Farmland Irrigation Research Institute, Chinese Academy of Agricultural Sciences, Xinxiang, Henan Province, 453002, China.
Sustiainable Agriculture Sciences, Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, United Kingdom.
Ecotoxicol Environ Saf. 2020 Apr 15;193:110306. doi: 10.1016/j.ecoenv.2020.110306. Epub 2020 Feb 25.
The impact of iron plaque (IP) on bioavailability of heavy metals to plants has been well documented, but the role of zinc (Zn) in modulating the associated processes remains elusive. We took Iris pseudacorus used in wetland for remediating Cd-contaminated water as an example and systematically studied the combined influence of Cd and Zn concentration on formation of IP and its consequence for immobilization and plant uptake of Cd. The experiment was conducted in hydroponic culture and in each treatment, we measured the physiological traits, activity of antioxidant enzymes (SOD, POD, CAT), mass of the IP, as well as the Cd content in both plant tissues and IP. The results showed that increasing Cd concentration resulted in a steady reduction in IP while the impact of zinc on IP was complicated and appeared to be coupled with Cd. When the Cd concentration was low (0.5 mg L measured as CdCl 2·5HO) increasing Zn concentration reduced IP, while when the Cd concentration was increased to 5 mg L increasing zinc concentration led to an increase in IP mass first followed by a decline after Zn concentration exceeded 100 mg L (measured as ZnSO·7HO). The change in IP as affected by Zn had a strong consequence for immobilization and plant uptake of Cd. When Cd concentration was low, the IP was comparatively abundant and hence adsorbed most Cd. In contrast, when Cd concentration was high, the IP reduced and the amount of Cd taken up by plant roots and translocated to shoots and leaves increased. Both Cd immobilization and its plant uptake were modulated by Zn concentration. At low Cd concentration the combined Cd immobilized and taken up by plant peaked when the Zn concentration was 50 mg L, while at high Cd concentration the combined Cd reached maxima when theZn concentration was 100 mg L. The activity of the antioxidant enzymes changed significantly with Zn rather than with Cd. Regardless of Cd concentration, the activity of all three antioxidant enzymes increased first with zinc concentration before declining when the Zn concentration exceeded approximately 100 mg L in all treatments, comparable with the change in immobilization and plant uptake of Cd as the Zn concentration increased. SEM analysis did prove the formation and variation of IP on the root surface of Iris pseudacorus in different treatments. We also found that the plant developed a survival strategy by scarifying its leaves with high Cd content. The results presented in this paper has wide implications as it revealed that care needs to be taken in applying Zn to enhance Cd immobilization and its plant uptake as exceeding the optimal application rate might reduce remediating efficiency rather than increase it.
铁斑（IP）对植物中重金属生物利用度的影响已有充分的记录，但锌（Zn）在调节相关过程中的作用仍然难以捉摸。我们以用于修复 Cd 污染水的湿地植物鸢尾为例，系统地研究了 Cd 和 Zn 浓度对 IP 形成的综合影响及其对 Cd 固定和植物吸收的影响。该实验在水培条件下进行，在每个处理中，我们测量了生理特性、抗氧化酶（SOD、POD、CAT）活性、IP 质量以及植物组织和 IP 中的 Cd 含量。结果表明，随着 Cd 浓度的增加，IP 不断减少，而锌对 IP 的影响复杂，似乎与 Cd 耦合。当 Cd 浓度较低（以 CdCl2·5H2O 计为 0.5mg/L）时，增加 Zn 浓度会降低 IP，而当 Cd 浓度增加到 5mg/L 时，增加 Zn 浓度会先增加 IP 质量，然后在 Zn 浓度超过 100mg/L（以 ZnSO4·7H2O 计）后下降。Zn 对 IP 的影响变化对 Cd 的固定和植物吸收有很大影响。当 Cd 浓度较低时，IP 相对丰富，因此吸附了大部分 Cd。相反，当 Cd 浓度较高时，IP 减少，植物根系吸收并转运到茎叶的 Cd 量增加。Cd 的固定和植物吸收都受到 Zn 浓度的调节。在低 Cd 浓度下，当 Zn 浓度为 50mg/L 时，植物固定和吸收的 Cd 总量达到峰值，而在高 Cd 浓度下，当 Zn 浓度为 100mg/L 时，植物固定和吸收的 Cd 总量达到峰值。抗氧化酶的活性随着 Zn 而不是 Cd 而显著变化。无论 Cd 浓度如何，在所有处理中，当 Zn 浓度超过约 100mg/L 时，所有三种抗氧化酶的活性都先随着锌浓度的增加而增加，然后下降，这与 Zn 浓度增加时 Cd 的固定和植物吸收的变化相似。SEM 分析确实证明了在不同处理中鸢尾根表面 IP 的形成和变化。我们还发现，植物通过对高 Cd 含量的叶片进行自噬来形成一种生存策略。本文的研究结果具有广泛的意义，因为它表明，在应用 Zn 来增强 Cd 的固定和植物吸收时需要谨慎，因为超过最佳应用率可能会降低修复效率，而不是提高修复效率。
