Water use strategy of Carex cinerascens and its response to water condition changes in Poyang Lake Wetland, China

Water is a key factor in maintaining plant growth and determining plant species distribution. Studying the water use strategies of plants under different water conditions is of great significance for understanding the wetland vegetation patterns and performing ecological regulation of wetlands. The present study aims to quantify the contribution rates of potential water sources to Carex cinerascens in the Poyang Lake Wetland using stable isotope techniques and to assess water use efficiency (WUE) and water niche breadth to reveal the water use strategy of C. cinerascens and its response to water condition changes. The results showed that soil water in the 0–20 cm soil layer replaced lake water, becoming the main source of water for C. cinerascens during the growing season as a result of the decrease in the lake water levels and the change in soil water contents. The contribution rates of soil water in the 0–20 cm soil layer to the development of C. cinerascens in the 12-, 13-, and 14-m elevation zones increased by 31.4, 11.0, and 21.1 %, respectively. In addition, the contribution rate of soil water from the 20–40 cm soil layer was lower than that from the 0–20 cm soil layer, while rainwater exhibited the lowest contribution rates to the development of C. cinerascens. The aboveground parts exhibited higher WUE values than those of belowground parts at the growth stage, except in the 14-m elevation zone, and lower WUE values than those of the belowground parts at the maturation and wilting stages of C. cinerascens. According to the calculated Levins index, the water niche breadths of C. cinerascens were reduced and increased under abundant and insufficient water amounts, respectively. C. cinerascens adjusted the water source, WUE, and water niche breadth during the entire growing season to adapt to changing water conditions in the Poyang Lake Wetland, thereby reflecting the strong adjustability and adaptability of C. cinerascens. This study provides further insights into the relationships between wetland vegetation and hydrological changes, as well as a scientific basis for wetland ecological and hydrological regulation and vegetation restoration in the Poyang Lake Wetland.