Factors influencing fine roots decomposition rates in response to nitrogen addition vary across root characteristics

Abstract Nitrogen (N) deposition strongly affects litter decomposition and nutrient release, thereby reshaping carbon cycling in terrestrial ecosystems. Although most studies have focused on above‐ground litter, the effects of N addition on fine root decomposition and their underlying drivers, particularly across different root characteristics, remain poorly understood. We synthesized a meta‐analysis of 144 observations from 30 studies to quantify the response of fine root decomposition rates to N addition and to identify the key factors that regulate these responses across root characteristics. On average, N addition reduced fine root decomposition rates and mass loss by 8.52% and 6.24%, respectively. Negative responses to N addition were most pronounced in roots ≤2 mm in diameter and in first‐ and second‐order roots. Soil microbial biomass N and clay content were the dominant drivers of these responses in roots ≤2 mm. Within different root characteristics, soil microbial biomass N and soil N content were the most important factors regulating the response of decomposition rates to N addition for roots ≤1 mm, while N addition amount was the key determinant for third‐ to fifth‐order roots. These results suggest that the controls on fine root decomposition under N addition vary with root characteristics. This highlights the need to incorporate root variability into ecosystem models to improve predictions of below‐ground carbon cycling under future climate change. Read the free Plain Language Summary for this article on the Journal blog.