ARBUSCULAR MYCORRHIZAE: POTENTIAL APPLICATIONS IN PHYTOREMEDIATION
Matthias C Rillig¹, C Rosier¹, J Driver¹ and M A Hamilton²
¹Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
(matthias@mso.umt.edu)
²Biotechnology Department, Idaho National Environmental and Engineering Laboratory,
Idaho Falls, ID 83415, USA
Arbuscular mycorrhizal fungi (AMF; phylum: Glomeromycota) are ubiquitous root symbionts forming mutualistic associations with the majority of plants on earth. AMF have a large influence on plant physiology, plant communities, and ecosystem productivity. Some of the more widely appreciated effects of AMF are in plant mineral nutrition, the fungus being in a key position at the interface of root and soil, with extensive amounts of fungal mycelium foraging in the soil beyond the root's depletion zone. Other effects of arbuscular mycorrhizae are related to plant water relations, resistance against root pathogens, and to the maintenance/ formation of soil structure.
Despite their huge impact on plant growth and soils AMF have been largely ignored in phytoremediation; this may be partly related to the fact that some plants widely used in phytoextraction (hyperaccumulators) are in the Brassicaceae, a plant family that is typically non-mycorrhizal. However, many plant species used in phytoremediation are mycorrhizal.
If the remediation goal is phytoextraction, AMF may enhance the uptake of the contaminant into the plant, or reduce uptake (i.e. interfere with phytoextraction). In the latter case, AMF have generally such a strong influence on plant growth/ biomass that the effect of AMF on phytoextraction is still positive overall.
If the goals is phytostabilization/ sequestration in the soil, AMF may be important through the production of the protein glomalin. Glomalin is a unique compound produced by AMF in relatively large amounts (several mg g-1 soil). Glomalin appears to be comparatively long-lived in soil (turnover time estimated at 40 years). Glomalin is highly correlated with soil aggregate stability, and hence soil stabilization, a desirable property in restoration/ reclamation. Furthermore, glomalin may be able to sequester certain contaminants.
Whatever the remediation goal and the contaminant of concern, it is becoming increasingly apparent that AMF species differ strongly in the "services" they provide to the host plant, and to ecosystems. This difference among AMF species could account for inconsistencies in the literature with respect to AMF effects. Also, this opens the possibility that tailored AMF inoculum may become available. "Managed" mycorrhizal symbioses may then be better suited for specific phytoremediation purposes.