Physiological and growth responses of riparian sedge transplants to groundwater depth

Understanding of the influence of groundwater depth on the physiology and growth of transplanted sedges is needed to improve revegetation efforts in degraded riparian meadows. In a greenhouse experiment, we exposed transplants of Carex lanuginosa, Carex nebrascensis, and Carex rostrata to three simulated groundwater depths (4, 19, and 35 cm). Groundwater depth was manipulated over two phases: (1) water depths were held constant for 16 wk and (2) water depths were then increased over the next 6 wk. Leaf gas exchange, water relations, and shoot growth were measured periodically during each phase, and aboveground and belowground biomass were measured at the end of each phase. All species adjusted rooting depth to groundwater depth in response to the constant groundwater treatments, and groundwater depth had no effect on net photosynthetic rate and stomatal conductance. Net photosynthetic rate and stomatal conductance of all species initially increased when groundwater levels dropped but decreased rapidly after 4 wk of lowering groundwater. This response indicates that anaerobic conditions hindered leaf gas exchange under shallow but constant groundwater depths and also indicates that transplants may be less tolerant of shallow groundwater than naturally established sedges because of their smaller root systems. Compared with the other species, net photosynthetic rate and stomatal conductance of C. rostrata were more sensitive to declines in leaf water potential, and this species allocated proportionately more root growth to saturated soil zones. Carex rostrata's growth and physiological characteristics indicate that its transplants have lower tolerance to dry soil and water stress than C. lanuginosa and C. nebrascensis.