nitrogen (n) is critically important for plant growth and development. the objective of this thesis is to examine how different rates of nitrogen affect the seedling growth in black spruce (picea mariana mill.). this paper investigates the effects of nitrogen fertilization on seedlings growth for blcak spruce (picea mariana mill.) with a range of fertilizer applications from 10 to 360 μmol mol-1n. the experiment was carried out in 2 environmentally controlled greenhouses in the forest ecology complex at the thunder bay campus of 阿根廷vs墨西哥竞猜 . after four months the fertilizer application, the seeding height, root collar diameter, and the height to diameter ratio were evaluated. seedling growth was significantly affected by the rate of nitrogen fertilizer, with an optimum rate at 150% nitrogen rate. the average heights were 38.31, 51, 46.01 43.93 and 47.81cm, respectively, for the 10, 150, 220, 290 and 360 umol mol- 1 n treatments. the nitrogen treatments also affected the variability of rcd but the patterns of variation were different from that of seedling height. both seedling heights and root collar diameter decreased after 150 umol mol-1 n, which indicating that saturating plant with high nitrogen levels, however, does not improve plant growth.