Sensitivity of Soil Organic Matter Priming to Warming Depends on Diurnal Temperature Cycle

Understanding soil organic matter (SOM) mineralization is critical for predicting soil carbon (C) cycling, yet the effects of diurnal temperature fluctuations and their interactions with labile C inputs remain unclear. Arable soils were incubated for 42 days under constant temperatures (15 or 25 °C) or diurnal temperature fluctuations, without or with 13C-glucose addition. Diurnal fluctuations enhanced cumulative SOM mineralization and priming effects, with a higher temperature sensitivity (Q10) of priming (2.6) than constant temperatures (2.4). The higher Q10 was associated with an increased response of C-degrading enzyme activities to warming. At the community level, fungal diversity declined with warming, particularly under diurnal fluctuations. Although microbial networks were restructured, their topology exerted little influence on SOM mineralization. Instead, fungal diversity and cellobiohydrolase activity were the primary drivers of variation in SOM mineralization and its Q10. These findings provide mechanistic insights into soil C cycling under climate change, emphasizing the importance of incorporating daily temperature fluctuations into predictive models.