Silicon Mediated the Detoxification of Cr on Pakchoi (Brassica Chinensis L.) in Cr-contaminated Soil

Abstract To test the hypothesis that exogenous silicon (Si) would mediate the detoxification of Chromium (Cr) on pakchoi ( Brassica Chinensis L.) growing in Cr-contaminated soil, a pot experiment that 0, 50, 100 and 200 mg·kg -1 Cr (Na 2 Cr 2 O 7 2H 2 O) were supplied to soil together with 0, 0.5, 1.0 and 1.5 g·kg-1 Si (Na2SiO3) for 48 days, was studied. Results showed that supplying Si improved the growth of pakchoi in low Cr level. However, the shoot dry weight decreased with the increasing Si supplied in high Cr level. Compared with under non-Cr stress, the application of Si significantly increased the activities of POD, SOD and CAT of pakchoi under excess Cr. However, antioxidant enzymes activities displayed no difference under three Cr levels supplied. Shoot Cr accumulation decreased, while root Cr concentration increased, which was ascribed to the formation of precipitation-bound, “organic matter bound” Cr and the reduction of exchangeable-bound Cr fractions in the soil. Furthermore, the rhizosphere soil pH increased with Si level under either Cr level, suggesting that exogenous Si would induce the alkalization in the rhizosphere mediated detoxification of Cr on pakchoi by promoting the formation of precipitation-bound, organic matter bound Cr in Cr-contaminated soil, thereby probably decreasing Cr uptake from Cr-contaminated soil. These results proved direct evidence that Si played a mediated role, which decreased Cr uptake and improved the stabilization of Cr in Cr- contaminated soil.