Effects of vesicular-arbuscular mycorrhizal fungi on heavy metal uptake by soybeans

Abstract

The uptake of heavy metals by soybeans may be affected by the colonization of roots with vesicular-arbuscular mycorrhizal (VAM) fungi. Soils with various heavy metal contents were collected from areas in close proximity to a Zn smelter in operation for nearly 100 yr. All soils were placed into pots and steam sterilized. One treatment was inoculated with mixed VAM fungi (600 spores per pot) and soil bacteria. The second treatment was inoculated with soil bacteria (minus VAM fungi) and the third treatment remained sterile. Soybeans ( Glycine max L. Merr. “Essex”) were sown into each soil. After 6 weeks of growth, the plants were harvested and the dry weight and the content of N, P, Zn, Cd, Cu, Mn and Fe were determined in plant leaves. The amount of VAM fungal colonization, nitrogenase activity and number and weight of nodules were also determined on plant roots. Results indicate that inoculation with soil bacteria and VAM fungi increased plant dry weight and foliar P and N contents. Inoculation with VAM fungi reduced Zn, Cd and Mn concentrations in plant leaves grown in soil with high concentrations of these metals. VAM fungi enhanced foliar concentrations of these heavy metals when the plants were grown in soils with low heavy metal concentrations. The colonization of roots by VAM fungi was reduced at the highest soil metal concentrations. These results indicate that the effect of VAM fungi on heavy metal uptake is dependent upon the initial soil metal concentration.