Effects of selenite and selenate application on growth and shoot selenium accumulation of pak choi (Brassica chinensis L.) during successive planting conditions.

Selenate and selenite are two main kinds of inorganic selenium (Se) sources in soil, but these substances can pose threats to the environment. Phytoextraction is an emerging technology to remove Se from polluted soils by using a hyper-accumulator. In this study, a pot experiment was conducted to investigate Se phytoextraction potential of pak choi (Brassica chinensis L.) and to determine the effects of Se on growth and Se accumulation of pak choi under successive planting conditions (four crops). Results showed that Se concentration in pak choi shoots significantly increased as selenate and selenite rates increased. Se concentration increased in successive crops on soil treated with selenite; by contrast, Se concentration decreased in crops on soil treated with selenate. Se concentrations of pak choi on soil treated with selenate were higher than those on soil treated with selenite. The maximum Se accumulations amount in crops on selenite- and selenate-treated soil were 7818 and 8828 μg · pot(-1), respectively. High bioconcentration factor (BCF) values indicated that pak choi could accumulate more Se from Se-contaminated soil. The Se phytoextraction efficiency of pak choi increased under successive planting conditions in selenite and selenate treatments; the maximum Se phytoextraction efficiencies of four successive crops of pak choi on selenite- and selenate-treated soil were 4.91 and 31.90 %, respectively. These differences between selenate and selenite treatments were attributed to the differences in Se forms in soil. Total and available Se contents in soil decreased significantly during repeated planting crops on soil treated with selenate; conversely, total and available Se contents decreased slightly in crops on soil treated with selenite. These results suggested that pak choi could highly tolerate and accumulate Se. Thus, pak choi may remove Se from contaminated soil; indeed, pak choi can be used in the phytoextraction of Se in polluted soil.