Water level requirements of a Carex hygrophyte in Yangtze floodplain lakes

Water level management is of great importance regarding conservation and rehabilitation of wetland plants. However, water level requirements (WLRs) of these plants are not well studied. In the present study, we conducted a systematic assessment of WLRs of Carex cinerascens regarding to each life history stage, based on field investigations and a series of simulation experiments in the Yangtze River floodplain. Results showed that C. cinerascens was well developed in lakes with intermittent water level fluctuations. Its rhizomes could not emerge underwater or in water-saturated conditions, and the optimum soil moisture for emergence was 15-30% with air temperature above 6 degrees C. Its growth was prohibited when the whole plant was inundated (i.e. inundation depth > plant height), and when rate of water level change exceeded 1.2 cm/d. Although summer inundation was not essential for C. cinerascens development, it was beneficial to the plant for excluding competitive species. The timing of habitat inundation was suggested to be after May when the plant matured. The timing of rhizome emergence in the second growing season was determined by when the habitat was exposed. With inclusion of temperature limits, the optimum timing of habitat exposure in autumn was October, and the duration of summer inundation was therefore 0-150 days. We finally combined WLRs of each life history stage and established an integrated WLRs model of C. cinerascens in Yangtze floodplain lakes. It is the first time that such a WLRs model was proposed for hygrophytes in lakes. Moreover, we presented a methodology for assessment of WLRs of hygrophytes which can be widely used in riverine lakes as well as other wetlands. Our results provide important implications for water level management regarding the conservation and rehabilitation of wetland plants.