Studies On The Mechanism Of Silicon Controlling The Adsorption Of Heavy Metal Chromium In Pakchoi (Brassica Chinensis)

The pollution of heavy metal chromium in soil has been becoming more serious at present. It has already become one of the pollution elements in soil and water. The suitable method of regulation and control is one of the effective methods to reduce the content of heavy metal in soil. This research regarding pakchoi as materials studied the silicon effect on pakchoi growth, chromium absorption and distribution, and probed into the laws of silicon migration among heavy metal chromium and pakchoi. Expounding the mechanism of silicon inhibiting the heavy metal Cr poison to the pakchoi was main aim. The result shows that:1. In the treatments of Cr₁ (added in the form of Na₂Cr₂O₇, amount was 50 mg per kilogram soil), Cr₂ (added amount was 100 mg·kg^-1 soil) and Cr₃ (added amount was 200 mg·kg^-1 soil), the fresh weight and chlorophyll content of pakchoi which was the highest in the treatment Si₁ (added in the form of Na₂SiO₃, amount was 0.5g per kilogram soil) reduced after increasing with the increase of silicon content. In the treatment of Si₁ the fresh weight of the pakchoi root, stem, leaf and total reduced after increasing with the increment of chromium content, while they reduced gradually in the treatments of Si₂ which added amount was 1.0 g per kilogram soil and Si₃ which added amount was 1.5g per kilogram soil2. In the treatment of Cr₁ chromium content in pakchoi root, stems and leaf with the increment of silicon concentration, In the treatment of Cr₂ the difference of chromium content in pakchoi stems and leaf were insignificant while chromium content in root reduced, the minimum chromium content in stem was in the treatment of Si₁, while the leaf is in the treatment of Si₃. In the treatment of Cr₃, with the increase of silicon density, the Cr content of leaf department reduced gradually leaf Cr of the pakchoi has the lowest content in the treatment Si₃; under the treatment of Cr₁, the chromium uptake of root and leaf reduced while chromium content in stem changed little. Under the treatments of Cr₂ and Cr₃, the total chromium content of root stem and leaf reduced.3. Ninety percent of the silicon added into soil existed in unavailable state because of precipitation and absorption reaction with clay mineral. The addition of silicon increased soil pH, precipitated form of chromium. Thus reduced the biological validity of chromium, and inhibited the pakchoi absorption of the heavy metal chromium.4. The accumulating amount of silicon was uneven in the different parts of pakchoi. the leaves distributed the most chromium, accounts for 68.1% of the total amount, secondly the stem took 20 % of the total amount, the root accounts for 11.9%; But the most chromium amount accumulated in leaf of pakchoi accounted for 68.1% of the total amount. secondly in the root (36.1%), stem account for 22.4%.5. The content of chromium in agricultural product was less than 0.5 mg·kg^-1 according to national standard. In different treatments of chromium, the largest Cr content in the stem and leaf was all smaller than the standard except root. According to the regression analysis when the chromium content was at the minimum the silicon concentration added into soil was 1.41, 1.15, 1.23 and 1.40 g·kg^-1 respectively. While the minimum uptake of chromium needed the silicon was 0.53, 2.00,1.10,1.33 g·kg^-1. Relevant analysis results show that: With chromium increased, the correlation between growth indexes and content of silicon added into soil got better and better. It showed that in the treatment of the high concentration of chromium, the concentration of silicon was closed to the growth of pakchoi.