Distribution characteristics of fluoride and aluminum in soil profiles of an abandoned tea plantation and their uptake by six woody species

Distribution characteristics of fluoride (F) and aluminum (Al) in soil profiles of an abandoned tea plantation in Hong Kong and their uptake by six woody species namely Camellia sinensis, Melastoma affine, Sterculia lanceolata, Ardisia crenata, Acacia formosa and Machilus thunbergii were investigated. C. sinensis accumulated both F (656 mg/kg in the leaves) and Al (8910 mg/kg in the leaves). M. Affine only accumulated Al (9932 mg/kg in the leaves), while S. lanceolata, A. crenata, A. formosa and M. Thunbergii were Al (26-115 mg/kg in the leaves) and F (20-25 mg/kg in the leaves) excluders. Water-soluble F and Al contents accumulated in surface soils (especially 0-3 cm) and decreased with depth along soil profiles: A layers (2.0 ± 0.6 and 31 ± 5.8 mg/kg) > B layers (1.5 ± 0.2 and 27 ± 3.5 mg/kg) > C layers (1.3 ± 0.2 and 20 ± 2.7 mg/kg), respectively. The water-soluble, NH₄Ac-extractable and HCl-extractable F in soil profiles were significantly correlated (P<.01). F concentrations in all soil layers (n = 51) of soil profiles (n = 17) were significantly correlated (P<.01) to Al concentrations in terms of water-soluble Al/F, HCl-extractable Al/F, HCl-extractable Al/F and NH₄Ac-extractable Al/F, due to the formation of Al-F complexes in soil. F contents extracted with deionized water (pH = 6.68), 1 mol/1 HCl and 1 mol/1 NH₄Ac in soil could be used to predict F concentrations in the leaves, stems and roots of the six plants.