Effects of arbuscular mycorrhizal fungi on crop growth and soil N2O emissions in the legume system

Arbuscular mycorrhizal fungi (AMF), which form symbiotic associations with 80% of land plants, provide host plants with soil phosphorus (P) and nitrogen (N) in exchange for carbon. The AMF often reduces nitrous oxide (N2O) emissions from soils with non-legume plants, as they acquire N from soils to plants. However, the effect of AMF on soil N2O emissions is still unknown in the legume system, a major source of this potent greenhouse gas. Therefore, we conducted the field and pot experiments to investigate the effects of AMF on plant growth and soil N2O emissions in legume systems. The results showed that AMF significantly increased soil N2O emissions from soils with soybean by 39% in the field experiment and by 63% in the pot experiment. The AMF significantly enhanced the root biomass, aboveground biomass, grain yield, plant N uptake, plant P uptake, and the nodule numbers. The AMF increased soil extractable N concentrations and DOC concentrations, but reduced soil available P concentrations. The AMF stimulated the N2O-producing microbes (nirS- and nirK-type) whereas they did not affect the N2O-consuming (nosZ-type) denitrifiers. The AMF reduced the yield-scaled N2O emissions in the field experiment and increased the net ecosystem economic budget. Our findings indicate that AMF increase soil N2O emissions from legume system through enhancing P acquisition for biological N-2 fixation and suggest that AMF benefit crop production for higher-yield with less N2O emissions.