Dynamics of nitrogen and phosphorus release during leaf and root litter decomposition and associated drivers under different land-use types in a subtropical region

Litter decomposition is a central process regulating nutrient cycling in terrestrial ecosystems, yet how land-use change alters nitrogen (N) and phosphorus (P) release from aboveground and belowground litter in subtropical regions remains insufficiently resolved. In this study, a 784 d in situ litter-bag decomposition experiment was conducted in subtropical China to quantify N and P release from leaf litter and fine roots during decomposition across three land-use types: cropland (Zea mays L.), shrubland (Sophora davidii Kom. ex Pavol.), and forest woodland (Platycladus orientalis (L.) Franco). The relative contributions of litter quality, soil microclimate, and microbial traits to nutrient release dynamics were further evaluated. Results showed that leaf litter released N and P significantly faster than fine roots, and both litter components showed rapid initial degradation within the first year, followed by a progressive decline in release rate. Land-use type altered N release trajectories. During leaf litter decomposition, shrubland maintained relatively stable N release, whereas woodland showed an immobilization-release pattern and cropland exhibited a sharp initial decrease followed by slower release. For fine roots, cropland showed initial N immobilization followed by release, while shrubland showed a decline-slow-rapid release pattern and woodland showed the opposite trend. Phosphorus release generally followed a leaching-immobilization-release sequence, although the timing of immobilization differed among litter types and land-use types. Nutrient release was jointly regulated by litter quality and environmental conditions throughout decomposition. Leaf litter N release was primarily controlled by the C : N ratio during early decomposition and shifted toward stronger regulation by the fungal : bacterial ratio during later stages. Leaf litter P release was initially regulated by C concentration and was subsequently co-modulated by N concentration and bacterial biomass. In fine roots, early-stage N and P releases were dominated by P concentration, whereas lignin concentration inhibited nutrient release during later decomposition.