Effects Of Interspecific Competition And Species Richness Of Emergent Plants On Water Quality In Aquatic Ecosystems

Eutrophication refers to the destruction of the structure and function of aquatic ecosystems due to the input of large amounts of exogenous nutrients.Aquatic plants can efficiently and continuously absorb nitrogen and phosphorus and promote the restoration of ecological functions of aquatic ecosystems,thus being widely used in ecological restoration.In theory,the combination of aquatic plants can promote the absorption of nitrogen and phosphorus.However,little attention has been paid to whether the changes in interspecific relationships brought by different plant combinations affect the efficiency of water purification.In this thesis,six common and ornamental emergent macrophytes were selected.According to the characteristics of plant growth and plant type,the six plants were classified into three growth forms,namely Slender type: Schoenoplectus tabernaemontani and Typha orientalis;Flat type: Iris sibirica and Acorus calamus;and Large type: Canna indica and Thalia dealbata.Three combination treatments were set up,monoculture,a two-species mixture(plants of the same growth form are mixed),and a six-species mixture to explore the effects of interspecific competition and species richness on plant growth and nutrient dynamics in aquatic environments,while exploring the effects of growth form on nutrient absorption.The result showed that interspecific competition lead to a decrease in the biomass of species with weaker competitive ability.There was no significant difference in the removal of total nitrogen and phosphorus between monocultures and two-species mixtures,indicating that interspecific competition did not affect the ability of emergent macrophyte communities on nitrogen and phosphorus absorption.For slender and flat growth forms,the strength of interspecific competition of the same growth type is probably weakened due to sufficient nutrient supply.For large plants,it may be that the plants have a strong assimilation ability for nitrogen and phosphorus,and the two can still maintain stable growth in the face of fierce interspecific competition.Additionally,there were significant differences in the removal of nitrogen and phosphorus among different growth forms,and the removal efficiency by large plants was significantly higher than that of slender and flat forms.The six-species mixture significantly improved the efficiency of emergent macrophyte community in water purification,which may be due to the complementation of ecological niches among different plants,in turn promoting resource utilization of the community as a whole.Secondly,the increased species richness may promote more development of microbial communities.Finally,the presence of key species,such as the large type plants,Canna indica and Thalia dealbata,may facilitate the positive interaction between roots and microorganisms,dominating the purification efficiency of the community.In summary,the negative effect of interspecific competition on plant biomass did not affect the absorption of nitrogen and phosphorus,which suggests that the assimilation of plants is not the only way to remove nutrients from aquatic ecosystems,and rhizosphere microorganisms may play a non-negligible role.The improvement of species richness realizes the division of ecological niches among species,promoting the flow of nutrients among plant communities.In addition,the characteristics and functions of specific emergent species should not be ignored.Therefore,in the actual practice of plant community constructions,it is necessary to take into account the characteristics of plant themselves and the selection of key species.Meanwhile,species richness should also be considered,in order to facilitate the complementary role of ecological niches among species,hence promoting the stability of plant community structure and function,as well as the self-sustainment and balance of aquatic ecosystems.