Anthropogenically increased nitrogen (N) deposition may affect the nutrient dynamics of forested ecosystems. To investigate the potential effects of excessive N deposition on Japanese forests, we treated the soil in a 20-year-old Japanese cedar (Cryptomeria japonica) stand with 10 l m-2 of 10 mM HNO3 solution, 10 mM NH4NO3 solution, or tap water (as a control), monthly for 7 years. A total of 168 and 336 kg N ha-1 year-1 was added in the HNO3 and NH4NO3 plots, respectively. Tree growth, the amount of nutrients and the carbon concentration of both current shoots and fine roots (<2 mm in diameter) in the surface soil (0-5 cm) were measured. The foliar N concentration increased in both N-fertilized plots during the first 3 years, particularly in the NH4NO3 plots. Similarly, the fine-root N concentration was greater in the N-fertilized plots than in the control plots. However, growth in both height and diameter at breast height of Japanese cedar trees were not significantly affected by N fertilization. The foliar K and P concentrations tended to decrease in treatment plots over time when compared with the control plots. Our study suggests that 7 years of excessive N fertilization had no positive or negative effect on the growth of young Japanese cedar trees, although the nutrient status of current shoots and fine roots was altered.
2015 Japanese Society for Root Research