Response of Carex cinerascens populations to groundwater level gradients in the Poyang Lake wetland

Poyang Lake has faced frequent extreme events such as floods and droughts owing to climate change and human activities. These changes in hydrological processes directly impact the ecological processes of the Poyang Lake wetland.Therefore,it is essential to investigate the relationship between hydrological processes and vegetation succession in Poyang Lake. In this study,the influence of groundwater on the development of Carex cinerascens populations was studied by controlled experiments. C. cinerascens,one of the dominant species in the Poyang Lake wetland,was planted at five groundwater level gradients(- 10,- 20,- 40,- 80,and- 120 cm relative to the soil surface). The number of C.cinerascens plants per barrel was surveyed and recorded at approximately 15-day intervals. The soil water content decreased significantly with decreasing groundwater level,though there was no difference in water content between the- 80 cm and- 120 cm groundwater level treatments. The groundwater level gradient did not significantly affect the characteristics of the C. cinerascens population in the spring. However,the density,growth form,diversity,and the relative heights of Artemisia selengensis and C. cinerascens showed significant differences between treatments in the summer. The density for the five groundwater levels exhibited similar changes; it decreased significantly with decreasing groundwater level. Plants in the-80 cm and- 120 cm levels exhibited decreases in growth earlier than plants in the other three groundwater treatments. The Simpson diversity index for the- 120 cm groundwater level treatment was significantly higher than that observed for the-10 cm,- 20 cm,and- 40 cm treatments. The height ratio of A. selengensis to C. cinerascens in the- 10 cm groundwater level treatment was always less than 0. 9,which was far smaller than the ratios observed for other groundwater treatments.At the end of the experiment,the height ratios in- 80 cm and- 120 cm treatments were 4. 7 and 4. 5 times greater than that of the- 10 cm groundwater treatment. A groundwater level of- 10 cm was advantageous with respect to the growth and stability of the C. cinerascens population compared with the other treatments,and a groundwater level of- 80 cm can cause degradation and succession of C. cinerascens populations. When the groundwater level was below- 120 cm,this effect is maximal. The results and findings in this paper are helpful to assess the effects of groundwater level fluctuation on th