Due to eutrophication submerged macrophytes have disappeared from many Chinese lakes. This is unfortunate as submerged macrophytes are important to improve water quality, and its re-establishment is therefore desirable. For this purpose a potential method to use is re-seeding, this being particularly attractive due to the high seed productivity of V. natans. We conducted laboratory studies to investigate the effects of five environmental variables (temperature, substratum, oxygen, light availability, and burial depth) on the seed germination of V. natans. Our results showed that a wide temperature range (25-35°C) was favorable for germination; that seeds germinated well under both gravel and silt; that anaerobic condition proved to accelerate seed germination although the final germination percentage did not rise; and that light and burial acted as limiting factors. These results suggest that V. natans is a potential candidate for successful restoration of vegetation in lakes recovering from eutrophication.

Seedling survival and growth of two common Vallisneria species in China, Vallisneria natans and Vallisneria spinulosa were quantified experimentally for current velocities from 0 to 40 mm/s. At the same time, changes in the concentrations of three hormones (IAA, ZR, and GA 3 ) in the leaves were compared to identify how current velocity influenced the two Vallisneria seedlings growth discrepantly. All plants survived in all treatments and showed positive growth. The most rapid growth for both species was found at the velocity of 10 mm/s. Although V. spinulosa showed faster growth than V. natans at the beginning of the experiment, there was no significant difference on final biomass. Higher IAA and ZR contents were measured in seedlings of both species grown under low current velocity. The time reaching the maximum for IAA and ZR was just around the time of a maximum seedling growth rate. IAA and ZR contents were positively correlated with growth rate. However, GA 3 was negatively associated with growth rate and more GA 3 in V. natans seedlings was induced by high current velocity.

The riparian zones of reservoirs associated with regulated rivers in China experience annual fluctuations in water level of up to 30 m that may vary in timing from year to year. Few plant species can tolerate such hydrological perturbation but short-lived riparian annuals might be evolutionarily pre-adapted to such conditions. This study investigated plasticity of life history in four annual species: one typically associated with free-flowing rivers (Panicum bisulcatum) and three that colonize reservoir margins (Cyperus michelianus, Fimbristylis miliacea and Eclipta prostrata). We found that all four species produced non-dormant seeds that survived prolonged submergence; germination percentage was independent of the time of exposure by receding waters. Although growth was reduced as a result of shorter growing seasons, all four species completed their life cycles and produced seeds before winter. In addition, P. bisulcatum and C. michelianus allocated biomass to seed production, at the expense of roots and stems, in response to later establishment. All species responded to later establishment with a reduced vegetative growth period before seed production. C. michelianus, F. miliacea and E. prostrata could also delay the onset of flowering time by up to 2 months. P. bisulcatum, a plant that can flower only after exposure to short days, consequently had a fixed flowering time and could accommodate delayed establishment only with a progressively shorter period of vegetative growth. This lower flexibility might explain its absence from reservoir margins. The conceptual framework presented here offers a tool to predict the establishment of vegetation under hydrological disturbance in riparian environments and thereby provides insights into improved restoration practice.