Arbuscular mycorrhizal fungi: key players in avoiding cadmium accumulation in food crops

Background: Cadmium (Cd) levels of food crops can be elevated through management activities and geogenic factors. While emphasis is placed on reducing Cd in phosphorus (P) fertilizers, increasing evidence shows that Cd accumulation in plants is markedly influenced by arbuscular mycorrhizal fungi (AMF). Mycorrhizas are highly effective in reducing shoot Cd accumulation through various mechanisms including Cd immobilization in fungal structures and increasing root zinc (Zn) uptake. Scope: The increase in plant Cd concentrations in response to short- or long-term P fertilization is not necessarily related to fertilizer Cd concentration. Novel results suggest that this counterintuitive result is related to suppressed mycorrhizal colonization by P fertilization. When applied P fertilizers reduce mycorrhizal colonization, there is risk for concurrent increased Cd accumulation in plants. Although the mechanism is not fully understood, grain Cd concentrations in crop rotations are highest in plants grown after non-mycorrhizal (e.g. rapeseed), rather than mycorrhizal species (e.g., wheat), probably due to diminished mycorrhizal activity by non-mycorrhizal plants. These findings indicate that rapeseed-wheat rotations may enhance Cd concentrations in human diets. Published data also show that AMF contribute up to 50% of total Zn uptake in plants. Conclusions: Considering various soil and crop management factors that negatively affect mycorrhizal colonization, a priority should be to maintain functional AMF in soils to support healthy food systems. Considering also the fundamental role of AMF in root Zn uptake and the global prevalence of human Zn deficiency, improving functioning of AMF may provide a dual benefit to healthy and nutritious food production.