Study On Resistance Mechanism Of Tall Fescue To Naphthalene And Pyrene Of Polycyclic Aromatic Hydrocarbons

Polycyclic Aromatic Hydrocarbons（PAHs）belong to Persistent organic pollutants（POPs）which are widely distributed in our environment.Naphthalene（Nap）and Pyrene（Pyr）are compounds of 16 kinds of PAHs that give priority to controlling,because they were representatives 2-ring and 4-ring aromatic hydrocarbons,which have attracted more and more attention.Tall festuca（Festuca arundinacea Schreb）is a perennial grass plant with high resistance to toxicity of PAHs.It has been proved to have potential to remediate PAHs-contaminated soils.In this study,tall fescue were subjected to different concentrations of Nap and Pyr,and toxicity from PAHs on physiological and biochemical properties of tall fescue seedlings were carefully studied.Additionally,accumulation and degradation properties of Nap and Pyr in tall fescue were carefully illustrated as well.The aim of this study is to provide a pilot study for understanding potential of tall fescue in phytoremedation of PAHs contaiminated soils.The main conclusions are as follows:（1）After 14 days of hydroponic treatment with different concentrations of Nap and Pyr（0 mg/L、20 mg/L、100 mg/L）,the growth performance of tall fescue was different.Nap could promote the biomass of tall fescue at low and inhibit it at high,while Pyr had no significant difference in the growth of tall fescue.The chlorophyll content showed the same trend.As the concentration of Nap treatment increases,the electrical conductivity of tall fescue leaves showed a trend of first decrease and then increase.As the concentration of Pyr treatment increases,the electrical conductivity of tall fescue leaves decreased gradually.On the whole,the content of H₂O₂in the roots of tall fescue was higher than that in the leaves,and the content of MDA showed a decreasing trend.Further investigation of root morphology showed that Nap could promote the growth of tall fescue root at low and inhibit it at high,while Pyr had an inhibition effect on the longitudinal growth of tall fescue root.（2）After 14 days of hydroponic treatment with different concentrations of Nap and Pyr（0 mg/L、20 mg/L、100 mg/L）,the photosynthetic characteristics of tall fescue were different.Under Nap treatment,φ_P0decreased gradually,indicating that the ability of PSII donor captured light energy to reduce Q_Adecreased gradually.Under the treatment of Pyr,φ_P0first decreased and then increased,indicating that low concentration of pyrene inhibited the ability of PSII donor side to reduce Q_A,but high concentration of pyrene could slow down this inhibition.The trend of PI_ABSand PI_totalalso proves this point.The L-band amplitudes of the experimental treatment groups were obvious,indicating that the oxygen-releasing complex OEC was damaged,the hydrolysis system on the donor side of the electron chain in PSII was damaged,and the downward electron transport of the primary quinone receptor Q_Awas blocked.In addition,δ_R0also showed a gradual decreasing trend,indicating that the Nap and Pyr not only damaged the internal PSII,but also blocked the electron transfer between PSII and PSI.Under the treatment of Nap and Pyr,the ETR increased first and then decreased,indicating that Nap and Pyr can promote the activity of the electron donor side of the PSII reaction center at low concentration,but can cause damage and inhibit its activity at high concentration.The non-photochemical quenched NPQ and q N showed a trend of first decreasing and then increasing under the stress of Nap and Pyr,which indicated that tall fescue itself had a certain self-protection mechanism.In order to avoid excessive light energy causing photoinhibition or photodamage,the excess energy was discharged in the form of heat energy and fluorescence.（3）In 100 mg/L Nap and Pyr hydroponics treatment,tall fescue was incubated for different time.Samples were taken at 0.5d,3d and 9d according to the time gradient,to investigate the accumulation characteristics of polycyclic aromatic naphthalene and pyrene in tall fescue.The physiological toxicity of Nap was greater than that of Pyr,and the tolerance of Pyr was better in tall fescue.The shoots of tall fescue showed better absorption capacity for Nap.And the roots of tall fescue showed better absorption capacity for Pyr.Through GC-MS qualitative analysis,the metabolic process of plant degradation of pyrene was further studied,and five kinds of intermediate metabolites of Pyr were found,which were labeled as compound A,B,C,D,E.They named 1-Hydroxypyrene,Phenaleno[1,9-bc]thiophene,1,9-Dihydropyrene,4,5-Dihydropyrene,2-Aminobiphenyl.According to the internal standard5-alpha-androstane（5AA）,the contents of the five degradation products increased significantly with time,indicating that the tall fescue had the characteristics of rapid absorption and metabolism of Pyr.And the degradation product E was only generated on the 9th day,indicating that E was further metabolized by other degradation products.