| Asexual reproduction is the main way for aquatic plants. The influence of environmental factors on asexual reoriduction may affect the population dynamic state, distribution pattern and community structure of aquatic plants. These will finally alter the performance of aquatic ecosystem. To understand the influence of environmental factors on asexual reoriduction of aquatic plants has great means on theory and practice. The environmental factors include biological factors and non biological factors. Most of previous studys paid attention on effect of non biological factors, there are only a few studys about the effect of biological factors which are important on ecology such as population atate and community structure, and the stuys on interaction of them are even less. Water nutrient is a important influence factor for aquatic plants, however not like sediment nutrient, there are few studys about the effect of water nutrient on asexual reproduction of aquatic plants. We studied the influence of water nutrient, population density, community structure and their interactions on a cosmopolitan species, submerged macrophytes Potamogetonaceae Potamogeton crispus L., and inveatigated the asexual reproduction strategy of Potamogetonaceae Potamogeton crispus. The main contents and conclusions are as follows.1. Significant differences were found between different communities on production of P. crispus turions and success rate of P. crispus asexual reproduction. And increase of P. crispus plant density would be advantageous to both production of P. crispus turions and success rate of P. crispus asexual reproduction in every community. The experiment planted germinative P. crispus turions with different densities (2,4,8) into different aquatic plant communities{Potamogeton maackianus community, Myriophyllum spicatum L. community, Hydrilla verticillata community, Potamogeton maackianus+Myriophyllum spicatum L.+ Hydrilla verticillata community) in glass steel tanks. After two growth seasons, we found that P. crispus planted in communities which include Potamogeton maackianus produce significantly fewer and smaller turions, and the P. crispus population declined either, even extincted from the communities. However, P. crispus produced alarge number of turions and the population increased rapidly when planted in Hydrilla verticillata community. P. crispus could exist and increase slowly in Myriophyllum spicatum L. community. High population density could increase the production of P. crispus turions in all kind of communities, however it could not avoid the decline of P. crispus population in communities which include Potamogeton maackianus.2. We found that P. crispus turions can be classify to different types. High water nutrient enhanced the production and average biomass of P. crispus turions and altered the proportion of different types of turions. High population density increased the total turion production of P. crispus population but decreased the turion production of one single P. crispus plant, and altered the proportion of different types of turions. Other aquatic plants in community significantly decreased the production of P. crispus turions and altered the proportion of different types of turions. The experiment planted germinative P. crispus turions with different densities (3,12) into different aquatic plant communities (bare land, Potamogeton maackianus+Myriophyllum spicatum L.+Hydrilla verticillata community) in glass steel tanks. The tanks were filled with water under different nutrient level:fresh lake water (N 0.71±0.01 mg/L, TP 0.04±0.01 mg/L), water added ammonium nitrate (TN 2.00±0.02 mg/L, TP 0.04±0.01 mg/L), water added potassium dihydrogen phosphate (TN 0.71±0.02 mg/L, TP 0.20±0.01 mg/L). The experiment continued for a complete life history of P. crispus. We learned that P. crispus turions can be classified to small type which has 3 to 4 axillary buds and large type which has over 5 axillary buds, there are great differences between small and large turions on size and biomass. P. crispus produced few only large turions in Potamogeton maackianus+Myriophyllum spicatum L.+Hydrilla verticillata community, and in this condition water nutrient had hardly any effects but high population density could increase a few turion production. High population density increased the total production of turions and the ratio of small turions, however it drcreased the production of one single P. crispus plant. High water nutrient level increased the production and average biomass of turions, and high phosphorous content will alleviate the effect of high population density.3. We tested the differences between small and large turions on competitive ability and reproductive performance. The experiment planted germinative P. crispus turions with different densities (6,12) and different proportions (2:1,1:1,1:2) in glass steel tanks. After a growth season, there was no significantly different between small and large turions on competitive ability and reproductive performance. The population density affected both reproduction of turions and vegetative growth of P. crispus. The biomass and the number of ramets of one single P. crispus plant were significantly higher in high density population, and the turion production per ramet was also higher, however the turion biomass per ramet was lower.4. To discuss the results of the experiments, we found that P. crispus plants achieve its asexual reproduction strategy based on producing different proportion of small and large turions by one single remat. A single remat will produce at least one large turion under any possible situation. If the environment is fit for it, a remat continue produces large turion, otherwise it will produce multiple small turions. One P. crispus plant always has many remats, and the habitats of the remats can hardly be the same fitness. The sum of the strategies of the remats living in different microhabitats compose the strategy of one single P. crispus plant. |
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