Arbuscular Mycorrhizae Shift Community Composition of N-Cycling Microbes and Suppress Soil NO Emission.

Mycorrhizae are ubiquitous symbiotic associations between arbuscular mycorrhizal fungi (AMF) and terrestrial plants, in which AMF receive photosynthates from and acquire soil nutrients for their host plants. Plant uptake of soil nitrogen (N) reduces N substrate for microbial processes that generate nitrous oxide (NO), a potent greenhouse gas. However, the underlying microbial mechanisms remain poorly understood, particularly in agroecosystems with high reactive N inputs. We examined how plant roots and AMF affect NO emissions, NO-producing (K and S) and NO-consuming (Z) microbes under normal and high N inputs in conventional (CONV) and organically managed (OM) soils. Here, we show that high N input increased soil NO emissions and the ratio of K to S microbes. Roots and AMF did not affect the (K + S)/Z ratio but significantly reduced NO emissions and the K/S ratio. They reduced the K/S ratio by reducing K- but increasing S- in the CONV soil while decreasing K- but increasing S- in the OM soil. Our results indicate that plant roots and AMF reduced NO emission directly by reducing soil N and indirectly through shifting the community composition of NO-producing microbes in N-enriched agroecosystems, suggesting that harnessing the rhizosphere microbiome through agricultural management might offer additional potential for NO emission mitigation.