Effects of plant size on the growth of the submersed macrophyte Vallisneria spinulosa S.Z.Yan at different light intensities: implications for lake restoration

The growth and reproduction of plants are highly size-dependent and markedly affected by light intensity. Vallisneria spinulosa S.Z.Yan is a common submersed macrophyte and is widely used in current lake restoration projects. The size of plants to be used to get optimal restoration results is not known, however, and may vary with water clarity. In this study, the effects of different plant sizes (large, medium and small, i.e. approximately 2.40 g, 1.01 g and 0.27 g per plant) on the growth and reproduction of V. spinulosa were tested under three light intensities (high, medium, low, i.e. 25%, 6% and 1% of full sunlight, respectively). Both plant size and light intensity were found to be of great significance for plant growth and reproduction. The relative growth rate (RGR) of biomass was higher for small than for large plants at both high and low light, while the absolute growth rate (AGR) of biomass was higher for large-sized plants at medium and high light intensity. Asexual reproduction of V. spinulosa was positively correlated with plant size and more affected by plant size than by light intensity, while sexual reproduction was most affected by light intensity. RGR and AGR of plant height were highest for medium-sized plants at moderate light intensity. Therefore, the size of submersed macrophytes should be considered when using this species in connection with lake restoration. Verification of our results under field conditions is needed, though, before firm conclusions can be reached about the optimal plant size of V. spinulosa to be used in lake restoration as also other factors like, e.g. periphyton shading and wave actions may play a role.