Influence of drought intensity on soil carbon priming and its temperature sensitivity after rewetting

Global climate change can affect the soil thermal and moisture condition, potentially disrupting microbial-mediated soil respiration and altering the soil C cycle. However, the complex relationship between the soil C turnover and transient thermal and moisture conditions is not fully understood. Specifically, quantitative understanding is lacking regarding the impact of drought-rewetting events and temperature on the response of soil organic carbon (SOC) decomposition rate to exogenous C input, known as the priming effects (PEs). Herein, we quantified glucose-induced PEs during the rewetting of soils incubated under two drought intensities [with 20 % and 33 % water holding capacity (WHC)], at different incubation temperatures (15, 25, and 35 °C). Moreover, the effect size of drought intensities on PEs and the temperature sensitivity of PEs were quantified using lnRR (Response Ratio) and Q₁₀ of PEs. Glucose input triggered positive PEs after 21 d incubation and increased SOC decomposition by 29.7-72.7 %. Drought intensity showed positive effect (lnRR > 0) on PEs at lower temperatures (15 and 25 °C) but showed negative effect (lnRR < 0) on PEs at higher temperature (35 °C). At moderate drought intensity (33 % WHC) before rewetting, PEs increased significantly with incubation temperature (Q₁₀ = 1.65). Contrastingly, at high drought intensity (20 % WHC), temperature did not significantly influence PEs during the 21-d incubation after rewetting (Q₁₀ = 0.96). The combination of drought, temperature change and glucose addition significantly changed the abundances in the dominant bacterial phyla (Proteobacteria, Actinobacteria, and Chloroflexi) and fungal phylum (Ascomycota), which likely affect PEs. Furthermore, the decrease in the demand for microbial-driven N mining, which is a crucial factor in promoting positive PEs, was associated with drought intensity at high temperature (35 °C). Our study provided a quantitative and mechanistic understanding of the impact of drought intensity on PEs before rewetting and its temperature sensitivity.