Kalis Erwin J J, Temminghoff Erwin J M, Town Raewyn M, Unsworth Emily R, van Riemsdijk Willem H
Dep. of Soil Quality, Wageningen Univ., the Netherlands.
J Environ Qual. 2008 Oct 23;37(6):2221-31. doi: 10.2134/jeq2007.0543. Print 2008 Nov-Dec.
The total metal content of the soil or total metal concentration in the soil solution is not always a good indicator for metal availability to plants. Therefore, several speciation techniques have been developed that measure a defined fraction of the total metal concentration in the soil solution. In this study the Donnan Membrane Technique (DMT) was used to measure free metal ion concentrations in CaCl(2) extractions (to mimic the soil solution, and to work under standardized conditions) of 10 different soils, whereas diffusive gradients in thin-films (DGT) and scanning chronopotentiometry (SCP) were used to measure the sum of free and labile metal concentrations in the CaCl(2) extracts. The DGT device was also exposed directly to the (wetted) soil (soil-DGT). The metal concentrations measured with the speciation techniques are related to the metal adsorption at the root surface of ryegrass (Lolium perenne L.), to be able to subsequently predict metal uptake. In most cases the metal adsorption related pH-dependently to the metal concentrations measured by DMT, SCP, and DGT in the CaCl(2) extract. However, the relationship between metal adsorption at the root surface and the metal concentrations measured by the soil-DGT was not-or only slightly-pH dependent. The correlations between metal adsorption at the root surface and metal speciation detected by different speciation techniques allow discussion about rate limiting steps in biouptake and the contribution of metal complexes to metal bioavailability.
土壤中的总金属含量或土壤溶液中的总金属浓度并不总是衡量植物可利用金属量的良好指标。因此，人们开发了几种形态分析技术来测量土壤溶液中总金属浓度的特定部分。在本研究中，采用唐南膜技术（DMT）测量了10种不同土壤的CaCl₂提取物（模拟土壤溶液并在标准化条件下进行）中的游离金属离子浓度，而采用薄膜扩散梯度技术（DGT）和扫描计时电位法（SCP）测量了CaCl₂提取物中游离和不稳定金属浓度的总和。DGT装置也直接暴露于（湿润的）土壤中（土壤-DGT）。用形态分析技术测得的金属浓度与黑麦草（Lolium perenne L.）根表面的金属吸附有关，以便随后预测金属吸收情况。在大多数情况下，金属吸附与通过DMT、SCP和DGT测得的CaCl₂提取物中的金属浓度呈pH依赖性关系。然而，根表面的金属吸附与土壤-DGT测得的金属浓度之间的关系不依赖于pH值或仅略微依赖于pH值。根表面的金属吸附与不同形态分析技术检测到的金属形态之间存在相关性，这有助于讨论生物吸收中的限速步骤以及金属络合物对金属生物有效性的贡献。
