CAS Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China.
Sci Total Environ. 2022 Feb 1;806(Pt 3):151306. doi: 10.1016/j.scitotenv.2021.151306. Epub 2021 Oct 29.
Improving phytoremediation techniques requires a thorough understanding of the mechanisms of plant uptake and the replenishment of the bioavailable pool of the target element, and this may be effectively explored using stable isotope methods. A repeated phytoextraction experiment over five successive crops of cadmium (Cd) and zinc (Zn) hyperaccumulator Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu (Crassulaceae) was conducted using four agricultural soils differing in soil pH and clay content. The isotopic composition of total Zn and NHOAc-extractable Zn in soils before phytoextraction and after the fifth crop were determined, together with Zn in shoot samples in the first crop. S. plumbizincicola preferentially took up light Zn isotopes from the NHOAc-extractable pool (ΔZn = -0.42 to -0.16‰), indicating the predominance of Zn low-affinity transport. However, after long-term phytoextraction NHOAc-extractable Zn became isotopically lighter than prior to phytoextraction in three of the soils (ΔZn = -0.39 to -0.10‰). This was resulted from the equilibrium replenishment of Zn bound to iron (Fe) and manganese (Mn) oxides based on Zn isotopic and chemical speciation analysis. Zinc showed opposite fractionation patterns to Cd in the same plant-soil system with heavy Cd isotope enrichment in S. plumbizincicola (ΔCd = 0.02-0.17‰) and in the NHOAc-extractable pool after repeated phytoextraction (ΔCd = 0.07-0.18‰). This indicates different mechanisms of membrane transport (high-affinity transport of Cd) and supplementation of the bioavailable pool in soil (Cd supplied mainly through complexation with root-derived organic ligands) of the two metals. The combination of chemical speciation and stable Zn isotope ratios in the plant and the bioavailable soil pool reveal that the Zn pool related to Fe and Mn oxides became increasingly bioavailable with increasing crop generations. Capsule: Stable isotope analysis indicates that soil Fe- and Mn-oxide bound Zn replenishment boosted Zn uptake by the hyperaccumulator Sedum plumbizincicola during long-term remediation.
利用稳定同位素方法可以深入了解植物吸收和目标元素生物可利用池补充的机制，这对于改进植物修复技术至关重要。我们在 5 个连续的镉（Cd）和锌（Zn）超积累植物Sedum plumbizincicola X.H. Guo et S.B. Zhou ex L.H. Wu（景天科）作物周期中进行了反复的植物提取实验，实验所用的土壤具有不同的 pH 值和粘粒含量。在植物提取之前和第五个作物周期之后，测定了土壤中总 Zn 和 NHOAc 可提取 Zn 的同位素组成，以及第一个作物周期中植物地上部分的 Zn。Sedum plumbizincicola 优先从 NHOAc 可提取池中吸收轻的 Zn 同位素（ΔZn = -0.42 至-0.16‰），表明 Zn 低亲和力运输占主导地位。然而，在长期的植物提取后，在三种土壤中，NHOAc 可提取 Zn 的同位素变得比植物提取前更轻（ΔZn = -0.39 至-0.10‰）。这是基于 Zn 同位素和化学形态分析，Zn 与铁（Fe）和锰（Mn）氧化物结合物的平衡补充导致的。在同一植物-土壤系统中，Zn 和 Cd 表现出相反的分馏模式，在 Sedum plumbizincicola 中富含重的 Cd 同位素（ΔCd = 0.02-0.17‰），并且在重复植物提取后，NHOAc 可提取池中的 Cd 同位素也变得更重（ΔCd = 0.07-0.18‰）。这表明两种金属的膜转运机制不同（Cd 是通过高亲和力转运），以及土壤中生物可利用池的补充途径不同（Cd 主要通过与根衍生的有机配体络合而供应）。植物和生物可利用土壤池中化学形态和稳定 Zn 同位素比值的结合表明，与 Fe 和 Mn 氧化物相关的 Zn 池随着作物代际的增加而变得越来越具有生物可利用性。总之，稳定同位素分析表明，在长期修复过程中，土壤中 Fe 和 Mn 氧化物结合的 Zn 补充促进了超积累植物 Sedum plumbizincicola 对 Zn 的吸收。
