Influence of Pak choi plant cultivation on Se distribution, speciation and bioavailability in soil

AIMS: The study was aimed to provide better understanding on how plant cultivation affects Se distribution, transformation, and bioavailabilty in soil treated with exogenous selenite or selenate. METHODS: Pak choi (Brassica chinensis L.) was planted in loess soil (Eum-Orthic Anthrosol) spiked with different concentrations of exogenous selenite or selenate. Soil samples were collected from all pots before planting and after harvest to determine Se fraction and speciation. Se concentrations in pak choi were measured after harvest. RESULTS: The influence of pak choi on Se distribution differed among various soil fractions in selenite- or selenate-treated soil. Se distribution and speciation remained constant between selenite-treated soil after harvest and before planting, and Se mainly existed as exchangeable Se(IV) (59.8 %–61.6 %). By contrast, a considerable transformation of soluble Se(VI) to exchangeable Se(IV) was observed in selenate-treated soil. In addition, I R values increased, which quantitatively described the relative binding intensity of Se with soil, and MF values (mobility factor) decreased under selenate treatment. Changes in these two parameters indicated the reduced bioavailability of Se in soil after plant cultivation. Moreover, soluble Se(VI) content, organic Se content in soil, and Se concentrations in pak choi shoots and roots exhibited significant correlation in selenate-treated soil. Furthermore, the contents of soluble and exchangeable Se(IV) in selenite-treated soil were significantly correlated with Se concentration in pak choi roots, whereas soluble Se(VI) content was correlated with Se concentration in the shoots. CONCLUSIONS: Plant cultivation decreased Se bioavailability in selenate-treated soil but only minimally influenced the bioavailability of this element in selenite-treated soil. Moreover, soluble Se(VI) content was considered a suitable indicator for assessment of soil Se bioavailability. Organic matter-bound Se also can be a source of available Se in selenate-treated soil, but only exchangeable Se(IV) content can be used to assess Se availability in selenite-treated soil.