The effect of grazing on the abundance, composition, and methane (CH 4 ) uptake of methanotrophs in grasslands has been well documented in the past few decades, but the dominant communities of active methanotrophs responsible for CH 4 oxidation activity in grazed soils are still poorly understood. In this study, we characterized the metabolically active, aerobic methanotrophs in grasslands with three different levels of grazing (light, medium, and heavy) by combining DNA-stable isotope probing (SIP) and quantitative PCR (qPCR) for methane monooxygenase ( pmoA ) gene– and 16S rRNA gene–based amplicon sequencing. The CH 4 oxidation potential was as low as 0.51 μmol g dry weight −1 day −1 in the ungrazed control, while it decreased as grazing intensity increased in grazed fields, ranging from 2.25 μmol g dry weight −1 day −1 in light grazed fields to 1.59 in heavily grazed fields. Increased CH 4 oxidation activity was paralleled by twofold increases in abundance of pmoA genes and relative abundance of methanotroph-affiliated 16S rRNA genes in the total microbial community in grazed soils. SIP and sequencing revealed that the genera Methylobacter and Methylosarcina (type I; Gammaproteobacteria ) and Methylocystis (type II; Alphaproteobacteria ) were active methanotrophs responsible for CH 4 oxidation in grazed soils. Light and intermediate grazing stimulated the growth and activity of methanotrophs, while heavy grazing decreased the abundance and diversity of the active methanotrophs in the typical steppe. Redundancy and correlation analysis further indicated that the variation of bulk density and soil C and N induced by grazing determined the abundance, diversity of active methanotrophs, and methane oxidation activity in the long-term grazed grassland soil.

中文翻译：

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放牧对草地土壤中活性甲烷氧化菌丰度和组成及甲烷氧化活性的影响

在过去的几十年中，放牧对草地甲烷氧化菌的丰度、组成和甲烷 (CH 4 ) 吸收的影响已有详细记载，但在放牧土壤中负责 CH 4 氧化活性的活性甲烷氧化菌的主要群落仍然很差明白了。在这项研究中，我们通过结合 DNA 稳定同位素探测 (SIP) 和甲烷单加氧酶 ( pmoA ) 的定量 PCR (qPCR) 来表征具有三种不同放牧水平（轻度、中度和重度）的草地中代谢活跃的好氧甲烷氧化菌。基于基因和 16S rRNA 基因的扩增子测序。在未放牧的对照中，CH 4 氧化电位低至 0.51 μmol g 干重 -1 天 -1，而随着放牧地中放牧强度的增加，CH 4 氧化电位降低，范围为 2。25 μmol g 干重 -1 天 -1 在轻度放牧的田地中至 1.59 在重度放牧的田地中。CH 4 氧化活性的增加伴随着放牧土壤中总微生物群落中 pmoA 基因丰度和甲烷氧化菌相关 16S rRNA 基因丰度的两倍增加。SIP 和测序显示甲基杆菌属和甲基八叠球菌属（I 型；Gammaproteobacteria）和甲基囊藻属（II 型；Alphaproteobacteria）是负责放牧土壤中 CH 4 氧化的活性甲烷氧化菌。轻度和中度放牧刺激了甲烷氧化菌的生长和活性，而重度放牧降低了典型草原活跃甲烷氧化菌的丰度和多样性。