Effects of Nitrogen Load on Growth and Leaf Nutrient Status of Japanese Evergreen Broad-leaved Tree Species

Two-year-old seedlings of Castanopsis cuspidata, Lithocarpus edulis, Quercus glauca and Quercus acuta were grown for two growing seasons in brown forest soil treated with N as NH4NO3 solution at a rate of 0 (N-0), 10 (N-10), 50 (N-50), 100 (N-100) or 300 (N-300) kg ha-1 year-1. Whole-plant dry mass of C. cuspidate and Q. glauca were significantly reduced by the N-100 and N-300 treatments, and by the N-300 treatment, respectively. In L. edulis seedlings, whole-plant dry mass was significantly increased by the N-50 treatment, while it was significantly reduced by the N-300 treatment. Whole-plant dry mass of Q. acuta seedlings increased with increasing amounts of N added to the soil. In C. cuspidate, L. edulis and Q. glauca seedlings, whole-plant dry mass was negatively correlated with the ratio of Mn concentration to Mg concentration (Mn/Mg) in the leaves. In conclusion, there is great difference in the sensitivity to N load among the four evergreen broad-leaved tree species, C. cuspidata being tolerant to high N load, and the concentration ratio of Mn/Mg in the leaves is a useful indicator for evaluating the negative effects of N load on the growth of Japanese evergreen broad-leaved trees.