论文摘要：

Emissions of nitrous oxide (N₂O) contribute to global warming and stratospheric ozone depletion. Anthropogenic N₂O emissions predominately result from the addition of synthetic nitrogen (N) fertilizers to terrestrial ecosystems. Usually, an exponential increase in N₂O 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 N₂O flux under eight N addition levels and the mechanisms regulating these changes in a Tibetan alpine steppe. Our results showed that N₂O emission rate increased linearly with increasing N additions. Even when soil N availability exceeded plant N uptake, no sharp N₂O 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 N₂O 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 N₂O fluxes in this alpine steppe, and the exponential N₂O emission-N rate relationship observed in warm regions may not be simply extrapolated to alpine ecosystems.