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We conducted a literature search of peer-reviewed studies on the Web of Science and China National Knowledge Infrastructure databases before June 2024, using the following search term combinations: (fine root OR litter OR belowground) AND (decomposition OR decay OR breakdown) AND (N deposition OR N addition OR N application OR nutrient fertilization OR N supply OR N enrichment OR N availability). Here, we conducted a meta-analysis of 137 pairs of observed values to investigate the responses of fine root decomposition rate to N addition and to identify the primary factors influencing these responses under different roots classifications (i.e., root diameter and root order). We hypothesized that (1) N deposition would inhibit fine root decomposition rate and (2) experimental factors would significantly impact the response of fine root decomposition rate to N addition. Our results suggest that N addition inhibits fine root decomposition rate. The factors influencing the response of fine root decomposition rate to N addition varied inconsistently across different fine root classifications. Soil microbial biomass N and soil N were the primary factors of the response of decomposition rate to N addition of fine root with diameters 0-1mm, while climate was key drivers for fine roots with diameters ≤ 2mm. The decomposition duration and amount of N addition were key factors of the response of decomposition rate to N addition for first to second-order and third to fifth-order roots, respectively. These results offer valuable insights into below-ground processes in response to N addition within the framework of different fine root classifications. Future earth models should consider classification methods of fine root to enhance their accuracy.