Effects of dam impoundment on the soil seed bank in a plateau wetland of China

Dam impoundment, which rapidly changes hydrologic regimes and greatly alters aquatic environments, plays a critical role in the seed germination and seedling growth of wetland plants, especially influencing their seed banks. In this study, a soil seed bank experiment was carried out along a water level gradient for the Lake Lashi wetland in the Northwest Yunnan Plateau of China. The objectives of this study were to determine the effect, driver and dynamic mechanism of dam impoundment on the soil seed bank of plateau wetlands using partial least squares (PLS) regression and chaotic dynamic methods. The results showed that the soil seed bank had significant differences in seed density, species composition, and water ecotype of the plant species between the flood zone (perennially flooded area, seasonally flooded area, and flood plain area) and nonflood zone (control area) in the plateau wetland. The seed bank density was obviously lower in the perennially flooded area and higher in the seasonally flooded area and flood plain area, with values that were 39.88%, 153.53%, and 146.47% that of the control area, respectively. After dam impoundment, the number of plant species gradually increased; however, the dominance of the dominant species became less obvious, and the species diversity indices decreased significantly, e.g., by 15.47% for the Simpson diversity index and 72.39% for the Shannon Wiener diversity index. Our study showed that dam impoundment has made the Lake Lashi wetland complex chaotic ecosystem switch between order and disorder through self-organization and that the species composition of the soil seed bank continuously experienced self-adaptation. These results provide a reference for scientific evaluations of the effects of dam impoundment on wetland ecosystems and provide guidance for the protection and management of plateau wetland ecosystems.