Journal Article Research Support, Non-U.S. Gov't Letter root anatomy 7440-44-0 Carbohydrates Carbon Cell size N762921K75 Nitrogen Nutrients absorptive roots alpine coniferous forests branch order carbon supply-consumption hypothesis cell wall chemical composition drought fine root traits leaf economics spectrum mycorrhizal association nitrogen deficiency non‐structural carbohydrates number of cell layers nutrient absorption nutrient absorption-transportation hypothesis nutrient transportation plant roots root architecture root cortex root cortex and stele