Selenate redistribution during aging in different Chinese soils and the dominant influential factors.

To date, few works have attempted to determine the effect of soil types on Selenium aging process and the possible influential factors. In this study, the differences in Se speciation distribution and availability in 15 Chinese typical agricultural soils were investigated using spiked selenate for the entire year. Results evidenced that after one year of incubation, Se transformed from soluble fraction to Fe/Mn oxides and organic matter bound fractions in neutral or alkaline soils (pH 7.09-8.51) and from exchangeable fraction to residual fraction in acidic soils (pH 4.89-6.82). The available Se content in all soils declined rapidly at the initial stage of aging, with most of the neutral or alkaline soils reaching equilibrium after 109 d, whereas the acidic soils reached equilibrium after only 33-56 d. The available Se content in soil decreased constantly during the entire aging process in S4 (Xinjiang Gray desert soil), S12 (Anhui Yellow brown earths), and S15 (Hunan Krasnozems). Elovich model was the best model (R2 > 0.80) in describing the Se aging process. Estimated time for exogenous Se reaching the distribution of available Se in corresponding native soils extended from 9.7 y to 50.2 y, indicating a much longer time was required for spiked soil to reach equilibrium. Soil pH was the most significant factor directly and negatively influencing the aging process (p < 0.05), while organic matter played a dual role on Se speciation. Results could provide reference for the selection of unified equilibrium time on Se-spiked experiment.

[Differences of selenium uptake pattern of pakchoi and the possible mechanism when amended with selenate and selenite].

In order to produce selenium-enriched crops and provide a theoretical basis of phytoremediation to selenium contaminated soil, pot experiment and lab analysis were carried out to examine the differences of selenium uptake pattern and bioavailability to pakchoi (Brassica chinensis L.) when amended with selenate and selenite. Meanwhile, dynamic changes of soil available Se was analyzed to explore the reason. The results showed that no significant differences in pakchoi shoot biomass between selenate and selenite treatment were observed. The Se concentration in pakchoi decreased rapidly across time in the selenate treatments, while increased with the growing period in the selenite treatments. For the selenate treatments, the pakchoi shoot Se concentration was significantly higher than that in roots, but the opposite results were found in the selenite treatments. In the whole growth period of pakchoi, Se concentration in selenate treatment was 2-60 times higher of that in selenite treatments. The content of available Se in soil slightly decreased with the growth of pakchoi in the selenite treatments, but it decreased rapidly in the selenate treatments. The significant correlations between soil available Se and Se concentration in shoots and roots of pakchoi was found in selenate treatments, the correlation coefficients were 0.901 and 0.864, respectively. On the contrast, no significant correlation was observed between soil available Se and Se concentration of roots and shoots in selenite treatments. The results indicated that the differences between the Se uptake pattern of selenate and selenite on pakchoi were the comprehensive function of the ability of soil providing Se and crop uptake ability.