EFFECTS OF LIGHT QUALITY ON GROWTH AND N ACCUMULATION IN BIRCH SEEDLINGS

We studied the effects of light quality and nutrient supply on growth and nitrogen accumulation in silver birch (Betula pendula Roth) seedli ngs to test three hypotheses: (1) growth Of birch seedlings is sensiti ve to changes in light quality; (2) the response of birch seedling gro wth to light quality depends on nutrient supply; and (3) assimilation and allocation of nitrogen by birch seedlings are affected by light qu ality. The two light regimes simulated the spectral quality of sunligh t and shadelight, but did not differ in photosynthetic photon flux den sity, and the two nutrient supply regimes differed in the rate of supp ly, but not in the composition, of mineral nutrients. Accumulation and allocation of dry weight and nitrogen were strongly affected by nutri ent supply regime, but light quality had little effect. During the fir st 15 days of the experiment, the largest effect of light quality was on height growth, which was greater in seedlings in simulated shadelig ht than in seedlings in simulated sunlight. Light quality had little e ffect on dry weight and nitrogen allocation to the stem during this pe riod. However, at the end of the experiment (Day 29), there was an inc rease in N concentration per unit dry weight in leaves and stems of se edlings in the simulated shadelight plus high nutrient supply treatmen t.