Soybean root exudates increase the physiological diversity of bacteria in cadmium-treated soil
Abstract
Three soybean cultivars with contrasting retention of cadmium (Cd) in the root were grown in Cd-spiked nutrient solution and used to determine that symplastic compartmentalization of Cd in roots is probably responsible for retention of Cd in roots. Roots of the low Cd-accumulator AC Hime treated with 30 mM Cd exuded up to 10-fold higher concentrations of citric, succinic, fumaric and malic acids into the hydroponic solution when compared to control; concentrations of the same organic acids from the high Cd-accumulator Westag 97 increased by up to 3-fold. The same cultivars were grown in Cd-spiked soil and the physiological profiles of the rhizosphere bacteria were assessed using Biolog® EcoPlatesTM to test the hypothesis that bacterial community diversity increases in response to organic acids exuded by the plant. Bacteria in the rhizosphere of AC Hime, the cultivar with the highest Cd-induced exudation of organic acids, had a distinct carbon utilization pattern, illustrating important interactions among rhizosphere bacteria, plants and toxic metals as a result of metal contamination.