Abstract: The study with in-door experiment showed that the germination and seedling rates of Potamogeton crispus were increased under light but without matrix. Matrix promoted root growth, but light could not. The internode’s length was obviously longer under dark than under light. After treated with dark, the permeability of leaf plasma membrane raised apparently. Under light condition, the Chla and Chlb contents and Chla/Chlb ratio of seedling’s leaf fluctuated, depending on with or without matrix. The maximum and minimum value of Chla/Chlb ratio was 4.4 and 2.8, respectively when the matrix existed, and was 4.2 and 2.7 when the matrix was absent. After 40 days of seedling growth, there was a significant difference in the permeability of leaf plasma membrane between the treatments with light and matrix, and with light but without matrix (P＜0.01). A significant difference was also observed in F_v/F_m, and F_v/F_o at the late growth period between the treatments of full (100%) and partial (50%, 20% and 10%) natural light, while no significant difference was found between the treatments of different partial natural light. It was suggested from the measurements of F_v/F_m, F_v/F_o, ETR, qP and qN that weak light promoted the photosynthesis, and slowed down the senile of P. crispus.

Key words: Filter feeding bivalves, Phytoplankton, Indirec t enhancement effect, Community proliferation