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Arbuscular mycorrhizal ( AM) fungi are one of the widely spread micro鄄organisms, which could form symbionts with more than 80% of the vascular plants in natural ecosystems. It has been showed that AM symbionts could improve plant nutrients and water absorption; increase the resistance ability to stress conditions, thus AM fungi could enhance the host plant growth. The plant soil鄄borne diseases caused by soil鄄borne pathogens, including fungi, nematodes and bacteria, are considered as one of the most difficult controlling diseases in agriculture ecosystem. Previous studies have been demonstrated that AM symbionts could increase plant resistance to diseases, and to antagonize soil鄄borne pathogens. Thus, using AM fungi as a biological control method to antagonize soil鄄borne pathogens has received increasing interests by phytopathologists and ecologists. On the basis of this, the mechanisms of resistance to diseases induced by AM fungi were summarized in this paper. Mechanisms covered in this review include root morphology alteration, regulation of secondary metabolite production, improvement of rhizosphere environments, competition with pathogenic microorganisms on invasive sites and on nutrition distribution in host plants, and formation of defense systems in plants. Firstly, the characteristics of root morphology alterations were explained, including how AM fungi influence their structures and functions. Secondly, the regulation of AM fungi to secondary metabolites was illustrated. Several types of products, including phytoalexin, callose, alkaloid and phenols were reviewed. Thirdly, AM fungi could improve the rhizosphere environments by influence soil physical and chemical proprieties, and enhance the growth of other beneficial microorganism in rhizosphere soil. Fourth, AM fungi could compete with pathogenic microorganisms. The two kinds of microorganisms maybe compete for the same invasive sites in root http: / / www.ecologica.cn systems, and thus they could regulate the nutrition distribution. Fifth, AM fungi could induced the host plant to form the defense systems in plants, including improvement the concentrations of phytohormone, induced the production of signal substrates, regulation of genes expression and enhanced the proteins production, thus AM fungi could enhance the resistance ability of host plant to pathogenic microorganisms. The aim of this paper was to enhance the potential use of AM fungi as a biological control method for preventing plant diseases in future.

Heavy鄄metal pollution in soil is a major threat to human health and the whole ecosystem, while bioremediation has become a promising option to recover the contaminated soils for its effective, non鄄intrusive and inexpensive. In particular, the application of symbiotic micro鄄organisms such as mycorrhizal fungi to enhance bioremediation efficiency has been paid more and more attention. Arbuscular mycorrhizal ( AM) fungi are one of the widely spread micro鄄organisms, which could form symbionts with most of the vascular plants in natural or artificial ecosystem. It has demonstrated that AM symbionts could increase the stressed ability of host plants in heavy metal polluted soil. Nowadays, using bioremediation methods to recovery heavy metal polluted soils with AM fungi has been one of the hotspots in environmental and ecological science. In order to review the physiological and molecular mechanism of heavy metals tolerance induced by AM fungi, four strategies were discussed in this paper: 1 ) the physical defense system formation, 2 ) the regulation to physiological metabolism of plants, 3) the production of biochemical antagonist material and 4) the regulation of gene expression. On the basis of this, this paper indicated that the possibility of using the system of AM鄄soil microbiology鄄host plant for remediation of heavy metals polluted soil in the future. For this purpose, to enhance the studies below would be necessary: 1 ) molecular mechanisms that AM fungi regulate heavy metal uptake and translocation; 2 ) phytoremediation of polymetal鄄 contaminated soils through selection of heavy metal tolerant AM fungi strains by genetic engineering; 3) the combination of other remediation techniques and AM鄄assisted bioremediation.