Studies On Plant Functional Diversity Of Constructed Wetland In Subtropical Zone

Constructed wetlands are a natural alternative to technical methods of wastewater treatment, and have consequently been widely applied for water quality amelioration. An integrated vertical flow constructed wetland was built in Hangzhou Botanical Garden, Zhejiang Provinec, China, to purify eutrophic water from Jade fish-seeing pond. In this paper, we studied the biological characteristics of the plants growing in this wetland and their landscape function, nutrient removal role of plants, photosynthesis of plants, rhizosphere microbe and soil enzymatic activity of plants, and purification efficiency and benefit of this constructed wetland.Integrated vertical flow constructed wetland had good purification performance and benefits for low eutrophic sightseeing water. Most indexes of its effluent reached or near the first class standard of Chinese surface water (GB3838-2002), such as NH₄-N, NO₃-N, TP, COD,BOD, etc. During operation of the constructed wetland, water quality in fish chamber could remain good status without changing water. And the operation of wetland also greatly reduced the underground water demand in the area, elevated the underground water level and restored the flow of the dried Jade Springs. Furthermore, this constructed wetland could bring great economic, ecological and social benefits.Plants are an important component of constructed wetland. This wetland system mainly collocated 26 species, belonged to 13 families. All plants were herbage, excepted Salix babylonica, which was arbor. Excepted Zizania caduciflora, Typha augustifolia and Iris psendacorus were hydrophytes, the other plants were mesophytes or wet-enduring plants. Based on height, these plants could be divided into 4 levels. Based on the growth period of plants, these plants could be divided into 5 types. The root depth of 12 species in constructed wetland was between 12.33 and 38.67 cm. The root biomass of these species was between 36.49 and 284.14 g m^-2 , and mostly centralized in the layer of 0¹0 cm.Through 105 days, mean total biomass ranged from 155 to 1317 g m^-2 for 17 plants. Except for Commelina communis, above /belowground biomass ratios of plants varied between 1.18 and 4.29. Aboveground concentrations of nitrogen and phosphorus ranged from 10.99 to 34.74 mg g^-1 and from 0.59 to 3.81 mg g^-1, respectively. Belowground concentrations of nitrogen and phosphorus ranged from 6.20 to 29.50 mg g^-1 and from 0.72 to 3.83 mg g^-1, respectively. The concentrations of nitrogen and phosphorus between above and belowground biomass differed significantly (p<0.05). Plant accumulations of nitrogen and phosphorus ranged from 2.10 to 24.48 g m^-2 and from 0.23 to 1.95 g m^-2, respectively. The results showed that plant uptake played a major role in nitrogen and phosphorus removal in this constructed wetland treating low eutrophic water. Its contribution was 46.8% and 51.0%, respectively. Plant accumulations of nitrogen and phosphorus displayed significant positive linear correlation to plant biomass and concentrations of nitrogen and phosphorus. So plant species for constructed wetland can be selected by biomass.This paper studied the photosynthetic characteristics of 11 plants in down-flow chamber andup-flow chamber of constructed wetland. The results showed that, Rumex japonicus, Iris pseudacorus, Iris tectorum and Sambucus chinensis were only suitable to the down-flow chamber. Tradescantia virginiana, Oenanthe javanica, Commelina communis, Reineckia cornea, Lolium perenne, Carex nemostachys and Corydalis edulis were suitable to the both chamber, and Oenanthe javanica was partial to the up-flow chamber. Iris tectorum, Commelina communis, Reineckia carnea and Corydalis edulis had strong shade tolerance; Rumex japonicus, Iris pseudacorus and Sambucus chinensis were sun plants; Tradescantia virginiana, Oenanthe javanica, Lolium perenne and Carex nemostachys were suitable to multiform light environment.The rhizosphere microbe of 18 plants in constructed wetland were determined, and the results showed that the rhizosphere bacteria, fungus, actionmycetes, ammonifying bacteria, denitrifying bacteria, phosphorus bacteria were 1.08 X106 24.65 X106,1.07 X 104³1.69 X104,0.87 X 105⁷.30 X105, 2.40X106²7.64X106, 0.34X104²5.15X 104 and 0.59X 105³3.39X 10s cfu/g dry soil, respectively. The rhizosphere microbe of most plants was higher than the control. It proved that most plants had obvious rhizosphere effect. Miscanthus sacchariflorus had higher bacteria amount. Miscanthus sacchariflorus, Saccharum arundinaceum and Acorus calamus had higher fungus amount. Reineckia carnea, Iris pseudacorus and Iris tectorum had higher actionmycetes amount. Five plants had higher ammonifying bacteria amount, two plants had higher denitrifying bacteria amount, and eight plants had higher phosphorus bacteria amount. In general, the plants which had higher amount of special rhizosphere microbe have higher function.The rhizosphere soil enzyme activity of 18 plants in constructed wetland were determined, and the results showed that the enzyme activity of catalase, urease, acid phosphatase, alkali phosphatase and protease were 0.10-0.41 ml g"^ 8.26-306.31 ug g1 d"1 ^ 3.38-68.14 ug g"1 h"1 ^ 0.43-33.78 ug g"1 h'1 ^P 1.08-65.70 ug g"1 d^\ respectively. Coix lacryma-jobi, Acorus calamus and Miscanthus sacchariflorus had higher catalase activity. The urease activity of Miscanthus floridulus and Sambucus chinensis were higher. Miscanthus floridulus, Saccharum arundinaceum, Reineckia carnea, Sambucus chinensis and Colocasia esculenta had higher acid phosphatase, and Sambucus chinensis, Miscanthus floridulus, Reineckia carnea, Iris tectorum, Colocasia esculenta and Canna indica had higher alkali phosphatase. The protease activity of Arundo donax and Arundo donax var.versicolor were obvious higher.The whole study analyzed the plant functional diversity in constructed wetland, confirmed the plant functional group, choosed the plant species which adapted to different constructed wetlands, and provided reference for plant collocating model. This study established the theoretical basis of botany for new constructed wetland, and also provided reference for treating environment with constructed wetland.