Soil fluoride fractions and their bioavailability to tea plants (Camellia sinensis L.)

摘要

Drinking teas containing high fluoride (F) imposes fluorosis risk. The soil F bioavailability is an important factor influencing its uptake and contents in teas. The present work was conducted to investigate F fractions in soil and their bioavailability to tea plants. Tea seedlings were cultivated on 6 typical soils treated with a mixture consisting of dolomite, lime, peat and KCl at variable rates in the pot experiment. Soils and young shoots were collected in pairs from 63 sites of 21 plantations in a field experiment. Soil fluoride was sequentially separated into hot water soluble , exchangeable (by 1 mol L-1 MgCl2, pH = 7.0), F bound to Mn and Fe hydroxides [F-(oxides,F-s)], and organic matter [F-(OM,F-s)] or extracted independently by water or 0.01 mol L-1 CaCl2 solution . Averaged , , F-(oxides,F-s) and F-(OM,F-s) accounted for 51, 14, 5 and 30 % of the total sequential extracts, respectively. There were significant correlations among , and F-(OM,F-s). Fluoride contents in leaves correlated with (r = 0.71, p < 0.001), (r = 0.93, p < 0.001) and F-(OM,F-s) (r = 0.69, p < 0.01) but not other fractions in the pot experiment and with (r = 0.43-0.57, p < 0.001) and (r = 0.42-0.79, p < 0.001) in the field experiment. It was concluded that 0.01 M CaCl2 extractable fluoride can be a good indicator of soil F bioavailability to tea plants. The significant correlations among some of the F fractions suggested that F in solution, AlF complexes (AlF2+, AlF2+) and those bound to organic matter likely represent the available pools to tea plants.