ROOT-GROWTH AND NITROGEN UPTAKE IN SYCAMORE (ACER PSEUDOPLANTANUS L) SEEDLINGS IN RELATION TO NITROGEN SUPPLY

Acer pseudoplatanus L. trees were grown in sand culture for 2 years an d, in 1988, supplied with either 1.0 mol N m(-3) (low N) or 6.0 mol N m(-3) (high N) to precondition their growth. In 1989, the same trees r eceived either high or low nitrogen, producing four treatments; High N in 1988/High N in 1989; High N in 1988/Low N in 1989; Low N in 1988/L ow N in 1989; and Low N in 1988/High N in 1989. Plant growth was affec ted by N supply in both years. In 1989 the Low N/High N treated trees had the same overall mass, leaf mass and stem girth as the High N/High N treatment. Early spring growth of foliage and roots was conditional on nitrogen supplied in the previous season. Later, the rapid increas es in leaf, stem and root growth under high N was through root uptake. Internal partitioning of growth was affected, with the Low N/High N t reatment producing more new leaves on axillary shoots, and more new wh ite roots on existing structures, than the Low N/Low N treatment. Desp ite effects of the N preconditioning on the structure of both canopy a nd root system, nitrogen uptake was solely dependent on the current ni trogen supply.