NosZ + Rhizobial Inoculant Enable Climate-Smart Legume Cultivation Across Diverse Soil and Environmental Conditions –Study Case on Soja Cultivated on Soils Free of Indigenous Symbiotic Rhizobia

Legume crops play a central role in sustainable agriculture by biologically fixing nitrogen, yet their root residues particularly nodules can contribute to soil N 2 O emissions. Different studies indicate that the inoculation of legumes with a nosZ + rhizobial strain encoding nitrous oxide reductase could reduce N 2 O fluxes from legume crops by promoting N 2 O reduction to N 2 . The current study aims at testing the effect of the use of a nosZ + rhizobial strain for reducing soil N 2 O emission in a soil, naturally able to reduce N 2 O, cultivated with soybean and free of indigenous symbionts. During a greenhouse experiment, N 2 O fluxes from soil pots cultivated with soybean were measured. The experimental design involved an acidic and an alkaline soil subjected to two different hydric regimes and the use of both a nosZ + and a nosZ- rhizobial strains. Inoculating soybean with a nosZ + rhizobial strain significantly reduces N 2 O fluxes during both the growing and decomposition phases, across acidic and alkaline soils maintained under wet or alternating dry–wet conditions. Emissions remained low throughout plant growth, but peaked during nodule decomposition in the absence of nosZ . In nosZ + treatments, N 2 O peaks were suppressed by over an order of magnitude without compromising plant biomass. Mitigation persisted even in alkaline soils with high inherent N₂O-reducing capacity. These results demonstrated the potential of nosZ + inoculants as a trait-based microbial intervention for reducing the climate impact of legume systems, with relevance across diverse agroecological contexts.