| With the development of industry and agriculture, the soil heavy metal pollution has become more and more serious. Lead(Pb) is a heavy metal with highly biological toxicity, not only reduced the yield and quality of agricultural products, but also migrated in the soil-plant-products system, which leads to a high lead concentration in some domestic cigarettes. Taking tobacco as test materials, several experiments was conducted to study the migration characteristics of lead in soil-tobacco system and effects of silicon and phosphorus on migration of lead form soil to tobacco, which clarify the forms transformation of lead in rhizosphere soil and lead uptake, accumulation and distribution characteristics of tobacco, in order to explore effective measures for reducing Pb concentration in tobacco leaf. The main results were as follow:(1) The concentration of Pb in root, stem and leaf increased with the increasing of Pb treatment during growth periods. Pb concentration in different organs ranged from 13.89 mg·kg-1 to 180.74 mg·kg-1. The peak of lead uptake appeared in peak to squaring stage, which accounts for 44.9% to 57.5% of the total accumulation amount. Meanwhile, peak to squaring stage were the key periods for Pb transport from root to shoot in tobacco plants. The concentration of Pb in different organs showed the follows sequence:root>stem> leaf. The concentration of Pb in different leaves showed the follows sequence:lower leaf> middle leaf> upper leaf. Under the condition of CK, it mainly existed with NaCl-extractable, HAc-extractable and HCl-extractable Pb and with percentage of 66.4%-72.4%. With the increasing concentration of applied Pb in soil, the concentration of ethanol-extractable Pb increased significantly. The concentration of Pb in Subcellular distribution showed the follows sequence:cell wall> soluble fraction> organelles. With the increasing concentration of applied Pb in soil, the percentage points of organelles on tobacco root increase by 9.9% to 24.3%, which could be conducive to the Pb migration. Along with the rising of growing stages, Pb concentration, bio-concentration factor and translocation factor of tobacco leaf showed a falling-and-rising trend. Therefore, Pb uptake and transport ability was strong at late-growth period in tobacco.(2) It mainly existed with exchangeable, carbonate-bound and Fe-Mn-oxides-bound Pb in Pb-treatmented soil with percentage from 60.8% to 84.34%. The rhizosphere effect of tobacco showed that the percentage of Fe-Mn-oxides-bound Pb was decreased compared to the non-rhizospheric soil, the percentages of carbonate-bound, while, organic-bound and residue Pb were increased. Along with the rising of growing stages, the concentration of exchangeable, carbonate-bound Pb was decreased and the concentration of organic-bound and residue Pb were increased. The rhizosphere effect of tobacco in peak and squaring stage was stronger than rosette and mature stage.(3) Phosphorus transformed exchangeable and carbonate-bound of lead into Fe-Mn oxide-bound and Residual lead in rhizospheric and non-rhizospheric soil, which reduced exchangeable lead form 23.8% to 46.1%. Silicon transformed exchangeable of lead into Fe-Mn oxide-Bound and Residual, which reduced exchangeable lead form 6.0% to 34.1%. Phosphorus and silicon-mediated transformed exchangeable of lead into Fe-Mn oxide-bound, organic-bound and Residual lead, which reduced exchangeable lead form 50.1% to 50.7%. Only by applying excessive phosphorus to reduce the availability of lead in soil is limited, However, phosphorus and silicon-mediated was more effective. Applied phosphorus significantly decreased bio-concentration factor and translocation factor of lead in tobacco leaf with a decrement of 42.2%-62.5%and 32.54%-40.7%, respectively. Applied silicon significantly decreased bio-concentration factor and translocation factor of lead in tobacco leaf with a decrement of 6.3%～10.7% and 14.7%-22.3%, respectively. Application of phosphorus and silicon-mediated were significantly decreased bio-concentration factor and translocation factor of lead in tobacco leaf with a decrement of 52.6% and 13.8%, respectively. Application of phosphorus and silicon were effective measures to inhibit migration of Pb in soil-tobacco system, which Significantly reduing lead concentration of tobacco leaf, and phosphorus and silicon-mediated was more effective. |
