Effects Of Arbuscular Mycorrhizal Fungi On Pb And Cd Uptake By Viola Baoshanensis

Phytoextraction, as an environmentally friendly and cost-effective approach tocleaning up sites contaminated by heavy metals has received more attention in recentyears, and to employ the indigenous arbuscular mycorrhizal （AM） fungi ofhyperaccumulator species is considered as a potential strategy to enhance theefficiency of remediation. Therefore, it is of great importance to elucidate the effectsof AM fungi on plant HM uptake.V. baoshanensis is one of the rare cadmium （Cd） hyperaccumulators found inChina and field experiment showed that V. baoshanensis had a relatively strong abilityto remove Cd and lead （Pb） from the contaminated soil. To date, it is the first time tostudy the effect of AM colonization on Cd and Pb uptake by this hyperaccumulator.The present study aims to investigate the effect of indigenous AM fungi on Cd and Pbuptake by V. baoshanensis under varying soil Cd and Pb concentrations （Exp.1）, Pavailability （Exp.2）, time course （Exp.3） and species density （Exp.4）. Major resultsare listed as follows:1. High availability of Pb, Cd and P significantly inhibited the AM colonization ofV. Baoshanensis. Applied Pb at500mg kg^-1inhibited AM colonization, and theinhibition increased with increasing soil Pb concentration, while both applied Cd at200mg kg^-1and applied P at500mg kg^-1significantly inhibited AM colonization.AM colonization increased with time till9weeks, and became relatively stablethereafter, while species density had no significant effect on AM colonization.2. Soil P availability was the main factor affecting the role of AM fungi in shoot Pconcentration of V. Baoshanensis. Available Pb and Cd，and species density also hadcertain effect, while time course had no significant effect. In mine soils, inoculationwith AM fungi significantly increased shoot P concentration regardless of P availability. In paddy soils with applied Pb or Cd, however, the effect of AM fungi onshoot P concentration of V. baoshanensis was inconsistent: no significant effect wasobserved in Exp.1while inoculation significantly increased shoot P concentration intreatments of Pb1000and Cd100in Exp.3.3. Soil P availability was the main factor affecting the role of AM fungi in shootgrowth of V. Baoshanensis. In mine soil with low P availability, the effect of AMfungi on shoot growth was positive without P addition, and became neutral with Paddition at50or250mg kg^-1, and negative at applied P of500mg kg^-1. However, inpaddy soil with high P availability, P was no longer the limiting factor of growth of V.baoshanensis. In the treatments with Pb addition, the main factor affecting the role ofAM fungi in shoot growth was available Pb: the effect was negative at Pb addition of500mg kg^-1, and became neutral or positive at applied Pb of1000or1500mg kg^-1. Inthe treatments with Cd addition, the main factor affecting the role of AM fungi inshoot growth was species density.4. Soil Pb availability was the main factor affecting the role of AM fungi in shootPb concentration of V. baoshanensis. When DPTA-extractble Pb was no more than221mg kg^-1, AM fungi increased shoot Pb concentration, while AM fungi decreasedshoot Pb concentration at DPTA-extractrable Pb no less than379mg kg^-1. Innon-inoculated treatments, shoot Pb concentrations and TF values of V. baoshanensisdecreased with increasing P availability, while in inoculated treatments no effect wasobserved with varing P availability. In addition, species density and time course hadno significant effect on the role of AM fungi in shoot Pb concentration of V.baoshanensis.5. AM fungi decreased shoot Cd concentration of V. baoshanensis whenDPTA-extractable Cd was no less than11.5mg kg^-1, and the effect was regardless ofP availability. The inhibition on shoot Cd concentration was realised by decreased TFvalues at DPTA-extractable Cd no more than23.0mg kg^-1, whereas the inhibition wasachieved via decreasing root Cd concentration at higher Cd availability. Speciesdensity had certain effect on the role of AM fungi in shoot Cd concentration while nosignificant effect was observed in time course.The results indicated at low available Pb, AM fungi increased shoot Pbconcentration of V. baoshanensis, while at high available Pb concentration AM fungidecreased shoot Pb concentration. AM fungi decreased shoot Cd concentration of V.baoshanensis, but the mechanism of inhibition depended on Cd availability. At low available P, Pb and Cd, AM fungi increased the removal of Pb or Cd in the shoots of V.baoshanensis. At high bioavailable Pb and Cd, AM fungi decreased shoot Pb or Cdconcentration of V. baoshanensis, and this was probably the main mechanisminvolved in enhancing HMs tolerance of V. baoshanensis by AM fungi.