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 australis and exotic Spartina alterniflora to 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. australis and S. alterniflora soils, 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. alterniflora and soil microbial biomass was lower than that on P. australis. Generally, waterlogging treatment increased the activity of sucrase, cellulase, urease, and dehydrogenase in S. alterniflora soil. Increased salinity decreased all the assayed extracellular enzyme activity in both P. australis and S. alterniflora soils. The synergistic effects of waterlogging and increased salinity treatments on the enzyme activities in P. australis soil were significant, whereas only the effect on the cellulase activity was significant in S. alterniflora soil. This study indicated a greater ability of the microbial community and extracellular enzyme activity of S. alterniflora soil to adapt to waterlogging and increased salinity compared with those of P. australis soil due to the lower sensitivity of S. alterniflora growth and soil nutrients to stress.