The Strengthen Effect Of Rhizosphere Fungi On Phytoextraction Of Soils Contaminated With Cadmium

Heavy metal pollution is increasing with metals exploitation andapplication．It becomes the hotpot to use plants and microorganisms toco-remediate the soil which polluted by heavy metals. Using the microbeand accumulator plant species isolated from indigenous soils can improvethe efficiency. So the study of the indigenous heavy-metal-resistantstrains and accumulator plants is significant for phytoextraction．Fivestrains with higher resistance were selected in rhizosphere soil ofQingshuitang district in Hunan province, China. We screened severalaccumulator plant species, through soil and vegetation investigation in thepolluted soil of the Qingshuitang industrial zone. On the basis of thiswork，the oilseed rape was chosen as a material to study the ability of Cduptake．Pot experiments were conducted to investigate the strengtheneffect of rhizosphere fungus on phytoextraction of soils contaminatedwith cadmium, and research the poisonous concentration of Cd in soil toGuizhou oilseed rape. The mechanisms of Cd tolerance and accumulationin the oilseed rape were study at the molecular level．The distribution of Cd in rhizosphere soil of Qingshuitang districtwas detected and evaluated by adopting the single factor pollution indexmethod. The result showed that the soil of Qingshuitang district waspolluted seriously by Cd. The Cd content in plant rhizosphere soilchanged in the range of1.03~278.49mg/Kg, the average was53.35mg/Kg.20superior plant species were collected from Qingshuitangdistrict, and had the strong capacity to tolerate and accumulate Cd. Highaccumulation of Cd concentration in oilseed rape was observed (150.61mg/Kg). It suggested that oilseed rape could be used as pioneer plant inphytoextraction.Five strains resisted to high concentration of heavy metals wereisolated from the polluted rhizosphere soil. The result showed that theX19(bacteria), X22（bacteria）,Z1（fungs） strains could secretesiderophore. The ability of secreting siderophore were Z1> X19> X22,judged by color variation of them. The two strains Z4and Z8which couldresistant higher heavy metal were characterized by morphologicalobservation，scanning electron microscope (SEM) and ITS sequence analysis. The strains Z4and Z8were identified as Mucor circinelloidesand Mucor rcacemosus respectively. The heavy metal resistance ability ofMucor rcacemosus Z8was the best among the isolates, and the researchabout its growth was done. The optimum conditions for the fungus Z8growth were as followings: pH8; carbon source, glucose; nitrogen source,KNO3; osmotic pressure0.09.Pot experiments were conducted to study the effect of two strains(Z4and Z8) on the growth and accumulation of Cd of Guizhou oilseedrape and Golden oilseed rape. The result showed that the biomass of twoplants was promoted to certain extent by inoculating strains Z4and Z8.The highest fresh weight-promoting effect was observed in Z4/Z8. Theconcentrations of heavy metals in the two plants were significantlyincreased when inoculated with Z4and Z8. Translocation factor (TF)values were decreased when fungus was inoculated. The lowest TF valuewas found in the plant with Z4/Z8. Compared with the Guizhou oilseedrape, the Cd adsorption ability of Golden oilseed was lower.Based on the plant MT sequence analysis，the MT gene from oilseedrape was identified as MP1．The MT gene can be considered as thepractial and effective bioaccumulated ways to treat enviroluental Cdcontamination. Guizhou oilseed rape-Mucor rcacemosus Z8was the bestcombination of the remediation of heavy metal contamination in farmland.The critical poisonous concentration of Cd in soil to Guizhou rape wasabout148.41mg/Kg, while Guizhou rape inoculated with Z4/Z8thecritical poisonous concentration of Cd was improved to175.35mg/Kg.