Effect of light and nutrients on interspecific interactions between submerged macrophytes: implications for restoration of multispecies aquatic vegetation in eutrophic lakes

Constructing multispecies submerged vegetation systems and maintaining stable seasonal succession is crucial for restoring shallow eutrophic lakes. However, little is known about the interactions between successional and existing species of different growth forms, particularly under the low light and high nutrient conditions of eutrophic lakes. We measured the functional traits of mature Vallisneria natans(Lour.) Hara plants and Potamogeton crispus L. shoots in monoculture and mosaic patterns under different light and nutrient conditions. The effect of light on functional traits of the submerged macrophyte species was more significant than that of nutrients, but the reverse was true for P. crispus biomass allocation.Moreover, interspecific interactions affected only the submerged macrophytes under the low light condition and varied with species. Specifically, the interaction of P. crispus to V. natans was biased towards competition, while the interaction of V. natans to P. crispus was converted from facilitation to competition by eutrophication, particularly in the homogenous mosaic growth pattern. This study demonstrates that sufficient light is a prerequisite and patch planting is an effective means to form a multispecies submerged vegetation system. In addition, we emphasize that the coexistence of eutrophication and low light will likely result in a competition between submerged macrophytes thus simplifying the vegetation, even if their growth forms and growing seasons are different. These findings help explain the collapse of multispecies submerged vegetation and guide the restoration of aquatic plants in eutrophic lakes.