Response Of Ectomycorrhizal Fungi To Al³⁺ And Mn²⁺ Stresses

With the accelerated industrialization and urbanization in China,environmental pollution is an increasingly serious problem.CO2,H2S and other gas emissions make acid rain harmfulness more serious in some areas,accelerate forest soil acidification and increase active Al³⁺ and Mn²⁺ in soils,by which inhibits the normal growth of trees and endangers the stability of forest ecosystems.In addition,there are many aluminum and manganese mines in Southwest China and meanwhile,soil remediation in mining areas is urgent.Some ectomycorrhizal fungi could form symbionts with trees,whereby promotes tree growth and increases their stress resistance.Ectomycorrhizal fungi could thus provide restoration technical supports for soils remediation in fragile ecological system of forest and mining areas.Scientists found that some ectomycorrhizal fungi were extremely resistant to Al³⁺stress,but those resistant to Mn²⁺ and to both Al³⁺ and Mn²⁺ has not been reported yet.In present experiment,the growth,nutrient absorption and organic acid efflux by ectomycorrhizal fungi were studied by the addition of Al³⁺ and Mn²⁺ alone and together in to culture solution.The main objective is to provide scientific information for the selection of ectomycorrhizal fungi resistant to Al³⁺ and Mn²⁺,The main results as follows:1.Both Al³⁺ and Mn²⁺ affected significantly the growth of ectomycorrhizal fungi.Under Mn²⁺ stress,the biomass of Pt 715,Sl 13 and Cg 04 correlated negatively with the metal concentrations supplied.The biomass of Pt 715 decreased less than SI 13 and Cg 04 under Mn²⁺ stress,suggesting higher abilities of Pt 715 against Mn toxicity.Ectomycorrhizal fungi showed the different tolerance to A;³⁺and Mn²⁺.Al³⁺ increased the biomass of Cg 04 but decreased those of Pt 715 and Sl 13.Additional reduction in the growth of ectolycorrhizal fungi was observed in the presence of Al³⁺ and Mn²⁺together compared to Al³⁺ or Mn²⁺ added separately.Pt 715 showed best abilities tolerant to both Al³⁺ and Mn²⁺.Mycorrhizal fungi such as Sl 1,Sl 7 and Sl 12 from South China were more tolerant to Al³⁺ than those from North China?Sb 05 and Sl 20?.Among them,Sl 1 had better tolerance against Al³⁺ than any others.2.Under the stress of Al³⁺ and Mn²⁺,ectomycorrhizal fungi could exude organic acids but varied in the amounts and types according to fungal species.All experimental fungi effused oxalic acid.The fungi assistant to Al³⁺ released more oxalic acdd under Al³⁺ stress,much higher than those sensitive to Al³⁺ such as Sb.05 and Sl 20.Pt 715 could release not only oxalic acid but also succinic acid.Thus fungal oxalic acid efflux could not be a sole Al³⁺-resistant index of ectomycorrhizal fungi.There was a relationship between fungal efflux H+ and Al³⁺-resistantanc.3.The nutrient uptake of Al³⁺-resistant fungal was higher than that of Al³⁺-sensitive fungal under the stress of Al³⁺ and Mn²⁺.Under the stress of Mn²⁺,fungal absorbed less nutrient were Cg 04>Sl 13>Pt 715.Al³⁺ and Mn²⁺ decreased the nutrient uptake by the fungi particularly by Sl 13 which showed more obvious reduction than Ptl 15 and Cg 04.Under the stress of Al³⁺,the N,P uptake of Sl 1,Sl 7,Sl 12 were higher than that of Sb 05,Sl 20.