Spartina alterniflora invasion affects methane emissions in the Yangtze River estuary

Purpose: Wetlands are the largest natural sources of atmospheric methane (CH ₄ ) and are often susceptible to plant invasion and hydrological fluctuations. However, the effect of plant invasion on wetland CH ₄ emissions is still controversial, and little is known about the variation of invasion-induced CH ₄ emissions under heterogeneous conditions. Materials and methods: A pairwise experimental design between Spartina alterniflora (invasive plant) and Phragmites australis (native plant) stands in high elevation sites (H-sites) and S. alterniflora and Scirpus mariqueter (native plant) stands in low elevation sites (L-sites) of the Yangtze River estuary was used to investigate how plant invasions affect CH ₄ emissions and whether CH ₄ emission changes significantly differ between the H- and L-sites with heterogeneous conditions. A static closed chamber method was used to conduct gas sampling measurements at both H- and L-sites. In addition, plant biomass and soil properties were investigated in both invasive and native plant stands. Results and discussion: CH ₄ emissions from the S. alterniflora stands were all significantly higher than those from the native plant stands at both H- and L-sites. Furthermore, the difference in CH ₄ emissions between S. alterniflora and P. australis stands in the H-sites was significantly lower than that between S. alterniflora and S. mariqueter stands in the L-sites. Plant biomass, soil organic carbon, and microbial biomass in S. alterniflora stands were all significantly higher than those in the native plant stands in both H-sites and L-sites. The soil properties also changed. Our results indicate that the S. alterniflora invasion significantly enhanced CH ₄ emissions from wetlands in the Yangtze River estuary. The invasion-related CH ₄ emissions were highly spatially variable; this variability may have been driven by the soil’s anaerobic environments, induced by hydrological dynamics. Conclusions: These results can have important implications for improving our ability to predict invasion-induced changes in CH ₄ emissions from wetlands in the context of global climate change.