Soil Temperature Dynamics Modulate N₂O Flux Response to Multiple Nitrogen Additions in an Alpine Steppe

Abstract

Abstract Emissions of nitrous oxide (N 2 O) contribute to global warming and stratospheric ozone depletion. Anthropogenic N 2 O emissions predominately result from the addition of synthetic nitrogen (N) fertilizers to terrestrial ecosystems. Usually, an exponential increase in N 2 O emissions occurs as N addition rates increase to exceed plant demands. However, most evidence to date is from temperate areas, with little information available for alpine ecosystems. Here we examined the changes in N 2 O flux under eight N addition levels and the mechanisms regulating these changes in a Tibetan alpine steppe. Our results showed that N 2 O emission rate increased linearly with increasing N additions. Even when soil N availability exceeded plant N uptake, no sharp N 2 O emissions were observed. The likely explanation was that decreased soil temperature limited the growth of nitrification‐related microorganisms, mainly ammonia‐oxidizing archaea, which further attenuated the positive response of N 2 O emissions to excess N supply. These findings suggest that the N‐induced changes in soil temperature regulate the growth of nitrifying microorganisms and the subsequent N 2 O fluxes in this alpine steppe, and the exponential N 2 O emission‐N rate relationship observed in warm regions may not be simply extrapolated to alpine ecosystems.