Study On The Effects Of Endophytic Fungal （AMF And DSE） Inoculation On Maize In Farmland Contaminated By Heavy Metals In Huize,Yunnan

Comtamination with excessive heavy metals is a global environmental concern.Especially,comtaminants with heavy metals in arable soilsusually cause food production reduction,economic losses and even seriously threaten human health.Thus,it is an urgent need to restore and remediate the pollutants of arable soils.In this thesis,different maize cultivars were targeted and inoculated with AMF or DSE as experimental groups in heavy metal contaminated farmland in Zhehai Town,Huize County,Yunnan Province,to explore the followings: 1)Effect of inoculation with AMF or DSE on the maize growth and development of different maize cultivars under complex heavy metal stresses.2)fungal colonization characteristics in the roots of three maize cultivars and differences in heavy metal absorption.3)Heavy metal distribution in different maize organs and their changes in different maize growth stages.Our results were alternative to in this thesis provide a scientific basis for using mycorrhizal techniques to gain safe cultivation of crops in metal-polluted soils,as well to restore and remediate heavy metal-polluted arable soils.The main results and conclusions of the thesis are as follows:1.The colonization characteristics of AMF and DSE in the root systems of different maize cultivars: Using the traditional stainings and micromorphological observations,we found that the roots of field maize,regardless of the additional fungal inoculations or not,were all colonized with AMF and DSE simultaneously and developed their respective typical structures,indicating that the indiginous AMF and DSE in the field can colonize different maize roots.Among the 3 maize varieties,the maximum colonization intensities of AMF and DSE were observed in the roots of AMF-treated HD4 and DSE-treated ZYY9,and the highest colonization rates were66.5% and 33.7%,respectively.Interestingly,we found that the AMF colonization rate were always higher the AMF-inoculated treatments than that in the DSE-inoculations for one given maize cultivar,indicating that different strains have various colonization ability to the same maize variety.We also noted that the AMF inoculation always decreased the natural colonization rate of DSE in field,and verse versa,the inoculation with DSE also inhibited the natural colonization of indigenous AMF,indicating that maize inoculated with AMF or DSE have systemic autoregulatory effects on colonization between AMF and DSE.2.Effect of inoculation with AMF or DSE on maize biomass: Base on the data of maize plant height,dry weight and total grain weight,we found that the inoculation with AMF and DSE strains had no significant effects on both growth ZYY and HD4,while both fungal inoculations significantly increased the total dry weight and grain weight of SY8,which suggesting that the response of the inoculatins of both AMF and DSE was dependent on different maize varieties.3.Effect of inoculation with AMF on heavy metal absorption and accumulation in maize: The comparative analyses of heavy metal concentrations in all 4 organs（i.e.roots,stems,leaves,grains）in the 3 growth periods of maize（i.e.seedling,flowering and reproductive stages）showed that AMF inoculation reduced the absorption of Cd in the roots,stems and leaves of HD4,compared with their respective non-inoculated controls.And there were a lower values in the AMF inoculated ZYY9,including the reduced amounts of heavy metals in the grains and roots,and the increased heavy metal accumulation in maize shoots.Incontrast to ZYY9,inoculation with AMF decreased the concentrations of heavy metals in the aboveground parts（stem,leaf,grain）and increased metals in root of SY8.These results indicated that there were distinct responses of various maize cultivars to AMF inoculation in the accumulation of heavy metal.4.Effect of DSE inoculation on the metal accumulation in maize: Inoculation with DSE decreased the concentrations of heavy metals in roots of both ZYY9 and HD4,but increased the uptake of heavy metals in the shoots,as well as the reduced metals in HD4 grains.While,as for SY8,the DSE inoculation reduced the concentrations of Cd,but increased the accumulation of Pb and Zn.The above results indicated that DSE had different effects on the absorption and accumulation of heavy metals in different maize varieties.A comprehensive comparison of the effects of AMF and DSE on heavy metals in all organs of the same maize variety throughout the growth periods showed that the various fungal inoculations had different effects on the accumulation of heavy metals,depending on maize cultivars,fungal inculations,plant growth periods,and maize organs.5.Heavy metal accumulation in different organs during different maize growth periods: Our results showed that there were distinct metal accumulation patterns during the 3 growth stages,and the minimux metal accumulation occurred in the flowering periods.And for the whole growth stages of a given maize cultivar,maize initially accumulated the largest amounts of metals at the seedling stage,then decreased with the bottom values of metal accumulation in the flowering period,and gradually increased to the reproductive period.Interestingly,there was a similar trend of heavy metal concentrations in maize roots during the three periods with the shift of the DTPA-extractable metals in their corresponding rhizosphere soils.In addition,due to the differences in the chemical properties of various heavy metals,their distribution in different maize organs were different,and the highest metal accumulation was roots,followed by leaf,stem,grain,respectively.And there also were distinct absorption and accumulation patterns among 3 heavy metals in maize organs（root,stem,leaf,grain）and their orders were Zn > Pb > Cd.