The negative effects, caused by high light, on algae, terrestrial and marine aquatic plants are well documented, those negative effects on freshwater submerged plants are, however, not well known. We determined the negative effects of two common submerged species, Myriophyllum spicatum and Vallisneria natans, on their growth and reproduction in a shallow water experiment along an irradiance gradient. Our results highlighted that the plant mass, relative growth rate (RGR) and shoot height of V. natans and M. spicatum, and root mass and root length : root mass of M. spicatum and leaf mass and shoot height : shoot mass of V. natans were significantly negatively affected in shallow water with high light regime (> 50% of full light). While the ramet number of the two species was stimulated by from 20.0% to 36.4%, and root length, root : shoot, chlorophyll (a : b), chlorophyll (a + b), leaf carbon, nitrogen and phosphorus contents of the two studied macrophytes were not significantly impacted by light. Our results indicated that the high light inhibition of plant growth were greater on the shoots than on the roots of the plants, although these effects were significantly different between the two studied submerged species and among the measured traits. Accordingly, we should avoid negative effects caused by high light to improve the performance of submerged species when we conduct submerged aquatic vegetation restoration programs in eutrophic lakes.

Background The effects of biodiversity on community function and services are frequently studied in the history of ecology, while the response of individual species to biodiversity remains great elusive. In this study, we determined the biodiversity effects on community productivity as well as species level plant mass and carbon (C) and nitrogen (N) metabolism of eight submerged plants. These macrophytes in Lake Erhai were selected and planted in a water depth of one meter along a diversity gradient of 1, 2, 4 or 8 species. Then, the community productivity or species level plant mass, soluble protein, free amino acid and soluble carbohydrate were correlated to species richness to determine the biodiversity effects on community and single species. Results The results showed that the community level biomass was positively correlated to plant species richness although the species level plant mass of individual species responded differently to the overall plant species richness. Namely, only one plant mass positively correlated to species richness and the others decreased or showed no significant correlation with the increase of species richness. The soluble proteins of most macrophytes were positively correlated to species richness; however, both the free amino acid and soluble carbohydrate of the plants were negatively or not significantly correlated to species richness. Conclusions These results indicated that the selection effects might dominate in our aquatic communities and the negative impacts of biodiversity on C and N metabolism of the macrophytes increased with the increase of species richness, which might result from the strong competition among the studied species. The biodiversity effects on the plant mass, and C and N metabolism of individual submerged species were first reported in this study, while more such field and control experiments deserve further research.

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