Growth and nutrient uptake of tea under different aluminium concentrations

BACKGROUND: The uptake of essential nutrients such as P, Fe, K, Ca and Mg is depressed by Al in most plants. This study aimed to investigate the concentrations at which Al could be toxic to C. sinensis. The suppression of nutrient uptake was investigated by comparing growth and nutrient uptake at different Al doses. The quantification of Al in apoplasm, symplasm and cell wall of C. sinensis was also studied. RESULTS: In the absence of Al, the growth of C. sinensis was retarded. Test doses over 1 mM Al were toxic to C. sinensis. At concentrations of 0.25 or 0.5 mM, distinct rhizostimulation was noted, and within a short period (2 weeks), the biomass of these seedlings increased by 44 and 35%, respectively, compared to 0 and 14% in control and 1 mM Al, respectively. In general, at beneficial doses (0.25, 0.5), Al stimulated the uptake of Ca, Mg, K and Mn, whereas the uptake of Fe, Cu and Zn was retarded. Fine roots of the seedlings had the highest levels of Al, compared to leaves, branches and main roots. In the root tips, most of the Al was present in the soluble fractions of the apoplasm and symplasm, and very low levels of Al was bound to the cell walls, which was in good agreement with the observed mobility of Al in C. sinensis. CONCLUSION: The results of the present study support the view that Al plays a nutritive role for C. sinensis. The rhizostimulatory effects of Al on C. sinensis have been explained as a consequence of enhanced nutrient uptake.