Abstract
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 nosZgene-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.