Genetic Variation Of Aquatic Macrophytes In Diverse Environments And Their Phenotypic Adaptation To Interference

Aquatic macrophytes (Myriophyllum spicatum L., Ceratophyllum demersum L., Hydrilla verticillata (L. f.) Royle, Nymphoides peltatum (Gmel.) O. Kuntze and so on) are important components of plant communities in wetland ecosystems. Because of human interference, these aquatic plants have to adapt to new environmental conditions. In this study, ISSR molecular marker technique was used to analyze genetic diversity of aquatic macrophytes. We also simulated flooding and mechanical perturbations to explore the adaptative responses of these plants to interferences. The results were as follows:1. We collected177samples of M. spicatum from five lake populations (Erhai Lake, Caohai Lake, Taihu Lake, Honghu Lake and Liangzihu Lake; including34subpopulations) for genetic analysis. Twelve ISSR primers were used and we found the ratio of amplified polymorphic bands was up to100%. Genetic diversities of the five lake populations were different. Genetic diversity of Erhai Lake was the highest and Taihu population had the least diversity. Genetic variation among populations was28.14%, among subpopulations17.42%and within subpopulations54.45%, indicating that most of the variation occurs within populations and subpopulations. Genetic differentiation coefficient among Erhai subpopulations was the largest and that among Caohai subpopulations was the least. Genetic distance and geographic distance was positively correlated among subpopulations within a lake, but the genetic distance and geographic distance did not have significant correlative relationships among populations, suggesting that geographic isolation may not be the main reason for genetic differentiation. One of the possible explanations is the long-term adaptation of the populations to local environmental factors.2. One hundred and seventy-four samples of C. demersum were collected from five lakes as above and Weishanhu Lake (including33subpopulations) for genetic analysis. Nine ISSR primers were used and we found the ratio of amplified polymorphic bands was up to100%. Genetic diversity of Taihu Lake was the highest and population of the Liangzihu had the least diversity. Genetic variation among populations was32.50%, among subpopulations21.44%and within subpopulations46.06%. Genetic differentiation coefficient among Erhai subpopulations was the largest and among Caohai subpopulations was the least. Genetic distance and geographic distance was positively correlated among subpopulations within a lake, but the genetic distance and geographic distance did not have significant correlative relationships among populations.3. Hydrilla verticillata, M. spicatum, C. demersum are submerged plants. The biomass and the growth rate of H. verticillata and C. demersum in the control treatments were higher than those in the simulated flood treatment, but those of M. spicatum in the50cm water were the highest. When these three species were cultivated in mixture, H. verticillata had a significant competitive advantage and was able to adapt to flooding under the experimental conditions. However, M. spicatum and C. demersum showed negative growth rate; M. spicatum adapted to the flood by increasing the content of total nitrogen in plants, and C. demersum mainly depended on morphological plasiticity to adapt to changes in water levels.4. Myriophyllum spicatum and N. peltatum were treated with three different levels of mechanical interference. Plants of M. spicatum interfered could not grow as well as those in control treatments. However, N. peltatum could tolerate moderate to severe interference by regulating biomass allocation into organs.