The adverse effects of the heavy metals on all living forms make rehabilitation of heavy metal-contaminated soils very difficult. In this paper, the effects of seedling inoculation with arbuscular mycorrhizal fungi (AMF) on post-transplant growth and metal uptake of five woody species: (Senna multijuga (L.C. Rich.) Irwin et Barneby (cássia verrugosa), Luehea grandiflora Mart. et Zucc. (açoita-cavalo), Enterolobium contortisiliquum (Vell.) Morong (tamboril), Albizia lebbeck (L.) Benth. (albizia) and Senna macranthera (Collard.) Irwin et Barneby (fedegoso)) in soil mixes containing increasing proportion of a heavy metal-contaminated soil (PCS) were studied. The experiment was carried out under greenhouse conditions at the Department of Soil Science of the Federal University of Lavras, Lavras (MG) during 180 days, from April to November of 1996. It was found that increasing the PCS in the soil mix reduced plant growth and mycorrhizal colonization. Such effects resulted from increased plant metal uptake, mainly Cd and Zn. Inoculation with AMF at the seedling stage enhanced post-transplant growth in the non-contaminated soil and in the soil mixes containing low PCS. Mycorrhizal colonization was reduced from 70 to 90% in the non-contaminated soil to near zero at high PCS. The critical toxicity levels (dry matter reduction by 10%) in the soil were in mg dm-3: 83, 57, 153, 256 and 16 for Zn and 1.3; 0.9; 0.8; 4.0 and 1.6 for Cd for "açoita-cavalo", "cássia verrugosa", "fedegoso", "tamboril" and "albizia", respectively. At this level of soil contamination, non-mycorrhizal plants yielded only 39% (mean for all species) of the maximum yield, therefore indicating the mycorrhizal benefits for outplant growth. Such benefits were related to lower contents of metals in the shoots. Although the mechanisms involved in these responses are not known, AMF was found to be important for the initial tree growth and for rehabilitation of heavy metal-contaminated soils in the tropics.
soil pollution; land rehabilitation; root symbiosis; mycorrhiza; Glomalean fungi; heavy metals