Soil and plant characteristics during two hydrologically contrasting years at the lakeshore wetland of Poyang Lake, China

The main objective of this research was to examine the effects of inter-annual water regime variation on soil and plant characteristics, and soil–vegetation relationship at the lakeshore wetland of Poyang Lake, China. Six transects which paralleled the lakeshore were established at a typical Carex lakeshore wetland of Poyang Lake. We performed the field investigation and sampling in the autumn growing seasons in a flooding year (2017) and a drought year (2018). Paired t test was carried out to determine the effects of inter-annual water regime variation on various soil and plant parameters. Redundancy analysis was used to examine the relationships of plant species composition with flooding and soil variables in both years. Soil water content (SW), soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), the ratio of SOC to TP (C/P ratio), the ratio of TN to TP (N/P ratio), ammonia nitrogen concentration (NH4-N), and nitrate nitrogen concentration (NO3-N) were 21 ~ 71% higher in the flooding year than in the drought year. Plant Shannon–Wiener indices were significantly lower in the drought year than in the flooding year, whereas aboveground and belowground plant biomass showed opposite patterns. Flooding and soil variables could strongly determine plant communities in both years. Flooding duration was the most important variable among all flooding and soil variables. After eliminating the effects of flooding duration, pH and SW still significantly affected plant community composition in the flooding year, while only NH4-N significantly impacted on plant species distribution in the drought year. The results provided direct evidences that the inter-annual water regime variation not only could dramatically modify soil and plant variables but also could change the soil–vegetation relationship in the wetlands. Our studies have great implications for the conservation and restoration of the wetlands, especially for the lake wetlands in the middle and lower reaches of Yangtze River.