Sonneratia apetala introduction alters methane cycling microbial communities and increases methane emissions in mangrove ecosystems

Mangrove ecosystems are important methane (CH4) sources driven by microbial activities. Mangrove reforestation has been practiced as a strategy to restore the ecological functions of coastal environments. However, it remains unclear how introduced mangrove species impact their sediment microbial communities and CH4 emissions. Here we compared the changes in CH4 emissions, sediment properties, methanogenic and methanotrophic communities between two distinct mangrove habitats: one dominated by Kandelia obovata (KO, native species) and the other dominated by Sonneratia apetala (SA, introduced species). Compared with the KO sediment, the SA sediment had significantly (P < 0.05) higher levels of CH4 emissions (1643 vs. 593 μmol m−2 day−1), pH value (7.1 vs. 6.4), and ammonium (6.5 vs. 5.1 mg kg−1), but lower levels of salinity (3.8 vs. 11.9 ppt), total carbon (12.3 vs. 40.7 g kg−1), total nitrogen (2.3 vs. 4.5 g kg−1), and sulfate (1865 vs. 2959 mg L−1). Analysis of the methyl coenzyme M reductase (mcrA) and particulate methane monooxygenase (pmoA) genes showed that SA introduction led to a significant (P < 0.01) shift of sediment CH4-cycling microbial communities with increased alpha-diversity of methanogenic communities, and decreased abundances of methanotrophs compared with the KO sediment. Specifically, the relative abundance of Methanosarcina increased, while the relative abundance of type II methanotrophs decreased in the SA sediment, so the increased CH4 emissions in the SA sediment could be attributed to greater capacity of CH4 production and reduced CH4 consumption. Also, salinity, pH, total carbon, total nitrogen and sulfate were found to be important environmental factors shaping the CH4-cycling microbial community structure. This study provides insights into the impact of mangrove introduction on CH4-cycling microbial communities and CH4 emissions, which has very important implications about mangrove ecosystems in regulating global climate change.