Responses of the submerged macrophyte Vallisneria natans to a water depth gradient.

This study investigated responses of the submerged macrophyte Vallisneria natans to a water depth gradient of 0.3-1.5 m in shallow lakes, and examined changes of morphology, physiological parameters, leaf-epiphytic bacteria community, and water purifying ability. Results of the morphological and physiological parameters (shoot height, root length, total chlorophyll, contents of soluble protein (SP) and malondialdehyde, activities of superoxide dismutase, catalase, peroxidase, glutamine synthetase, and alkaline phosphatase) indicated that 0.9-1.2 m was the optimal water depth for planting. Vallisneria natans suffered photoinhibition at the shallow water depth of 0.3-0.6 m and lipid peroxidation damage in water 1.2-1.5 m deep. Microbial analyses indicated that at the water depth of 0.6 m, the accumulated cyanobacteria led to the suppression of microbial organics decomposition and nutrient metabolism in the leaf biofilms. The water quality indicators (chemical oxygen demand, total nitrogen, total phosphorus, and fluorescent dissolved organic matter) also confirmed that 0.9-1.2 m was the optimal planting depth of Vallisneria natans. The results of this study provided theoretical guidance and technical support for the restoration of submerged macrophytes in natural shallow lakes.