Nitrogen deposition stimulated winter nitrous oxide emissions from bare sand more than biological soil crusts in cold desert ecosystem

Dryland ecosystems are often nitrogen-limited, and small nitrogen inputs may produce large responses to dryland ecological processes, such as gaseous nitrogen emission. The effect of increased anthropogenic nitrogen deposition on N2O and NO emissions in desert ecosystems is unclear, especially in non-growing seasons when the surface is covered with snow. In this study, nitrogen applications were performed on biological soil crusts (lichen crust and moss crust, bare sand for control) in the Gurbantunggut Desert, Northwest China. We measured the fluxes of N2O and NO and related nitrogen cycle functional gene abundances in winter for three-years period. Nitrogen addition significantly affected N2O emissions and increased the abundances of key functional gene for nitrogen cycle, while it only slightly influenced NO emissions. These effects of nitrogen addition depended on composition of biological soil crusts. For bare sand and lichen crust, nitrogen addition significantly increased N2O emissions, whereas for moss crust, only a negligible effect was observed. Meanwhile, significant differences in nitrogen cycle functional gene abundances were found among different composition of biological soil crusts. Abundance of amoA, narG, and nosZ genes were highly related to N2O and NO emissions. Thus, our results indicate that gaseous nitrogen emissions were generally increased by nitrogen addition through their effects on related functional microbial groups. The effects were regulated by composition of biological soil crusts which can buffer the effects of increasing nitrogen addition during winter.