Warming and wetting-induced soil acidification triggers methanotrophic diversity loss and species turnover in an alpine ecosystem

Increases in temperature and precipitation have continually occurred in the past few decades, both globally and in China, which have probably impacted the dynamics of net methane (CH4) emissions by regulating soil CH4 oxidization. An alpine ecosystem is quite sensitive to climate changes, but how these two climatic factors regulate the community of soil aerobic methane-oxidizing bacteria (aMOB) remains elusive in such an ecosystem because of the lack of high-resolution soil sampling datasets. Here, we employed a hybrid approach of gridded field surveys and random forest prediction to discern the above question in the Qinghai-Tibetan Plateau (QTP). Results indicated that type Ic aMOBs exhibited a preference for drier, colder areas, while type IIa, TUSC-like and RA21-like aMOBs probably occurred in wetter and relatively warmer areas. There were no remarkable shifts in alpha-diversity and bacterial community compositions from the driest and coldest regions to moderate ones, while the alpha-diversity decreased and community compositions changed substantially from moderate arid and cold areas to wetter, relatively warmer ones. These trends were mainly regulated by soil pH, a potentially secondary effect shaped by the interactions of mean annual precipitation (MAP) and temperature (MAT) and an aridity index (AI) in the QTP. A slight decline in soil pH from the driest and coldest areas to moderate ones might regulate aMOB diversity and community structure by the stochastic extinction of individuals adapted to a higher pH and the unstable colonization of individuals preferring a moderate pH. A great decline in soil pH from the moderate arid, cold to wetter, relatively warmer areas might lead to the deterministic exclusion of species with a high pH adaptability and the stable colonization of species preferring the acidic habitat. This study implies that soil acidification probably induces aMOB diversity loss and species turnover in the arid, cold areas of the QTP under climatic warming and wetting, shedding a new light on projecting the impact of climate changes on an alpine ecosystem's structure and function on unprecedented spatial scales.