Effects of aluminium on growth and nutrition in birch seedlings under magnesium- or calcium-limiting growth conditions

Growth and nutrition of birch seedlings (Betula pendula Roth) with and with out 0.5 mM Al3+ were studied. The seedlings were cultivated at growth-limit ing Mg- or Ca-conditions by adding one of these elements at relative additi on rates (R-Mg, R-Ca) of 0.15 day(-1). The concentration of Ca2+ in the Mg- limited treatments was 0.01, 0.1 or 1 mM and Mg2+ was given in equal molari ties in the Ca-limited treatments. The relative growth rates, R-G, of the p lants and plant parts attained values close to R-Mg or R-Ca and were not af fected by the concentration of Ca2+, Mg2+ or Al3+ in the culture solution. Uptake of Ca, at Ca-limitation, increased significantly in the roots after addition of Al, and decreased in all plant parts when the Mg concentration of the culture solution was raised. Less clear effects were found on Mg upt ake at Mg-limitation. The inhibitory effect of Al on Mg uptake decreased wi th time as a result of the growth technique. The root mass fraction was sig nificantly larger in plants limited in Ca (24%) than in plants limited in M g (20%). The usefulness in using the balance between Ca and Al or ratios be tween Ca,Mg,K and Al as diagnostic tools for assessing the nutritional stat us of trees is discussed.