Warming-induced enhancement of soil N2O efflux linked to distinct response times of genes driving N2O production and consumption

Temperature responses of denitrifying microbes likely play a governing role in the production and consumption of N2O. We investigated temperature effects on denitrifier communities and their potential to produce N2O and N-2 by incubating grassland soils collected in multiple seasons at four temperatures with N-15-enriched NO3 (-) for similar to 24 h. We quantified [N2O] concentration across time, estimated its production and reduction to N-2, and quantified relative abundance of genes responsible for N2O production (cnorB) and reduction (nosZ). In all seasons, net N2O production was positively linked to incubation temperature, with highest estimates of net and gross N2O production in late spring soils. N2O dynamics were tightly coupled to changes in denitrifier community structure, which occurred on both seasonal and incubation time scales. We observed increases in nosZ abundance with increasing incubation temperature after 24 h, and relatively larger increases in cnorB abundance from winter to late June. The difference between incubation and in situ temperature was a robust predictor of cnorB:nosZ. These data provide convincing evidence that short-term increases in temperature can induce remarkably rapid changes in community structure that increase the potential for reduction of N2O to N-2, and that seasonal adaptation of denitrifying communities is linked to seasonal changes in potential N2O production, with warmer seasons linked to large increases in N2O production potential. This work helps explain observations of high spatial and temporal variation in N2O effluxes, and highlights the importance of temperature as an influence on denitrification enzyme kinetics, denitrifier physiology and community adaptations, and associated N2O efflux and reduction.