Effects of Greenhouse and Open-field Cultivation on Heavy Metal Uptake During Carrot Growth 温室与大田种植方式对胡萝卜生长过程中重金属吸收的影响

Clarifying the absorption dynamics of heavy metal(loid)s by crops under different cultivation methods is critical for risk management and control for heavy metal pollution. Here, taking carrots as an example, the pH, cation exchange capacity (CEC), and contents of heavy metals in soil and carrots were analyzed. We compared the absorption and transport characteristics of six metal(loid)s (As, Cd, Cr, Cu, Pb, and Zn) during the three key growth periods under greenhouse and open-field cultivation methods. In addition, the effects of planting methods on carrot biomass and heavy metal content over time were studied, and a health risk assessment was conducted. The results showed that the greenhouse and open-field cultivation methods had the following in common: ① As the carrots continuously grew, the metal uptake and biomass in the belowground part (edible part) and the metal(loid) concentrations in the aboveground and belowground parts both showed trends of increasing first and then decreasing or stabilizing. ② The absorption of As, Cd, Cr, and Pb in carrots was mostly accumulated in the aboveground part. ③ The content of Cd in the edible part exceeded the standard, and the total target hazard quotient was>1, indicating potential adverse health risks, most of which were contributed by As and Cd. Compared to that under open-field, the short-term greenhouse cultivation had a harvest time approximately 15 d earlier. The As, Cd, and Pb concentrations in the aboveground part during the seedling and fast-growing periods were significantly lower in the greenhouse than that in the open-field (P<0.05) but did not differ between greenhouse and open-field (except As) at the mature stage. The concentrations of As and Cd in the belowground part of greenhouse carrots were lower in the greenhouse than those of carrots grown in the open-field at the seedling stage (P<0.05). The absorption of As and Cd was decreased significantly from 0 to 95 d (P<0.05), and there was no significant difference in the metal concentration and absorption in the rest of the growth stages. The bioconcentration factors (BCF) of As, Cd, and Pb in the aboveground part in all stages and those of As and Cd in the belowground part in the seedling stage were lower in the greenhouse than that in the open-field. This study emphasizes the possibility of short-term changes in cultivation mode to reduce the risks of metal(loid)s in contaminated farmland vegetables.