Cd Activation Mechanisms of High-Enriched Rapeseed (Brassica Napus L.) in Rhizosphere Soil

The study aimed to explore the Cd activation mechanisms of high-enriched rapeseed in rhizosphere soil. A pot experiment was carried out to compare the differences of pH, organic matter, oxidation reduction potential, cation exchange capacity and organic acids in rhizosphere soil among high-enriched (H), middle-enriched (M) and low-enriched (L) cultivars under slightly and moderately Cd contaminated farmlands (5 and 10 mg kg^− 1). Bioconcentration factor and removal efficiency in shoot of H were on average 25.5% and 15.5% higher than that of M, and 41.5% and 20.8% higher than that of L, respectively, owing to higher Cd concentration in plant (shoot and root). However, the ability to transport Cd from rapeseed roots to shoots did not have a promoting effect. Compared with M and L, H roots secreted more malic acid (MA) and citric acid (CA), leading to a significant increase in effective Cd concentration (EC). However, organic matter, pH, cation exchange capacity and oxidation reduction potential in rhizosphere soil, and tartaric acid and succinic acid secreted by rapeseed roots had no difference among different rapeseed cultivars. Besides, EC was positively correlated with Cd concentration in shoot (r = 0.969, p < 0.01) and root (r = 0.976, p < 0.01). Therefore, MA and CA were main Cd activation mechanisms in the remediation of Cd contaminated farmland by high-enriched rapeseed.