Changes in Methane Emission and Community Composition of Methane-Cycling Microorganisms Along an Elevation Gradient in the Dongting Lake Floodplain, China

Yijie Ren,Rong Sheng,Yonghong Xie,Lianlian Zhu,Chengyi Zhang,Xinsheng Chen,Fengjin Xiao,Yeai Zou,Feng Li,Xiaoyan Zhang,Xian Chen,Zhengmiao Deng

doi:10.3390/atmos11090997

Abstract

Methane (CH4) emission and environmental controls of CH4-cycling microorganisms are unclear in inland floodplains. Here, we examined soil CH4 emissions and the community composition of CH4-cycling microorganisms under three vegetation types—mudflat (MF, no vegetation cover), Carex meadow (CM, mainly Carex brevicuspis), and reed land (RL, mainly Miscanthus sacchariflorus)—from water-adjacent areas to higher-elevation land in the Dongting Lake floodplain, China. The results showed that CH4 emission is the highest in CM, while significant absorption was observed in the RL site. The abundance ratio of methanogen/methanotroph was the highest in CM, intermediate in MF, and lowest in RL. The Methanosarcinaceae family represented the dominant methanogens in the three sampling sites (41.32–75.25%). The genus Methylocystis (60.85%, type II methanotrophs) was dominant in CM, while Methylobacter and Methylosarcina (type I methanotrophs) were the dominant genera in MF (51.00%) and RL (50.24%), respectively. Structural equation model analysis showed that methanogen and methanotroph abundance were affected by water table depth, soil water content, and pH indirectly through soil organic content, total nitrogen, microbial biomass carbon, and microbial biomass nitrogen. These results indicated that the Dongting Lake floodplain may change from a CH4 source to a CH4 sink with vegetation succession with an increase in elevation, and the methanogen/methanotroph ratio can be used as a proxy for CH4 emission in wetland soils. The continuous increase in reed area combined with the decrease in Carex meadow may mitigate CH4 emission and enhance the CH4 sink function during the non-flood season in the Dongting Lake floodplain.

Highlights

Methane (CH4 ) is an important greenhouse gas with a global warming potential 28 times higher than that of carbon dioxide (CO2 ) on a 100-year scale [1].Natural wetlands are considered the main natural CH4 source for the atmosphere because of their high productivity and low redox capacity
We found that Methylocystis represented the dominant methanotrophic bacteria in the Carex meadow (CM)
This study provided fundamental insights into soil CH4 emissions, the community structure of

Summary

Introduction

Methane (CH4 ) is an important greenhouse gas with a global warming potential 28 times higher than that of carbon dioxide (CO2 ) on a 100-year scale [1].Natural wetlands are considered the main natural CH4 source for the atmosphere because of their high productivity and low redox capacity. Methane (CH4 ) is an important greenhouse gas with a global warming potential 28 times higher than that of carbon dioxide (CO2 ) on a 100-year scale [1]. 172 Tg CH4 y−1 (1σ SD, ± 12 Tg CH4 y−1 ), accounting for approximately 62% of the annual global (natural) CH4 budget [2,3]. CH4 emissions and microbial production mechanisms from high-latitude peatlands have been well studied [4,5,6,7,8], relatively little data have been published on the low-latitude wetlands, which is the most important source of uncertainty on the methane budget [2]. Low-latitude seasonal floodplains are prolific sources of CH4 because of their substantial net primary productivity and high seasonal temperatures [9]. I.e., water table depth (WTD), soil water content (SWC), etc., and C and N concentrations in the soil, i.e., soil organic content (SOC), nitrogen, dissolved organic carbon (DOC), etc., along with the elevation gradient, may act as critical factors influencing

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Conclusion