| Sulfonamide antibiotics(SAs)are highly polluted in China.There were different degrees of detection in surface water,groundwater,natural wetlands and drinking water sources.The SAs pollution in Huixian wetland in Guangxi has reached a certain degree,and in-situ remediation of natural wetlands by plant combined with microorganisms is a feasible scheme.Therefore,in order to study the influence mechanism of rhizosphere environment of different wetland plants on SAs degradation,the dominant wetland plants Vallisneria natans(Lour.)Hara),Typha orientalis Presl,Phragmites communis and Cladium chinense Nee were selected as the research objects to carry out the experiment.Root exudates of different plants were collected by root soaking method under blank conditions and 0.10 μg/L sulfadiazine(SD)and sulfachloropyrazine(SCP)stress conditions.The components of root exudates were determined by GC-MS.A total of five organic compounds were detected in root exudates under blank conditions : alkanes,esters,aldehydes,amides and alcohols.Only alkanes and esters were detected under antibiotic stress,and some compounds were not detected.Compared with the components of root exudates under the blank condition,the components with the highest relative concentration in root exudates changed to organic acids after SD and SCP stress,which were methyl oleate and methyl trans-9-octadecenoate,respectively.Compared with the blank group,the removal rate of antibiotics was significantly improved after adding plant root exudates in the rhizosphere microbial degradation test of four plant groups of Vallisneria natans(Lour.)Hara),Typha orientalis Presl,Phragmites communis and Cladium chinense Nee.Compared with the highest removal rate under the above two conditions,the removal rates of SD and SCP in Vallisneria natans(Lour.)Hara)group were increased by 39.71% and 41.71%,respectively.The removal rate of Typha orientalis Presl group increased by 42.22%and 40.76% respectively.Phragmites communis group removal rate increased by43.45%,46.67% and Cladium chinense Nee group removal rate increased by 55.85%,54.44%.In the four plant groups,the removal rates of SD and SCP in Cladium chinense Nee group were the highest,ranging from 83.27% to 92.91% and from82.28% to 91.44%,respectively.The removal rates of SD and SCP in Vallisneria natans(Lour.)Hara)group were the lowest,ranging from 49.33% to 65.38% and from 37.00% to 65.23%,respectively.By setting different temperature and p H conditions,it was found that the removal rate of antibiotics by microorganisms was high in the range of T=25 °C–30 °C and p H value of 6–7,and it was not suitable for microorganisms to degrade antibiotics when the temperature was too low and the p H value was acidic or alkaline.Under the conditions of p H=7 and temperature T=25 °C,the removal rates of SD and SCP in each plant group increased with the increase of degradation time.The rhizosphere soil at 0 h and 96 h of the experiment was taken for microbial community structure detection.It was found that the rhizosphere microbial community structures of the four plants were similar at the phylum and genus levels at 0 h of the soil.However,after 96 h of antibiotic degradation,the community structures and dominant genera of the rhizosphere microorganisms of each plant were changed.UPLC-MS/MS method was used to detect and analyze the metabolites after the degradation of antibiotics for 96 h.Through the detected metabolites,it was deduced that the degradation pathways of SD and SCP in plant rhizosphere mainly included hydroxylation,aminozation,and the cleavage of C-S bond and S-N bond. |
