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

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.