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We examined the stable carbon and nitrogen isotope variation in the submersed macrophyte Vallisneria natans in several shallow Chinese lakes relative to physicochemical parameters of the lake water and V. natans tissue. Of the parameters examined, the δ15N values of V. natans were correlated only with different inorganic nitrogen concentrations in the water column, suggesting that V. natans could be a sensitive bioindicator for monitoring nitrogen input into lakes. The δ 13C of V. natans varied widely and was correlated only with the inorganic carbon concentration of the water, possibly reflecting complex photosynthetic fixation and adaptations of V. natans to utilize inorganic carbon sources of different types. [ABSTRACT FROM AUTHOR]

The growth, morphological traits, and biomass accumulation and allocation pattern of Vallisneria natans grown from buds were observed in a non-rooted suspended state in the laboratory. Submersed anchored V. natans were about 229% higher in height, 208% higher in leaf number, 719% greater in total root length, 64% higher in lacunal root volume, and 1473% greater in total biomass dry weight compared with suspended V. natans. However, insignificant differences existed in root diameter, specific root length, and biomass allocation patterns. These results indicate that when V. natans is not anchored to a substrate in the normal mode, the growth will be markedly suppressed. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to investigate seed germination under natural temperature and light regimes and to evaluate the influence of freshwater microalgae on seed germination of three Vallisneria species. Seeds exposed to natural seasonal temperature and light changes for 24 months germinated only in spring, perhaps indicating an annual dormancy/non-dormancy cycle. The ecological background of the natural habitat seems to play predominant roles in seed germinability. Mean cumulative seed germination percentages of Vallisneria natans, V. denseserrulata, and V. spinulosa of the first year were 35.2, 19.2, and 11.2%, respectively, and of the second year were 80, 72, and 32.4%, respectively. Germination rates differed significantly among the three Vallisneria species exposed to natural seasonal temperature and light changes in the first year, but differed only between Vallisneria spinulosa and the other two species in the second year. The differences of germination may influence the geographical distribution and thus be related to different survival strategies of the species. Seed germination rates in culture solution inoculated with algae were significantly higher than in solution with no algae. A strong correlation occurred between total biomass of freshwater microalgae and seed germination of the three studied species. Apparently, the extracellular products of freshwater microalgae may play an important role in seed germination. These results support the hypothesis that Vallisneria colonization may be mediated by algae facilitation. [ABSTRACT FROM AUTHOR]