Effect Of Woody Plant Diversity On Purifying Function Of Constructed Wetland Ecosystem

In this study,four woody plants including Ligustrum obtusifolium,Hibiscus mutabilis,Hibiscus syriacus,and Nerium oleander were selected.The artificial wetland microcosm was used as the experimental platform.The simulation experiment is equipped with 3 species richness levels(1,2,4)and 11 plant diversity combinations,namely 4 single colonies,6 two-species mixed colonies,and one four-species mixed colony to explore plant diversity The impact of nature on the purification effect of the constructed wetland ecosystem,plant growth,nitrogen and phosphorus accumulation,microbial diversity and community structure,provides a scientific basis for the selection and diversified configuration of constructed wetland species.The main conclusions are as follows:(1)As the species richness of constructed wetlands increases,the removal effect of constructed wetlands on pollutants is enhanced.The removal rate of TN,NH₄⁺-N,TP and TOC in the four-species mixed system is significantly higher than that of the single-species system.Different woody plant combinations have obvious differences in the purification ability of water bodies.Among them,the four-species mixed system of Ligustrum obtusifolium×Hibiscus mutabilis×Hibiscus syriacus×Nerium oleander has the best purification effect on TN and NH₄⁺-N,and the single Nerium oleander system has the best purification effect on TP and TOC.Under the same species richness,the species composition also has a great influence on the pollution removal of constructed wetlands.The presence of Nerium oleander has a significant positive effect on the removal of water pollutants;the presence of water wax has a negative effect on the removal of water pollutants.(2)With the increase of species richness,the aboveground,underground and total growth of constructed wetland plants have an upward trend;there are no significant differences in the underground growth,aboveground growth and total growth of wetland systems under different species richness.In terms of species composition,the single-species system of Nerium oleander has the highest underground growth,above-ground growth and total growth,and the single-species system of Hibiscus mutabilis has the lowest.(3)With the increase of species richness,both the N and P accumulations of constructed wetland plants have an upward trend.There is no significant difference in the N and P accumulations of the constructed wetland microcosm under different species richness.The plant with the strongest N-enrichment ability is the Hibiscus mutabilis×Nerium oleander hybrid system,and the plant with the strongest P-enrichment ability is the Nerium oleander single species system.The existence of Nerium oleander has a significant positive effect on promoting the absorption and assimilation of N and P elements in the environment by woody plants.(4)With the increase of abundance,the five diversity indicators of Chao1,Simpson,Shannon,Pielou's evenness,Faith's PD,etc.all have an upward trend,but the correlation is not significant.The bacterial Simpson index not only has a significant positive effect on NH₄⁺-N removal rate,TN removal rate,and TP removal rate.Shannon index has a significant positive correlation with NH₄⁺-N removal rate,while Chao1 index has no significant correlation with TN,NH₄⁺-N,TP and TOC removal rate.Among the 11 woody plant combinations,the evenness of the bacterial community in the Ligustrum obtusifolium×Nerium oleander group,Ligustrum obtusifolium×Hibiscus mutabilis×Hibiscus syriacus×Nerium oleander group is higher,and the evenness of the bacterial community in the Hibiscus syriacus group is the lowest.The Faith's PD index was the highest in the Ligustrum obtusifolium×Nerium oleander group,and the Faith's PD index was the lowest in the Hibiscus syriacus group.(5)In constructed wetland matrix bacteria,Proteobacteria and Firmicutes dominate at the phylum level,followed by Cyanobacteria,Actinomycetes,and Patescibacteria;at the genus level,Clostridium sensu stricto 1,Clostridium sensu stricto 5.Saccharimonadales is a common dominant genus of woody plant constructed wetlands.