Impacts of Spartina alterniflora invasion on C-cycling functional genes and microbial communities in salt marsh wetlands during cold season

Abstract Background The invasiveness of Spartina alterniflora Loisel. into the estuarine coastal wetlands has impacted the stability of soil organic carbon, as well as the functional genes of soil microorganisms. However, the mechanisms by which S. alterniflora invasion affects soil organic carbon, especially at the micro-level, is still unclear. Therefore, this study compared the differences in soil carbon cycling (C-cycling) functional genes between invaded and native areas during the cold season, as well as the changes in microbial communities involved in differential functional genes’ expression. Results Our results showed that in salt marsh wetlands dominated by Suaeda salsa (L.) Pall., invasion by S. alterniflora negatively impacts soil microbial biomass carbon (MBC) and reduces the diversity of C-cycling functional genes. The invasion species significantly increased the relative abundance of carbon fixation genes, while decreasing the relative abundance of carbon degradation genes. Additionally, the differential genes-expressing microbial communities exhibited notable differences across groups. At the class level, both generalist taxa (e.g., Gammaproteobacteria, Deltaproteobacteria) and specialist taxa (e.g., Nitrospiria, Flavobacteriia) collectively influenced the abundance of C-cycling functional genes. Correlation and hierarchical partitioning analyses revealed that the increased soil carbon fixation capacity was closely associated with increased soil organic carbon (SOC) and decreased MBC, whereas the decline in soil carbon degradation capacity was linked to higher soil electrical conductivity (EC) and a lower C:P ratio. Conclusions Our study filled a gap in research during the cold season and revealed that the invasion of S. alterniflora significantly impacts both soil C-cycling functional genes and their expressing microbial communities, thereby potentially affecting the soil organic carbon of salt marsh wetland ecosystems.