Reactive nitrogen restructures and weakens microbial controls of soil N(2)O emissions

The global surplus of reactive nitrogen (N(r)) in agricultural soils is accelerating nitrous oxide (N(2)O) emission rates, and may also strongly influence the microbial controls of this greenhouse gas resulting in positive feedbacks that further exacerbate N(2)O emissions. Yet, the link between legacy effects of N(r) on microbial communities and altered regulation of N(2)O emissions is unclear. By examining soils with legacies of N(r)-addition from 14 field experiments with different edaphic backgrounds, we show that increased potential N(2)O production is associated with specific phylogenetic shifts in communities of frequently occurring soil microbes. Inputs of N(r) increased the complexity of microbial co-association networks, and altered the relative importance of biotic and abiotic predictors of potential N(2)O emissions. Our results provide a link between the microbial legacy of N(r) addition and increased N(2)O emissions by demonstrating that biological controls of N(2)O emissions were more important in unfertilized soils and that these controls are weakened by increasing resource levels in soil.