Nitrate and sulphate dynamics in peat subjected to different hydrological conditions: Batch experiments and field comparison

International audienceConservation of ecosystems that depend on water management and water quality has to be considered. We combined a field monitoring and batch experiments to better understand the impact of hydrological perturbations on peatland functioning. Factors influencing the dynamics of nitrate and sulphate concentration observed in two sites with different hydrological conditions in a south Normandy peatland were determined through the comparison of field and lab experiment. The effects of nitrate input, and oxic or anoxic conditions on nitrate and sulphate concentrations were investigated in bioreactors, using peat samples from field sites influenced by different hydrologic regimes. In this experiment, peat samples were subjected to similar conditions to address the effects of NO 3 and O2 concentrations (chemical effects), and the effect of hydrologic regimes and peat soil moisture (physical effects) on nitrate and sulphate dynamics. Cl , SO2 4 and NO 3 were monitored for 215 h. Nitrate was significantly reduced in most experiments. A complete nitrate reduction after 215 h in soil under anoxic conditions was observed. A denitrification process was also found under aerobic conditions depending on the peat site sampling, i.e. depending on the hydrological conditions. This process was interpreted as a heterotrophic denitrification. Sulphate monitoring revealed that 400 mg L 1 were produced in peat from the peat site with high hydrologic fluxes under aerobic conditions. Clear differences in chloride concentration (deviance analysis, P < 0.05), sulphate concentration and nitrate consumption dynamics (deviance analysis, P < 0.0001) were observed, for similar experimental chemical conditions, between the samples from the two peat sites. These differences were related to the field chemical variations observed and they indicate that part of the field nitrate and sulphate dynamics is linked to different bacterial activity and not only to nutrient fluxes variations

L'influence des circulations hydrologiques sur la structure des communautés bactériennes à l'interface sol-nappe

325 p.Water composition, relative to biological active elements such as nitrates is controlled by microbial processes that are dependent of in situ physical and chemical conditions. Chemical conditions and bacterial community structures are intimately linked but hydrological circulations effect on microbial diversity is rather poorly constrained. This becomes important since hydrological circulation that depends on landscape settings is important in determining biochemical processes. Hydrological fluxes and functioning ecosystems relationships are here discussed in 3 parts: (i) Influence of vertical fluxes on nitrates reducing bacterial community structure (narG gene); (ii) Influence of vertical fluxes on integrative (ARNr 16S gene) and functioning (narG gene) bacterial community structure; and (iii) Influence of forcing parameters on proteins expression (Metaproteomic approach).The first part is carried out using bioreactors simulating different redox conditions and nutriment availability. The second part consists in monitoring changes in the community structure through time (high and low water table periods) and depth. Finally the third part experimentally deals with varying forcing parameters (amount and nature of carbon, and amount of nitrogen) influence on water sampled at high depth. For each bioreactor, a peptidic fingerprint (metaproteomic analyze) is performed to simulate functioning ecosystem.Hydrological circulation influence on bacterial community is confirmed with a direct effect on community structure and an indirect outcome via resources availability. Cells proteomes exposed to two Carbone sources appear significantly different, suggesting a system specific response to the nature of an induced pollution.La composition des eaux pour les éléments biologiquement actifs comme les nitrates est contrôlée par les processus microbiens, qui dépendent eux-mêmes des conditions physico-chimiques du milieu. Les conditions chimiques et la structure des communautés bactériennes sont étroitement liées et l'influence des circulations hydrologiques sur la diversité microbienne est relativement mal contrainte. Or ces circulations hydrologiques issues de la structure physique du paysage sont déterminantes dans les processus biogéochimiques. Les relations entre les flux hydrologiques et le fonctionnement de l'écosystème sont abordées par 3 axes: (i) l'influence des flux verticaux sur l'activité et la structure des communautés bactériennes réduisant les nitrates (gène narG) ; (ii) l'influence des flux verticaux sur la structure des communautés bactériennes intégratives (gène de l'ARNr 16S) et fonctionnelles (gène narG); et (iii) l'influence des modifications des paramètres de forçage sur l'expression protéique par une approche Métaprotéomique. Le premier axe a été analysé en utilisant des bio-réacteurs stimulants différents états redox et disponibilité en nutriment. Le second a consisté à suivre les changements de structure de communautés dans le temps (suivant les périodes de hautes et de basses eaux) et suivant la profondeur. Le troisième axe est abordé sous des conditions expérimentales à partir d'eau échantillonnée en profondeur, en contrôlant les paramètres de forçages (quantité et nature du carbone, quantité d'azote). Pour chaque bio-réacteur, une analyse du Métaprotéome par des empreintes peptidiques a été réalisée pour modéliser le fonctionnement de l'écosystème. L'importance des circulations hydrologiques sur les communautés bactériennes a été confirmée en agissant directement sur la structure des communautés ou indirectement sur la disponibilité de ressources. Le manque de connaissance actuel dans les bases de données ne nous a pas permis d'aller aussi loin que nous l'aurions souhaité dans les expériences de protéomique. Il nous est impossible à l'heure actuelle de proposer un modèle de fonctionnement de niche écologique. Cependant, le protéome des cellules exposées aux deux sources de carbones a été montré comme significativement différent, laissant suggérer une réponse différentielle du système suivant la nature de la pollution induite

Genomic tools application in an environmental problematic, the 2D-DIGE example

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Genomic tools application in an environmental problematic, the 2D-DIGE example

communication oral

L'influence des circulations hydrologiques sur la structure des communautés bactériennes à l interface sol-nappe

Les relations entre les flux hydrologiques et le fonctionnement de l écosystème sont abordées par 3 axes: l influence des flux verticaux sur l activité et la structure des communautés bactériennes réduisant les nitrates (gène narG); des flux verticaux sur la structure des communautés bactériennes taxonomiques (gène de l ARNr 16S) et fonctionnelles (gène narG); et des modifications des paramètres de forçage sur l expression protéique par une approche Métaprotéomique. Les analyses de diversités ont été réalisées par une approche de T-RFLP, complétées par une approche phylogénétique sur le gène de l ARNr 16S. L importance des circulations hydrologiques sur les communautés bactériennes a été confirmée en agissant directement sur la structure des communautés ou indirectement par la distribution de ressources. Le protéome des cellules exposées à deux sources de carbones ont été montré comme significativement différents, suggérant une réponse différentielle suivant la nature de la pollution induite. De plus la nature du carbone est un facteur primordial pour réduire efficacement les nitrates.The relationships between water-fluxes and ecosystem functioning were addressed by three axes: (1) influence of horizontal fluxes on the structure of nitrates reducers community (narG gene); (2) influence of vertical fluxes on the structure of taxonomic (16S rRNA gene) microbial community and nitrates reducers (narG gene) more specifically; and (3) influence of the modifications of forcing parameters on proteins expressions. Diversity analyses were performed by a T-RFLP approach, and completed by phylogeny on the 16S rRNA gene. The importance of hydrological fluxes on microbial communities was confirmed by acting directly on the community structure or indirectly by resource distribution. The proteome of exposed bacterial cells to two carbons sources were shown as significantly different, suggesting a differential response face to the nature of pollution. Moreover, the carbon nature is a fundamental parameter to an efficiency nitrate removal.RENNES1-BU Sciences Philo (352382102) / SudocRENNES-Géosciences (352382209) / SudocSudocFranceF

Microbial diversity and activity in a pristine aquifer

International audienc

Etude expérimentale des paramètres influençant la réactivité potentielle du milieu

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A survey of denitrifying communities in a wetland

1 p.A hydrological and geochemical survey of a wetland (Normandy, France) highlighted the presence of a major spatiotemporal variability of sulphates and nitrates concentrations related to a distinct hydrologic regime represented by the stream proximity. An experimental approach was carried out to determine the factors influencing the dynamic of nitrate and sulphate concentrations observed in field; and the denitrifiers' community structuration related to different environmental stresses. We investigated the effects of stream proximity and associated nutrients fluxes, on microbial activity. Experiments were performed with peat sampled from different plots along a hydrologic flow gradient to characterize the biogeochemical processes and estimate the potential reactivity. We used bioreactors containing the peat-soils and a synthetic solution (similar to the field stream composition) to understand biogeochemical fluxes related to different nitrate availability and redox conditions. The evolution of nitrates and sulphates concentrations was analysed over time. The results demonstrated a spatial variability of the potential reactivity and a biological activity reacting unevenly to experimental conditions. We highlighted the control of the temporal evolution of nitrate and sulphate concentration by redox conditions and nitrate availability (nitrates, P<0.001; sulphates, P<0.001) and by distinct hydrologic regime (nitrates, P <0,001; sulphates, P<0,001). We established the reduction of nitrate is a heterotrophic denitrification and the sulphate production is related to bio-geochemical processes. The fate of microbial activity seems to be regulated by hydrogeological fluxes especially at the stream-soil, soil-water interface. Spatial and temporal dynamic of denitrifying community composition is currently investigated by a narG gene analysis and t-RFLP

Soil biodiversity monitoring in France

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