Phytoremediation, including phytoextraction, phytostabilization and phytovolatilization, is an in situ remediation technology with considerable promises for restoring heavy metal-contaminated sites. In recent years the application of symbiotic microorganisms such as mycorrhizal fungi to enhance phytoremediation efficiency has attracted more and more attention.
It is well known that arbuscular mycorrhizae (AM) are ubiquitous symbiotic associations found in both natural and agricultural ecosystems, including heavy metal contaminated sites. AM fungi provide direct links between soil and roots, and consequently may have an essential contribution to phytoremediation by influencing heavy metal availability and enhancing plant tolerance. The mechanisms exerted by AM fungi to attenuate heavy metal stresses to plants may include chelation/immobilization of heavy metal in the extraradical mycelium, improved mineral nutrition (especially P), changes in rhizosphere pH, regulation of metal transporter gene expressions, etc. Furthermore, AM fungi also affect metal uptake by plants from soil and translocation from root to shoot, however, mycorrhizal effects may depend on elements, plant and fungal species/ecotypes. For the remediation of agricultural soils, phytoextraction is an ideal strategy. In this case, AM fungi may stimulate phytoextraction by essentially improving plant growth and increasing total metal uptake, even if metal concentration in plant tissues may be decreased by dilution effect. For the restoration of mine spoils or tailings, AM fungi may make a contribution to phytostabilization by retention of heavy metals in roots and improving plant adaptation to environmental stresses.
Future studies on AM-assisted phytoremediation may focus on: (1) the molecular mechanisms that AM fungi regulate heavy metal uptake and translocation; (2) the interaction between AM fungi and other beneficial microorganisms; (3) the combination of other remediation techniques and AM-assisted phytoremediation; (4) the selection of proper plants with the effective AM fungi; (5) the role of AM consortium and indigenous AM fungi; (6) AM-assisted phytoremediation of polymetallic soils; and (7) demonstration of AM-assisted phytoremediation in field.