Change in phytoextraction of Cd by rapeseed (Brassica napus L.) with application rate of organic acids and the impact of Cd migration from bulk soil to the rhizosphere.
Change in phytoextraction of Cd by rapeseed (Brassica napus L.) with application rate of organic acids and the impact of Cd migration from bulk soil to the rhizosphere.
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DOI：
10.1016/j.envpol.2020.115452
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发表时间：
2020-08
影响因子：
8.9
通讯作者：
D. Qiao;Hongfei Lu;Xiaoxian Zhang
中科院分区：
文献类型：
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作者：
D. Qiao;Hongfei Lu;Xiaoxian Zhang
添加外源低分子量有机酸是改善Cd污染土壤植物修复的有效技术，但施酸量对修复效果的影响及其潜在的限制因素尚不清楚。我们研究了这一点，采用盆栽试验与油菜（甘蓝型油菜L.）作为模型植物。塑料盆填充的桑迪壤土镉污染4.838 mg/kg的修订与乙酸，草酸，柠檬酸，苹果酸和酒石酸，分别在0.0至12.0 mmol/kg的应用率梯度变化。种植5个月后，每个盆中的植物收获，然后我们测量了根际交换态，碳酸盐，铁锰氧化物，有机和残留镉，以及镉在根和地上部。结果表明，有机酸均能促进植物对Cd的吸收，与不加酸的对照相比，有机酸能使植物对Cd的吸收提高100%以上。根际交换态Cd含量的增加是Cd提取量增加的主要原因。植物Cd含量与根际提取Cd的单位体积损失量呈弱相关（R2= 0.06），但用根生物量归一化后，二者呈良好的负相关（R2= 0.36）。质量平衡分析表明，土壤（根际和非根际土壤）中Cd的平均含量远高于根际Cd的含量，酸处理后Cd的迁移性提高是由于螯合作用的增强。由于配体在水中的扩散比Cd离子的扩散小一个数量级，因此，外源有机酸处理后，Cd从土壤中向根际的迁移是限制油菜提取Cd的主要因素。
Adding exogenous low-molecular weight organic acids is an effective technique to improve phytoremediation of Cd-contaminated soil and has been well documented, but how acid application rate affects remediation efficiency and its underlying limiting factors remains elusive. We investigated this using pot experiments with rapeseed (Brassica napusL.) as the model plant. Plastic pots packed with a sandy loam contaminated by Cd at 4.838 mg/kg were amended with acetic acid, oxalic acid, citric acid, malic acid and tartaric acid, respectively, at an application rate gradient varying from 0.0 to 12.0 mmol/kg. Plants in each pot were harvested after growing for five months, and we then measured the exchangeable, carbonate, Fe–Mn oxide, organic and residual Cd in the rhizosphere, as well as Cd in both roots and shoots. The results showed that all organic acids improved plant uptake of Cd and, compared with the control without acid addition, they could improve Cd uptake by more than 100%. The enhanced Cd extraction was due to the increase in exchangeable Cd in the rhizosphere. Plant Cd was weakly correlated to the amount of Cd lost from a unit volume of the rhizosphere due to root extraction (R2= 0.06), but a good negative correlation was found between them after normalizing the lost Cd by root biomass (R2= 0.36). Mass balance analysis revealed that the average Cd content in soil (rhizosphere and bulk soils combined) was much higher than the Cd content in the rhizosphere, and the improved Cd mobility after acid addition was thus due to the increased chelation. As diffusion of ligands in water is one order in magnitude smaller than diffusion of Cd ions, our results suggested that Cd migration from the bulk soil into the rhizosphere was a major factor limiting Cd phytoextraction by rapeseed after adding the exogenous organic acids.