Effects of waterlogging and elevated salinity on the allocation of photosynthetic carbon in marsh plants and soils

Abstract Background and aimCoastal marshes, termed the “blue carbon (C)” ecosystems, are vulnerable to sea-level rise (SLR) and its consequent effects. In this study, we explored the effects of changed hydrology on the accumulation and allocation of photosynthetic C within a widely distributed marsh species and rooted soils.MethodsThe plant–soil mesocosms of Phragmites australis were grown under waterlogging and elevated-salinity conditions to investigate the responses of photosynthetic C allocation in different C pools (plant organs and soils) based on 13CO2 pulse-labeling technology.ResultsWaterlogging and elevated salinity treatments decreased photosynthetic C. Both hydrological treatments reduced 13C recovery in the plant organs of P. australis while significantly increased the 13C allocation percentage in the belowground tissues. Waterlogging and slight salinity had no notable effects on 13C recovered in rhizosphere soils, while high salinity (15 and 30 ppt) significantly reduced 13C recovered in soils, indicating a decrease in C input from roots in a saline environment. Waterlogging strengthened the effects of salinity on the 13C allocation pattern, especially during the late growing season. The responses of C allocation in plant organs and rhizosphere soils to the hydrological treatments can be related to changes in nutrient, ionic concentrations and microbial biomass.ConclusionThe adaptation strategy of P. australis led to increased C allocation in belowground organs under changed hydrology. The expected SLR projection might notably decrease the total C stock and alter the C allocation pattern in the marsh plant–soil systems, due to amplifying effect of prolonged flooding and elevated salinity.