Role of microbial diversity in mitigating the emissions of the greenhouse gas n2o in relation to agricultural practices

EA SPE ECOLDURNational audienceAgriculture is the main source of terrestrial N2O emissions. This gas is the main depleting substance of the ozone layer and contributes to about 6% of total global warming. The unique known biological process able to convert N2O is its reduction to N2 by organisms possessing the nosZ gene, which encodes the nitrous oxide reductase. A recent publication (Jones et al., Nature Climate Change, in press) showed that the abundance and the diversity of a recently discovered clade of nosZ_carrying microorganisms are important players of soil N2O sink capacities. Therefore, enhancing the comprehension of the role of the abundance and the diversity of microbial populations in N2O emissions and looking for agricultural practices that could favour microbial populations able to reduce N2O into N2 is key in determining N2O emissions mitigation strategies. In this study, two experimental sites comprising nine management strategies that differ in crop rotation, tillage depth, fertilization, straw incorporation and cover crop were chosen. To characterize the activity of soil microbial communities, potential denitrification rates and N2O/N2O+N2 emission ratios were measured. The abundance of the different microbial guilds involved in N-cycling was quantified by real-time PCR, and the diversity of the nosZ gene was determined by 454 pyrosequencing. Our results suggest that the agricultural practices we tested were not sufficient to modify deeply the abundance and the diversity of denitrifying microbial communities related to the N2O emissions. However, the diversity and the abundance of these guilds were strongly dependent on the experimental site and responded to soil physico-chemical parameters (e.g.: pH, loam). We also confirmed the link between the diversity of nosZ microorganisms and the soil N2O sink capacity (Fig.1), which emphasize the importance of microbial diversity for ecosystem functioning