Differences in arbuscular mycorrhizal colonisation influence cadmium uptake in plants

Cadmium (Cd) is one of the most toxic heavy metals found in soil. Arbuscular mycorrhiza (AM) is known to reduce Cd translocation in plants by immobilising Cd in the root system. The effect of mycorrhiza on plant Cd uptake is usually studied in simple systems with single strains of mycorrhizal fungi and few levels of Cd. Here we studied how a wide range of soil Cd concentrations affected plant AM colonisation, and how the species-specific differences in AM colonisation affected uptake, translocation, and toxicity of Cd in plants in a system with naturally occurring mycorrhizal fungi. Six plant species were grown in pots in a greenhouse across seven levels of Cd, which made it possible to model dose-response curves, and calculate EC(50)( )for each plant species. We found a remarkable trend where Cd at moderate levels stimulated mycorrhizal colonisation until a certain threshold where the symbiosis breaks down. Our results support the existence of a protective effect of AM fungi against Cd, as the symbiosis reduces Cd translocation to shoots, especially in plants with very high AM colonisation. Thus, we conclude that it is the combination of plant species and AM colonisation that determines Cd uptake in plants. AM is therefore an essential trait to consider when growing plants in Cd-polluted soil.