Study On Response Of Four Constructed Wetland Emergent Plants To Sulfamethoxazole Stress

Sulfonamide is one of the most widely used antibiotics,among which sulfamethoxazole(SMX)is the most biotoxic.SMX has been widely and massively detected in constructed wetlands.As the main plant type in constructed wetlands,emergent plants play an important role in removing pollutants from water.Four major water emergent plants including typha(Typha orientalis Presl),scirpus tabernaemontani(Scirpus validus Vahl),loosestrife(Lythrum salicaria),and phragmites(Phragmites australis)are suitable for planted in northern constructed wetlands.To reveal the response of the four plants under the stress of SMX,this experiment aimed to study the effect on the main indexes of traits,photosynthesis,membrane permeability,antioxidant enzymes and soluble protein,as well as the purification ability of conventional pollutants under the stress of SMX.The results will provide an important theoretical basis for constructing constructed wetlands to treat effluent deeply from sewage plants,especially from pharmaceutical plants.The growth morphological indexes of the 4 emergent plants were seriously affected by the increase of the stress concentration and the stress duration under the SMX stress.The growth concentration thresholds of typha,scirpus tabernaemontani,loosestrife,and phragmites were:0.5mg·L-1,0.1mg·L-1,05mg·L-1,and 1.0g·L-1,respectively.The plant height of scirpus tabernaemontani and typha was greatly affected by SMX,which decreased to 67.3%and 42.8%,respectively compared to the control group.The relative growth rates of loosestrife and phragmites were significantly affected by SMX,which decreased to 34.6%and 75.9%,respectively compared to the control group.Secondly,the biochemical reactions of the 4 plants under SMX stress were determined.The main experimental methods were to determine the physiological indexes of each plant under different SMX concentrations,in order to compare the differences of photosynthesis,cell membrane permeability,antioxidant enzymes and soluble proteins to reflect the antioxidant function and stress resistance of plants.The increase of SMX stress concentration and the stress duration resulted in the accumulation of malondialdehyde(MDA)in four plants.Chlorophyll content of all plants decreased under different concentrations of SMX stress.Among them,chlorophyll of phragmites is the most sensitive to the increase of stress concentration.Under high concentration stress,chlorophyll content of loosestrife and phragmites decreased obviously with the extension of stress time.Superoxide dismutase(SOD)and peroxidase(POD)were mainly induced in typha,loosestrife and phragmites australis under SMX stress.The activities of SOD and POD in scirpus tabernaemontani were significantly lower than those in the other three plants,but the activities of catalase from micrococcus lysodeiktic(CAT)in scirpus tabernaemontani were much higher than those in the other three plants.Finally,under the stress of SMX,the removal efficiency of COD,total nitrogen,ammonium nitrogen and total phosphorus in a simulated wetland reactor composed of the four wetland emergent plants was measured,which quantitatively indicated the stress effect of SMX on the water purification capacity of the constructed wetland system.Under the high concentration stress of 2.0mg·L-1 SMX,the removal effects of the four plants on COD,ammonia nitrogen,nitrate nitrogen and total phosphorus were significantly decreased,and the removal rate was 20%～35%lower than that of the control group.The COD removal rate of phragmites and scirpus tabernaemontani was the highest,about 70%.The removal rates of nitrate nitrogen and total phosphorus were the highest in phragmites with 61.2%and 63.5%,respectively.The removal rate of ammonia nitrogen in loosestrife was the highest,which reached 58.7%.