Methane emissions and microbial communities under differing flooding conditions and seasons in littoral wetlands of urban lake

Wetlands are the largest natural sources of methane (CH4) emissions worldwide. Littoral wetlands of urban lakes represent an ecotone between aquatic and terrestrial ecosystems and are strongly influenced by water levels, environmental conditions, and anthropogenic activities. Despite these littoral zones being potential “hotspots” of CH4 emissions, the status of CH4 emissions therein and the role of physicochemical properties and microbial communities regulating these emissions remain unclear. This study compared the CH4 fluxes, physicochemical properties, and CH4-cycling microbial communities (methanogens and methanotrophs) of three zones (a non-flooded supralittoral zone, a semi-flooded eulittoral zone, and a flooded infralittoral zone) in the littoral wetlands of Lake Pipa, Jiangsu Province, China, for two seasons (summer and winter). The eulittoral zone was a CH4 source (median: 11.49 and 0.02 mg m−2 h−1 in summer and winter, respectively), whereas the supralittoral zone acted as a CH4 sink (median: −0.78 and −0.09 mg m−2 h−1 in summer and winter, respectively). The infralittoral zone shifted from CH4 sink to source between the summer (median: −10.65 mg m−2 h−1) and winter (median: 0.11 mg m−2 h−1). The analysis of the functional genes of methanogenesis (mcrA) and methanotrophy (pmoA) and path analysis showed CH4 fluxes were strongly regulated by biotic factors (abundance of the mcrA gene and alpha diversity of CH4-cycling microbial communities) and abiotic factors (ammonia nitrogen, moisture, and soil organic carbon). In particular, biotic factors had a major influence on the variation in the CH4 flux, whereas abiotic factors had a minor influence. Our findings provide novel insights into the spatial and seasonal variations in CH4-cycling microbial communities and identify the key factors influencing CH4 fluxes in littoral wetlands. These results are important for managing nutrient inputs and regulating the hydrological regimes of urban lakes.