Anthropogenic-driven global change, including changes in atmospheric
nitrogen (N) deposition and precipitation patterns, is dramatically
altering N cycling in soil. How long-term N deposition, precipitation
changes, and their interaction influence nitrous oxide (N2O) emissions
remains unknown, especially in the alpine steppes of the Qinghai-Tibetan
Plateau (QTP). To fill this knowledge gap, a platform of N addition and
altered precipitation experiments was established in an alpine steppe of
the QTP in 2013. N addition significantly increased N2O emissions, and
alterations in soil NO3-N, pH, temperature, and belowground biomass
modulated N2O emissions. In addition to abiotic parameters,
ammonia-oxidizing bacteria dominated N2O emissions in nitrification
compared with ammonia-oxidizing archaea. Changes in the denitrifying
microbial community, namely a high ratio of (nirS+nirK) gene-containing
to nosZ gene-containing organisms, were responsible for N2O emissions in
denitrification. Altered precipitation did not affect N2O emissions.
This unexpected finding, which is inconsistent with the conventional
view that N2O emissions are controlled by soil water content, indicates
that N2O emissions are particularly susceptible to N deposition in the
alpine steppes. Notably, whereas N2O emissions were affected by N
addition as a single factor, they were not significantly affected by the
combination of precipitation changes and N addition, indicating that
altered precipitation patterns may mitigate the positive feedback effect
of N addition on N2O emissions. Consequently, our study suggests that
the response of N2O emissions to N deposition in future global change
scenarios will be affected by precipitation regimes in the alpine
steppes.
Global change and biological soil crusts: effects of ultraviolet augmentation under altered precipitation regimes and nitrogen additions
