EFFECTS OF WATER-DEPTH GRADIENTS, MATRICES, LIGHT AND REMOVAL OF PLANTLETS ON GERMINATION OF TURIONS OF POTAMOGETON CRISPUS L.

Potamogeton crispus L., as an important fodder source for herbivorous fish, can grow well in polluted lakes. However, seeds of the plant can rarely germinate in the nature, and thus sowing the plant turions has been considered as a major method for introduction of the plant. By field investigations and germination experiments, the authors investigated the effects of water-depth gradients on the germination rates of the turions in Lake Liangzi in Hubei Province of China and compared the results with those obtained from other four lakes also in the province. The effects of matrices, light and removal of the initial plantlets on the germination were also examined in the present study. In the environment with light, the turions displayed higher germination rates than those in the absence of light. However, the effect of different bottom matrices was not observed. Moreover, removal of plantlets had an increase impact on the further germination rates. Germinations of the turions in the five lakes were recorded at the beginning of July, with the average germination rates varying inversely with the average water depth through until December. From July to December, the deeper the water in Lake Liangzi, the lower the germination rates observed, indicating that increased water depth may caused delays of the germination. But, at the early December high germination rates of more than 95% were observed in all areas of the lake with different water depths. It is suggested that the high germination rates and the potential of germinating a second or third plantlet are probably two important mechanisms to maintain the plant as a dominant species in lakes.