Chamber-based continuous measurement of N2O fluxes in a winter wheat field: comparison of tillage treatments and identification of emission peak dynamic

Agriculture is the first anthropogenic source of N2O, notably through fertilized croplands. Though, few publications have studied through continuous measurement the N2O emissions in cultivated lands. We conducted this study to assess the effect of farming practices and climate on N2O emissions from a winter wheat crop. The experiment was held in an experimental field in the loamy region in Belgium from March 2016 till crop harvest in August 2016. The N2O fluxes are measured on two nearby parcels in a winter wheat field with restitution of the residues from previous crop. For the past 8 years, one parcel was subjected to a reduced tillage (RT, 10 cm depth) and the other one to a conventional tillage (CT, 25 cm depth). On each parcel, the N2O emissions were assessed with homemade automated closed chambers. Measurement continuity and good temporal resolution (one mean flux every 4 hours) of the system allowed a fine detection and quantification of the emission peaks which usually represent the major part of N2O fluxes. In addition to gas fluxes, soil water content at various depths and surface temperature were measured continuously. Soil samples were taken regularly to determine soil pH, soil organic carbon and nitrogen pools (total, NO3- and NH4+) and study microbial diversity and nitrification/denitrification gene expression. Measurements are still in progress. First results suggested that fluxes were about 3 times larger in the RT parcel than in the CT parcel. Several emissions peaks were observed during the measurement period. The peaks occurred after fertilization events and seemed to be triggered by an elevation of soil water content. A comparison of the emissions between RT and CT and a discussion on peak temporal dynamics, focusing on their intensity, duration and starting time will be presented.AgriGE

Biology and ecology of biofilms formed by a plant pathogen Phytophthora parasitica: From biochemical ecology to ecological engineering

AbstractIn nature, the organisation of microbial species into biofilms has a great influence on local environments and in human or plant diseases. This important trait of prokaryotes and eukaryotes is poorly understood while the knowledge of the related biological processes could constitute a novel base for controlling diseases. A study is developed on the oomycete Phytophthora parasitica belonging to a major class of eukaryotic plant pathogens to understand molecular and ecological basis of biofilm formation. The identification of signalling molecules and the definition of their spectrum of activity within the biofilm community will improve our understanding of fundamental biological processes, our ability to forecast pathogen behaviour and to elaborate new tools dedicated to plant diseases management with low environmental impact

Evaluation of the bacterial diversity in contaminated soils of Chernobyl and characterization of the interaction between Microbacterium strain and uranium.

Les accidents nucléaires des centrales de Tchernobyl et de Fukushima rendent primordial la compréhension des transferts de la contamination radioactive dans l'environnement et de ses conséquences écologiques. Bien que certaines études aient été réalisées sur les organismes supérieurs, trop peu ont étudié les communautés bactériennes telluriques, qui jouent pourtant un rôle essentiel dans la mobilité des contaminants dans les sols en diminuant ou en améliorant leur transfert vers d'autres compartiments (eau, végétaux, animaux). Cependant, les radionucléides (RNs) peuvent avoir des effets toxiques sur les bactéries, entrainant une inhibition de leur rôle dans ce transfert. Les objectifs de cette étude étaient (1) d'évaluer l'impact d’une contamination radioactive sur les communautés bactériennes d’un sol de la zone d’exclusion de Tchernobyl (sol de la tranchée n°22) et (2) d’étudier les interactions bactérie-uranium pour une souche résistante, isolée à partir de ce sol.The nuclear power plants accidents of Chernobyl and Fukushima demonstrate the importance of the understanding of the transfers of the radioactive contamination in the environment and their ecological consequences. Although certain studies have been realized on superior organisms of the food chain, studies on telluric bacterial communities are scarce. The later play nevertheless an essential role in the mobility of contaminants in soils by decreasing or by improving their transfer towards other compartments (water, vegetables, and animals). Moreover, radionuclides (RNs) can have toxic effects on bacteria, leading to an inhibition of their participation in such transfer. The objectives of this study were (1) to estimate the impact of radioactive contamination on bacterial communities belonging to a soil of a Chernobyl exclusion zone (trench n°22) and (2) to study the uranium-bacteria interactions of a resistant strain, isolated from this soil

Evaluation of the bacterial diversity in contaminated soils of Chernobyl and characterization of the interaction between Microbacterium strain and uranium.

Les accidents nucléaires des centrales de Tchernobyl et de Fukushima rendent primordial la compréhension des transferts de la contamination radioactive dans l'environnement et de ses conséquences écologiques. Bien que certaines études aient été réalisées sur les organismes supérieurs, trop peu ont étudié les communautés bactériennes telluriques, qui jouent pourtant un rôle essentiel dans la mobilité des contaminants dans les sols en diminuant ou en améliorant leur transfert vers d'autres compartiments (eau, végétaux, animaux). Cependant, les radionucléides (RNs) peuvent avoir des effets toxiques sur les bactéries, entrainant une inhibition de leur rôle dans ce transfert. Les objectifs de cette étude étaient (1) d'évaluer l'impact d’une contamination radioactive sur les communautés bactériennes d’un sol de la zone d’exclusion de Tchernobyl (sol de la tranchée n°22) et (2) d’étudier les interactions bactérie-uranium pour une souche résistante, isolée à partir de ce sol.The nuclear power plants accidents of Chernobyl and Fukushima demonstrate the importance of the understanding of the transfers of the radioactive contamination in the environment and their ecological consequences. Although certain studies have been realized on superior organisms of the food chain, studies on telluric bacterial communities are scarce. The later play nevertheless an essential role in the mobility of contaminants in soils by decreasing or by improving their transfer towards other compartments (water, vegetables, and animals). Moreover, radionuclides (RNs) can have toxic effects on bacteria, leading to an inhibition of their participation in such transfer. The objectives of this study were (1) to estimate the impact of radioactive contamination on bacterial communities belonging to a soil of a Chernobyl exclusion zone (trench n°22) and (2) to study the uranium-bacteria interactions of a resistant strain, isolated from this soil

Reduced Tillage generates higher N2O emissions: results of continuous chamber-based measurement in a winter wheat field.

Agriculture is one of the most important contributors to GHG emission, notably through fertilized croplands. Though, few publications have studied simultaneously and through continuous measurement the N2O and CO2 emissions in cultivated lands. We conducted this study to assess the effect of farming practices and climate on both N2O and CO2 emissions from a winter wheat crop. The experiment was held in an experimental field in the loamy region in Belgium from March 2016 till crop harvest in August 2016. The fluxes were measured on two nearby parcels in a winter wheat field with restitution of the residues from previous crop. For the past 8 years, one parcel was subjected to a Reduced tillage (RT, 10 cm depth) and the other one to a conventional tillage (CT, 25 cm depth). On each parcel, the emissions are assessed with homemade automated closed chambers. Measurement continuity and good temporal resolution (one mean flux every 4 hours) of the system allowed a fine detection and quantification of the emission peaks which usually represent the major part of N2O fluxes. In addition to gas fluxes, soil water content and temperature were measured continuously. Soil samples were taken regularly to determine soil pH, soil organic carbon and nitrogen pools (total, NO3- and NH4+) and study microbial diversity and nitrification/denitrification gene expression. Surprisingly, results showed N2O emissions twice as large in the RT parcel as in the CT parcel. On the contrary, less important CO2 emissions were observed under RT. Several emission peaks of N2O were observed during the measurement period. The peaks occurred after fertilization events and seemed to be triggered by an elevation of soil water content. Interesting links could be made between soil NH4-N and NO3-N pools and N2O emissions. Nitrification being the main process originating the fluxes was suggested on the one hand by the temporal evolution of nitrogen pools and N2O emissions and on the other hand by the relation between spatial variability of the emissions with the soil nitrate content. A comparison of the emissions between ST and CT and a discussion on peaks temporal dynamic, focusing on their intensity, duration and starting time will be presented

Exploration of Deinococcus-Thermus molecular diversity by novel group-specific PCR primers

International audienceThe deeply branching Deinococcus-Thermus lineage is recognized as one of the most extremophilic phylum of bacteria. In previous studies, the presence of Deinococcus-related bacteria in the hot arid Tunisian desert of Tataouine was demonstrated through combined molecular and culture-based approaches. Similarly , Thermus-related bacteria have been detected in Tunisian geothermal springs. The present work was conducted to explore the molecular diversity within the Deinococcus-Thermus phylum in these extreme environments. A set of specific primers was designed in silico on the basis of 16S rRNA gene sequences, validated for the specific detection of reference strains, and used for the polymerase chain reaction (PCR) amplification of metagenomic DNA retrieved from the Tataouine desert sand and Tunisian hot spring water samples. These analyses have revealed the presence of previously undescribed Deino-coccus-Thermus bacterial sequences within these extreme environments. The primers designed in this study thus represent a powerful tool for the rapid detection of Deinococcus-Thermus in environmental samples and could also be applicable to clarify the biogeography of the Deinococcus-Thermus phylum

No favorable effect of reduced tillage on microbial communities in a silty loam soil (Belgium)

To date, only a few studies have applied metagenomics to investigate the influence of different tillage regimes and types of crop residue management on soil microbial communities. These studies were conducted under specific climates on soils characterized by particular land-use histories. A very different ecological context is to be found in certain areas of Western Europe, such as central Belgium, whose loess-derived soils are among the most fertile in the world and have long been used for intensive agriculture. Specific objectives were to determine diversity levels and changes in microbial community composition under different combinations of tillage regime (conventional vs. reduced) and crop residue fate (residue removal R- vs. residues left R+ on the field). As reduced tillage results in two contrasting zones (the first centimeters of soil are mixed each year, while the soil below remains unperturbed), we chose to perform the analysis at two depths: 0 to 5 cm and 15 to 20 cm

Effet du travail du sol sur les émissions de gaz à effet de serre par une culture de maïs et dynamique des flux de N2O.

N2O is a potent greenhouse gas produced by nitrifying and denitrifying microorganisms. In agricultural soils, the uppermost soil layer constitutes the main source of N2O emissions, which are driven by climatic events such as precipitations, but also by soil properties such as N and C availability. Farming practices like tillage can influence these soil properties and consequently affect greenhouse gas emissions. Between June and October 2015, CO2 and N2O fluxes were measured on a maize crop located in Gembloux (Belgium), using a homemade automated set of dynamic closed chambers. Two tillage treatments were compared: reduced tillage and conventional tillage, both applied since 2008. A significant impact of tillage was observed on GHG emissions: mean emissions were twice larger (CO2) and six times larger (N2O) under reduced tillage than in conventional tillage, presumably because of higher total organic C and total N content, and greater microbial biomass in the upper soil layer. An emission peak of N2O was observed in both treatments mid-June less than 24h after heavy precipitations. The absence of peak later during the experiment was attributed to maize growth and competition for soil N. In reduced tillage, soil temperature explained ~10% of N2O background flux variability, but no significant relationship was found for conventional tillage. No clear pattern (e.g. daily cycle) was identified in N2O background fluxes. Our results highlight the need for continuous measurements as peaks can happen several months after fertilization, and the need for high temporal resolution measurements to understand the dynamics behind N2O emissions.AgriGE