Research On The Response Of Soil Environmental Factors In Longdong Loess Plateau To The Ecological Restoration Of Petroleum-contaminated Soil

The bioremediation has gradually become the first preferred ecological restoration technology in the field of environmental protection with its advantages of low cost,friendly environment and no secondary pollution.The technology of plant microbial combined remediation has attracted much attention recently.However,the technology is easily affected by many environmental factors in the process of ecological restoration,including all kinds of environmental factors in the plant rhizosphere,which affect the effect of combined plant microbial remediation.Due to the regionality distribution of plants,drought and poor soil in the Loess Plateau area of Eastern Gansu,the application of plant and microbial ecological restoration in this area can make full use of "species adaptation",that is,the study of the ecological restoration of oil contaminated soil sites by using local suitable plants and indigenous petroleum degrading bacteria groups,which has certain scientific significance.In order to verify the above scientific problems,this study uses the indigenous petroleum degrading bacteria in Longdong area to build a "suitable" oil pollution degradation bacteria group,combined with the local plant Medicago sativa and Gerber a jamesonii in the different concentrations of oil contaminated soil(10000,30000,50000 mg/kg)for a period of 4 months.Seven different treatments were set up,including the conctrol group(CK),microbial inoculant repair group(M),alfalfa repair group(Z),Gerbera restoration group(F),microbial inoculant + alfalfa combined repair group(M+Z),microbial inoculum + Gerbera combined repair group(M+F)and microbial inoculant+Alfalfa + Gerbera the joint repair group(M+Z+F).After the repair period,the physiological indexes,rhizosphere soil nutrient and enzyme activity,petroleum hydrocarbon degradation rate and soil microbial community diversity were measured respectively,and the above environmental factors were fitted to the non metric multidimensional scale analysis(NMDS)sequence of different repair treatments to analyze the soil factors under different treatments.The relationship between the environmental factors and the response of soil environmental factors in the Loess Plateau Area of Gansu Province to the ecological remediation of plant microorganism combined with oil contaminated soil provides a scientific basis and data basis for the implementation of the remediation work of oil contaminated soil sites in this area.(1)The petroleum degrading strains G1,G2,G3,G4 and G5 were isolated and screened by petroleum inorganic salt medium,and identified identified as G1 Ochrobactrum,G2 Acinetobacter,G3 Bacillus,G4 Bordetella and G5 Pseudomonas;the orthogonal experiment of selecting G1,G3 and G5 with higher degradation rate was optimized by orthogonal experiment.The petroleum hydrocarbon degradation efficiency of the mixed petroleum degradation agent was 82.59 + 0.12%when the G1,G3 and G5 dosage of the strain was added to 1:3:3,and the subsequent pot repair experiment was carried out with this mixed fungus.(2)The results of pot experiment showed that with the increase of soil petroleum hydrocarbon content,the root length,height,biomass dry,wet weight and root shoot ratio of Medicago sativa and Gerbera jamesonii were significantly decreased(P<0.01);the soluble sugar was different in response to different concentrations of oil stress,and the content of soluble sugar in Gerbera jamesonii was sltrong with oil:.pollution.The content of soluble sugar in Medicago sativa increased first and then decreased(P<0.05),and the activity of malondialdehyde(MDA),chlorophyll,superoxide dismutase(SOD)and peroxidase(POD)in two kinds of tested plarnts increased gradually(P<0.05)with the increase of oil pollution concentration(P<0.05).In all,the resistance of Gerbera jamesonii was stronger than that of Medicago sativa.(3)In terms of soil enzyme activity,soil CAT activity in Z treatment group was significantly higer than that of F treatment group;Secondly,the activity of the enzyme in M+F and M+F+Z treated groups was significantly higher than that of other treatments(P<0.05)when the activity of soil dehydrogenase activity(DHA)in petroleum hydrocarbon concentration increased to 30000 and 50000 mg/kg;the soil urease(UE)activity in M+Z group was the highest at TPHs=10000 mg/kg(P<0.05),and the activity of plant microbial combined repair group(M+F,M+Z and M+F+Z)was lower than that of the phytoremediation group(F and Z)(P<0.05)in severe oil pollution(TPHs=50000 mg/kg);the soil invertase enzyme could be effectively improved under the influence of low and medium oil concentration(P<0.05),but the activity of the enzyme in F and M+F+Z groups was significantly higher than that of other treatments(P<0.05);In addition,the activity of soil cellulase(CAS)in the F treatment group was the highest(P<0.05)under the influence of low and medium concentration of petroleum hydrocarbons(P<0.05).It shows that alfalfa has high oil pollution tolerance and can effectively enhance soil CAT activity,but Gerbera can effectively improve the activity of DHA,PPO and CE in different concentrations of soil,except soil CAS activity.(4)In soil physical and chemical properties,the nitrogen content of soil in the Z treatment group was significantly higher than that of the F group(P<0.05),the nitrogen content of the single plant combined microbial inoculant treatment group(M+F and M+Z)was between the M+ F+Z group and the other groups(M,F and Z);The phosphorus content in each treatment group were higher than that of the CK group,and the M+F+Z treatment group was significantly higher than the other treatments(P<0.05);The content of soil available potassium in the M+F+Z treatment group was significantly lower than that of the M+F and M+Z treatment groups(P<0.05),indicating that Gerbera showed a higher resistance to severe petroleum hydrocarbon pollution.The Pearson correlation analysis showed that the efficiency of petroleum hydrocarbon conversion in different kinds of plant combined microorganism agents is not the same(P<0.05).Increasing the diversity of suitable plants can significantly increase the rate of petroleum hydrocarbon degradation.(5)The soil microbial community diversity index showed the M+Z treatment group The Shannonn-Winner index(H)was significantly higher than that of other treatments(P<0.05)when the petroleum hydrocarbon concentration increased to 50000 mg/kg;Secondly,there was no significant difference in the Patrick richness index(S)of Gerbera(F,M+F and M+F+Z),and significantly higher than that of the Z and M+Z groups.The results showed that the effects of alfalfa and gerbera were different on soil microbial Patrick richness index(S).Third,the Pielou evenness index(J)of soil microbial community in 6 groups in different oil contaminated soils was significantly higher than that of their CK groups(P<0.05),but there is no significant difference between the treatment groups,which indicates that different plants can effectively improve the distribution of microbe in the Interplant microenvironment.(6)In order to clarify the response of the soil environmental factors in each treatment group and different petroleum hydrocarbon concentrations,based on the Bray-Curtis dissimilarity index,the measured 16 soil environmental factors were fitted to the non metric multidimensional(NMDS)sequence diagram of the soil microbial community structure of different oil concentration,and the results of the Pearson phase relationship analysis were shown.The distribution of Z and M+Z treatment groups in the NMDS sorting chart were different from other soil environmental factors,including UE(r2=0.8027,P=0.014),total Phosphorus(r2=0.7364,P=0.019)and alkali hydrolysable Nitrogen(r2=0.6416,P=0.037)in the low concentration(TPH=10000 mg/kg)oil contaminated soil;The soil DHA activity,CE activity,Pielou evenness index(J),CAS activity,and Shannon-Winner diversity index(H)were the major environmental factors make F and Z treatment groups difference in medium oil concentration(TPH=30000 mg/kg).The results of Pearson phase analysis showed that R2DHA activity-Pielou evenness index =0.994,R2 CE activity-Shannon-Winner diversity index =0.922,R2 CAS active-Shannon-Winner diversity index,R2 CAS activity-Shannon-Winner diversity index =0.793.Secondly,M,M+F,M+Z and M+Z+F were different from other groups,due to the content of available Potassium,the content of available Phosphorus,the activity of PPO,the activity of CAT,the richness index of Patrick,and the CAT activity was significant positive correlation with the number of availablePhosphorus,PPO activity and Patrick richness(S)(P<0.05);The available Phosphorus content,CAT activity,DHA activity and PPO activity lead to M+F,M+Z and M+Z+F treatment groups were different from other treatment groups in the high concentration oil pollution experiment group,combined with correlation analysis,R2DHAactivity-available phosphorus =0.999(P<0.01),R2DHA active-CAT activity=0.922(P<0.05).Under the influence of high concentration oil pollution,the toxic effect of petroleum hydrocarbon made the soil environmental factors greatly changed.At the same time,the rhizosphere of Gerbera and alfalfa alleviated the inhibition effect of heavy concentration of oil pollution on soil environmental factors.