Belowground responses of phragmites Australis and suaeda salsa to salinity and water depth changes

© 2018, Pakistan Botanical Society. All rights reserved. Mesocosm experiments were conducted to examine belowground responses of Phragmites australis and Suaeda salsa to the combined stresses of increased salinity and water depth. The results demonstrated that: (1) belowground biomass of P. australis responded negatively to both increased salinity and water depth, whereas belowground biomass of S. salsa mainly responded negatively to increased water depth; (2) belowground biomass of S. salsa negatively responded to increased water depth more strongly than that of P. australis, thus S. salsa might disappear before P. australis in wetlands experiencing prolonged water-logging; (3) P. australis and S. salsa responded to increased salinity and/or water-logging by shifting their resource allocations towards aboveground biomass; (4) belowground biomass of P. australis tended to have more negative responses to increased salinity and water depth at deeper versus shallower soil depths, hindering P. australis from utilizing resources in deeper soil; in contrast, belowground biomass of S. salsa tended to have more negative responses to increased water depth at shallower versus deeper soil depths, greatly decreasing the overall root density and thereby increasing the chance of uprooting disturbance to S. salsa. These responses would accelerate sediment loss due to compromised sediment-binding abilities of P. australis and S. salsa, leading to an adverse positive feedback between environmental changes associated with sea level rise and performance of P. australis and S. salsa, resulting in faster deterioration of coastal wetlands than might otherwise be expected.