Relationship between extractable metals in acid soils and metals taken up by tea plants
2006
Zhang, M. | Zhou, C. | Huang, C.
The accumulation of heavy metals in plants is related to concentrations and chemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate-bound, organic matter-bound, oxides-bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mg Cu kg(-1), 0.03 to 1.09 mg Cd kg(-1), 3.43 to 31.2 mg Pb kg(-1), and 31.0 to 132.0 mg Zn kg(-1). The concentrations of exchangeable and carbonate-bound fractions of the metals depended mainly on the pH, and those of organic matter-bound, oxides-bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L(-1) CaCl2, NH4OAc, and DTPA-TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long-term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.
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