1National Marine Biodiversity Institute at Korea, 2University of Massachusetts
Conversion of tropical forest to pasture has lead to increased production of greenhouse gases such as methane. This is especially important in tropical rain forests that play a central role in the global climate change. In the present study we compared the methane-oxidizing bacterial community (MOB) of Western Amazon soils under different land uses, including primary forest, cattle pastures established at different ages, and secondary forest. The methane oxidation potential was determined in soil microcosms, but interestingly, the methane oxidation rate was significantly higher in all pasture soils than in the soils sampled from forest and secondary forest. The age of the pasture had no influence on methane oxidation rates. The diversity of methanotrophs in different land use systems was investigated by two strategies, 16S rRNA pyrosequencing and clone libraries of pmoA gene fragments (coding for a subunit of the particular methane monooxygenase). The abundance of methanotrophs was quantified by qPCR of the pmoA gene. In both strategies, members of the MOBII cluster within the alphaproteobacteria predominated all land use types, most were related with Methylocystis. In addition, members of the Type Ib cluster of the gammaproteobacteria were detected. Primary forest was dominated by the methanotroph group USCα, and pasture soils were dominated with Type II related with Methylocystis sp. The pmoA gene of Type II methanotrophs was abundant at pasture soils in qPCR assays. Methane oxidation potential and the abundance of Type II pmoA were highly correlated (r=0.737). A combined data analysis of methane oxidation potential and community analysis showed that the Type II methanotrophs may be mainly responsible for atmospheric methane consumption, and changes in diversity and oxidation potential were affected by land use change. This study is providing new insights into identity and activity of methanotrophs in the Amazon rainforest.
keywords:Amazon,land use,methane oxidation,forest,Methylocystis sp.