Comparative Studies On Applicability Of Different Woody Plant Species To Constructed Wetland In The Subtropical Area

As a main part of constructed wetland system,plant plays an important role in wastewater purification and landscape beautification.To increase plant diversity and improve purification capacity of constructed wetland,ten woody plant species,including Adina rubella,Ligustrum japonicum‘Howardii',Salix rosthornii,Callicarpa dichotoma,Nerium oleander,Hibiscus mutabilis,Pittosporum tobirai,Distylium buxifoliumi,Ligustrum obtusifolium,and Ligustrum lucidum were studied by establishing the micro-universe systems of constructed wetland.Their adaptability,enzyme activity of matrix at rhizosphere,decontamination ability,and purification effect were analyzed,and their applicability was comprehensively evaluated by hierarchical clustering analysis.The main resulus are as follows.Seven plant species,including Adina rubella,Salix rosthornii,Callicarpa dichotoma,Nerium oleander,Hibiscus mutabilis,Ligustrum obtusifolium,and Ligustrum lucidum,could survive in the constructed wetlands,while three species,Ligustrum japonicum‘Howardii',Pittosporum tobirai,and Distylium buxifoliumi,couldn't adapt to the environment of constructed wetland and died.Survival rates of four plant specieswere 100%,including Adina rubella,Salix rosthornii,Callicarpa dichotoma,and Nerium oleander.Biomass growth had significant differences among various species of woody plants.The biomass growth of Nerium oleander was the highest among different woody plants.The second is Callicarpa dichotoma.Biomass growth of the seven species of plant in descending order is Nerium oleander,Callicarpa dichotoma,Salix rosthornii,Adina rubella,Hibiscus mutabilis,Ligustrum obtusifolium,Ligustrum lucidum.There were also significant differences in photosynthetic characteristics among different plants.Salix rosthornii had the highest maximum photosynthetic rate,followed by Nerium oleander,Adina rubella,Hibiscus mutabilis,Callicarpa dichotoma.And the maximum photosynthetic rates of Ligustrum obtusifolium and Ligustrum lucidum were close to zero.The maximum photochemical efficiency of Ligustrum lucidum was 0.732,which was significantly lower than that of the other six species of plant,indicating that its growth was stressed.Adina rubella,Salix rosthornii,and Nerium oleander had higher chlorophyll content,while Ligustrum lucidum is the lowest.According to biomass growth and photosynthetic physiological characteristics in the constructed wetlands,adaptability of Adina rubella,Salix rosthornii,Callicarpa dichotoma,Nerium oleander,and Hibiscus mutabilis were strong,while that of Ligustrum obtusifolium and Ligustrum lucidum were weak.Ligustrum japonicum‘Howardii',Pittosporum tobirai and Distylium buxifoliumi couldn't adapt to the environment of constructed wetland.The purification effects of different woody plant species in the constructed wetlands on TN,TP,NH₄⁺-N,and COD were significantly different.The constructed wetland with Salix rosthornii c had the highest effect on purifying TN,TP,NH₄⁺-N,and COD,whereas the purification effects of constructed wetland with Ligustrum obtusifolium and Ligustrum lucidum were poor.The N and P accumulation of different woody plant species in the constructed wetlands were significantly different.The ability of Callicarpa dichotoma and Nerium oleander to absorb and store N and P were stronger among seven survived plants,while the N and P accumulation of Ligustrum obtusifolium and Ligustrum lucidum were weaker.The direct purification capacity of different plants to TN was successive as follows:Nerium oleander>Callicarpa dichotoma>Salix rosthornii>Adina rubella>Hibiscus mutabilis>Ligustrum lucidum>Ligustrum obtusifolium.The direct purification capacity of different plants to TP was successive as follows:Nerium oleander>Callicarpa dichotoma>Salix rosthornii>Adina rubella>Hibiscus mutabilis>Ligustrum lucidum>Ligustrum obtusifolium.In the constructed wetlands,the presence of plants can increase phosphatase and urease activity of matrix.There were significant differences in phosphatase and urease activity of matrix at rhizosphe of different plant species.Salix rosthornii had the highest phosphatase activity of matrix at rhizosphe in,which was 2.2 times higher than CK and significantly higher than that of other plant species,followed by Nerium oleander,Adina rubella,and Hibiscus mutabilis.Ligustrum obtusifolium had the lowest phosphatase activity of matrix at rhizosphe.Among the seven plant species,Salix rosthornii also had the highest urease activity of matrix at rhizosphe,50.6 times higher than CK,followed by Callicarpa dichotoma,Nerium oleander,and Hibiscus mutabilis.Ligustrum lucidum had the lowest urease activity of matrix at rhizosphe Based on the analysis of enzyme activities of matrix at rhizosphe,Salix rosthornii,Nerium oleander,and Hibiscus mutabilis have higher potentials in purifying nitrogen and phosphorus.According to the comprehensive evaluation of the applicability of the 10 woody plant species,they can be divided into four groups.The first group is with excellent applicability for constructed wetland,including Callicarpa dichotoma,and Nerium oleander.The second group is with moderate applicability for constructed wetland,including Adina rubella,Hibiscus mutabilis,and Salix rosthornii.The third group is with poor applicability for constructed wetland,including Ligustrum obtusifolium and Ligustrum lucidum.The fourth group cannot adapt to constructed wetland,including Ligustrum japonicum‘Howardii',Pittosporum tobira and Distylium buxifolium.