Purpose

Many selenium (Se)-enriched soils suffer from severe lead (Pb) contamination. Many studies indicated that soil humus can effectively absorb heavy metal ions, and Se can alleviate Pb accumulation in plants. However, few studies explored the effects of exogenous Se levels on humus composition in Se-enriched soil and Pb enrichment in Brassica juncea (B. juncea).

Materials and methods

We conducted a pot experiment. First, the Se-enriched soil sample was mixed with 200 mg·kg⁻¹ level of Pb and maintained in a stable equilibrium for 2 months. Second, the soil was treated in different ways. Six treatments were performed as follows: one control treatment (CK) was included, and five different doses of Na₂SeO₃ (S1, S2, S3, S4, and S5) were applied to the pots. Each treatment was prepared in triplicate. Then, the B. juncea seeds were sown in each pot. Finally, on the 40th day, B. juncea plants in each pot were harvested and soil was sampled for subsequent experimental analysis.

Results and discussion

The different levels of selenite decreased the Pb content in roots, stems, and leaves of B. juncea by 5.43–48.70%, 5.13–39.86%, and 6.62–31.91%, respectively, and significantly increased the Se contents by 7.22–24.21, 5.91–34.11, and 12.49–57.06 folds compared with control treatment, respectively. The total Pb in the soil was reduced by 1.06–13.68% and soil pH was increased by approximately 0.06–0.21 units in all treatments. Exogenous Se also reduced diethylenetriaminepentaacetic acid (DTPA)-extracted Pb and exchangeable and iron-manganese oxide-bound Pb but increased the content of carbonate-bound and residual Pb. The composition of humus followed this order as follows: humic acids (HA) < fulvic acids (FA) << humin (HM); the adsorption isotherms of HA and FA for Pb²⁺ were well described by the Langmuir adsorption model, and the adsorption process were positively correlated with the Pb²⁺ concentration (P < 0.05). The Se levels, contents of humus components, and Pb concentration in soil were negatively correlated with each other.

Conclusions

The addition of low Se levels can effectively antagonize Pb in Se-enriched soil and contribute to the adsorption of Pb by soil humus components, inhibiting the migration of Pb in soil-B. juncea systems to reduce the Pb accumulation in B. juncea.

Graphical abstract

中文翻译：

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外源硒水平对芥菜富硒土壤腐殖质特征和铅积累的影响

目的

许多富含硒（Se）的土壤都遭受严重的铅（Pb）污染。许多研究表明，腐殖质可以有效吸收重金属离子，而硒可以减轻植物体内铅的积累。但是，很少有研究探索外源硒水平对富硒土壤中腐殖质组成和芥菜（B. juncea）中铅富集的影响。

材料和方法

我们进行了锅实验。首先，将富硒土壤样品与200 mg·kg ^-1的Pb混合，并保持稳定平衡2个月。第二，对土壤进行了不同的处理。如下进行六种处理：包括一个对照处理（CK），并将五种不同剂量的Na ₂ SeO ₃（S1，S2，S3，S4和S5）应用于盆中。每种处理均重复三次。然后，在每个盆中播种芥菜种子。最后，在第40天，收获每个盆中的芥菜芽孢杆菌植物，并取样土壤用于随后的实验分析。

结果和讨论

不同含量的亚硒酸盐使芥菜根，茎和叶中的铅含量分别降低了5.43–48.70％，5.13–39.86％和6.62–31.91％，并使硒含量显着提高了7.22–24.21，与对照相比，分别为5.91–34.11和12.49–57.06倍。在所有处理中，土壤中的总铅减少了1.06-11.38％，土壤pH值增加了约0.06-0.21个单位。外源硒还减少了二亚乙基三胺五乙酸（DTPA）提取的Pb和可交换的铁锰氧化物结合的Pb，但增加了碳酸盐结合的Pb和残留Pb的含量。腐殖质的组成遵循以下顺序：腐殖酸（HA）<富里酸（FA）<<腐殖质（HM）；HA和FA对Pb ²⁺的吸附等温线Langmuir吸附模型很好地描述了这些元素，并且吸附过程与Pb ²⁺浓度呈正相关（P  <0.05）。土壤中的硒水平，腐殖质成分含量和铅浓度呈负相关。

结论

低硒水平的添加可以有效拮抗富硒土壤中的铅，并促进土壤腐殖质组分对铅的吸附，从而抑制铅在芥菜土壤中的迁移，从而减少芥菜中铅的积累。

图形概要