Effects of enclosure time on the community composition of methanotrophs in the soils of the Inner Mongolia grasslands

Purpose: Despite the great number of studies about methane uptake and its response to grazing in the Inner Mongolia grasslands, only a few focused on the methanotrophic composition. This study aimed to investigate the methanotrophic community structure and abundance, then to analyze the abiotic driving factors of methanotrophic community structure in different enclosed times in this area. Materials and methods: In this study we chose typical grasslands in the Xilin River Basin of Inner Mongolia, China to investigate methanotrophic community structure and abundance under different enclosure treatments as follows: 79E (grassland enclosed since 1979), 99E (grassland enclosed since 1999), and G (freely grazed grassland). A clone library was used to reveal the methanotroph community structure, and their relationships with abiotic factors were analyzed by redundancy analysis. Methanotroph abundance was determined by real-time PCR. Results and discussion: The OTUs of the three treatments mainly belonged to Type I methanotrophs, probably caused by the high pH value. Among all OTUs, only OTU1 belonged to upland soil cluster γ (USC-γ), whose abundance was the largest in all OTUs, indicating the USC-γ cluster was the main one to oxidize CH₄ in the Inner Mongolia grasslands. Methanotrophic abundance (represented by the pmoA gene copies per gram of dry weight soil) decreased with the enclosure time as G (4.5 × 10⁷) > 99E (2.8 × 10⁷) > 79E (2.0 × 10⁷), mainly caused by the lower soil moisture content in G. Lower soil moisture content facilitates more CH₄ and O₂ diffusive into soil thus leading to the proliferation of methanotrophs. Conclusions: This study found a high abundance of methanotrophs in the soils of the Inner Mongolia grasslands, with the USC-γ cluster having the largest abundance, which may play a key role in oxidizing CH₄ in the Inner Mongolia grasslands. Combined with those of previous studies, the results showed an obvious change of methanotrophic community composition with the increase of enclosure time.