Study On Degradation Characteristics Of Atrazine In Water By AMF-Canna Symbiotic System

As a triazine herbicide,atrazine is widely used in agriculture and forestry.Due to its use for a long time,with its soil leaching,it entered the surface runoff and leaching into groundwater.As a kind of potential human carcinogens and endocrine disrupting chemicals,the remediation methods of residual atrazine pollution in the environment appears to be necessary and imperative.Phytoremediation has great potential in remediation of organic pollutants.But as the herbicide,atrazine can inhibit the growth of plants.Especially in the apply period of herbicide,recession flow because of the rain from farmland contains a high concentration of atrazine,and it has seriously affected the normal growth of plants,thus cut down the efficiency of phytoremediation and affect the stability of phytoremediation.Therefore,this study chooses the arbuscular mycorrhizal fungi(AMF)to construct AMF-Canna symbiotic system,and it will enhance the growth and stress resistance of Canna.At the same time,the response of AMF-Canna symbiotic system to atrazine and the influence of AMF on the atrazine degradation are investigeted systemly,providing a technical support for the phytoremediation of atrazine with constructed wetlands.In the period of Canna seedlings,AMF-Canna symbiotic system was constructed by AMF inoculation.In the early establishment of the symbiotic system,the colonization rate of Canna root,growth,photosynthesis,and atrazine removal efficiency were studied.The results show that the two species of arbuscular mycorrhizal fungi,Funnelliformis mosseae(FM)and Rhizophagus intraradices(RI)can form a symbiotic system with Canna.The mycorrhizal colonization rate of the two arbuscular mycorrhizal fungi is 24.5±2.9% and 22.0±2.5%,respectively,and the FM inoculation presents a better facilitative effect on the growth and photosynthesis than Rhizophagus intraradices.The atrazine removal rate of the FM inoculated symbiotic system achieves 95.7% for the biggest,higher than that of Rhizophagus intraradices(84.4%).Furthermore,the atrazine threshold concentration for the FM inoculated symbiotic system is proved to be 7.36mg·L-1,which is higher than that of Rhizophagus intraradices as 5.83mg·L-1.The influence of AMF on the growth and physiological of Canna with atrazine stress was analyzed.The results show that the growth and development of Canna are inhibited by the atrazine stress,while AMF inoculation can reduce the growth inhibition effects.When the atrazine concentration is between 9.6~10.3mg·L-1,Arbuscular mycorrhizal fungi inoculation presents the highest acceleration influence on the growth and biomass.At the same time the suppressions on net photosynthetic rate,stomatal conductance and transpiration by atrazine stress are relieved.As a result,the utilization efficiencies of light,carbon and water are improved reasonably.Furthermore,from the physiological and biochemical aspects,arbuscular mycorrhizal fungi alleviates the subcellular structure damage and enhance the tolerance against the oxidative stress response caused by atrazine stress,resulting in a higher tolerance threshold concentration of atrazine as about 5mg·L-1.The effect of symbiotic system on atrazine degradation was studied.The results show that the Canna displays a high degradation rate of atrazine,and can work as the ideal choice of plant species for phytoremediation of atrazine in water.Arbuscular mycorrhizal fungi inoculation can improve the atrazine remediation efficiency of Canna plants in water,and reduce the half-life of atrazine.The study on atrazine metabolites and metabolic pathways of atrazine in the symbiotic system shows that the AMF inoculation promote the further degradation of atrazine in water,and the complete degradation rate increases from 62.1% to 72.1%.The main atrazine metabolic pathways is the de ethylation and hydroxylation metabolic pathways.Inoculation of AMF can promote hydroxylation reaction of atrazine,and the atrazine metabolites in Canna contain hydroxyisopropylatrazine.Through the study of atrazine degradation mechanism in AMF-Canna symbiotic system,the results show atrazine degradation mechanism by Canna mainly relies on the detoxification by cytochrome P450 and hydroxylation by benzoxazinone,and the detoxification of cytochrome P450 appears to be the major degradation pathway in Canna.Inoculation of AMF can promote promote plant uptake of atrazine,improve the activity of cytochrome P450 and increase content of benzoxazinone especially in under-ground part of Canna,affect the rhizosphere enzyme activity and microbial community,and finally improve the atrazine degradation ability in Canna and water by the AMF-Canna symbiotic system.This study constructed a AMF-Canna symbiotic system with excellent atrazine degradation performance,and it has the characteristics of fast degradation rate,short half-life and depth of degradation.The degradation pathway of atrazine was studied in this AMF-Canna symbiotic system.From this study,the degradation mechanism of atrazine and the enhanced effect of AMF inoculation on atrazine degradation by Canna are confirmed,overcoming the problem in atrazine phytoremediation as atrazine harming the plants and affecting the efficiency of phytoremediation,providing a theoretical support for phytoremediation of atrazine with constructed wetlands.