Decoupling of nitrogen and phosphorus release from fine and coarse roots during seven years of decomposition

Belowground litter decomposition represents an important source of the limiting nutrients nitrogen (N) and phosphorus (P) to forest soils. However, the rates and drivers of nutrient immobilization and release from root litter remain poorly understood. To address this gap, we conducted a seven-year field decomposition experiment using roots from three species, across five diameter classes (up to 20 mm) in a temperate forest. All roots released P to the surrounding soil within the first year of decomposition but immobilized N for much longer, particularly coarse roots. Long-term N release was mainly related to initial nutrient stoichiometry of the substrate, whereas P release was better predicted by substrate carbon (C) quality and decomposition rate. Initial root nutrients well predicted the difference between long-term N versus P release. Our results highlight the fact that N and P dynamics should be considered separately when modeling nutrient release during root decomposition.