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

The increase in nitrogen (N) deposition has significant effects on litter decomposition, nutrient release, and soil organic matter cycling, which has altered carbon allocation patterns in terrestrial ecosystems. Although most studies on the effects of N addition have focused on aboveground litter decomposition, the responses of fine root decomposition rate to N addition and their drivers, particularly across different root characteristics, remain unclear.<br>We synthesized 144 observations from 30 peer-reviewed publications and used meta-analysis to elucidate the responses of fine root decomposition rate to N addition and to identify the primary factors influencing these responses under different root characteristics.<br>N addition reduced fine root decomposition rate and mass loss by 8.52% and 6.24%, respectively. Specifically, fine roots with diameters ≤ 2 mm and first- and second-order roots exhibited negative responses to N addition. Overall, soil microbial biomass N and soil clay content were the main factors affecting the fine root decomposition rate in response to N addition. Within different root characteristics, soil microbial biomass N and soil N content were the primary factors regulating the response of fine roots ≤ 1 mm decomposition to N addition, while the N addition amount was the key factor of third to fifth-order root decomposition in response to N addition.<br>Our results suggested that the primary factors regulating the response of fine root decomposition rate to N addition varied across fine root characteristics. These differences in controlling factors highlighted the importance of incorporating fine roots characteristics into ecosystem models to predict the responses of belowground carbon and nutrient release to future climate changes.