Labile C input to the soil can cause the priming effect (PE) that in turn changes the soil organic C (SOC) content. However, little information is available to predict the magnitude of the PE in different soils, especially under concurrent changes in nutrient inputs. We took advantage of a natural gradient in labile C input in the surroundings of wood ant nests in a temperate coniferous forest which arises through the long-term effects of wood ant foraging on the inputs of honeydew to soil. We collected soils from the surface mineral horizon (high-SOC content) (A horizon) and the subsoil mineral horizon (low-SOC content) (B horizon) at 4 m (low labile C input and higher SOC content) and 70 m (high labile C input and lower SOC content) from four nests. In a 6-month laboratory microcosm experiment, we monitored microbial activity and PE as affected by no nutrient addition (control) or fortnightly additions of labile C alone or in combination with N and/or P (C, CN, CP, CNP). Microbial activity and PE after C addition increased more at 70 m than at 4 m in the B horizon, that is, were higher with a lower SOC content. However, microbial activity and PE in the B horizon were not affected by additions of N and/or P with C. In the A horizon, microbial activity and PE were lower after combined CN addition but increased by combined CP addition relative to C addition alone. In conclusion, labile C inputs had a larger effect on decomposition and PE in low-SOC than high-SOC soils, whereas N and P inputs had greater effects in high-SOC soils than in low-SOC soils. This suggests that low-SOC soils such as those subjected to a high long-term labile C input or those from the subsoil mineral horizon might be more susceptible to increase microbial activity in relation to changes in labile C inputs but less susceptible in relation to changes in N and P inputs relative to high-SOC soils.

输入土壤的不稳定碳会引起启动效应（PE），进而改变土壤有机碳（SOC）含量。但是，很少有信息可用来预测不同土壤中PE的量，特别是在养分输入同时变化的情况下。我们利用温带针叶林中的木蚁巢周围不稳定的碳输入的自然梯度，这是由于木蚁觅食对蜜瓜向土壤输入的长期影响而产生的。我们在4 m（不稳定的C输入和较高的SOC含量）和70 m（低的C输入量）下从地表矿物层（高SOC含量）（A层）和地下土壤矿物层（低SOC含量）（B层）收集土壤。高不稳定的C输入和较低的SOC含量）。在为期6个月的实验室缩影实验中，我们监测了微生物活性和PE，不受单独添加营养素（对照）或每两周添加不稳定的C或与N和/或P（C，CN，CP，CNP）组合的影响。在B层中，添加C后的微生物活性和PE在70 m处比在4 m处增加更多，也就是说，在SOC较低的情况下更高。但是，B层中微生物活性和PE不受碳和N和/或P的影响。在A层中，CN联合添加后微生物活性和PE较低，但CP联合添加使微生物活性和PE相对于C单独增加。总之，在低SOC土壤中，不稳定的碳输入对分解和PE的影响大于高SOC土壤，而在高SOC土壤中，氮和P的输入比在低SOC土壤中的影响更大。