Transformation and bioavailability for Pak choi (Brassica chinensis) of different forms of selenium added to calcareous soil
不同价态外源硒在石灰性土壤中的形态转化及其生物有效性

The bioavailability of selenium in soils for plants depends more on its forms than on its total content. The aim of this study was to investigate transformation and bioavailability of additional selenite and selenate in calcareous soil to pak choi. A pot experiment was performed and a sequential extraction scheme was used in this study. Content of each selenium species in soil increased significantly with the added selenium (p < 0.01). The main selenium species in selenate-added soil was soluble form, while in selenite-added soil, it was mostly exchangeable and carbonate-bound selenium. Added selenate was hardly fixed by soil, and hence had relatively higher mobility than selenite in soil. Added selenite could transform from the soluble form to the other three forms, which would decrease its bioavailability. Monod model fitting results showed that the affinity of pak choi roots to selenate was larger than selenite. Estimated maximal selenium contents of pak choi shoots and roots in selenate-treated soils were 5 times and 2 times larger than in selenite-treated soils. In selenite-treated soils, estimated maximal selenium content of pak choi roots was 2.3 times larger than that in shoots, while in selenate-treated soils, the estimated maximal selenium contents of pak choi shoots and roots were approximately the same. In pak choi roots, adsorption was the dominant selenium accumulation method. In conclusion, selenate has higher bioavailability than selenite in calcareous soil.