Different microbial mechanisms for the enhanced methane emission by Spatina anglica and Phragmites australis in temperate tidal salt marsh.

Spartina anglica and Phragmites australis are notorious invasive plants in temperate tidal salt marshes in East Asia and North America, respectively. Although the invasive context, surrounding environment, and ecological conditions are different, the invasion of both plants consistently increases methane emission. Previous studies illustrated that the invasions alter quality or quantity of methanogenic substrates, therefore methane production is enhanced. However, the microbial mechanisms involved in that phenomenon are not clearly determined. In this study, we tried to compare the different responses of methane emission and microbial community affected by the S. anglica and P. australis, and determine the differences in the related microbial processes such as decomposition, methanogenesis, and methane oxidation. We found that stimulated methanogenesis in the deep soil layer (30-100cm deep) may play a key role in the enhanced methane emission by P. australis. Meanwhile, the enhanced methane emission by S. anglica may be due to the stimulated methanogenesis in the surface soil layer (0-30cm deep). In particular, the competitive inhibition between methanogen and sulfate reducing bacteria substantially influences the methane emission. Our results revealed the key microbial mechanisms which are responsible for the enhanced methane emission by the plant invasion, and they are varied depending on the plant species and soil layers.