Impacts of precipitation, warming and nitrogen deposition on methane uptake in a temperate desert

Desert soils are a significant global sink for methane (CH4). However, it remains unclear how CH4 uptake in temperate deserts could respond to elevated precipitation, nitrogen (N) deposition and warming. An in situ field experiment was conducted to investigate these effects on CH4 uptake in the Gurbantunggut Desert, northwest China, from September 2014 to August 2017. This desert was a weak sink for CH4 (0.83 kg C ha(-1) year(-1)) over this period, with the non-growing season (November-March) accounting for 30.5% of the annual CH4 uptake. Pulse CH4 uptake was found to result from increased water addition (by 30% or 60 mm year(-1)) and low N deposition (30 kg N ha(-1) year(-1)) which enhanced annual CH4 uptake by 62.3 and 52.6%, respectively. However, no significant impact of high N deposition (60 kg N ha(-1) year(-1)) was found. Warming in open topped chambers (OTCs) had a variable effect on CH4 uptake, which mainly depended on variation in soil moisture. The response in CH4 uptake to the interaction between water and N addition was less than that for the individual factors, except under conditions of warming. In addition, CH4 uptake was significantly positively correlated to water-filled pore space (WFPS), differing from observations in forest and grassland ecosystems. Structural equation modeling indicated that CH4 uptake was significantly enhanced by soil moisture and the underground biomass of ephemerals. Overall, the CH4 sink of this desert was significantly enhanced by increasing precipitation and low N deposition, rather than warming, which may become a feedback for future climate.