Low concentration of copper inhibits colonization of soil by the arbuscular mycorrhizal fungus Glomus intraradices and changes the microbial community structure.

Common agricultural practices result in accumulation of copper in agricultural soils worldwide. The effect of bioavailable copper ([Cu](bio)) on colonization of soil by the AM fungus Glomus intraradices and other soil microorganisms was investigated in microcosms containing copper-amended soil. To avoid indirect effects through the plant, copper was only added to root-free microcosm compartments. [Cu](bio) was measured using a Pseudomonas fluorescens biosensor strain. In the range of 0-1.5 μg g(-1) [Cu](bio), a log-log linear relationship between added copper and [Cu](bio) was found. Microbial colonization of the root-free compartment was evaluated by whole-cell fatty acid analysis (WCFA) and amplified rDNA restriction analysis (ARDRA). The WCFA analysis showed that the AM fungus soil colonization was severely inhibited by Cu with a 50% reduction of mycorrhizal growth at 0.26 μg g(-1) [Cu](bio). The growth of other main microbial groups was not significantly affected by copper. However, ARDRA analysis showed a very strong effect of copper on the bacterial community composition probably caused by an increased proportion of Cu-resistant bacteria. Our results suggest that problems with plant yield may arise when converting slightly copper-contaminated soils to land uses such as low-input and sustainable agriculture that are dependent on AM fungal symbiosis.