induced a vegetation transition from shrubs towards graminoids several centuries earlier, but which were abandoned a century ago. Studying HMGs allowed me to address: 1. The potential stability of reindeer-induced vegetation shifts; 2. The ecological mechanisms contributing to the long-term stability of these vegetation shifts; and 3. How such long-lasting vegetation changes influence soil carbon- and nutrient cycling. I found that trampling by reindeer is an important mechanism by which reindeer cause vegetation change. Addressing HMGs further revealed that this vegetation change can be hightly persistent, as the studied HMGs showed only a low encroachment at the surrounding borders in the last 50 years. The vegetation in the core areas of all studied HMGs had remained strikingly stable, and were hardly invaded by surrounding shrubs. Interestingly, soil nutrient concentrations and microbial activities were still different from the surrounding area as well, and even comparable to actively grazed areas. Even after many centuries of changed vegetation composition and soil processes, there was no difference in total carbon sequestration. This suggests that the environmental conditions for microbial decomposition were more important than vegetation composition for the soil carbon stocks, in our study site. After studying the contemporary habitat use of HMGs by reindeer and other herbivores, investigating the potential plant-soil feedbacks mechanisms and detailed soil analyses, I concluded that several ecological mechanisms contribute to the long-term stability of HMGs: first, the altered soil biotic and abiotic conditions appear to have a stronger advantage for HMG vegetation than for the surrounding tundra vegetation. Furthermore, I found a clear browsing preference of small rodents on single shrubs proliferating in HMGs, causing a strong limitation on shrub expansion. Moreover, the dense established sward of graminoids likely poses a strong direct competition for space and nutrients, hindering seedling establishment. Finally, I conclude that HMGs are highly stable on relevant ecological timescales, and propose how the concepts of historical contingency and ASS can be applied to understand stability of these reindeer-induced vegetation transitions.

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