Characteristics of nitrogen mineralization in the soil of Japanese cedar (cryptomeria japonica) and their responses to environmental changes and forest management

Knowledge of nitrogen mineralization in the soils of sugi (Cryptomeria japonica) stands is important for understanding the ettects ot forest management ana environmental cnanges on nutrient cycling in the future. We summarized recent studies about nitrogen mineralization in the soils of sugi stands, and discussed directions of future studies. We first examined the methodology and associated problems for evaluating nitrogen mineralization, then investigated environmental factors and soil properties that control nitrogen mineralization in the soil. Rate of nitrogen mineralization, ratios of mineralized to total nitrogen and nitrified to mineralized nitrogen were calculated from published and unpublished data. These values were 93.7 mg kg-1 4 weeks -1, 1.3% and 70% respectively. In the future, studies about nitrogen dynamics in the soil with tracer experiments under field conditions, and analyses of the relationship between direct uptake of organic nitrogen by tree roots and nutrition of fine roots will be required. We suggest that integrated studies about nutrient cycling for understanding the effects of environmental changes such as global warming and nitrogen saturation and forest management on nitrogen dynamics in the soils should be conducted.