Manganese Nutrition and Improved Performance of Soybean Inoculated with Rhizobia and Arbuscular Mycorrhizas in Soil with Moderately Elevated Cadmium

The growth and element nutrition of soybean inoculated with Bradyrhizobium diazoefficiens and two arbuscular mycorrhizas (AM) (Claroideoglomus etunicatum and Rhizophagus sp. R10) were evaluated in potted soils with moderately elevated cadmium (Cd). Each independent experiment was setup as a randomized 3×4 factorial with soil Cd (0, 3, and 6 mg Cd kg-1 soil) and inoculation (rhizobium, AM fungi, rhizobium + AM fungi, uninoculated control) treatments. Elevated soil Cd decreased root colonization by C. etunicatum, but the reverse was the case with Rhizophagus sp. R10. In both experiments, dual inoculation had the best growth while Cd at 6 mg kg-1 soil lowered plant performance and effectiveness of B. diazoefficiens single inoculation. The Cd toxicity to nodules observed in single rhizobium treatment was minimized in dual inoculation, and nodule resilience against Cd was better when Rhizophagus sp. R10 was the co-inoculant. Compared to control, Rhizophagus sp. R10 decreased the Cd and Mn concentrations in the root, stem, and leaf; while C. etunicatum supported greater Cd phytoaccumulation but minimized Cd-induced fluctuations in root Mn and modulated Mn concentration in the leaf via increases in available soil Mn. Arbuscular mycorrhizas variably modulate Mn with Cd for improved performance of soybean in soils with moderately elevated Cd.