Scale-dependent key drivers controlling methane oxidation potential in Chinese grassland soils

- Key environmental drivers controlling CH4 oxidation rate were scale-dependent.
- In steppe regional scale, total nitrogen was key controlling CH4 oxidation rate.
- In Inner Mongolia steppe, TOC and soil texture were key controlling factors.
- In Xinjiang steppe, the key controlling factors were aridity index and MAT.
- In Tibetan steppe, total nitrogen was best to explain CH4 oxidation rate.

Methane (CH4) oxidation plays a critical role in mitigating global warming. However, the key environmental drivers shaping CH4 oxidation rate at regional and sub-regional 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 Autonomous Region (XAR) and Tibetan Plateau (TP). Potential CH4 oxidation rate was measured, and the compositions and abundances of methanotrophs were analyzed by quantitative PCR (qPCR) and Miseq sequencing technique. The factors controlling CH4 oxidation potential at regional and sub-regional 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 compositions and abundances of methanotrophs varied at different sub-regions. Type I methanotrophs were predominant in soils from the Inner Mongolia steppe and Xinjiang Autonomous Region, whereas pxmA methanotrophs mainly distributed in the Tibetan alpine steppe soil. Measured environmental variables explained the variations of CH4 oxidation potential well at both regional and sub-regional scales in these Chinese grassland ecosystems. However, the contributions of different variables to CH4 oxidation potential were scale-dependent. At the regional scale, total nitrogen (TN) was the environmental variable that best explained the potential CH4 oxidation rate, and its influence might be mainly associated with its effects on plant growth and methanotrophic community traits. At sub-regional scales, the main controlling variables were total organic carbon (TOC) and soil texture in Inner Mongolia steppe, aridity index (AI) and mean annual temperature (MAT) in Xinjiang Autonomous Region, and TN in Tibetan alpine steppe. 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.