The driving effects of nitrogen deposition on nitrous oxide and associated gene abundances at two water table levels in an alpine peatland
Alpine peatlands are recognized as a weak or negligible source of nitrous oxide (N 2 O). Anthropogenic activities and climate change resulted in the altered water table (WT) levels and increased nitrogen (N) deposition, which could potentially transition this habitat into a N 2 O emission hotspot. However, the underlying mechanism related with the effects is still uncertain. Hence, we conducted a mesocosm experiment to address the response of growing-season N 2 O emissions and the gene abundances of nitrification (bacterial amoA ) and denitrification ( narG , nirS , norB and nosZ ) to the increased N deposition (20 kg N ha −1 yr −1 ) at two WT levels (WT − 30 , 30 cm below soil surface; WT 10 , 10 cm above soil surface) in the Zoige alpine peatland, Qinghai-Tibetan Plateau. The results showed that the WT did not affect N 2 O emissions, and this was attributed with the limitation of soil NO 3 − . The higher WT level increased denitrification ( narG and nirS gene abundance) resulting in the depletion of soil NO 3 − , but the consequent NO 3 − deficiency further limited denitrification, while the WT did not affect nitrification (bacterial amoA gene abundance). Meanwhile, the N deposition increased N 2 O emissions, regardless of WT levels. This was associated with the N-deposition induced increase in denitrification-related gene abundances of narG , nirS , norB and nosZ at WT − 30 and narG at WT 10 . Additionally, the N 2 O emission factor assigned to N deposition was 1.3 % at WT − 30 and 0.9 % at WT 10 , respectively. Our study provided comprehensive understanding of the mechanisms referring N 2 O emissions in response to the interactions between climate change and human disturbance from this high-altitude peatland.
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