EFFECTS OF ALUMINUM ON GROWTH AND ROOT REACTIONS OF PHOSPHORUS STRESSED BETULA-PENDULA SEEDLINGS

The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and P-32 uptake capacity on sub-optimal (P-limited) Betu la pendula seedlings grown in sand culture was examined. Seedling grow th was under optimum controlled conditions in a growth chamber where n utrient additions were made at a predetermined relative addition rate (R(A)) of 10% day(-1). Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a P-32-labelled solution for 15 minutes to measure their c apacity for P uptake, Growth was determined by weighing the roots, ste ms and leaves of the seedlings. Growth data showed that relative growt h rate (R(G)) should equal the R(A) Of P the most limiting nutrient, w hich was supplied at P/N 3% instead of an optimal 15%. Therefore, Inge stad's theory can also be used succesfully in sand culture and this ma y be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P suppl y significantly lowered the R(G) Of the birch seedlings by further red ucing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with opti mumal P supply did not show any effect of Al on growth untill the Al w as in excess of 3 mM. Aluminium was not directly toxic to the plants a nd therefore roots could respond to the P-32 bioassay.