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.