Responses of soil methanogens, methanotrophs, and methane fluxes to land-use conversion and fertilization in a hilly red soil region of southern China

Abstract

Changes in land-uses and fertilization are important factors regulating methane (CH₄) emissions from paddy soils. However, the responses of soil CH₄ emissions to these factors and the underlying mechanisms remain unclear. The objective of this study was to explore the effects of land-use conversion from paddies to orchards and fertilization on soil CH₄ fluxes, and the abundance and community compositions of methanogens and methanotrophs. Soil CH₄ fluxes were quantified by static chamber and gas chromatography technology. Abundance and community structures of methanogens and methanotrophs (based on mcrA and pmoA genes, respectively) were determined by quantitative real-time PCR (qPCR), and terminal restriction fragment length polymorphism (TRFLP), cloning and sequence analysis, respectively. Results showed that land-use conversion from paddies to orchards dramatically decreased soil CH₄ fluxes, whereas fertilization did not distinctly affect soil CH₄ fluxes. Furthermore, abundance of methanogens and methanotrophs were decreased after converting paddies to orchards. Fertilization decreased the abundance of these microorganisms, but the values were not statistically significant. Moreover, land-use conversion had fatal effects on some members of the methanogenic archaea (Methanoregula and Methanosaeta), increased type II methanotrophs (Methylocystis and Methylosinus), and decreased type I methanotrophs (Methylobacter and Methylococcus). However, fertilization could only significantly affect type I methanotrophs in the orchard plots. In addition, CH₄ fluxes from paddy soils were positively correlated with soil dissolved organic carbon contents and methanogens abundance, whereas CH₄ fluxes in orchard plots were negatively related to methanotroph abundance. Therefore, our results suggested that land-use conversion from paddies to orchards could change the abundance and community compositions of methanogens and methanotrophs, and ultimately alter the soil CH₄ fluxes. Overall, our study shed insight on the underlying mechanisms of how land-use conversion from paddies to orchards decreased CH₄ emissions.

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