Tesis sobre el tema "Abiotic and biotic"

With the predicted climate change and an ever-growing population there is increasing pressure to develop crop plants with improved stress responses, increased yield and high nutritive value. We have explored transcriptomic changes in the leaves and roots of rice plants (Oryza sativa japonica cv Nipponbare) in response to drought and the root-knot nematode Meloidogyne graminicola. A glasshouse model was developed to mimic conditions experienced by rice plants in the field. The plant responses under simultaneous biotic and abiotic stress were dominated by the drought element accompanied by a unique set of genes that were only responsive to the simultaneous stress. Highlighted within this group were novel members of stress-responsive gene families for example cytochrome P450, wall-associated kinases, lipid transfer proteinlike proteins and new candidate genes that may play important roles in the response of rice to multiple stresses. The genes that were differentially regulated between the multiple and the drought stress treatment were explored using loss-of-function mutants. The loss-of-function mutant for peroxidase precursor gene (per) showed improved growth and yield compared to the wildtype Nipponbare plants. The experiments conducted in growth rooms were validated in a field study. Both Nipponbare rice plants, and the popular lowland indica rice cv IR64 were grown under prolonged vegetative drought stress accompanied by cyst nematode or root-knot nematode infection. Reduction of phytate, an anti-nutrient, has been adopted as a major strategy to improve the nutritional value of crop plants. Nematode susceptibility of low phytate Arabidopsis plants was studied to determine the effect of reduced phytate content on the plant’s defence response. The study has provided insight into the genome-wide transcriptional changes in rice under a combined biotic and abiotic stress. It has led to better understanding of the stress responses in plants that will be advantageous in developing crop varieties with improved yield and nutritive value.

L’eterogeneità delle risposte fisiologiche delle microalghe ai cambiamenti ambientali rappresenta uno dei fattori più importanti nel determinare le interazioni tra le specie in ambiente. La mia ricerca ha rivelato che specie differenti sono diversamente inclini a modificare la propria composizione cellulare in risposta ai cambiamenti ambientali. La scelta tra acclimatazione e omeostasi dipende anche dal tipo e dalla durata della perturbazione in esame. La maggior parte delle alghe considerate nel mio studio, per esempio, ha mostrato una risposta omeostatica ai cambiamenti nelle concentrazioni ambientali di CO2 e nella forma di azoto disponibile. Non è stato ritrovato nessun legame tra la strategia di risposta e la tassonomia delle alghe. Particolare attenzione è stata rivolta a Chromera velia, parente prossima dei parassiti Apicomplexa e probabile simbionte di coralli dell’ordine Scleractinia. C. velia si è dimostrata perfettamente in grado di vivere ad alta CO2. Questa condizione ha stimolato la produzione di C organico da parte di C. velia, incrementato la sua efficienza di utilizzo dei nutrienti e ha determinato cambiamenti nei rapporti stechiometrici tra gli elementi. Si può ipotizzare, dunque, che l’elevata concentrazione di CO2 rinvenuta all’interno dei tessuti del corallo che circondano il simbionte possa facilitare la vita di quest’alga in simbiosi. Infine, ho potuto dimostrare che le interazioni tra alghe e ambiente possono avere conseguenze nei rapporti tra alghe e loro predatori. I miei esperimenti hanno mostrato che i copepodi (ma non i rotiferi) possono discriminare tra alghe che sono identiche in ogni aspetto tranne che nella composizione cellulare. La storia nutrizionale delle alghe, dunque, essendo uno dei principali determinanti della loro composizione cellulare, risulta un elemento di grande importanza nelle relazioni tra alghe e predatori.
Algae exhibit a large variety of physiological responses to the environmental changes. Such heterogeneity of responses, which is a major determinant of species interaction in natural algal assemblages, was the target of my research. My results show that different species are differently prone to change their cell composition in response to environmental changes, depending on the type and duration of the perturbation. When algae are exposed to changes in the N source and in the CO2 availability, for instance, homeostasis appears as a much more common strategy than usually believed. No link between the response modes and the taxonomy of the examined species was found. I paid special attention to Chromera velia, a photosynthetic relative of apicomplexan parasites that is likely involved in symbiotic associations with scleractinian corals. This alga seems perfectly capable of copying with very high CO2. Life at high CO2 stimulates the overall organic C production of C. velia, increases its nutrient use efficiency and changes the stoichiometric relationships among elements within the cell. The high CO2 concentrations that has been reported in the animal tissue surrounding the photosynthetic cells may therefore facilitate C. velia life in symbiosis. Finally, I have demonstrated that the interactions between algae and environment can affect the relationships between algae and their grazers. My experiments show that the copepods are able to discriminate among algae identical in all aspects but in cell composition, while the rotifers are not. Therefore, the nutritional history of algae, which has the potential to affect algal cell composition, appears as a major determinant of the relationships between algae and grazers.

Medicinal plants have always been considered a rich source of secondary metabolites that promote human health. Quality and property of medicinal plants strictly depend on secondary metabolites profile. They also play important roles in plant physiological processes and in ecological systems. The environment exerts a selective pressure on plants and these molecules actively participate to the plant response and adaptation. Amongst secondary metabolite, the phenolic compounds possess properties able to prevent oxidative stress. Therefore, an enhancement of the amount of phenolic compounds can be observed under different environmental factors. With this project we aimed to study the phenolic compounds of the medicinal plant Achillea collina Becker ex Rchb. cv “SPAK”, and their implication in physiological and biochemical response to abiotic and biotic stresses. We seek the possibility to increase the synthesis of phenolics with health properties or useful as potential control agents of insect pests. Abiotic stress. Hydroponic culture was used to evaluate the effect of long-term mineral, nitrogen starvation (abiotic stress) in A. collina. By means of HPLC-DAD-ESI/MS and NMR techniques, the content and the qualitative profile of A. collina methanol soluble phenolics, were evaluated. We concluded that the methanol extracts of A. collina leaves and roots are rich in hydroxycinnamic acids such as chlorogenic acid (2.33 ± 0.3 mg g-1 Dw), 3,5-di-O-caffeoylquinic acid (10.7 ± 4.2 mg g-1 Dw) and 4,5-di-O-caffeoylquinic acid (0.88 ± 0.24 mg g-1 Dw). The content of hydroxycinnamic acids significantly increased in plants growth under mineral nitrogen starvation, respect to the control plants. Chlorogenic acid increased by 2.5 and 3-fold and 3,5-di-O-caffeoylquinic acid increased by 8.5 and 35-fold in leaves and root, respectively. Biotic stress. A. collina plants cultivated in soil were infested with the phloem feeders aphids. We set up the system (e.g., age of plant, type of the cage, number of insects per plant, duration of infestation) to co-cultivated the plants with specialist (Macrosiphoniella millefolii) and generalist (Myzus persicae Sulzer) aphids. Plant growth, water and total protein content were evaluated. Based on a preliminary assessment of phenolic fingerprint, further extractions and separations were performed on A. collina leaves, to obtained soluble and cell wall-bound fractions and their sub-classes. Our results showed that A. collina plants were strongly affected by aphid infestation. Twenty days after infestation, the fresh weight was twenty-fold and seven-fold increased, in control and infested plants. Water and protein content, condensed tannins and methanol soluble phenolics content, were not affected by the aphid infestation. Cell wall-bound phenolics content increased in infested plants. The main phenolics were found to be chlorogenic acid and 3,5-di-O-caffeoylquinic in methanol soluble fraction, and caffeic acid in cell wall fraction. The chromatographic profiles showed that the main hydroxycinnamic acids were present in control and in both M. persicae and M. millefolli infested plants. The quantitative analysis indicated that the levels of chlorogenic acid and 3,5-di-O-caffeoylquinic acid, were 44% and 37% higher in M. persicae infested plants, respectively. The levels of chlorogenic acid and 3,5-di-O-caffeoylquinic acid, were 27% and 39% higher in M. millefolli infested plants, respectively. Twenty days after infestation the content of caffeic acid was resulted 43% and 34% higher in M. persicae and M. millefolli infested plants, respectively. These differences should indicate the different evolutionary interaction between plant and generalist/specialist aphid. We hypotheses that the increase of these molecules may represent a plant resistance mechanism against aphid attack. Finally, a chemometric approach, by means multivariate statistical analysis, was applied on chromatogram profiles to verify whether there is difference between methanol soluble fraction of infested and non infested A. collina plants. The discriminant analysis showed a significant effect of phloem feeders aphids on soluble phenolic compounds and indicated two peaks, not yet identified, that separate control from infested plants. In conclusion the model system developed to cultivate A. collina was useful to understand the metabolic basis of the environment interactions. The main hydroxycinnamic acids identified, were resulted increased in both abiotic and biotic stress, suggesting their implication in A. collina protection to environmental controversies.

Many ecological communities show variation from place to place; understanding the causes of this variation is the goal of community ecology. Differences in community composition will be the result of both stochastic and deterministic processes. However, it is difficult to know to what degree deterministic processes will shape community composition. In this thesis I combined observational and experimental approaches to quantify deterministic processes within a particular ecological community -- they phytotelmata of bromeliad plants. In my thesis I describe three studies at different scales of organization: 1) do organisms of different size respond equally to changes in their environment 2) how do predators interact to influence prey survival 3) what mechanisms underly the response of similar species to the same environmental gradient, bromeliad size. In Chapter 1, I tested an hypothesis developed from previous observational data -- that smaller organisms respond less than larger ones to the same environmental gradient -- different bromeliad species that occur under different forest canopies. After removing variation caused by dispersal, I found that environmental variation explained little variation for bacteria, more for zooplankton and most of all for macroinvertebrates. In my second chapter, I examined ecological determinism on a smaller scale -- within a single trophic level (macroinvertebrate predators). I found that predators may interfere with each other, reducing predation rates and increasing prey survival. In Chapter 3, I examine macroinvertebrate responses to bromeliad volume. I use both null models and a field experiment to show that for at least one such pair, a difference in abiotic tolerances may be the plausible mechanism. Together these results illustrate when, and to what degree, bromeliad communities respond to deterministic factors. All three chapters first demonstrate a pattern, testing it against a suitable null distribution, before attempting to quantify possible mechanisms with a field experiment. This combination of observation and experiment is an approach which can contribute to our understanding of how ecological systems work.
Science, Faculty of
Graduate

Roots and their associated mycorrhizal fungi have long been recognised as major determinants of nutrient cycling. Their measurement has been limited because soil limits accessibility. The use of in-situ camera techniques in conjunction with minirhizotrons and image analysis software now make the acquisition of accurate root longevity data possible. The current literature was reviewed in relation to root longevity - both measurement techniques and available data. Four main experiments were employed to study the root longevity of a number of tree species, grass and clover subject to differing environmental conditions and grass and clover and poplar roots with and without colonisation by Arbuscular Mycorrhizal fungi. The data was analysed in a number of different ways including the use of the powerful statistical technique for censored data - survival analysis. This technique proved to be very useful for analysing temporal changes to root longevity. The data indicate that root longevity can be extremely short but is dependent upon environment and for some species, colonisation by Arbuscular Mycorrhizal fungi. Preliminary calculations were completed to determine the role of root death in nutrient cycling and these predict that large quantities of nitrogen, phosphorus and carbon are flowing from the live to the dead root pool on an annual basis.

One central question in ecology is why some areas have many species and others have few. Many explanations have been proposed and often the forces that drive species richness are context-dependent. These forces are divided into two general categories: biotic drivers and abiotic drivers. Biotic drivers are most commonly described in terms as top-down and bottom-up effects while abiotic drivers are commonly described in terms of climate and habitat disturbance. The objective of this thesis is to determine how these drivers affect species richness in terrestrial ecosystems. To test this I examine an insect herbivore assemblage in a disturbed forest fragment landscape in southern Canada. I use geographic information systems techniques to determine the impact of a natural episodic disturbance (i.e. an abiotic natural driver) and a chronic human disturbance (i.e. an abiotic human driver) on forest habitat quality (Chapter 1) and on a forest-dwelling caterpillar assemblage (Chapter 2). I show that ice storms result in a heterogeneous pattern of spatial damage across a forest landscape, differing depending on the type of coarse woody debris examined. These different types of coarse woody debris provide habitat for a diversity of taxa. In contrast with natural disturbance, I found that human-based disturbance do not have a positive impact on caterpillar assemblages. Pursuant to this, I explore the concept of habitat quality from the perspective of host plant identity (Chapter 3) and host plant quality (Chapter 4). I found that caterpillar assemblages have strong host plant preferences and that these preferences may depend on quadrat-scale foliar qualities (i.e. a biotic bottom-up driver) and parasitoid densities (i.e. a biotic top-down driver) at different times in the growing season. This thesis adds to a growing body of literature aimed to better understand the drivers of insect species richness across disturbed landscapes. In addition, this thesis develops several management-specific tools for measuring forest disturbance and provides valuable insight into how the selection of different tree species for planting initiatives can have important impacts on forest communities.
Les communautés forestières qui habitent les parcelles de forêts qui subsistent aujourd'hui sont affectées par les perturbations ainsi que par la qualité de l'habitat que leur procure les plantes-hôtes. Ces deux phénomènes ont un impact particulièrement important dans les paysages modifiés par l'activité humaine. Développer une meilleure compréhension de ces phénomènes va faciliter la prise de décision et les efforts de conservations visant à préserver et protéger la biodiversité des forêts. L'objectif global de cette thèse est d'étudier les divers aspects reliés à la qualité de l'habitat dans les parcelles forestières des collines montérégiennes du sud-est du Québec, Canada. J'utilise des techniques en système d'information géographique pour déterminer l'impact d'une perturbation naturelle épisodique (tempête de verglas) ainsi qu'une perturbation anthropogénique chronique (sentiers récréationnels) sur la qualité des habitats forestiers (Chapitre 1) et un assemblage de chenilles vivant en forêt (Chapitre 2). J'ai démontré que les dégâts engendrés par les tempêtes de verglas sont distribués de façon hétérogène à travers le paysage forestier, différant selon le type de débris ligneux grossiers examiné. Ces différents types de débris ligneux grossiers servent d'habitat à divers groupes taxonomiques. J'ai découvert que les perturbations anthropogéniques, au contraire des perturbations naturelles, n'ont pas eu d'impacts positifs sur les assemblages de chenilles vivants en forêt. J'ai également exploré le concept de qualité d'habitat en considérant l'identité de la plante hôte (Chapitre 3) et la qualité foliaire à l'échelle du quadrat (Chapitre 4). J'ai découvert que l'assemblage de chenille démontre des préférences marquées pour certaines plantes hôtes et que ces préférences peuvent dépendre de différentes qualités foliaires à l'échelle du quadrat à différentes périodes durant la saison de croissance. Cette thèse contribue à la documentation croissante sur les facteurs qui affectent la richesse spécifique des communautés d'insectes vivant dans les forêts des paysages perturbés. De plus, cette thèse propose plusieurs outils spécifiques à la gestion pour évaluer les perturbations en milieu forestier et donne un aperçu de l'impact que peut avoir la sélection de différentes espèces d'arbres sur les communautés forestières lors de l'élaboration d'initiatives de plantation d'arbres.

Over half of the carbon (C) taking part in the global C cycle is held in terrestrial systems. Because of the sensitivity of the C cycle to changes in such soil-based pools of carbon, it is important to understand the basic mechanisms by which soil C is stored and cycled between the range of di erent pools which occur belowground. In the context of climate change mitigation, it is considered that increasing soil-based stocks of C, either by reducing losses from soils, or by actively sequestering new carbon, is a potentially important strategy . Organic carbon is the main form of carbon in soil and as such has received most focus. Cont/d.

Plants are continuously exposed to different abiotic and biotic stresses in their natural environment. Their capacity to survive depends on the capacity to perceive external signal and quality amount a defence response for protection from the stress perceived. The purpose of this project was to study the impact of combined abiotic stress and biotic stress on the outcome of the disease inducing Arabidopsis thaliana – Pseudomonas syringae interaction. This study included a focus on the role of ABA in these interactions and also whether 3´-O-β D- ribofuranosyl adenosine (hereafter it called ‘400’ compound), a novel adenosine derived compound induced during compatible interactions, was involved. The later involved the targetted disruption of a putative 400 biosynthetic pathway involving analysis of knockout mutants of enzymes; APD-ribose diphosphatase NAD binding / hydrolases of the NUDIX class, glucosyl transferases, ribosyltransferases, a ribose-phosphate pyrophosphokinase3 and galactosyltransferases. Unfortunately, none of these targeted interventions modified the host response to Pseudomonas infection, nor altered levels of 400 in challenged leaves. The primary research investigated the interaction between abiotic and biotic stresses in Arabidopsis plants focussing on the modulation of plant defence against multiple, and possibly antagonistic, stress responses and the role plant hormones play in this process. We showed that high light caused enhanced susceptibility to the already virulent Pseudomonas syringae DC3000pvsp61. The pathways contributing to this enhanced susceptibility were largely ABA independent. Subsequent characterization of transgenic lines expressing the soluble Arabidopsis abscisic acid receptors, PYRABACTIN RESISTANCE1-LIKE4-6 provided compelling evidence for a role for these receptors in DC3000 virulence strategies, but they contribute to a lesser extent to the enhanced susceptibility under high light. This was corroborated genetically by using mutants of the immediately downstream targets of PYLs, the type two protein phosphatase, specifically the triple mutant hab1-1/abi2-1/abi1-2. A number of epitope and fluorescent constructs were generated to facilitate future studies of the role of ABA signaling. Targetted profiling suggested that SA dynamics were altered under DC3000 challenged Arabidopsis grown under high light. Furthermore, differential accumulation of flavonoids suggested these may also play a role in attenuating host defences under high light. Finally we provide evidence based on comparative analysis of that the photoreceptors phytochrome double mutant phyA-211/phyB-9 and cry1/cry2 behave antagonistically in Arabidopsis response to DC3000. Overall our studies support the conclusion that plants abiotic stress (HL) response takes precedence over biotic stress (DC3000) responses and that abiotic stress is detrimental to plant immunity. The luciferase transgenic PYL lines showed high level of expression of ClucP::PYL5 plant tissues challenged 2hpi of DC3000 (OD600: 0.15) in comparison with C1lucP::PYL6. This result opposes to what RT-PCR reported; which was that three PYLs genes display similar expression level at 6hpi of hrpA or 18hpi of DC3000. The epitope tags of CaMV::HA transgenic plants showed HA-tagged signal with stunted phenotype in a range of PYL4, 5 and 6 plants but none of the plants displayed any differences in susceptibility to DC3000. Although, RT-PCR assay showed high levels of expression in the three PYLs, 6hpi of hrpA but no signal was detected in B8eGFP::PYL5 transgenic line either followed the DC3000 and hrpA infection or by examined plant seedlings at early stages under confocal microscopy.

When active venting has ceased, reduced minerals in hydrothermal mounds and sediments continue to provide an inorganic energy source for chemolithotrophic microbes. This research focuses on the nature of microbially-mediated metal transformations in hydrothermal sediments during sulphide alteration and their impact on the ultimate fate of hydrothermal sulphides on the seafloor. The core studied is more seawater altered than other cores studied at TAG and provides an insight into the bacterial and archaeal communities as well as the geochemical processes taking place in highly altered metalliferous sediments. This study combines geochemical approaches with microbiological and organic biomarker measurements within the suboxic transition zone of sulphidic sediments to characterise the reactions and microbial communities present. This integrated approach demonstrates that (a) there is biogeochemical zonation within the sediment sequence with distinct microbial communities present at the sulphide-oxic seawater transition, (b) the microbes identified are associated with Fe and S redox cycling, (c) Marinobacter sp. are dominant at the sulphide interface. There is a significant shift in the microbiological community across the redox transition zone in these sulphidic sediments. The microbial assemblage of the suboxic transition zone is dominated by Bacillus sp. which are microaerophilic whereas the sulphide layer assemblage is dominated by Marinobacter sp. which are Fe oxidisers. Based on biomarker assemblages and genetic analyses, archaeal (and to a certain degree bacterial) communities are comparable to other hydrothermal settings despite the low biomass present. Processes inferred to be important in this sediment include the S, Fe and N cycle, all potentially coupled to the release and uptake of a range of transition metals. Significant recycling of redox active species occurs in the suboxic transition zones present in the sediment core. Uranium concentrations are low compared with other less altered sulphidic hydrothermal sediments, and U is associated with the upper regions of the suboxic transition zone and is associated with enrichment of a suite of other transition metals (e.g. Cu, Mo, As and V). Massive electrodes were constructed from CuFeS2 (from Ireland and TAG) and FeS2 (from TAG) and studied in oxygenated artificial seawater under circumneutral conditions using electrochemical methods. The results can be explained by existing hypotheses about pyrite and chalcopyrite oxidation and their oxidation products. The oxidation status of Cu in covellite could be identified as Cu+1. Impurities found (as expected because natural samples were used) have no effect on the electrochemical behaviour of the electrodes. The impact of Marinobacter sp. on sulphide alteration was studied in detail using an electrochemical approach. The results demonstrate that Marinobacter aquaeolei enhances the rates of oxidation. Marinobacter species seem to be of special importance for weathering reactions on the seafloor and in hydrothermal settings like the TAG area.

In Arabidopsis thaliana, eight histidine kinases (HKs) have been identified which function in hormone signalling, stimuli perception, and plant development. To better elucidate HK roles in signalling, the function of the least characterised HK, AHK5, in stress tolerance was investigated using a T-DNA insertion knockout line (ahk5-1). Reduced inhibition of seedling root growth was seen in ahk5-1 in response to salinity when compared to wild-type Col-0 in tissue culture assays. In mature plants, ahk5-1 showed greater fresh weight gain under either salinity or drought stress. Loss of AHK5 function did not alter cold stress tolerance, nor basal and acquired heat stress tolerance in terms of seedling root elongation. Infection with the biotrophic pathogen Pseudomonas syringae pv. tomato DC3000 revealed ahk5-1 is compromised in disease resistance, exhibiting increased chlorosis and in planta bacterial growth. Levels of the plant hormones salicylic acid, jasmonic acid, and abscisic acid, alongside the bacterial phytotoxin coronatine, were lower in pathogen challenged ahk5-1 mutants compared to wild-type plants. The ahk5-1 mutant was also more susceptible to the necrotrophic pathogen Botrytis cinerea, supporting more fungal growth and displaying accelerated symptom development. Hydrogen peroxide production has been linked with both resistance and susceptibility towards B. cinerea; in ahk5-1, 3,3-diaminobenzidene (DAB) staining suggested reduced hydrogen peroxide production in response to infection. Complementation and expression of AHK5 with either full-length genomic AHK5 under the 35S CaMV promoter or full-length AHK5 cDNA under the native promoter rescued the ahk5-1 mutant stress response phenotypes. In summary, AHK5 was found to negatively regulate abiotic stress tolerance whilst positively contributing towards resistance against pathogens employing different lifestyles. To begin to establish an AHK5 signalling network, tandem affinity purification coupled with LC-MS/MS was employed for identification of possible AHK5 interacting proteins. Suggestions for further optimisation of the purification method are presented. The role of AHK5 in regulation of plant stress responses through modulation of reactive oxygen species and hormone signalling and through protein-protein interactions are reviewed. Suggestions for further investigation are also discussed.

This investigation was focused on the assessment of genetic diversity for resistance to stem rust and stripe rust in an international wheat nursery, genetic characterisation of adult plant stripe rust resistance in Australian wheat cultivar Sentinel, understanding of genetic relationship between two stem rust resistance genes (Sr36 and Sr39) located on chromosome 2B and assessment of genetic diversity for physiological traits among a set of wheat landraces. Ten seedling stem rust resistance genes (Sr8a, Sr8b, Sr9b, Sr12, Sr17, Sr23, Sr24, Sr30, Sr31 and Sr38) and seven stripe rust resistance genes (Yr3, Yr4, Yr6, Yr9, Yr17, Yr27 and Yr34) were postulated either singly or in combinations in an international wheat nursery. Genotypes carrying uncharacterised resistance for stem rust and stripe rust against the Australian rust flora were identified for genetic analysis. Three consistent QTL (QYr.sun-1BL, QYr.sun-2AS and QYr.sun-3BS) were demonstrated to condition high level of adult plant stripe rust resistance in Sentinel. QYr.sun-1BL, QYr.sun-2AS and QYr.sun-3BS explained on an average 18.0%, 15.6% and 10.6% variation in stripe rust response, respectively. Additive nature of three QTL to condition high level of stripe rust resistance was demonstrated through comparison of recombinant inbred lines (RILs) carrying these QTL in all different combinations. Detailed characterisation of these loci will be performed. Stem rust tests on F3 populations involving Sr39 on a large and a shortened Aegilops speltoides translocation with Sr36 on a Triticum timopheevi segment showed complete repulsion linkage. The molecular cytogenetic analysis however indicated that these can be recombined using large F2 population. Significant variation for water-use efficiency related physiological traits was observed among wheat landraces. Genotypes with low and high mesophyll conductance, stomatal conductance and other physiological attributes will be useful in designing crosses to achieve high water-use efficiency in future wheat cultivars.

Le piante crescono in ambiente aperto in continuo cambiamento e sono sottoposte a stress. Gli stress possono essere classificati come interni e esterni. Lo stress interno porta a mutazioni o a abnormi divisioni cellulari e infine a una ripartizione anomala della crescita, dell’allocazione e della ripartizione del carbonio. Stress esterni possono essere abiotici o biotici. Siccità, freddo, caldo, alta salinità, fitotossine rilasciate da lettiere indecomposte o altri residui organici sono fra i fattori che più drasticamente riducono la crescita, lo sviluppo e la produzione delle piante. Fra gli stress biotici quelli da patogeni (batteri, funghi, fitoplasmi, virus) sono i più pericolosi per la produzione. Nei prossimi anni per consentire livelli elevati di produzione capaci di rispondere alla crescente domanda di olio e vino, ogni regione produttiva dovrà rispondere con un incremento delle superfici coltivate nelle zone agroecologiche in cui sono attualmente coltivate oppure dovrà espandersi in nuove zone. Questo richiederà in ogni caso un cambiamento di tecniche di coltivazione e di gestione degli impianti che dovranno di conseguenza fronteggiare maggiori stress biotici (nelle zone meno vocate) o stress dovuti al reimpianto (se impiantati negli stessi appezzamenti). Questo progetto ha lo scopo di valutare la risposta fisiologica della vite e dell’olivo a stress biotici e abiotici. In particolare sono oggetto stati di studio gli effetti del legno nero (fitoplasma) e del accartocciamento virale (GLRaV-3 virus) sugli scambi gassosi e sulla produzione di vite Chardonnay and Cabernet Franc, rispettivamente. Sono stati inoltre approfonditi gli effetti di residui colturali di olivo indecomposti e di sansa proveniente da un frantoio a due fasi su olivo cv. Arbequina and Frantoio. L’infezione con fitoplasmi e virus ha indotto una riduzione significativa della fotosintesi, della traspirazione e della conduttanza stomatica in entrambi i vitigni durante l’estate dopo l’allegagione. La riduzione degli scambi gassosi e del metabolismo ha indotto una riduzione della produzione, della crescita dei tralci e della loro lignificazione. In definitiva la riduzione della produzione è stata pari al 70 e 40% rispettivamente. L’applicazione di residui colturali di olivo e di sanse di olivo su piante in vaso ha ridotto la crescita radicale e dei germogli in funzione della dose applicata, mentre ha portato in proporzione ad un aumento del contenuto di sostanza organica nel substrato. In conclusione, nel caso di fitoplasmi e virus è necessaria un’attenta profilassi per evitare la diffusione attraverso il materiale di vivaio e una volta presenti in campo deve essere prevista una campagna di eradicazione delle piante infette che possono sopravvivere all’infezione e funzionare da inoculo. Nel caso dell’olivo si deve invece tenere conto che applicazioni localizzate di residui indecomposti e di sanse hanno un’azione temporanea fortemente tossica per le radici e quindi per poter sfruttare al meglio il miglioramento indotto del contenuto di sostanza organica e non avere ripercussioni negative sulle produzioni serve un’attenta programmazione delle dosi e del momento dell’intervento.
Plants grow and develop in an open field, with continuously changing weather condition that induces stress. Stress are broadly classified as external and internal. Internal stress is that drive from mutation or abnormal cell divisions and to unbalanced growth and carbon allocation and partitioning. External stress can have abiotic and biotic origin. Drought, cold, high-salinity, heat and phytotoxin released from undecomposed litter and manure are major abiotic stresses that severely reduce the plant growth, development and yield. Whereas, pathogen (bacteria, fungi, phytoplasma, virus) are the major biotic stress that severely reduce yield. To meet the current increase in global demand of agricultural good in general and olive oil and wine in particular, each growing region has to respond either by incorporating new olive and grape orchard in the existing agroecological zone and/or expanding to new agroecological zones or by changing mode of cultivation and orchard management, facing different biotic stress and external stress in replanting condition. This project aimed at evaluating the physiological responses of grape and olive to biotic and abiotic stress respectively. In particular, effect of Bios noir (BN, a phytoplama disease) and grapevine leafroll associated virus 3 (GLRaV-3, viral disease) on gas exchange and yield of Vitis vinifera cv. Chardonnay and Cabernet Franc respectively; and effect of undecomposed olive shoot residue (OSR, originated from pruning and leaf shedding) and fresh two-phase olive mill waste (TPOMW, coming from two-phase decanter) were studied on shoot growth, root proliferation and biomass partition of Olea eropaea L. cv. Arbequina and Frantoio. Biotic stress originated from BN and GLRAV-3 infection showed that Photosynthesis, stomatal conductance and transpiration were significantly reduced in the symptomatic Chardonnay and Cabernet Franc vines through the summer after the fruit set. The reduction in metabolism due to BN and GLRaV-3 infection in cv. Chardonnay and Cabernet Franc had a direct influence on the decrease in total berry production, vine size and cane lignifications of symptomativ vines. Indeed, they suffered a drastic decrease of about 70 and 40% in yield respectively. Whereas, application of OSR and TPOMW in the pot altered shoot and root growth, biomass partition and relative growth rate of fine root and shoot; while increasing soil total organic matter and carbon, total N and polyphenol content of the growing substrate. Hence there is no chemical spray develop to control the infection of BN and GLRaV-3 pathogens, planting phytoplasma and virus free root stocks during the vineyard establishment and uprooting the infected vine and replanting new to avoid spread during pruning and by insect vectors is the best way to minimize the adverse effect of BN and GLRaV-3 on quality and quantity yield. To avoid antagonistic effect of OSR and TPOMW on root and shoot growth and improve soil fertility knowing the exact quantity, for each types olive orchards, and when to apply in play major role.

Biological invasions are a major component of global environmental change and are increasing in frequency. Most community-level impact studies of invasions are concerned with interactions between exotic and native species. However, interactions among exotic species are becoming increasingly common, potentially altering their respective impacts on invaded ecosystems. This research identifies one possible outcome of such interactions: the growing phenomenon of 'exotic species replacement', whereby a newly arriving exotic species surpasses the abundance of a functionally similar incumbent exotic species. This phenomenon is explored here using two Eurasian dreissenid bivalves that invaded the St. Lawrence River in the early 1990s, the zebra mussel (Dreissena polymorpha) and quagga mussel (D. bugensis). I review the general replacement pattern of the zebra mussel by its congener, and examine environmental factors and life history traits that mediate this replacement in a navigational canal connected to the river. Since the 1990s, quagga mussels have replaced the zebra mussel as the dominant dreissenid mussel, but the contemporary adult distribution and abundance is spatially structured: quagga mussels dominate the deep zone, while zebra mussels remain common in the shallow margins of the canal. Field surveys and in situ field experiments are used to examine the relative importance of pre-settlement, settlement and post-settlement processes, in the context of life history trade-offs and environmental gradients, in determining patterns of adult mussel distribution and abundance. Despite the potential importance of larval supply and behavior, including substrate selection at settlement, none of these processes determined adult dreissenid distribution and abundance. Rather, the main determinants were post-recruitment processes involving condition-specific competition. Adult zebra mussels generally had lower body condition, growth, shell length, and survivorship than quagga mussels, and these differences were most pronounced in the deep zone of the canal. This case highlights the importance of subtle differences in life history and abiotic tolerances among closely-related species in understanding changing patterns of distribution and abundance in an invaded community.
Les invasions biologiques sont une composante majeure des changements environnementaux au niveau mondiale et leurs fréquences continuent à augmenter. La plupart des études sur l'impact des invasions à l'échelle communautaire s'intéressent principalement aux interactions entre les espèces exotiques et indigènes. Par contre, on observe de plus en plus des interactions entre des espèces exotiques, ce qui pourrait modifier leurs impacts respectifs sur les écosystèmes envahis. Cette recherche a pour but d'examiner le 'remplacement d'espèces exotiques', un phénomène par lequel l'abondance d'une espèce exotique nouvellement arrivée surpasse l'abondance d'une espèce exotique déjà présente et dominante, qui possède également une similarité fonctionnelle. Ce phénomène est exploré ici à l'aide de deux bivalves Eurasiennes de la famille des Dreissenidés qui ont envahi le fleuve Saint-Laurent au début des années 1990, la moule zébrée (Dreissena polymorpha) et la moule quagga (D. bugensis). J'examine le schéma général de remplacement de la moule zébrée par son congénère dans un canal de navigation relié au fleuve. J'examine également les facteurs environnementaux et les traits d'histoire de vie de ces moules qui peuvent influencer se remplacement. Depuis les années 1990, la moule quagga a remplacé la moule zébrée en tant que le dreissenidé dominant. Par contre, la distribution et l'abondance contemporaines des adultes sont structurées de façon spatiale: les moules quagga dominent la zone profonde, tandis que les moules zébrées demeurent communes dans la région peu profonde du canal. Des études sur le terrain et des expériences in situ ont été utilisées pour examiner l'importance relative des processus de pré-établissement, d'établissement et de post-établissement, sur la distribution et l'abondance des moules adultes. Malgré l'importance potentielle de l'approvisionnement et du comportement larvaire, y compris la sélection du substrat durant l'établissement, aucun de ces processus ne joue un rôle important dans la détermination de l'abondance et la distribution des dreissenidés adultes. Plutôt, les principaux facteurs déterminants étaient les processus de post-recrutement impliquant la compétition mediée par l'environnement. En générale, la condition, la croissance, la longueur de coquille et la survie des moules zébrées adultes étaient inférieures à celles des moules quagga, et ces différences étaient plus prononcées dans la zone profonde du canal. Cette étude met en valeur l'importance des différences subtiles des traits d'histoire de vie et des tolérances abiotiques d'espèces étroitement liées dans la compréhension des schémas changeants de distribution et d'abondance d'individus dans les communautés envahies.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995.
Includes bibliographical references (leaves 63-65).
by Henry Matthew Spliethoff.
M.S.

This study covered genetic and molecular analyses of stripe rust and leaf rust resistance in common wheat landraces and investigation of response of drought and short term leaf temperature changes among a set of 20 durum wheat genotypes. Three all stage resistance genes (YrAW5 in Aus27430 and YrAW6 and YrAW7 in Aus27492) were identified. YrAW5 and YrAW7 were located on chromosomes 6AS and 5AL, respectively. The location of YrAW6 was inconclusive. While Aus27430 was concluded to carry Yr18, Aus27492 appears to carry an uncharacterized adult plant resistance gene. Four QTL for stripe rust resistance (QYr.sun-1BL, QYr.sun-2AL, QYr.sun-5AL and QYr.sun-3BS) were detected in Aus28166/AvS RIL population. QYr.sun-1BL and QYr.sun-5AL also conferred resistance to leaf rust in Aus28166. QYr.sun-1BL and QLr.sun-1BL corresponded to the pleiotropic locus Lr46/Yr29/Sr58/Pm39/Ltn. The co-located loci QYr.sun-5AL and QLr.sun-5AL appear to represent a new pleiotropic resistance locus. Durum wheat genotypes showed significant variation for mesophyll conductance in response to water stress and short-term variation of leaf temperature highlighting the potential for improving durum wheat for drought and heat stress.

Tomato (Lycopersicon esculentum Mill., Solanum lycopersicon L.) is one of the most popular vegetable throughout the world, and the importance of its cultivation is threatened by a wide array of pathogens. In the last twenty years this plant has been successfully used as a model plant to investigate the induction of defense pathways after exposure to fungal, bacterial and abiotic molecules, showing triggering of different mechanisms of resistance. Understanding these mechanisms in order to improve crop protection is a main goal for Plant Pathology. The aim of this study was to search for general or race-specific molecules able to determine in Solanum lycopersicon immune responses attributable to the main systems of plant defense: non-host, host-specific and induced resistance. Exopolysaccharides extracted by three fungal species (Aureobasidium pullulans, Cryphonectria parasitica and Epicoccum purpurascens), were able to induce transcription of pathogenesis-related (PR) proteins and accumulation of enzymes related to defense in tomato plants cv Money Maker,using the chemical inducer Bion® as a positive control. During the thesis, several Pseudomonas spp. strains were also isolated and tested for their antimicrobial activity and ability to produce antibiotics. Using as a positive control jasmonic acid, one of the selected strain was shown to induce a form of systemic resistance in tomato. Transcription of PRs and reduction of disease severity against the leaf pathogen Pseduomonas syringae pv. tomato was determined in tomato plants cv Money Maker and cv Perfect Peel, ensuring no direct contact between the selected rhizobacteria and the aerial part of the plant. To conclude this work, race-specific resistance of tomato against the leaf mold Cladosporium fulvum is also deepened, describing the project followed at the Phytopathology Laboratory of Wageningen (NL) in 2007, dealing with localization of a specific R-Avr interaction in transfected tomato protoplast cultures through fluorescence microscopy.

Tomato (Lycopersicon esculentum Mill., Solanum lycopersicon L.) is one of the most popular vegetable throughout the world, and the importance of its cultivation is threatened by a wide array of pathogens. In the last twenty years this plant has been successfully used as a model plant to investigate the induction of defense pathways after exposure to fungal, bacterial and abiotic molecules, showing triggering of different mechanisms of resistance. Understanding these mechanisms in order to improve crop protection is a main goal for Plant Pathology. The aim of this study was to search for general or race-specific molecules able to determine in Solanum lycopersicon immune responses attributable to the main systems of plant defense: non-host, host-specific and induced resistance. Exopolysaccharides extracted by three fungal species (Aureobasidium pullulans, Cryphonectria parasitica and Epicoccum purpurascens), were able to induce transcription of pathogenesis-related (PR) proteins and accumulation of enzymes related to defense in tomato plants cv Money Maker,using the chemical inducer Bion® as a positive control. During the thesis, several Pseudomonas spp. strains were also isolated and tested for their antimicrobial activity and ability to produce antibiotics. Using as a positive control jasmonic acid, one of the selected strain was shown to induce a form of systemic resistance in tomato. Transcription of PRs and reduction of disease severity against the leaf pathogen Pseduomonas syringae pv. tomato was determined in tomato plants cv Money Maker and cv Perfect Peel, ensuring no direct contact between the selected rhizobacteria and the aerial part of the plant. To conclude this work, race-specific resistance of tomato against the leaf mold Cladosporium fulvum is also deepened, describing the project followed at the Phytopathology Laboratory of Wageningen (NL) in 2007, dealing with localization of a specific R-Avr interaction in transfected tomato protoplast cultures through fluorescence microscopy.

Todo en la tierra es química. Esta afirmación tiene profundas implicaciones para las interacciones ecológicas. Los organismos vivos promueven y controlan flujos de materia y energía entre la atmosfera, hidrosfera y litosfera; modificando la composición química de la tierra de muchas maneras diferentes. La estequiometría ecológica estudia el balance y el papel de múltiples elementos químicos en las interacciones ecológicas y nos ayuda a entender patrones y procesos en la naturaleza. Representa el enlace entre la biogeoquímica y el funcionamiento de los ecosistemas, permitiéndonos describir procesos a todos los niveles de organización biológica, desde estructuras sub-celulares a ecosistemas. En esta Tesis he usado la estequiometría ecológica para describir procesos a nivel de organismo y ecosistema en tres condiciones ambientales terrestres diferentes. La estequiometría de los autótrofos se establece cuando estos usan luz para fijar carbono (C) y simultáneamente asimilan nutrientes. Las plantas son capaces de almacenar nutrientes en la vacuola intracelular y en diferentes órganos, lo que hace que su estequiometría sea muy flexible (baja homeostasis) y se adapten a diferentes ambientes, incluyendo condiciones del suelo limitantes para el desarrollo de las plantas. También, la interacción planta suelo se puede explorar a través de la estequiometría foliar, ya que se ha demostrado en todos los ecosistemas terrestres que el N:P foliar esta correlacionado positivamente con el N:P del suelo, sugiriendo que es un buen indicador de la disponibilidad de nutrientes. Las adaptaciones de las plantas a condiciones limitantes de nutrientes en el suelo son comunes en todos los ecosistemas terrestres, como es la fijación de nitrógeno, la asociación con micorrizas, producción de fosfatasas o la reabsorción de nutrientes desde las hojas senescentes para el reciclado interno de nutrientes. La composición elemental de las especies es afectada por esas interacciones abióticas y bióticas, y el intercambio de elementos químicos entre las especies y el espacio abiótico determinaran la composición elemental de las diferentes partes del ecosistema. En el Capítulo 2 exploramos el efecto biótico de la composición de las comunidades sobre la composición química foliar de distintas especies vegetales, a través del nicho biogeoquímico de cada especie. Encontramos que cada especie presenta su propio nicho biogeoquímico y fueron capaces de reajustar su composición química foliar en respuesta a las diferentes condiciones bióticas. Concluimos que las plantas pueden reajustar su composición elemental foliar cuando crecen en comunidades con diferente composición de plantas, a través del desplazamiento del nicho biogeoquímico, sugiriendo un uso diferencial de los recursos cuando los patrones de coexistencia cambian. En el Capítulo 3 hemos explorado el cambio en la composición química del sistema planta-suelo debido a la expansión de arbustos en los pastizales subalpinos del Pirineo. Esta expansión representa la transición desde pastizales puros a matorrales. Los pastizales son un ecosistema dominado por especies de ciclo de vida corto, rápido intercambio de nutrientes entre los compartimientos planta-suelo, altas concentraciones de nitrógeno (N), fósforo (P) y potasio (K) en el sistema planta-suelo, con alta productividad pero capacidad limitada de acumulación de biomasa. En cambio, los matorrales se caracterizan por ser un ecosistema dominado por especies de ciclo de vida largo, con estrategias más conservativas, con un intercambio de nutrientes más lento (relación de C:nutrientes altos en la biomasa aérea y baja concentración de N y P en el sistema planta-suelo) y mayor almacenamiento de nutrientes en la biomasa aérea de las plantas. La matorralización incrementa la dependencia de la adquisición de nutrientes como el N a través de micorrizas desde los pastizales puros a matorrales. Todos los cambios en el almacenamiento y composición elemental del sistema planta-suelo a lo largo de la sucesión desde pastizales a matorrales sugiere una desaceleración del ciclo biogeoquímico en las áreas montañosas donde la expansión de arbustos está presente. En el Capítulo 4, describimos la distribución de C y los nutrientes más importantes para el desarrollo de las plantas (N, P, K) en el sistema planta-suelo de bosques tropicales maduros en suelos pobres de la Guyana Francesa. También estudiamos el proceso de reabsorción de nutrientes desde las hojas senescentes, un mecanismo de nutrición de las plantas para evitar la perdida de nutrientes poco estudiado en este ecosistema. Nuestros resultados muestran que el P es el elemento más escaso presente en hojas, hojarasca y suelo. Las eficiencias de reabsorción de K y P fueron más altas que la de N y la estacionalidad solo afecto la reabsorción de K. La reabsorción de P fue la única que mostró una correlación, aunque débil, con el P en el suelo (total y disponible). Las relaciones entre la reabsorción de nutrientes y los rasgos funcionales de las especies (tasa de crecimiento, densidad de madera, diámetro a la altura del pecho y el área foliar específica) fueron débiles y variaron dependiendo del nutriente, en tanto que la relación filogenética no explica la variabilidad en las eficiencias de reabsorción de nutrientes de las especies. Nuestros resultados sugieren que la alta reabsorción de K y P desde las hojas senescentes es una estrategia adaptativa de las especies que les permite lidiar con la escasez de estos nutrientes en el suelo. Asimismo, el nivel de inmovilización de los nutrientes en los compuestos foliares (N > P > K) parece determinar significativamente el proceso de reabsorción. Concluimos que la reabsorción de nutrientes desde las hojas senescentes es un proceso clave de las plantas para la conservación de nutrientes en los bosques tropicales de la Guyana Francesa, especialmente para K y P, elementos que presentan una disponibilidad baja en el suelo, y esta depende principalmente del material parental y del proceso de lixiviación. En resumen, en esta Tesis hemos demostrado como la composición elemental del sistema planta-suelo refleja procesos e interacciones ecológicas, como son las interacciones intra e inter específica entre plantas (Capítulo 2), procesos fisiológicos poco estudiados en las plantas como la reabsorción de nutrientes (Capítulo 4) y la importancia de los estudios de estequiometría para describir cambios a nivel de ecosistema y predecir escenarios futuros (Capítulo 3). Estos estudios aportan nuevos conocimientos en el campo de la estequiometría ecológica y resaltan la importancia de este enfoque en los estudios ecológicos.
Everything on Earth is based on chemistry. This statement has profound implications for ecological interactions. Living organisms generate and control fluxes of energy and matter among the atmosphere, lithosphere and the hydrosphere, shaping the chemistry of the Earth in many different ways. Ecological stoichiometry aims to explore the balance and role of multiple chemical elements in ecological interactions and help us to understand patterns and processes in nature. It represents the link between the biogeochemistry and the ecosystems’ function and allows to describe processes across different levels of biological organization, from cellular structures to ecosystems. In this Thesis I use ecological stoichiometry to describe processes at organism and ecosystem levels in three contrasting terrestrial environment conditions. Autotrophs’ stoichiometry is established when these organism use light to fix carbon (C) and simultaneously assimilate nutrients. Plants are able to store nutrients in the cells’ vacuole and in different organs, which make them highly flexible (less homeostatic) in terms of their elemental composition. This feature explains the high adaptability of plants to different environments, including soil nutrient limitation conditions. Furthermore, plant-soil interaction could be explored through the foliar stoichiometry, because it has been shown that the foliar N:P is positive correlated with the N:P of soil in all terrestrial ecosystem, suggesting that foliar stoichiometry is a good indicator of the resource availability. Plant adaptations to soil nutrient limiting conditions are quite common in all terrestrial ecosystems, such as nitrogen fixation, mycorrhiza association, production of phosphatases and nutrient resorption before leave abscission. The species’ chemical composition is affected by all these abiotic and biotic interactions, and these exchange of chemical elements between the species and the abiotic part of the system determine the elemental composition of different components of the ecosystems. In Chapter 2, we explore the biotic effect of the community composition on the species foliar stoichiometry, taken as a proxy of the species’ biogeochemical niche. We found that each species has its own biogeochemical niche and is able to readjust its chemical composition in response to different biotic conditions. We conclude that plants can readjust their foliar element composition when they grow in communities with contrasting plant composition through the biogeochemical niche displacement, suggesting a differential use of the resources when the patterns of species coexistence change. In Chapter 3 we explore the plant-soil stoichiometry changes due the shrub expansion into the subalpine grassland in the Pyrenees. Shrub expansion had a clear impact on the plant-soil stoichiometry spectrum. This expansion represents the transition from pure grassland to shrubland. The grassland is an ecosystem dominated by short-lived species, fast nutrient turnover between the plant-soil compartments, high nitrogen (N), phosphorus (P) and potassium (K) concentrations in the plant-soil system, high productivity but low biomass stocks. The shrubland is an ecosystem characterized by long-lived species with more conservative strategy, slow nutrient turnover (low N and P concentrations in the plant-soil compartments, high C:nutrient ratios in the aboveground biomass) and high stocks of C and nutrients in the plant aboveground biomass. Shrub encroachment increase the acquisition of N through mycorrhizal associations. The changes in storage and elemental composition of the plant soil system along the succession from grassland to shrubland suggests that there is a slowdown of the biogeochemical cycle in the subalpine mountain areas where shrub encroachment occurred. In the Chapter 4, we describe the distribution of C and the most important nutrients for the plant development (N, P, K) in the plant and soil compartments in old-growth tropical forests growing in nutrient-poor soil in French Guiana. We also studied the nutrient resorption from senescent leaves, a poorly explored mechanism that plants use to avoid losing nutrients in this ecosystem. Our results showed that P was the scarcest nutrient in the leaf, leaf-litter and soil. Resorption efficiencies were higher for K and P than for N, and only K resorption efficiency was affected by seasonality. P resorption showed a negative and weak correlation with P in soil (total and available). Relationships between nutrient resorption and species functional characteristics (growth rate, wood density, diameter at breast height and specific leaf area) were weak and varied among the nutrients, and phylogenetic relatedness did not account for the variability in resorption efficiencies. Our results suggest that high K and P resorption from senescent leaves is an adaptive strategy allowing species to cope with soil nutrient scarcity. Furthermore, the level of nutrient immobilization in foliar compounds (N > P > K) seem to significantly determine the resorption process. We conclude that nutrient resorption from senescent leaves is a key process for plants to conserve nutrients in tropical forests of French Guiana, especially for K and P, where soil availabilities are low and depend mainly on soil parent material and leaching process. To sum up, in this Thesis we have demostrated how the elemental composition of the plant-soil system reflects ecological interactions and processes, such as intra and inter specific plant interactions (Chapter 2), poorly explored physiological processes such as nutrient resorption (Chapter 4) and the importance of stoichiometry studies for describing changes at ecosystem level and predicting future scenarios (Chapter 3). These studies add new knowledge to the ecological stoichiometry field and highlights the importance of this approach in the ecological studies.

Methane (CH4) plays an important role in regulating Earth’s climate. Its atmospheric concentrations are related to both biotic and abiotic processes. The biotic one can be formed either by chemoautotrophic or heterotrophic pathways by methanogens. Abiotic CH4 formation can occur from several sequential reactions starting with H2 production by serpentinization of Fe-bearing minerals followed by Fischer-Tropsch Type reactions or thermogenic reactions from hydrocarbons. In the presence of suitable electron acceptors, microbial oxidation utilizes CH4 and contributes to regulating its emission.  From the perspectives of astrobiology and Earth climate regulation, this thesis focuses on: (1) Dynamics of CH4 formation and oxidation in lake sediments (Paper I), (2) Constructing an automatic flux chamber to facilitate its emission measurements (Paper II), (3) dynamics of both abiotic and biotic CH4 formation processes related to olivine water interaction in temperature range 30 - 70°C (Paper III and IV). Paper I showed that potential CH4 oxidation strongly correlated to in situ its formation rates across a wide variety of lake sediments. This means that the oxidation rates could be enhanced in environments having the high formation rates. Thereby, the oxidation would likely be able to keep up with potentially increasing the formation rates, as a result diffusive CH4 release from freshwater sediments might not necessarily increase due to global warming. Paper II presented a new automated approach to assess temporal variability of its aquatic fluxes. Paper III and IV together revealed that H2 can be formed via olivine-water interaction. Abiotic CH4 formation was formed likely by Fischer-Tropsch Type reactions at low inorganic carbon concentration but by thermogenic processes at high inorganic carbon concentration. Paper IV showed that biotic methanogenic metabolism could harvest H2 and produce CH4. The dynamics of these processes seemed strongly affected by carbonate chemistry.
At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Submitted.

Aquatic insects are the most numerically abundant and diverse group of organisms found in lotic ecosystems in South Africa and the world over. They play vital roles in freshwater ecosystem functioning, processing nutrients and in turn forming integral links in stream food-webs. This thesis focussed on examining the macroinvertebrate fauna within three reaches of headwater streams of the Keiskamma River system: reaches that were considered to be fishless; reaches that were invaded by non-native salmonid species; and reaches that were dominated by native fish. I described the effects of predatory fish presence through detailed examination of macroinvertebrate assemblage composition; macroinvertebrate drift timing and density; and through niche utilisation determined from stable isotope data. Patterns in the macroinvertebrate assemblages of the headwaters of the Keiskamma River appear to be driven more strongly by flow rate and seasonal influences, but fish presence and biotope availability were also significant drivers. Niche shifts due to predator presence were not easy to detect and, while patterns of influence may have been evident, they were not found to be significant. However, I demonstrated that salmonids selectively feed on native fish species when the opportunity is presented, occupying significantly higher trophic levels when co-occurring with native fish than in invaded reaches where native fish are absent. Drift timing and density were demonstrated to be significantly different between reach for specific macroinvertebrate species from the Ephemeroptera and Plecoptera, under differing fish predation regimes, in agreement with what has been observed from studies in rivers elsewhere. In freshwater ecosystems of South Africa and worldwide, mitigation of negative effects of alien fishes through their removal using piscicides may also affect non-target organisms. To better understand the effects of just such a removal operation, employed for the first time in the history of freshwater conservation in South Africa, macroinvertebrate communities were assessed for non-target effects of rotenone. The fish eradication operations were demonstrated to have a short-term negative effect on the macroinvertebrate assemblage, through water quality index measurements and alteration of densities of macroinvertebrate taxa collected from stone surfaces. However, no long-term detrimental impact was observed as macroinvertebrate faunas returned to a comparable pre-treatment state within a year of each rotenone application.

Paulownia is a newly developed industry in Western Australia. Relying on high levels of fertiliser and irrigation to attain maximum growth, Paulownia often has nitrogen levels of 4.5 to 5 %. Alternaria, a pathogen with the potential to defoliate trees, has been isolated from blighted leaves of Paulownia for the first time in the literature. It was hypothesised that luxury fertiliser treatments may predispose Paulownia fortunei to disease. To test for the influence of luxury fertiliser regimes on Alternaria blight of Paulownia fortunei, clonal trees were grown in a glasshouse and fertilised using a nil, low, medium and high fertiliser regime. Plants were measured for height, stem diameter, gas exchange, chlorophyll, soluble protein and inorganic nutrient concentrations in the leaves. It was found that rising fertiliser supply resulted in all measures increasing, then plateauing at the two highest fertiliser rates. The only exceptions to this trend were leaf sodium and stem boron and potassium concentrations which dropped with increasing fertiliser. Photosynthesis and leaf nitrate were the only measures which were significantly higher in the highest fertiliser treatment. Thus, concluding that additional N, up to 46%, is of limited benefit to plant growth and function. Three inoculation treatments were conducted, leaf disc, excised leaf and in-situ. Each infection trial only produced lesions where leaves were wounded prior to infection. Fertiliser treatments had no effect on disease development in the leaf disc and excised leaf inoculation treatments. However, the in-situ inoculation trial had significantly (p < 0.01) larger lesions in the nil fertiliser treatment than all other fertiliser treatments. Unfortunately, there was no significant difference between the inoculated and control leaves within the nil fertiliser treatment. A systemic fungicidal influence on Paulownia by VAM was also examined. Seedlings inoculated with VAM were measured by the same methods as the nutrition trial with the exception of gas exchange. The presence of VAM increased plant height, root weight and approximately half of the nutrients analysed. Fertiliser treatment significantly increased the majority of plant biomass and function measurements. However, the inorganic nutrient analysis of the leaves revealed that the soil sterilisation process resulted in more nutrients becoming available to the plants. The infection of the VAM trial with Alternaria resulted in no lesions on the leaves and stems. There is no evidence to suggest that the luxurious fertiliser applied to field grown Paulownia predisposes them to infection by Alternaria. However, there is evidence that this pathogen may be opportunistic as only wounded leaves produced lesions during all nutrient infection trials. The impact of VAM on Paulownia growth is limited and needs further research.

The triumvirate of tectonics, lithology, and climate control landscape evolution. This study quantifies how lithologic variation and climate-mediated changes in ecosystems perturb steady state processes in the unglaciated, soil-mantled Oregon Coast Range (OCR). I first demonstrate that minor grain-scale differences in rock properties in a seemingly uniform sandstone control differences in rock strength, biotic bedrock-to-soil production efficacy, and erosion rates and influence relief at the watershed scale. I then build on sedimentology, paleoecology, and isotopic-derived paleoerosion data I collected from a new 50 ka sediment archive at Little Lake, OR to explore climate controls on soil production and erosion rates 21 ka across the OCR and spanning 50 ky within a single watershed. In Chapter III, I combine a mechanistic frost weathering model with a regional Last Glacial Maximum (LGM) climate reconstruction and paleovegetation data to demonstrate that accelerated frost-driven erosion was pervasive across the OCR during the LGM. My findings provide a new framework to quantify how the late Pleistocene affects modern erosion and soil formation rates in unglaciated environments and implies that most landscapes reside in a transient state. In Chapter IV, I document climate-mediated ecosystem influence on erosion rates over 3 climatic intervals. 10Be-derived erosion rates increase 3x (from 0.6 mm/yr to 0.21 mm/yr) as the OCR transitioned from the open forest-dominated marine isotope stage (MIS) climate interval (50-26 ka) into the periglacial subalpine MIS 2 glacial interval (26-13 ka). Measured erosion rates fell by more than half as the subalpine ecosystem gave way to the modern MIS 1 closed canopy Douglas-fir forest. Coupling paleovegetation-derived climate information with core observations I model frost weathering intensity from ~ 43 ka to 21 ka and establish a correspondence with increasing frost weathering intensity and increasing 10Be-derived erosion rates. Utilizing a transient mixing depth and erosion rate model, I am able to broadly replicate measured erosion rates at Little Lake through time. My findings contradict previous work that suggests climate has only weak control on erosion rates. This dissertation includes previously published and unpublished co-authored material.

This thesis was aimed to investigate the genetic response to abiotic and biotic stresses in durum wheat (Triticum turgidum L. var. durum), a cultivated tetraploid subspecies used for the production of pasta, couscous and various types of bread. Two research areas were focused: i) the high-throughput phenotyping (HTP) to detect novel drought tolerance quantitative trait loci (QTL) clusters and ii) the Kompetitive Allele Specific Polymerase chain reaction (KASP) marker development for the genetic dissection of Furarium head blight (FHB) resistance. Concerning the first area, I investigated drought adaptive traits on durum wheat elite accessions at Maricopa Agricultural Center (University of Arizona, US) which provided the experimental field and the high-throughput phenotyping platforms. The genome-wide association study (GWAS) detected thirty-one QTL clusters for two or more drought adaptive traits unrelated to the major loci responsible for phenology and plant height. Twelve of them overlapped with the major QTL for grain yield and related traits previously reported in studies carried out across a broad range of soil moisture availability and field drought conditions in wheat. Concerning the second area, I investigated two plant materials: i) 130 durum wheat accessions artificially inoculated with Fusarium culmorum and F. graminearum species and evaluated for incidence (INC), severity (SEV), FHB index, Fusarium-damaged kernels (FDK) and deoxynivalenol (DON) content; ii) 165 F6 recombinant inbred lines (RILs) from the cross between the cultivars Simeto and Levante evaluated for SEV using FG as inoculum. The genetic dissection led to sixteen QTL clusters, in part unrelated to the phenology and unknown in bread wheat, from which specific loci significantly influenced DON content. The haplotype analysis allowed me to validate KASP Single Nucleotide Polymorphisms (SNPs) suitable for marker-assisted selection (MAS) programs and to select cultivars for resistance/tolerance to DON content and other FHB traits.

This study evaluated the applicability of remote sensing instrumentation for site- specific management of abiotic and biotic stress on cotton grown under a center pivot. Three different irrigation regimes (100%, 75%, and 50% ETc) were imposed on a cotton field to 1) monitor canopy temperatures of cotton with infrared thermometers (IRTs) in order to pinpoint areas of biotic and abiotic stress, 2) compare aerial infrared photography to IRTs mounted on center pivots to correlate areas of biotic and abiotic stress, and 3) relate yield to canopy temperatures. Pivot-mounted IRTs and IR camera were able to differentiate water stress between the irrigation regimes, however, only the IR camera was effectively able to distinguish between biotic (cotton root rot) and abiotic (drought) stress with the assistance of groundtruthing. The 50% ETc regime had significantly higher canopy temperatures, which were reflected in significantly lower lint yields when compared to the 75% and 100% ETc regimes. Deficit irrigation up to 75% ETc had no impact on yield, indicating that water savings were possible without yield depletion.

Pharmaceuticals and personal care products found in the environment pose a significant hazard to human and ecosystem health. While there has been significant work on the fate and remediation of pharmaceuticals and personal care products in wastewater treatment, relatively little work has explored the fate, transport and remediation of these compounds in non-point source input. This is concerning given the increasing use of pharmaceuticals in livestock production and wastewater treatment derived biosolids frequently applied to land. These experiments aimed to quantify the abiotic adsorption and biotic transformation and uptake potential of woodchips and biochar-amended woodchips as a potential sorbent strategy for diffuse acetaminophen (ACT) pollution. Batch reactions were created in triplicate, supplied with 5 mM ACT, and analyzed over an eight hr period using ultraviolet spectrophotometry (298 nm). Ultraviolet absorbance readings for each time step then were compared to standard curves and solution ACT concentration was determined. Decreases in ACT from initial concentrations were the result of either abiotic and/or biotic. Overall, the woodchips and biochar-amended woodchips showed similar removal efficiency (16-21% of initial concentration). Whole model ANOVA analysis showed biologic activity having no significant effect on ACT solution concentration. However, within group ANOVA comparison showed significant differences between abiotic and biotic WC and abiotic and biotic WC treatments (controlling for media). Thus, the media effect could have masked the effect of biology on ACT removal. Species capable of degrading ACT exist and further study into their ability to grow and survive on these sorbents requires further work.
Master of Science

In contrast to documented increases in woody plant dominance of former savannas and grasslands of North America, oak (Quercus L.) savannas that form lower treelines in the southwestern United States and northwestern Mexico have been relatively stable over the past millennium. This research identified potential biotic and abiotic constraints on seedling recruitment of Quercus emoryi Torr. (Emory oak) within the context of potential shifts in lower treeline. Field surveys were used to describe seedling distribution at and below lower treeline, and to determine the potential for acorn dispersal from lower treeline into adjacent grassland. Field and greenhouse experiments designed to determine constraints on seedling establishment included reciprocal soil transfers, nutrient amendment studies, provision of artificial shade, and manipulation of seasonal precipitation inputs. Results indicate that rates of Q. emoryi recruitment within grasslands below treeline are relatively low, and are constrained by low rates of seed dispersal coupled with a low probability of seedling emergence. Seedling recruitment rates were directly correlated with quantity of summer precipitation, but were independent of winter precipitation. Results of this and complementary research suggest that lower treeline in southern Arizona is stabilized by self-enhancing feedback mechanisms of overstory shade, seed dispersal, and seedling establishment coupled with strong abiotic constraints beyond the current ecotone. The observed shift in treeline in the last millennium was less likely the result of slow, spatial progression of autogenic safe sites than the result of episodic and infrequent allogenic processes that simulated, or negated the importance of, conspecific, biogenic safe sites. Increases in summer precipitation are one such process that would facilitate (historic or potential future) downslope shifts in lower treeline. This interpretation is consistent with observations that downslope shifts in lower treeline which occurred 700-1700 ybp coincided with a period of particularly high summer precipitation in the region (i.e., the "Medieval Warm" period, 645-1295 ybp).

Coexistence among ecologically similar species is often facilitated through temporal or spatial partitioning mechanisms that reduce or eliminate direct interaction. However, in many communities exhibiting guild structure, wherein potential competitors may also prey on one another, sympatric relationships persist despite species' similar life history strategies, spatial and temporal restrictions imposed by ephemeral habitats, and resource limitations that promote competition and predation. To identify the ecological roles of species-specific behavioral patterns within aquatic guilds, I quantified larval intraspecific agonistic behavior among two species of intraguild (IG) predators, Ambystoma opacum and A. tigrinum, and their shared intraguild prey, A. maculatum. All species exhibited similar ontogenetic patterns of aggression, characterized by peaks of aggression early in development and subsequent gradual decreases through metamorphosis. However, the intensity of aggression varied considerably among guild species through development, as did behavioral responses to varying levels of ambient water temperature, invertebrate prey density, and presence of predatory odonate naiads. The observed patterns suggest that guild species, despite morphological and physiological similarities, exhibit unique behavioral responses through ontogeny and in response to habitat variables, suggesting that temporally staggered breeding phenologies have contributed to behavioral divergence among these sympatric congeners. However, in situ observations of larval behavior, although largely in agreement with laboratory results on timing of increased aggression, indicated that IG predators exhibited pond-level species partitioning and do not necessarily co-occur despite being regarded as sympatric. These results, taken together with observed species-specific impacts of IG predators on IG prey, suggest that ecologically similar IG predators exert widely differing predatory pressure on shared prey, and that similarities among guild species may ultimately result in habitat partitioning across local scales.

Les flors emeten compostos orgànics volàtils (VOCs) per tal d’atreure pol·linitzadors i estimular la fecundació creuada. Alguns volàtils florals però juguen altres funcions, com ara la defensa contra els herbívors. Aquesta dualitat de rols que tenen les olors florals les converteix en complexes mescles de compostos amb múltiples efectes sobre diferents organismes. La complexitat de comprendre i caracteritzar les emissions florals augmenta quan considerem que són variables en el temps i l’espai. A aquestes fonts de variabilitat cal afegir diversos factors ambientals biòtics i abiòtics que modifiquen les emissions de COVs florals de diverses maneres. L’objectiu principal d’aquesta tesi és esclarir quins són els factors que determinen les emissions florals de volàtils, i veure de quina manera les afecten a elles i a les seves funcions ecològiques. En el primer capítol de la tesi hem revisat el coneixement actual sobre les emissions florals de VOCs i hem identificat les qüestions que necessitaven ser investigades en aquest camp de recerca. Les emissions florals estan determinades en primer lloc per la diversitat de compostos que les espècies són capaces de produir, els seu potencial biosintètic i la seva capacitat d’emissió, que estan fortament lligades a la biologia de l’espècie. Hem testat i demostrat que les plantes pol·linitzades per insectes solen presentar major diversitat de volàtils florals i emeten una major quantitat d’aquests que les plantes pol·linitzades pel vent, que no necessiten volàtils florals per funcions d’atracció. Hem testat si els patrons estacionals de disminució de la competència que ocorren cada any entre plantes d’una mateixa comunitat vegetal han donat lloc a la selecció d’un patró de disminució de les emissions i les recompenses florals al llarg del període de floració de cada espècie. També hem observat que les plantes adapten la seva fisiologia per optimitzar les seves emissions florals sota les condicions climàtiques de la seva època de floració. Les emissions florals de COVs es veuen afectades per factors ambientals al nivell d’organisme o de teixit. Hi ha diversos estats fisiològics de la planta que poden modificar substancialment la composició i la quantitat de les emissions florals de COVs. Els nostres experiments han demostrat que la microbiota floral pot jugar un rol crucial sobre la quantitat i composició de les emissions florals de COVs. També hem mostrat que l’herbivoria de flors per part d’erugues de Pieris brassicae sobre plantes de Diplotaxis erucoides indueixen augments immediats de les emissions de compostos amb funcions defensives. A més, l’herbivoria de flors i fulles combinada va mostrar un efecte sinèrgic que augmenta la resposta defensiva. La recerca sobre els canvis que poden experimentar les emissions florals en resposta a diversos agents del Canvi Global són de gran interès degut als diversos efectes que aquests canvis poden tenir sobre les interaccions que s’estableixen mitjançant els COVs florals. Els nostres resultats revelen que els augments de temperatura previstos per al segle següent deguts a l’Escalfament Global poden conduir a augments significatius de les emissions totals de COVs i també a canvis importants en la composició relativa de les olors florals. També hem observat que l’ozó causa una degradació significativa dels compostos florals i provoca canvis en la composició relativa de les olors. Els testos de resposta indiquen que els canvis observats en les olors florals exposades a ozó resulten en la pèrdua de l’atracció de pol·linitzadors. Aquesta tesi proporciona una nova visió sobre els factors que determinen les emissions florals de volàtils i les seves repercussions sobre les interaccions planta-pol·linitzador, i garanteix una major consideració dels factors biòtics i abiòtics que afecten la química i l’ecologia de les olors florals en un ambient contínuament canviant.
Flowers emit volatile organic compounds (VOCs) to attract pollinators and stimulate reproductive outcrossing. Some floral volatiles can play roles other than attraction, such as defense against herbivores. This duality of roles of flower emissions converts floral scents into complex mixtures of compounds with multiple effects on different organisms. The complexity of understanding and characterising floral emissions increases when considering that they are variable in time and space. To all these sources of variability we can add diverse biotic and abiotic environmental factors that modify floral VOC emissions in many different ways. The main objective of this thesis was to shed light on which are the factors that determine floral volatile emissions, and how do they affect these emissions and their ecological functions. In the first chapter of this thesis we reviewed the current knowledge on floral VOC emissions. We identified the open questions that still needed to be addressed or investigated in more detail in the research field of floral VOC emissions. Floral emissions are first determined by the array of compounds that the species are able to produce and their potential biosynthetic and emission capacities, which are strongly related to the species biology. We tested and demonstrated that flowering plants pollinated by insects usually present higher diversities of floral volatiles and emit higher amounts of them, than do plants pollinated by wind which do not need floral volatiles for attractive purposes. We tested whether well-known seasonal patterns of decreasing competition occurring every year in a community among co-flowering plants for pollinators led to the selection of a pattern of decreasing emission of floral volatiles and decreasing production of floral rewards along the flowering period of each species. We also observed that plants adapt their physiology to optimize their floral emissions under the climatic conditions of the flowering period. Floral VOC emissions of the species are affected by environmental factors at the individual (organism) or tissular level. There are diverse physiological states of the plant that can substantially modify the emission profiles and amounts of floral VOCs. Our experiments demonstrated that floral microbiota can play a crucial role in the quantity and quality of floral VOC emissions. We also showed that flower herbivory by Pieris brassicae caterpillars on Diplotaxis erucoides plants induced immediate increases in floral emission rates of few compounds with known defensive functions. Leaf herbivory caused no changes in the emissions of intact flowers, but the combination of leaf herbivory with flower herbivory showed a synergistic effect with enhanced defensive response. The research on the potential changes that floral emissions could experience in response to diverse drivers of Global Change are of critical interest because of the diverse effects that such changes can have on the interactions that floral VOCs mediate. Our results revealed that temperature increases as those predicted for the next century as a result of Global Warming can lead to significant total increases in floral VOC emissions and also to important changes in floral scent relative composition. We also detected that ozone caused significant degradation of floral compounds and changes in their relative composition. Behavioural tests indicated that all the changes observed in floral chemical cues when exposed to ozone resulted in the loss of attraction effect on pollinators. This thesis thus provides new insights on the factors that determine floral volatile emissions and their repercussions on plant-pollinator interactions and warrant deep consideration of both biotic and abiotic factors driving floral scent chemistry and floral scent ecology in a continuously changing environment.

The Sardinilla plantation is a long-term facility for studying the links between tree species diversity and ecosystem function. Six native tree species were planted in 2001 in plots containing 1, 3 or 6 species. Soil respiration (SR) measurements were conducted from March to December 2004 on tree pairs. ANOVAs with repeated measure on days were used to test the main effects of species (monocultures), pair (single and two-species pairs), plot (pairs in monoculture, three-, and six-species plots), and season (dry vs. early wet season). ANCOVAs were run for each effect to determine possible biotic and abiotic covariates, including root, tree, and microbial biomass, soil moisture, surface temperature, and bulk density. Significant season and pair effects accounted for 89% and 2% of the variability in SR. Driven by soil moisture, SR increased seven fold during the seasonal transition. In the dry and wet season monocultures had significantly higher SR than two-species pairs.

Dissertation presented to obtain the Ph.D degree in Plant Sciences
"Common bean (Phaseolus vulgaris L.) is among the most important grain legumes for human consumption worldwide. Portugal has a promising common bean germplasm that resulted from more than five centuries of natural adaptation and farmers’ selection. Nevertheless, limited characterization of this resource hampers its exploitation by breeding programs. To support a more efficient conservation of the national bean germplasm and promote its use in crop improvement, we performed, for the first time, a simultaneous molecular marker and seed and plant morphological characterization of 175 accessions collected from Portuguese mainland and islands traditional bean-growing regions. Most of the Portuguese accessions grouped with the race representatives and wild relatives from the Andean region."
N/A

Streams are integrative systems spanning multiple spatial and temporal scales. Stream researchers, land-use managers, and policy decision makers must consider the downstream displacement of streams when approaching questions about stream ecosystems. The study of how anthropogenic land-use influences streams demands an ecosystem perspective, and this dissertation is an example of applying large scale analyses of stream reach responses, and linking the activity of humans in the landscape to stream structure and function. I investigate whether rural development and agriculture land-cover types influence abiotic and biotic stream responses. I establish a method for considering land-cover as an independent variable at multiple scales throughout a streamsâ watershed using hydraulic modeling. The travel time required for water to drain from the watershed to a stream reach provided a continuous index to delimit watershed sub portions along a spatial continuum. Within travel time zones (TTZs), I consider land-use at increasingly larger scales relative to a stream reach within which biotic responses are typically measured. By partitioning land-cover in TTZs, I was able to determine the spatial scale at which land-cover was most likely to influence in-stream responses. I quantified a suite of physical and biotic responses typical to the aquatic ecology literature, and found that streams did not respond much to rural development. Rural development influenced suspended and depositional sediments, and likely altered watershed hydrology though I was unable to find significant evidence supporting a hydrologic effect. Subtle differences in assemblages suggest that differences in sediment dynamics influenced macroinvertebrates and fish. Using the Land Cover Cascade (LCC) design, I link the influence of land-cover to biotic responses through a suite of multivariate models, focusing on sediment dynamics in an attempt to capture the subtle influence of hydrology and sediment dynamics. My dissertation provides future researchers with improved methods for considering land-cover as an independent variable, as well as introduces multivariate models that link land-cover to sediment dynamics and biota. My dissertation will assist future research projects in identifying specific mechanisms associated with stream responses to disturbance.
Ph. D.

Thesis (Ph.D.)--Kent State University, 2009.
Title from PDF t.p. (viewed Nov. 16, 2009). Advisor: Mark Kershner. Keywords: crayfish; stream; predation; current velocity; water depth; grain size; resource competition. Includes bibliographical references.