Impacts of Animal Herbivory and Water Depth on Seed Germination and Seedling Survival of Vallisneria natans (Lour.) Hara and Hydrilla verticillata (L. f.) Royle

摘要

Seed germination is an important reproductive pattern for submerged macrophytes. In order to investigate the effects of animal herbivory and water depth on seed germination and seedling survival of Vallisneria natans and Hydrilla verticillata, we conducted an in-situ field experiment at 3 water depths (0.5, 1, and 2 m) with net and non-net (control) groups in Hangzhou West Lake, China. The results showed that the highest germination rates appeared at 1 m water depth and the lowest germination rates appeared at 2 m water depth (p0.05) for both species. The mean time to germination (MTG) values that indicate the velocity of germination are greater at 2 m water depth than that at 0.5 m and 1 m water depths for both V. natans and H. verticillata. Net protection obviously promoted germination rates of both species at 0.5 m and 1 m depths, especially for H. verticillata at 1 m (p0.05). Germination rates of H. verticillata were higher than that of V. natans under any treatment (p0.05). In the control, seedlings of both species were greatly grazed by herbivorous animals and the remaining seedling number showed no significant difference at different depths (p0.05). Remaining seedling number in net group was significantly higher than that in control group (p0.05). Grazing rate of H. verticillata was significantly higher than that of V. natans in control group at all 3 depths (p0.05). Conclusively, both water depth and animal herbivory significantly influenced germination of V. natans and H. verticillata, and net protection proved to be an efficient method that could promote seedling survival for both species in the field.