ARBUSCULAR MYCORRHIZAL CONTRIBUTION TO HEAVY-METAL UPTAKE BY MAIZE (ZEA-MAYS L) IN POT CULTURE WITH CONTAMINATED SOIL

In two pot-culture experiments with maize in a silty loam (P2 soil) co ntaminated by atmospheric deposition from a metal smelter, root coloni zation with indigenous or introduced arbuscular mycorrhizal (AM) fungi and their influence on plant metal uptake (Cd, Zn, Cu, Pb, Mn) were i nvestigated. Soil was gamma-irradiated for the nonmycorrhizal control. In experiment 1, nonirradiated soil provided the mycorrhizal treatmen t, whereas in experiment 2 the irradiated soil was inoculated with spo res of a fungal culture from P2 soil or a laboratory reference culture , Glomus mosseae. Light intensity was considerably higher in experimen t 2 and resulted in a fourfold higher shoot and tenfold higher root bi omass. Under the conditions of experiment 1, biomass was significantly higher and Cd, Cu, Zn and Mn concentrations significantly lower in th e mycorrhizal plants than in the nonmycorrhizal plants, suggesting a p rotection against metal toxicity. In contrast, in experiment 2, biomas s did not differ between treatments and only Cu root concentration was decreased with G. mosseae-inoculated plants, whereas Cu shoot concent ration was significantly increased with the indigenous P2 fungal cultu re. The latter achieved a significantly higher root colonization than G. mosseae (31.7 and 19.1%, respectively) suggesting its higher metal tolerance. Zn shoot concentration was higher in both mycorrhizal treat ments and Pb concentrations, particularly in the roots, also tended to increase with mycorrhizal colonization. Cd concentrations were not al tered be tween treatments. Cu and Zn, but not Pb and Cd root-shoot tra nslocation increased with mycorrhizal colonization. The results show t hat the influence of AM on plant metal uptake depends on plant growth conditions, on the fungal partner and on the metal, and cannot be gene ralized. It is suggested that metal-tolerant mycorrhizal inoculants mi ght be considered for soil reclamation, since under adverse conditions AM may be more important for plant metal resistance. Under the optimi zed conditions of normal agricultural practice, however, AM colonizati on even may increase plant metal absorption from polluted soils.