| Lead is typically the most toxic heavy metal pollutants for plants, animals and humans in environment. There are three factors that influence the lead of intensity and quantity when accumulating of migrating from soil to tea. The first is the chemical and biological processes in rhizosphere, the second is the regulation of transport and distribution characteristics in crops, the third is the of the soil physico-chemical properties and environmental conditions, etc. The study on distribution characteristics, migration and transformation, influencing factors of lead in the soil-Kudingcha system can provide scientific basis for reducing potential of lead contamination in Kudingcha. It also has important practical significance for promoting the development and utilization of Hainan Kudingcha.The methods were established for determining tea trees and its soil samples by high pressure sealed digestion-Graphite Fμrnace atomic absorption spectrometry (GF-AAS) and microwave digestion-inductively coupled plasma emission spectrometry (ICP-AES). Having been collected tea trees and its soil samples in Hainan university Kudingcha germplasm resource pool, Chengmai Wanchang Kudingcha plantation and pot experiments Kudingcha, the content of lead in samples was determined by established methods. The results showed that:The Linear Range of the standard curve was at 0.0 ng·g-1～60.0 ng·g-1, linear correlation coefficient was 0.99989, and the method detection limit was 0.215ng·mL-1, RSD<5%, the results of recovery test was 92%-106% by high pressure sealed digestion-Graphite Fμrnace atomic absorption spectrometry. The Linear Range of the standard curve was at 0.0 ng·g-1～400.0 ng·g-1, linear correlation coefficient was 0.99995, and the method detection limit was 0.038 ng·mL-1, RSD<5%, the results of recovery test was 96%-107% by microwave digestion-inductively coupled plasma emission spectrometry. Besides Ilex centrochinese S,Y. Hu, the lead distribution characteristics of six kinds Ilex Kudingcha systems in Hainan university Kudingcha germplasm resource pool were:soil >>tea tree, rhizosphere soil>non-rhizosphere soil, absorbing roots>main roots, dead leaves>stem >old leaves>young leaves. The biological absorption coefficient(BAC) of young leaves that were used for firing tea were 0.005～0.016. The contents of lead were 0.10μg·g-1～0.47μg·g-1,and the distribution were Ilex cornuta Lindl.<Ilex kudingcha C. J. Tseng.<Ilex latifolia Thunb.<Ilex pentagona S.K.Chen, Y.X.Feng et C.F. Liang.<Ilex houshanesis Y.H.He.<Ilex centrochinese S,Y. Hu. The conents of lead in young leaves were all far less than limited amount index of lead(Pb≤5.0μg·g-1). Comparing with Chengmai Kudingcha plantation, the lead distribution of Ilex Kudingcha systems showed some differences in different planting places and planted time. The research on the speciation distribution of Pb in six kinds Ilex Kudingcha soils in Hainan university Kudingcha germplasm resource pool showed:residual species> organic matter species> carbonates species> Fe-Mn oxides species> exchangeable species. The relative content of various speciation of Pb in six Ilex Kudingcha trees was changed from the non-rhizosphere soil to rhizosphere soil.Though the change was various, in general, there was a downward trend in the carbonates Pb which has greater bioavailability and in the Fe-Mn oxides Pb, the organic Pb which have intermediate bioavailability,yet there was an upward trend in the content of the residual Pb which was difficult to be absorbed by plants.The rhizosphere environment of Ilex Kudingcha trees has a certain block function to reduce the contamination of Pb. In addition, this article also researched the speciation distribution of Pb in pot experiments Ilex Kudingcha soils when pH and oxidation-reduction potential(ORP) in soil changed. The results indicated:under acidic condition, it was help for reducing the hazards of lead for Kudingcha that the bioavailability of lead decline along acidic enhancement. In contrast, under alkaline condition, it was harmful for safety production of Kudingcha that the potential risk of lead pollution in Ilex Kudingcha tree increased along acidic enhancement. With the increase of ORP, effective state and potentially effective state of lead were increased in Kudingcha rhizosphere soil. It increased risk of lead contamination in Kudingcha.Having been changed pH,oxidation-reduction potential(ORP) and exogenous lead, cadmium, copper, the pot experiments showed the following results.①under acidic condition, lead was mainly held up in soils. Such as pH= 5.17, lead was enriched in middle soils and it was lower in roots, stems and leaves. In such a case, it was minimum for pollution risk of lead.②The lead contents in soil was enlarged first followed by reduced as ORP enlarging. The maximum content of lead in soil was 45.18 mg·kg-1 and the content of lead in leaf was minimum when ORP=260.5,.In this situation, the lead was enriched in surface soil, the vertical drop of lead in soil was preventd,and the migration or absorption was also held up from soil to Kudingcha tree.It can decreased the congtent of lead in Kudingcha tree.③Along the enlargement of exogenous lead, the lead in soil presented approximate linear increased, and the lead in soil presented enlarged first followed by reduced.④Along the enlargement of exogenous cadmium, the migration of lead was promoted in soil-Kudingcha system, which lead to the enrichment of lead in rhizosphere soil and leaf. This meaed that the cadmium had synergistic effect for the migration of lead.⑤Along the enlargement of exogenous copper, the migration of lead was promoted in Kudingcha tree, which was similar with the effects of exogenous cadmium.The orthogonal experiment showed that:when the concentration of exogenous lead was 200mg·kg-1, the concentration of exogenous copper was 100mg·kg-1, the concentration of exogenous cadmium was 10mg·kg-1, the concentration of compound fertilizer was 5g per pot, pH=4, the migrational degree of lead was highest in soil-Kudingcha system. This meaned that the combined pollution of various factors was strongest in above-mentioned condition in Kudingcha tree. Range analysising showed that the biology absorption coefficient of lead in Kudingcha leaf was respectively effected by the following factors:exogenous lead> pH> exogenous copper> ORP>exogenous cadmium. Variance analysising showed that the F test of each factor were all less that Fo(0.05). At the 95% confidence interval, the biology absorption coefficient of lead in Kudingcha leaf was respectively effected similar with the results of range analysis. |
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