The Role And Mechanism Of Arbuscular Mycorrhizal Fungi On Arsenate Tolerance Of Medicago Truncatula

We used conventional plant pots and compartmented rhizoboxes to investigate the effects of two arbuscular mycorrhizal fungi on uptake of arsenate by Medicago truncatula. In the pot experiment we inoculated the host plant with Glomus mosseae and in the rhizobox experiment we compared G mosseae with Glomus intraradices.Hyphal density was unaffected by As even at the highest application rate of 200 mg kg-1 As to the soil which strongly depressed the biomass of mycorrhizal plants and non-myconhizal controls. Myconhizal inoculation increased the EC50 of both shoot and root dry weights about threefold, perhaps by enhancing host plant tolerance to arsenate. Shoot P concentrations were maintained at relatively constant values following inoculation with G. mosseae but decreased sharply in non-mycorrhizal plants with increasing arsenate addition level. At intermediate and high arsenate addition levels (50, 100 and 200 mg kg-1), inoculation significantly reduced the shoot and root As concentrations. Thus, AM fungal colonization may have conferred enhanced tolerance to arsenate on the host plant by enhancing P nutrition and restricting root As uptake.At low soil arsenate levels (0 and 10 mg kg-1 added As) there was no significant difference in As content between mycorrhizal and non-myconhizal plants. However, at mtermaediate and high arsenate addition levels inoculation significantly reduced the shoot and root As concentrations.Although inoculation with either G. mosseae or G intraradices resulted in limited As translocation to the two fungi, G. mosseae appeared to be more tolerant to arsenate and to provide M. truncatula with more P than did G intraradices. Furthermore, the hyphal distributions of the two fungi differed greatly. While most of the external hyphae of G. mosseae were found near the host roots, the extrametrical hyphae of G intraradices tended to extend greater distances away from the roots.