Effects Of NaCl Contents On Growth Of Three Plants And Sewage Purification Of Wetlands

Constructed wetland sewage treatment is a new ecological treatment technology.Its construction and operation cost is low,and the ecological environment benefit is remarkable.However,the key to the normal and efficient operation of the technology is suitable wetland plant species selection.Hygrophytes type not only directly affects the removal effect of pollutants in the wetland,but also indirectly affect the water environment and the living environment of the root zone microbes.However,the growth of wetland plants is affected by water bodies,soil characteristics and climate.Salt of water or soil is a key factor.A large amount of accumulation of wetland salt content will affect the growth and physiological characteristics of wetland plants,and then affects the ability of wet plants to absorb pollutants.Although the existing studies have explored the effects of salt content on the growth physiological characteristics of wet plants,the results are different because of differences in the study area,matrix type and test control gradient.Therefore,this study intends to explore the response of growth and physiological characteristics of 3 wetland plants to the salinity of sewage,and to provide theoretical basis for the construction of constructed wetland and selecting suitable plants in inland salinization area.In this study,we constructed the submarine constructed wetland system with reed,cattail and iris as the materials.Under 0%(control),0.5%,1% of sewage NaCl content,the results showed the effects of sewage NaCl content on growth and physiological characteristics of wetland plants and purification efficiency of wetland sewage,screening out the saline sewage with wetlands to treatment suitable for growing plants.The results are as follows:1.With the increase of sewage NaCl content,the plant height,above dry weight,ground dry weight,total biomass,the leaf length,leaf width and leaf area of the three plant plants were significantly decreased,and specific leaf weight increased,the aboveground biomass decline was more than that of in the underground,resulting in a significant increase in root / shoot ratio,which indicated that the degree of inhibitionof aboveground roots was higher than that of root system,and the sensitivity of root to salt was lower than that of stem and leaf.Under the treatment of 0.5% and 1% NaCl of sewage,the plant height and total biomass of reed were significantly higher than that of cattail and iris.2.Under the treatment of 0.5% and 1% NaCl of sewage,the superoxide dismutase(SOD)activity and free proline(Pro)content in leaves of the 3 plants increased at first and then decreased with the extension of time,but they were significantly higher than those of the control.However,The content of malondialdehyde(MDA)and relative electrical conductivity(REC)continued to rise,and were significantly higher than those of the control.The SOD activity and Pro content of reed leaf were significantly higher than those of cattail and iris,MDA content and REC of reed leaf were significantly lower than those of cattail,cattail was significantly lower than those of iris.At the end of the experiment,the antioxidant capacity of the wetland plants decreased and the accumulation of free proline was not much,which caused the damage of the leaf cell membrane.3.Compared with the control,under the treatment of 0.5% and 1% NaCl of sewage,net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr),photosynthetic instantaneous water use efficiency(WUE)of 3 plants were significantly decreased,intercellular CO2 concentration(Ci)and stomatal limitation(Ls)of 3 species respectively decreased and increased,but there is no significant difference with control,indicating that the reason for the decrease of Pn was not completely the stomatal limitation factor.And the decrease of AMC with the increase of sewage NaCl content,the reason for the decrease of photosynthetic capacity was related to the non-stomatal limitation elements such as Ru BPCase activity.The photosynth-esis of reed leaves was significantly higher than that of cattail and iris.4.Under the treatment of 0.5% and 1% NaCl of sewage,the removal rate of CODcr,TN and TP in constructed wetland system was lower than that of control,and the treatment high NaCl content(1%)was significant.At the end of the experiment,the effluent concentration of CODcr,TN and p H in the wetland system reached thefirst class A standard of municipal sewage discharge,and the removal rate of CODcr and TN in the wetland system was 82.87% and 93.72% respectively.Compared with non plant wetland,the removal rate of CODcr and TN in the plant wetlands was higher,but TP was relatively smaller,indicating the contribution of plants to wetland phosphorus removal is very small.The removal rate of contaminants in reed wetland and cattail wetland were significantly higher than those in iris wetland.5.In consideration of plant biomass and its antioxidant capacity,osmotic adjustment ability,leaf photosynthetic capacity of 3 plants and sewage purification effect of wetland system under the treatment of sewage containing NaCl,the suitability of the three plants in the salt marsh wetlands is:reed > cattail >iris.