Arbuscular Mycorrhizae Shift Community Composition of N-Cycling Microbes and Suppress Soil N 2 O 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 (N 2 O), 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 N 2 O emissions, N 2 O-producing ( nir K and nir S) and N 2 O-consuming ( nos 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 N 2 O emissions and the ratio of nir K to nir S microbes. Roots and AMF did not affect the ( nir K + nir S)/ nos Z ratio but significantly reduced N 2 O emissions and the nir K/ nir S ratio. They reduced the nir K/ nir S ratio by reducing nir K- Rhodobacterales but increasing nir S- Rhodocyclales in the CONV soil while decreasing nir K- Burkholderiales but increasing nir S- Rhizobiales in the OM soil. Our results indicate that plant roots and AMF reduced N 2 O emission directly by reducing soil N and indirectly through shifting the community composition of N 2 O-producing microbes in N-enriched agroecosystems, suggesting that harnessing the rhizosphere microbiome through agricultural management might offer additional potential for N 2 O emission mitigation.