Water quality profits by the submerged macrophyte community consisting of multi-functional species-rich groups

The re-establishment of submerged macrophytes facilitates the formation of a clear-water state in shallow eutrophic lakes. But most restorations of submerged macrophytes are often unstable and cannot maintain a stable clear-water state, probably because the species and functional diversity have not been fully taken into account. In this study, we try to explore submerged macrophyte communities and water quality changes under different submerged macrophyte combinations through mesocosm experiments. We hypothesized that communities with high species and functional diversity would be more conducive to improving water quality. The results showed that the mean community biomass of single-species and 8-species were higher than 5-species. And the stability and mean relative growth rate of the 8-species community were higher than the 5-species community. With the same configuration of three functional groups, the 8-species community was more stable and had better water quality than the 5-species community. The path analysis revealed that different functional groups of submerged macrophytes play different roles. The erect and canopy-producing submerged macrophytes were conducive to reducing total suspended solids (TSS) concentrations in the water column during community construction. In contrast, bottom-dwelling submerged macrophytes were conducive to reducing total nitrogen, total phosphorus, and TSS concentrations during the stage of disturbances. Our results also suggested that canopy-producing groups may have a competitive advantage for light over bottom-dwelling species. Based on the above results and biodiversity insurance hypothesis, we conclude that the community consisting of multi-functional species-rich groups is conducive to building stable submerged macrophyte communities and obtaining a stable clear-water state. Our findings will improve water quality management and pollution control for eutrophic shallow lakes.