Inoculants of leguminous crops for mitigating soil emissions of the greenhouse gas nitrous oxide

Nitrous oxide (N 2 O) is a greenhouse gas which is also responsible for ozone depletion, that mainly originates from soils and agricultural activities. We investigated the ability of inoculants of Bradyrhizobium japonicum carrying the nosZ gene to mitigate soil N 2 O emissions. The consumption of N 2 O by strains of Bradyrhizobium japonicum ( USDA110 and MSDJ G49) was investigated both on inoculated soybean plants cultivated in soil pots during a greenhouse experiment and on detached nodules submitted to gradients of oxygen and N 2 O concentrations in laboratory conditions. During the greenhouse experiment, we switched from a system acting as an N 2 O source (soil + soybean inoculated with a nosZ gene depleted strain) to a system acting as an N 2 O sink (soil + soybean inoculated with strains carrying the nosZ gene). Nodules of Bradyrhizobium japonicum USDA110 and MSDJ G49 were both able to reduce N 2 O under aerobic conditions at rates increasing with N 2 O concentrations. Calculations using the obtained quantitative results clearly suggest an environmental benefit of this process on the field scale. This study demonstrates that the inoculation of rhizobia strains on leguminous crops is a promising area for mitigating N 2 O emission by cultivated soils and that further researches are required to best evaluate quantitative benefits.