Abstract: Aims The priming effect (PE) is a common phenomenon in terrestrial ecosystems, but its response to warming remains highly uncertain in the context of climate change. Most existing studies on the PE are based on laboratory incubation methods, which cannot accurately assess the changes induced by temperature increases in natural field environments. Methods In this study, based on an in-situ soil warming experiment located in a subtropical forest, 13C labeled glucose was added using an artificial root imitation device to simulate labile carbon input from root, to explore the responses of PE and the soil net carbon balance to warming. Four treatments were set up in the experiment: 1) ambient temperature + deionized water (CT-CK); 2) ambient temperature + glucose solution (CT-Glu); 3) warming temperature + deionized water (W-CK); 4) warming temperature + glucose solution (W-Glu). Important findings The results showed that both warming and glucose addition had a significant impact on the CO2 flux, with glucose addition increasing the total CO2 flux, while warming inhibited it. From May to October 2023, the cumulative Glu-derived CO2 in the CT-Glu treatment was 9.51 g CO2-C·kg–1 SOC (SOC, soil organic carbon), and this amount was reduced by warming to 5.41 g CO2-C·kg–1 SOC. Similarly, warming significantly suppressed the PE. The cumulative PE of the CT-Glu treatment was 12.31 g CO2-C·kg–1 SOC, while that of the W-Glu treatment was 6.54 g CO2-C·kg–1 SOC. In this study, warming significantly intensified microbial carbon limitation in the soil, which was the primary reason for the reduction in cumulative Glu-derived CO2 and the priming effect. In addition, warming significantly increased the soil net carbon balance. Specifically, the soil net carbon balance of the CT-Glu treatment was –1.81 g CO2-C·kg–1 SOC, while that of the W-Glu treatment was 8.05 g CO2-C·kg–1 SOC. Our findings quantified the impact of in-situ warming on the PE of SOC decomposition, which is beneficial for better understanding soil carbon cycling processes in terrestrial ecosystems and for reducing uncertainties in Earth system models that predict carbon dynamics.

Key words: in-situ warming, soil organic carbon, priming effect, Net carbon balance, subtropical forest