Allelopathic Suppression of Cyanobacterial Blooms by the Aquatic Plant Vallisneria natans Enhanced by Red and Blue LED Light Supplementation

Using allelochemicals produced by submerged plants to inhibit algal growth is an environmentally friendly approach to controlling harmful algal blooms in eutrophic lakes. This study aimed to evaluate the inhibition of cyanobacterial growth by allelochemicals accumulated by the aquatic plant Vallisneria natans, with enhancement through blue and red light-emitting diode (LED) supplementation. We conducted a laboratory experiment to assess the fluorescence parameters, enzyme activities, and phycocyanin contents of cyanobacteria Microcystis aeruginosa grown in different V. natans cultivation media. The fluorescence parameters in the BG-11 medium remained stable, but sharply decreased in both LED treatments, with nearly 100% inhibition observed after 12 h of incubation. Superoxide dismutase (SOD) and peroxidase activities were stable in the BG-11 treatment, but enhanced in both LED treatments, reaching maximum values within 48 h. Higher SOD activities were observed with blue LED compared with red LED, suggesting better performance with blue light. A constant high phycocyanin fluorescence intensity was observed in the BG-11 treatment, while both LED treatments showed lower intensities. These results provided strong evidence that LED supplementation enhances the inhibitory effects of V. natans on M. aeruginosa growth. The combination of aquatic plant growth with underwater LED light supplementation offers a promising approach to controlling cyanobacterial blooms.