Labile carbon (C) inputs strongly alter soil organic matter (SOM) turnover by priming, thus affecting soil C dynamics and soil fertility in the long term. The frequency of labile C inputs is expected to affect the intensity of priming effect. We evaluated the effects of single versus repeated additions of ¹³C-labeled glucose (with added ¹³C corresponding to 2% of soil organic C content) to five soils with increasing fertility level on the intensity of priming effect and soil C balance. Repeated glucose addition induced 61–108% greater C mineralization due to positive priming than the single addition in all soils. The intensity of priming effect declined with soil fertility level and mineral nitrogen (N) content, but increased with higher activities of N-acquisition enzymes (N-acetyl-glucosaminidase and leucine amino peptidase). Consequently, the decrease in N availability strongly increased the intensity of priming effect presumably by enhancing microbial N mining from SOM. Considering the C balance between SOM losses due to priming and glucose-C retention, glucose addition was responsible for net C losses in the low and moderate fertility soils (−14.0 to −0.30 mg C g⁻¹ SOC after 14 weeks) but led to C gains in the high fertility soils (+0.44 to +4.36 mg C g⁻¹ SOC). Greater retention of glucose-C was attributed to higher N availability and more intensive microbial growth, thus supporting microbial necromass formation and soil C sequestration. Compared to single addition, repeated glucose addition caused larger net C losses or lower C gains due to stronger SOM priming. In conclusion, the frequency of substrate addition and soil fertility are important regulators of SOM priming and the C balance. This knowledge should be informative to interpret soil C dynamics in response to labile C inputs in agroecosystems.

不稳定的碳（C）输入会通过引发而强烈改变土壤有机质（SOM）的转化，从而长期影响土壤C的动力学和土壤肥力。不稳定的C输入的频率预计会影响启动效应的强度。我们评估了单次添加或重复添加¹³ C标记葡萄糖（添加¹³C对应于土壤有机C含量的2％）到5个肥力水平提高的土壤上，这些土壤的启动效应强度和土壤C平衡。在所有土壤中，重复的葡萄糖添加导致的C矿化比正向添加增加了61–108％，这是由于阳性启动引起的。引发作用的强度随土壤肥力水平和矿质氮含量的降低而降低，但随着N捕获酶（N-乙酰氨基葡萄糖苷酶和亮氨酸氨基肽酶）活性的增加而增强。因此，氮利用率的降低可能通过增强从SOM开采微生物氮而极大地增强了启动效应的强度。考虑到引发引发的SOM损失与葡萄糖-C保留之间的碳平衡，在中低肥力土壤（−14.0至-0.30 mg C g14周后^-1 SOC），但导致高肥力土壤中的C增加（+0.44至+4.36 mg C g ^-1 SOC）。葡萄糖-C的更大保留归因于更高的氮利用率和更密集的微生物生长，从而支持了微生物坏死的形成和土壤C的固存。与单次添加相比，由于较强的SOM启动，重复添加葡萄糖会导致较大的净C损失或较低的C收获。总之，底物添加的频率和土壤肥力是SOM启动和碳平衡的重要调节剂。该知识应有助于解释土壤碳动态，以响应农业生态系统中不稳定的碳输入。