| The growth of plants depends on the environment,and the environment inevitably has natural disasters and various soil-borne diseases,which makes the growth process of plants themselves difficult.There is no denying that the rapid development of industry and agriculture has improved people’s living standards,but with it comes a variety of environmental problems,not only pollute the growing environment of plants,but also endanger human health.Among them,phthalates(PAEs),as the main plasticizers and typical pollutants,have become the focus of environmental control because they can be absorbed by plants and human body when exposed to the environment.Therefore,it is of great significance to construct synthetic microbial communities capable of degrading pollutants,promoting plant growth and preventing plant growth to repair agricultural soil PAEs pollution,relieve plant stress and reduce its absorption and accumulation of PAEs to ensure soil health and food security.In this paper,a multifunctional microbial community YJ-1 was established.On the basis of determining the composition of each community member and the optimum growth conditions of the community,The growth promotion and biocontrol properties of YJ-1 and its members and the synergistic degradation ability of PAEs composed of dibutyl phthalate(DBP)and di-(2-ethyl)hexyl phthalate(DEHP)were further investigated.At the same time,GC-MS and other detection methods were used to explore the possible pathway of YJ-1 degradation of PAEs.Combined with competitive growth,mutual invasion and semi-permeable membrane test methods,the stability of YJ-1 community and the interaction of its members during the degradation process were studied.The effects of YJ-1 community on degrading soil PAEs pollution and alleviating the effects of plant disease and pollution was explained by using the changes of cucumber fusarium wilt incidence,PAEs degradation rate,cucumber growth,physiological and biochemical indexes under potted conditions.The results are as follows:(1)A biocontrol strain DNYB-S1 with 61.66%inhibition rate against Fusarium oxysporum was obtained by plate face-off test.When the ratio of PAEs degrading bacteria DNB-S2 and DNHP-S2 to Fusarium oxysporum was 1:3:4,the microbial community YJ-1 was formed.The optimal culture conditions of YJ-1 were as follows:temperature 30 ~oC,rotational speed 150 r/min,p H 11,inoculation amount 3%,contaminant concentration 500 mg/L(DBP:DEHP=1:1)Under these conditions,the PAEs degradation capacity of YJ-1 was up to 91.23%,the bacteriostatic rate of YJ-1 was 71.25%,the phosphorus soluble concentration was 1.62μg/m L,the IAA production was up to 13.96μg/m L,the protease activity was up to 102.38 U/m L,and the ferritic synthesis rate was 42.27%.YJ-1 has higher PAEs repair ability and stronger plant growth promotion ability.(2)In the study on the ability of YJ-1 to co-degrade PAEs(DBP:DEHP=1:1),it was found that the degradation rate of YJ-1 was 18.92%higher than that of single strain DNB-S2 on DBP,and 38.76%higher than that of DHNP-S1 on DEHP.Based on Lotka-Volterra model,the fitness difference of YJ-1 community was 0.59,and the niche overlap value was-0.05,and the ecological stability was good in the process of synergistic degradation of PAEs.According to the GC-MS detection results,The intermediate products produced by YJ-1 during the degradation of PAEs include ethylhexyl benzoate(EHBA),phthalic acid(PA),dimethyl phthalate(DMP),diethyl phthalate(DEP),butyl phthalate 2-ethylhexyl ester(MEHP),diisobutyl phthalate(DIBP),butyl benzoate,etc.7 The degradation pathway of PAEs by synthetic colony YJ-1 was more complex than that by single bacteria.The growth of YJ-1 and its members in joint and separate cultures was investigated.The results showed that when the biomass of YJ-1 in the community increased to a stable period,the members of YJ-1 had a favoritic symbiosis.It was this interaction that maintained the stable and efficient degradation characteristics of YJ-1.(3)Pot experiment results showed that compared with the diseased soil treatment group,YJ-1could reduce the incidence of cucumber fusarium wilt by 45.31%,the disease index of cucumber was 10.87,and the disease prevention effect of YJ-1 was 19.85%higher than that of the single strain,which indicated that the application of YJ-1 inhibited the influence of cucumber fusarium wilt on plants.The residual concentration of pollutants and physiological and biochemical indexes of cucumber showed that YJ-1 had an excellent ability to degrade and detoxify PAEs in soil-plant system,and could reduce PAEs(DBP:DEHP=1:1)at a concentration of 30 mg/kg in soil within35 days.1)Degraded to 4.26 mg/kg with a degradation rate of 85.81%,and the final concentration was in line with the American soil PAEs management standard.At the same time,the concentration of PAEs in cucumber was reduced to 0.01 mg/kg,which was lower than the intake standard set by the Scientific Committee for Food of the European Economic Community.At the same time,the chlorophyll of cucumber treated with YJ-1 increased by 1.26 mg/g,and the enzyme activities of SOD,Pro,CAT and POD increased less than those of the pollution group,indicating that the degradation of PAEs by YJ-1 alleviated the stress of PAEs on cucumber.The growth of cucumber seedlings and their roots after 35 days showed that the plant height of cucumber seedlings in YJ-1treatment group was 1.67 cm higher than that in pollution-free control group,and the dry weight was increased by 0.17 g.The above results indicated that YJ-1 also showed excellent plant biological control and growth promotion ability in practical application. |
