Exotic Spartina alterniflora invasion increases CH 4 while reduces CO 2 emissions from mangrove wetland soils in southeastern China

Mangroves are critical in global carbon budget while vulnerable to exotic plant invasion. Spartina alterniflora , one of typical salt marsh plant grows forcefully along the coast of China, has invaded the native mangrove habitats in Zhangjiang Estuary. However, the effects of S . alterniflora invasion on soil carbon gases (CH 4 and CO 2 ) emission from mangroves are not fully understood. Accordingly, we conducted a field experiment to investigate the soil CH 4 and CO 2 emission during growing seasons in 2016 and 2017 at four adjacent wetlands, namely bare mudflat (Mud), Kandelia obovata (KO), Avicennia marina (AM) and S . alterniflora (SA). Potential methane production (PMP), potential methane oxidation (PMO), functional microbial abundance and soil biogeochemical properties were measured simultaneously. Our results indicate that S . alterniflora invasion could dramatically increase soil CH 4 emissions mainly due to the enhancement in PMP which facilitated by soil EC, MBC, TOC and mcrA gene abundance. Additionally, S . alterniflora invasion decreases soil CO 2 emission. Both heterotrophic microbial respiration ( 16S rRNA ) and methane oxidation ( pmoA and ANME-pmoA ) are responsible for CO 2 emission reduction. Furthermore, S . alterniflora invasion greatly increases GWP by stimulating CH 4 emissions. Thus, comparing with mangroves, invasive S . alterniflora significantly ( p < 0.001) increases CH 4 emission while reduces CO 2 emission.