The effect of fulvic acids on the toxicity of lead and manganese to arbuscular mycorrhizal fungus Glomus intraradices

The effect of fulvic acids (FA) on arbuscular mycorrhizal (AM) fungi and on the toxicity of lead and manganese toward these symbionts were demonstated in vitro. Incubation of root segments colonized with the AM fungus Glonius intraradices in undiluted fraction of FA (813 mg/L carbon) decreased an outgrowth of intraradical hyphae. Diluted FA solutions (<271 mg/L C) did not influence the proportion of root segments bearing proliferating hyphae; solution containing 27.1 mg/L C even increased the proliferation. A decrease of heavy metal toxicity toward the fungus was observed when FA (81.3 mg/L C) were added to the solutions containing higher concentrations (less than or equal to100 mumon) of Mn and Pb; the positive effect of FA was not significant at higher concentrations of metals (0.5 mmol/L). A short-term cultivation of six different saprophytic microorganisms - three actinomycetes and three filamentous fungi - on the FA media (81.3 mg/L C) did not result in a modification of hyphal proliferation from the root segments subsequently incubated in these media.