Diversity of methanotrophs in Chinese grassland soils

Methane (CH4) oxidation plays critical roles in mitigating global warming. However, the key factors shaping CH4 oxidation rate at different spatial scales in grassland ecosystems remain poorly understood. In this study, we collected soils from 21 sites at the regional scale across three steppes of China, including grasslands in Inner Mongolia Plateau (IMP), Xinjiang (XAR) and Tibetan Plateau (TP). The composition and abundance of methanotrophs were analyzed by qPCR and Miseq sequencing technique. The factors controlling CH4 oxidation potential at different spatial scales were evaluated by means of partial least squares path modeling (PLS-PM) and multiple regression on distance matrices (MRM). The results showed that the composition and abundance of methanotrophs varied in different regional scales. Type I methanotrophs predominantly distributed in soils from the IMP and XAR, whereas pxmA and AOB-like methanotrophs mainly distributed in the TP and IMP soils, respectively. Environmental variables explained the variation of CH4 oxidation potential well at both continental and regional scales in Chinese grassland ecosystems. However, the contributions of different variables to CH4 oxidation potential were scale-dependent. At continental scale, total nitrogen (TN) was the determined environmental variable in explaining potential CH4 oxidation rate, and its influence might be mainly associated with its effects on plant growth and methanotrophic community traits. At regional scales, the determined environmental variables were total carbon (TOC) in the IMP, aridity index (AI) and mean annual temperature (MAT) in XAR, and TN in TP. These results further suggested that the impacts of environmental variables on CH4 oxidation rate were realized either through their effects on methanotrophic communities, and/or by affecting soil properties in the grassland ecosystems.