Effects of waterlogging and increased salinity on microbial communities and extracellular enzyme activity in native and exotic marsh vegetation soils

Coastal ecosystems are vulnerable to plant invasion and expected sea level rise in China. This study explored the responses of microbial communities and extracellular enzyme activity in the marsh soils of native Phragmites australisand exotic Spartina alterniflorato waterlogging and increasing salinity (to mimic prolonged inundation and saltwater intrusion) based on the determination of phospholipid fatty acids and analysis of enzyme kinetics. The results showed that waterlogging and increased salinity treatments decreased the soil microbial biomass in both P. australisand S. alterniflorasoils, with waterlogging exacerbating the negative effects of salinity. Fungi/bacteria ratios decreased under both waterlogging and salinity treatments, whereas actinomycetes/bacteria ratios increased with increasing salinity. The degree of the adverse effects of salinity on plant growth of S. alternifloraand soil microbial biomass was lower than that on P. australis. Generally, waterlogging treatment increased the activity of sucrase, cellulase, urease, and dehydrogenase in S. alterniflorasoil. Increased salinity decreased all the assayed extracellular enzyme activity in both P. australisand S. alterniflorasoils. The synergistic effects of waterlogging and increased salinity treatments on the enzyme activities in P. australissoil were significant, whereas only the effect on the cellulase activity was significant in S. alterniflorasoil. This study indicated a greater ability of the microbial community and extracellular enzyme activity of S. alterniflorasoil to adapt to waterlogging and increased salinity compared with those of P. australissoil due to the lower sensitivity of S. alternifloragrowth and soil nutrients to stress.