Proton release from tea plant (Camellia sinensis L.) roots induced by Al(III) under hydroponic conditions

The mechanisms for soil acidification induced by tea plant growth are not well understood. Proton release from tea plant (Camellia sinensis L.) roots induced by aluminium (Al(III)) in solution-culture experiments was examined with an automatic titration system, to determine the effect of Al(III) uptake by the plants on soil acidification. Results indicated that the uptake of Al(III) by tea plants led to proton release from their roots and thus an increase in soil acidification. The uptake of Al(III) by tea plants and the amount of protons released from the roots were greater at pH 4.5 than at pH 5.0 and 4.0 and increased with increasing initial Al(III) concentration in the culture solutions. With the same initial pH, the amount of protons released from tea plant roots at a constant pH was much higher than that at non-constant pH. The presence of ammonium increased the amount of protons released from tea plant roots. Therefore, the uptake of Al by tea plants and subsequent release of protons from their roots may be an important mechanism by which they acidify soils in tea gardens.