Impacts of Cd on Temporal Dynamics of Nutrient Distribution Pattern of Bletilla striata , a Traditional Chinese Medicine Plant

Bletilla striata is an endangered medicinal plant the habitats of which are polluted by cadmium (Cd). Nutrient management is a potential way to mitigate Cd toxicity, providing reference for B. striata artificial cultivation. Pot experiments were undertaken to examine the effect of five levels of Cd concentration (control: 0.28 mg/kg; I: 0.37 mg/kg; II: 1.00 mg/kg; III: 7.39 mg/kg; IV: 54.6 mg/kg) on the temporal dynamics of nutrient allocation in B. striata components. The results showed that the content and accumulation of Cd increased significantly in all tissues of Bletilla striata as Cd concentration was increasing, and most accumulated in the roots and slightly transferred to the aboveground parts, while tubers were less likely to accumulate Cd. Excessive cadmium accumulation under long-term exposure reduced the biomass of all tissues of B. striata , and the yield was not significantly affected when cultivated in soil with a concentration of Cd ≤ 1 mg/kg. Potassium (K) was quickly transferred from the root to other tissues in response to the Cd stress. The absorption of zinc (Zn) increased at first and then decreased with increased Cd concentration. According to Pearson correlation analysis, a mechanism is suggested that Cd accumulation affects the absorption of nutrients but is positively and significantly correlated with translocation factor of K and Zn in the tuber. This may imply that B. striata tends to promote the absorption of nutrient elements to adapt to the Cd enrichment in tubers and to compensate for the interrupted mineral nutrition metabolism.