| Biological invasion has been occurring frequently in the south of China and cause serious damages. Since invasive plants in the north are often ignored, it will be difficult to control the spread once invasion forms. Sagittaria graminea, alien species, is found in wetland of Yalu River. For this alien plant, its reproductive strategies and ecological adaptability have only been known a little. Among the above studies, understanding the changes in reproductive strategies of S. graminea under different habitats could theoretically reveal the mechanism of certain alien species’improving ecological adaptability through their plasticity of reproductive strategies. Meanwhile, comparison between S. graminea (alien species) and S. trifolia (native species) might certain the effect of the possible population spreading of S. graminea on the local biological diversity. Besides, testing the introgression between S. graminea and S. trifolia. S. trifolia could estimate the possibility of forming natural hybrids, which is significant for the evolution pattern and ecological risk prevention of invasive species.This project aims to study the following four aspects of S. graminea:1) Testing the plasticity of reproductive strategies about S. graminea under different growthing conditions;2) Testing the ecological adaptability of S. graminea under different habitats;3) studying of introgression between S. graminea and S. trifolia;4) assessing ecological risk and control strategy of S. graminea(1) The alien plant S. graminea can reproduce sexually and clonally. Most S. graminea bloom and fruite between June and October. Under natural conditions, the germination rates>85%. S. graminea has strong asexual capacity. The corms only occurre beginning in the end of October, which are beneficial to S. graminea in excluding other species and forming mono-culture populations. These results suggest that the invasiveness of S. graminea is closely related to its reproductive traits.(2) Soil depth is significant influences on seed germination of S. graminea Seedling emergence is at its maximum (90.5%) on the soil surface but declined significantly with the increase of soil depth. Seedling emergence is significantly inhibited at buried depth of2cm. When depth in3cm, the seeding can not emerge. These results indicate that soil depth had significant influences on seed germination of S. graminea.(3) S. graminea weeds exhibite considerable nutrition-acclimation abilities. In a certain nitrogen range, root mass ratio (RMR) reduce with increasing nitrogen levels; total biomass, leaf mass ratio relative (LMR), flower and fruit mass ratio (FMR), total leaf area (TLA) and leaf area ratio (LAR), relative growth rates (RGR), branch number, as well as flower’s number increased with rising nitrogen levels. To phosphorus nutrient, LMR, LAR, TLA, RGR increase with rising phosphorus levels. It can adjust the reproductive traits by environment nutrient which promote its invasiveness in rich nitrogen and phosphorus environments.(4) Varied nutrient sources can influence the plasticity of reproductive strategies in monoecious species. We examine the plasticity of sexual and clonal reproductive components in distinct nutrient sources in a monoecious species, S. graminea. The results showe that for aboveground reproductive components, in rich-phosphorus and low-nitrogen conditions, the species produce more male flowers, whereas female flowers do not significantly increase in number compared to low-phosphorus and low-nitrogen conditions (control).In rich-nitrogen and low-phosphorus conditions, the species produce more flowers, particularly female, and more seeds, compared to the control conditions. In the rich-nitrogen and rich-phosphorus conditions, plants increase male flowers, female flowers, total flower number, synchronously, as well as seed production. For the belowground reproductive components, in the rich-phosphorus conditions, the plants produced bigger corms than in the rich-nitrogen and control conditions, which further enhanced their competitiveness against companion species. In rich-nitrogen conditions, the plants produce more medium and small corms, and relatively more and longer stolons, which are useful in expansion and invasion of more space. Furthermore, the species displaye trade-off relationships between the aboveground and belowground reproductive components in unbalanced nutrient conditions (add-N or add-P). However, in low nutrient levels (control) or in nutrient abundant (add-N+P) conditions, there are no significant trade-off relationships between the aboveground and belowground reproductive components, based on quantities.(5) The plants of S. graminea showe stronger tolerance on phosphorus and nitrogen conditions. Growth characteristics of S. graminea are curbed excess nitrogen.The relative growth rate is higher than controltreatment. They seem to develop a tolerance for nitrogen. Amounts of phosphorus can promote the growth of S. graminea.(6) Under low nutrient conditions×high density, relative growth rate, net assimilation rate, total biomass, leaf biomass, root biomass and flower biomass of S. graminea are significantly lower than other treatments. Under high nutrient×high density and high nutrient×low density conditions, relative growth rate, total biomass, leaf biomass, root biomass and flower biomass of S. graminea are larger as well as other treatments. Stem, root, leaf, flower and total biomass in S. graminea increase significantly with increasing nutrition, but decrease with increasing density.(7) The crossability of two species belonging to S. graminea and S. trifolia were studied in the aspect of seeding ratios of hybridization. Results showed the hybridizations of any combination among these two species were all successful and there were not obvious differences among seeding ratios of combinations. Group two involves the others, with higher seeding ratios of hybridization. Results of this study can contribute to furtherstudieson breeding of thisngenus, and also offer some references in studies on the phylogenesis of this genus. |
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