Soil Factors Affecting Nutrient Bioavailability -- Decomposition and Mineralization of Nutrients from Litter and Humus -- Integrated Root Responses to Variations in Nutrient Supply -- Internal Regulation of Nutrient Uptake by Relative Growth Rate and Nutrient-Use Efficiency -- Biological Nitrogen Fixation Associated with Angiosperms in Terrestrial Ecosystems -- Homeostatic Processes for the Opt…