【Objective】Litter quality is a key factor regulating the intensity and direction of the soil priming effect. However, it remains unclear whether inputs of litter from different organs of the same plant or litter with different carbon to nitrogen ratios (C/N) from the same organ differentially impact soil priming effect, as well as the underlying mechanisms.【Method】To address this gap, 13C-labeled seedlings of Phoebe bournei were used as study materials. Through fertilized and non-fertilized treatments, leaf, stem, and root tissues with low and high C/N ratios were obtained to investigate the effects of litter inputs with different C/N ratios on soil priming. Soil microbial biomass, enzyme activity, and soil available nitrogen contents (NH4+-N and NO3--N) were measured concurrently to elucidate the underlying mechanisms.【Result】After 180 days of incubation, the addition of high and low C/N ratio leaf litter and low C/N ratio root litter inhibited the mineralization of soil organic carbon (SOC) by about 11.09%, 9.05% and 8.07%, respectively, inducing a significant negative priming effect. However, the other treatments did not cause significant priming effects. The influence of different C/N ratios in the same organ of Phoebe bournei on soil priming effect was primarily observed within the first 8 days of incubation, with high C/N ratio litter inducing a stronger negative priming effect than low C/N ratio litter. The reason is that high C/N ratio litter input caused microbial nitrogen (N) immobilization, reducing soil available N content, which led to N limitation and suppressed microbial activity, thereby decreasing SOC decomposition. In the later stages of incubation, the effects of different C/N ratio litter on soil microbial biomass carbon and carbon metabolism-related enzyme activities were not significant, so the influence of C/N ratio on soil priming gradually diminished. Among different plant organs, leaf litter induced a stronger negative priming effect than root litter. Specifically, the negative priming effect induced by leaf addition weakened over time, while root addition continuously induced a negative priming effect. Stem addition caused a priming effect that fluctuated between positive and negative, but the cumulative effect offset, resulting in no significant change in SOC decomposition.【Conclusion】The impact of Phoebe bournei litter input on soil priming effect varied significantly among organs, whereas the influence of litter C/N ratio on soil priming effect was mainly concentrated in the early stages of litter decomposition. The main mechanism by which leaf litter induced a negative priming effect was through reducing soil available nitrogen, which inhibited microbial activity, thereby decreasing SOC decomposition. In contrast, the negative priming effect induced by low C/N ratio roots was because their high lignin content and low bioavailability, causing C limitation for microorganisms during decomposition, leading to reduced SOC decomposition.