Precipitation changes regulate the annual methane uptake in a temperate desert steppe.

Desert soils are an important sink of atmospheric methane (CH) and regulate the global CH budget. However, it is still unclear how CH fluxes respond to precipitation changes in desert-steppe soils. Therefore, a two-year in situ control experiment was conducted to investigate the effect of precipitation changes on CH uptake in desert steppe of Inner Mongolia in northwest China and its driving mechanism. The result showed that this desert steppe was an important sink of CH, with an annual uptake of 2.93 (2.64-3.22) kg C ha. It was found that CH uptake was reduced significantly for decreasing precipitation, especially in spring and summer. In contrast, an increasing trend of CH uptake was observed for increasing precipitation, although it was not statistically significant. Further analyses found that CH uptake was more sensitive to decreasing precipitation than increasing precipitation. This may be mainly due to the fact that only moderate water-filled pore space (WFPS) induced by precipitation promoted CH uptake, while too-high (>32%) or too-low WFPS inhibited its uptake. A structural equation model showed that the copy number of the pmoA functional gene was the most important factor affecting CH uptake. In contrast, soil moisture had a very important indirect effect on CH uptake, mainly through significantly affected soil porosity, the above-ground plant biomass and NO-N content, further affected CH uptake. Overall, CH sinks in desert steppe was still mainly controlled by methane-oxidizing bacteria containing the key functional gene pmoA and WFPS. Therefore, precipitation plays an important role in regulating the intensity of CH sinks in desert steppe, while it is worth noting that too-little precipitation will significantly weaken CH sinks.