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 N2 fixation and suggest that AMF benefit crop production for higher-yield with less N₂O emissions.