Effects Of Ecological Factors On Invasion Of Hydrocotyle Vulgaris Into Plant Communities

Exotic plant invasion is an important topic in the field of ecology. Factors influencing the invasion of alien plants are manifold. Productivity, the inter-specific and the intra-specific interaction of native or exotic plants may be changed by the biotic and abiotic part of the ecosystem. Hydrocotyle vulgarisis an exotic species which widely spreads in south China, demonstrating the invasiveness of this species. But few studies focus on the inter-specific relationship between the native plant community and H. vulgaris. In the research, four experiments were carried outto test the efforts of nutrient levels, community stage, aquatic and terrestrial habitats and interference of fragmentation on invasive alien plant H. vulgaris, which indicated some information to the management of exotic plants.Nutrient levels and plant community were set up to study the effort of nutrient levels on plant communities defend invasion of H. vulgaris. The results indicated that high nutrient level significantly increased the traits of H. vulgaris planting alone, but it had no significant effort on the H. vulgaris planting with the terrestrial plant community. High nutrient level significantly increased the biomass of the terrestrial plant community, and reduced the RDI of H.vulgaris.Species diversity and different growth stages of plant communities were set up to study the effort of species diversity and growth stages on plant communities defend invasion of H.vulgaris. The results indicated that increasing of species richness did not change the inter-specific interaction between terrestrial plant community and H.vulgaris. Time factor changed the inter-specific interaction between terrestrial plant community and H. vulgaris, and community which grew in shorter time and had more legume species revealeda more fierce competition with H.vulgaris.Aquatic and terrestrial habitats, with or without nitrogen deposition were set up to study the effort of habitats and nitrogen deposition on wetland plant communities defend invasion of H. vulgaris. Compared to the non-flooded treatment, the total mass, leaf mass, numbers of leaves and nodes, and relative dominance of H. vulgaris were significantly lower in the flooded treatment. Nitrogen deposition significantly increased the numbers of leaves and nodes in the unflooded treatment. Total mass of the other plant species combined and of P. cordata and M. aquaticum individually were significantly greater in flooded than in unflooded treatments. Neither nitrogen deposition nor the presence of H. vulgaris affected the biomassordiversity of the other four plant species.Different levels of fragmentation were set up to study the effort of fragmentation on the interrelation of wetland plant communities and H. vulgaris. The result indicated that fragmentation significantly reduced the leaf area of H. vulgaris. And there was no significant difference between different levels of fragmentation. Fragmentation of H. vulgarishadno significant effort on the aquatic plant community.This research showedthat high nutrient treatments enhanced the resistance of terrestrial plant communities, but weakened the resistance of aquatic plant communities. Inter-relation of plant communities and H. vulgaris depended on the time scale, but hadlittle relation with species richness. Invasion of H. vulgaris will not seriously affect the local plant communities. This reach is the first report systematic study of the effort of three part of ecosystem on the inter-specific relationship between native species and H. vulgaris. The research would provide theoretical basis to manageearly warning, invasion and spreadof exotic plants.