Abstract:
BACKGROUNDArbuscular mycorrhizal fungi (AMF) are ubiquitous soil fungi in natural and agricultural ecosystems. They are obligate symbionts that can form symbiotic association with the majority of terrestrial plants. AMF obtains carbohydrates from host plants to maintain its own growth; in return, AMF can help plants absorb mineral nutrients and water from the soil. Many studies demonstrate the importance of AM symbiosis in plant adaptation to various environmental stresses, including nutrient deficiency, drought stress and heavy metal (HM) contamination.
OBJECTIVESTo summarize the underlying mechanisms for the enhanced plant tolerance to HMs by AM symbiosis, and to overview the possible involvements of AMF in HM translocation, transformation and accumulation in the soil-plant continuum.
METHODSA literature review was conducted and a total of 189 publications were identified, from 1984 to 2018. Direct and indirect involvements of AMF in metal uptake and accumulation by host plants have been overviewed. Key factors influencing the mycorrhizal effects have been fully discussed.
RESULTSAMF can take an active part in HM uptake, accumulation and detoxification, resulting in protective effects on host plants against HMs. On one hand, AMF can directly immobilize HMs, influence bioavailability of HMs, and consequently influence HM uptake and accumulation by host plants. On the other hand, AMF can also indirectly influence plant tolerance to HM by improving plant mineral nutrition and promoting plant growth. The mycorrhizal effects can be influenced largely by HM type and contamination level, plant and AM fungal species, and soil chemo-physical properties.
CONCLUSIONSAMF can essentially influence plant metal uptake and tolerance, thus can be used for ecological restoration of HM contaminated soils. Future research should go deep into the stress physiology of AMF. The effectiveness of AMF in bioremediation is also expected to be tested under field conditions.
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