Does arbuscular mycorrhizal fungus affect cadmium uptake and chemical forms in rice at different growth stages?

Effects of the arbuscular mycorrhizal fungus (AMF) - Rhizophagus intraradices (a mix of root pieces, mycelium pieces and spores) on the temporal variation of Cd uptake and chemical forms in rice at four growth periods (tillering, jointing, flowering, and ripening stages) were investigated in soil added with 0, 2 and 10mgCdkg^-1. Results showed that the interactions amongst rice growth stages, soil Cd concentrations and mycorrhizal inoculation had significant effects (P˂0.001) on root biomass, straw and root Cd concentrations, and straw Cd chemical forms in rice. Root colonization rates fluctuated with growth stages, reaching its peak at jointing stage and then decreasing at flowering and ripening stages. AMF increased the grain yield in rice plant grown in soil added with 10mgCdkg^-1, whereas no effect was found in soil added with 2mgCdkg^-1. In soil added with 2mgCdkg^-1, the concentrations of ethanol and d-H₂O extractable Cd at flowering stage was significantly reduced in mycorrhizal treatments, which subsequently induce less Cd accumulation in grains due to the positive correlations between ethanol or d-H₂O extractable Cd and grain Cd concentrations at flowering stage. In soil added with 10mgCdkg^-1, AMF significantly elevated the proportions of NaCl extractable Cd at ripening stage which also lead to the reduced grain Cd concentrations, since there was a negative correlation between the percentage of NaCl extractable Cd and grain Cd concentration at this stage. Our study indicated that flowering and ripening stages were important periods for AMF to limit the grain Cd concentrations in rice, when grown in Cd-contaminated soil.