Impact of increasing chromium (VI) concentrations on growth, phosphorus and chromium uptake of maize plants associated to the mycorrhizal fungus Rhizophagus irregularis MUCL 41833

Arbuscular mycorhizal fungi (AMF) associated to plants may represent a promising phyto-remediation avenue due to the widely documented role of these fungi in alleviation of numerous abiotic (e.g. heavy metals) stresses. In the present work, it was the objective to study the dynamics of inorganic phosphorus (Pi) and chromium (VI) (Cr(VI))and total Cr uptake by the plant-AMF associates Zea mays thorn R. irregularis MUCL 41833, under increasing (i.e. 0,0.1, 1 and 10 mg L-1) concentrations of Cr(VI). The plant-AMF associates were grown in a circulatory semi-hydroponiccultivation system under greenhouse conditions. We demonstrated that Cr(VI) had an hormesis effecton root colonization of maize. Indeed, at 0.1 and 1 mg L-1 Cr(VI), root colonization was increased by approximately 55% as compared to the control (i.e. in absence of Cr(VI) in the solution), while no difference was noticed at 10 mg L-1 Cr(VI) (P <= 0.05). However, this did not result in an increased uptake of Pi by the AMF-colonizedplants in presence of 0.1 mg L-1 Cr(VI) as compared to the AMF control in absence of Cr(VI) (P <= 0.05). Conversely, the presence of 1 mg L-1 Cr(VI) stimulated the Pi uptake by non-mycorrhizal plants, which absorbed 17% more Pi than their mycorrhizal counterparts (P <= 0.05). In addition, the non-mycorrhizal plants absorbed, in average, 8% more Cr(VI) than the mycorrhizal plants. Overall, our results prompt the hypothesis that in presence of AMF, the regulation of uptake of Cr(VI) and Pi by plant roots is done mostly by the fungus rather than the root cells. This regulated uptake of roots associated to AMF would indicate that the symbiosis could benefit the plants by providing a stable Pi uptake in a Cr(VI) polluted environment.

Automated summary

This study found that AMF can promote root colonization of maize in the presence of Cr(VI), though it does not significantly increase the uptake of Pi at lower Cr(VI) concentrations. Additionally, the presence of 1 mg L-1 Cr(VI) stimulates non-mycorrhizal plants to absorb more Pi and Cr(VI) compared to mycorrhizal plants.