Growth of Potamogeton crispus L. from turions in darkness: Implications for restoring submerged plants in eutrophic lakes

Abstract

In the turbid water of eutrophicated lakes, sunlight becomes the primary limiting factor in restoring submerged plants in such lakes. Potamogeton crispus L., a species of pondweed, is widely used in such restoration because it can be easily propagated through its turions. However, little is known so far of the growth characteristics of turions growing under limited light or even in total darkness. The growth and physiological responses of plants raised from small, medium, or large turions (categorized on the basis of their weight) and growing in total darkness in an aquarium showed that plants raised from small turions were significantly shorter (33.4±4.8cm) than those grown from medium or large turions (49.9±4.3cm and 46.9±7.4cm, respectively; the difference between the two categories was not significant) when measured on the average of 48th, 62nd and 69th days after planting. Although the plant biomass was significantly different among the three groups of turions, it remained virtually the same within each group throughout. Plants raised from the three categories of turions, however, did not differ significantly either in terms of root length or with respect to soluble protein contents and peroxidase activity; the last parameter increased significantly after 48 days in all the three categories, whereas the activity of superoxide dismutase increased significantly after 62 days. These observations indicate that P. crispus plants growing in total darkness suffer from stress due to antioxidants, especially after 48 days of culture. Therefore, it is recommended that larger turions be chosen for planting and that suitable measures be taken to ensure that at least some light reaches the plants 48 days after planting. Three formulas are presented, depending on the level of turbidity and the weight of turions, to calculate the maximum water depth at which P. crispus could survive for restoration of P. crispus in eutrophic lakes.