Heavy metals in sewage sludges contribute to their adverse effects on the arbuscular mycorrhizal fungus Glomus mosseae

Applying sewage sludges to agricultural land is a widespread practice because of the sludges' agronomic value as a source of plant nutrients and organic matter. Nevertheless, sludges often contain micropollutants that can constitute a menace for health and the environment. Arbuscular mycorrhizal fungi are sensitive to sewage sludges that have been spiked, or not, with metallic trace elements (MTE). Here we have investigated if MTE in sewage sludges could be responsible for effects on mycorrhizal development between Glomus mosseae and Medicago truncatula. The impact of a dehydrated or composted urban sewage sludge spiked or not with MTE, was tested on spore germination and root colonization by G. mosseae. The sewage sludges depressed both the presymbiotic and in planta stages of development of the mycorrhizal fungus. This negative effect was more related to the metallic pollutant contents of the sludges than to the presence of antagonistic microorganisms or phosphorus.