No abstract

Ammonium pulse attributed to runoff of urban surface and agriculture following heavy rain is common in inland aquatic systems and can cause profoundly effects on the growth of macrophytes, especially when combined with low light. In this study, three patterns of NH 4 -N pulse (differing in magnitude and frequency) were applied to examine their effects on the growth of three submersed macrophytes, namely, Myriophyllum spicatum , Potamogeton maackianus , and Vallisneria natans , in terms of biomass, height, branch/ramet number, root length, leaf number, and total branch length under high and low light. Results showed that NH 4 -N pulse caused negative effects on the biomass of the submerged macrphytes even on the 13th day after releasing NH 4 -N pulse. The negative effects on M . spicatum were significantly greater than that on V . natans and P . maackianus . The effects of NH 4 -N pulse on specific species depended on the ammonium loading patterns. The negative effects of NH 4 -N pulse on P . maackianus were the strongest at high loading with low frequency, and on V . natans at moderate loading with moderate frequency. For M . spicatum , no significant differences were found among the three NH 4 -N pulse patterns. Low light availability did not significantly aggregate the negative effects of NH 4 -N pulse on the growth of the submersed macrophytes. Our study contributes to revealing the roles of NH 4 -N pulse on the growth of aquatic plants and its species specific effects on the dynamics of submerged macrophytes in lakes.

Human activities markedly modify diversity patterns of plant communities and their response to environmental conditions, with subsequent consequences for ecosystem functions. We measured 11 key functional traits of 47 plant species and assessed both taxonomic and functional composition as well as above‐ground biomass (AGB) of plant communities from 127 plots in the Lake Dongting wetland. Using a generalized multilevel path model, we examined the cascading effects of hydrological gradients on plant diversity and ecosystem functions in two distinct habitat types (short grassland with a natural community dominated by Carex spp. and tall grassland with a managed artificial community dominated by Triarrhena lutarioriparia and Phragmites australis). We found significant differences in the response of plant diversity and AGB to hydrological gradients. Species richness, Shannon–Wiener diversity, multiple‐trait functional diversity measures (i.e., functional richness, functional dispersion & Rao's quadratic entropy) and community‐weighted mean (CWM) of shoot height were all significantly higher and functional divergence and CWM of tuber significantly lower in tall grassland. AGB was significantly higher in short grassland, largely driven by variations of functional diversity rather than of taxonomic diversity. Moreover, we found a significant cascading effect of elevation and soil moisture on AGB, directly or indirectly induced by changes in functional diversity in the short grassland, while only direct effects of elevation on AGB were observed in the tall grassland. Therefore, our study provides strong evidence that human‐induced changes in habitat types uncoupled the cascading effects of hydrological gradients on ecosystem functions mediated by either the taxonomic or the functional diversity.