Effects of exogenous selenium levels on humus characteristics in selenium-enriched soil and lead accumulation in Brassica juncea

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 Na 2 SeO 3 (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)