Warming Reduces Priming Effect of Soil Organic Carbon Decomposition Along a Subtropical Elevation Gradient

The priming effects (PEs) of soil organic carbon (SOC) is a crucial process affecting the C balance of terrestrial ecosystems. However, there is uncertainty about how PEs will respond to climate warming. Here, we sampled soils along a subtropical elevation gradient in China and conducted a 126-day lab-incubation experiment with and without additions of C-13-labeled high-bioavailability glucose or low-bioavailability lignin. Based on the mean annual temperature (MAT) of each elevation (9.3-16.4 degrees C), a temperature increase of 4 degrees C was used to explore how PEs mediate the decomposition of SOC in response to warming. Our results showed that the magnitude of glucose-induced PEs (PEglu) was higher than lignin-induced PEs (PElig), with both PEs linearly increasing with MAT. Across the MAT (i.e., elevation) gradient, warming had consistent negative effects on PEglu, whereas rising MAT exacerbated the negative effects of warming on PElig. Moreover, the temperature sensitivity of SOC decomposition decreased after adding glucose and lignin across the MAT gradient, suggesting that fresh C inputs may prime microbial breakdown of labile SOC under warming. Taken together, warming alleviated the SOC loss due to PEs through varying mechanisms depending on substrate bioavailability, since warming mediated the PEglu by increasing available nitrogen and weakening microbial nitrogen-mining but inhibited the PElig by switching from microbial nitrogen-mining to microbial co-metabolization. Our findings highlight the role of warming in regulating the PEs and suggest that incorporating the suppression effect of warming on PEs can contribute to the accurate prediction of soil C dynamics in a warming world.