Multi-Functions Of Dark Septate Endophytes (DSE) Colonizing The Roots Of Two Key Reclaimed Plants In Huangmaoshan Tailing Ponds,Gejiu,Southwest China

More prevailing evidence reveals that dark septate endophytes(DSE)ubiquitously colonize the roots of diverse plant species under various environmental ecosystems at global.It is a group of multifunctional fungi that colonize in different plant roots,benefiting from the nutrition uptate and adaptation of hosts and play an important role in stress resistance to hosts.In this paper,193 DSE strains were previously isolated from two pioneer tree species in Huangmaoshan tailing ponds,in Gejiu city,southwest China,and used as materials.Firstly,the cadmium tolerance of these strains was evaluated.Six typical DSE strains were screened based on the combining results from cadmium tolerance and there taxonomic status.Then,the abilities of phosphate dissolving,siderphores producing and IAA producing were assessed.At the same time,six DSE strains were inculated to Populus yunnanensis seedlings by cuttage of poplar branches from by the Huangmaoshan mining pond and the sterile mine soil were used as the culture substrate in greenhouse.The influences of DSE on biomass,and the absorption of heavy metals Pb,Zn and Cd in P.yunnanensis and the content of heavy metals in the plants were evaluated.The main results of this paper are as follows:1.One hundred and ninety three DSE strains were evaluated for cadmium tolerance,and 91 DSE strains grew well in culture medium with 300 mg/L of Cd2+,accounting for 47.15%of the total number of strains.Subsequently,six representative DSE strains with high Cd tolerance were selected from the 91 DSE strains.The phylogenetic and taxonomic status of six DSE strains were analyzed by ITS sequences.The six DSE strains were identified as 2 Cladosporium strains(4611,151M),1 Cyphellophora strain(3452),1 Leptosphaeria strain(6411),2 Phialophora strains(3232,192M).2.The abilities of phosphate dissolving,siderophore producing and IAA producing of six DSE strains were evaluated.In the phosphate-dissolving experiment,we observed that there was a higher soluble phosphorus concentration in the liquid fermentation broth supplemented with the indissolvable organic phosphorus(phytin)than that from indissolvable inorganic phosphorus(tricalcium phosphate,TCP).While,Cladosporium 6411 showed a strong solubility for both organic phosphorus and inorganic phosphorus,with the maximum concentration of soluble P in the phytin(215.3±0.9mg/L),and in the TCP treated culture solutions(92±8.8 mg/L),respectively.In the siderophore experiment using CAS plate method,all six DSE strains contained the ability to produce siderophore,and fungi 4611,6411 and 151M were identified as high-yield siderophore strains.The detection of IAA(indole acetic acid)by HPLC(high performance liquid chromatography)showed that all 6 DSE culture solutions contained IAA,and 3232,6411 and 3452 strains produced a higher IAA concentration in their culture solutions,with the maximum IAA concentration 3.88±0.53?g/mL for Phialophora sp.3232.3.In the inoculation experiment of P.yunnanensis,two strains(3452,192M)of the six strains successfully colonized the roots,with a colonization intensity of 41.83±3.60%and 49.17±2.17%for DSE hyphae and microsclerotia,respectively.Compared with the non-inoculated controls,the inoculation of 3452 and 192M both significantly promoted the growth and increased the biomass of P.yunnanensis with a promotion of net plant height and net fresh weight.We found that both DSE strains 192M and 3452 reduced the absorption and accumulation of heavy metals(Pb,Zn,Cd)in poplar roots,twigs and leaves,except the enhanced Cd concentrations in leaves.Interestingly,Cyphellophora sp.3452 significantly promoted the transport of Cd from the roots of P.yunnanensis to their aerial leaves,with the maximum Cd transfer factor for poplar leaves.In conclusion,our results showed that the DSE strains from the mine soils were multi-functional fungi,which not only contained great metal-tolerance,but also had the abilities of phosphate dissolving,siderphores producing and IAA producing.More importantly,the 2 representative DSE strains could alleviate the inhibition by the metal-polluted stresses and promoted the growth of poplar.All the above functional aspects of DSE suggest their combined phytoremediation potentials with their diverse plants in Yunnan mine areas.