Changes in temperature sensitivity of soil respiration with decadal warming

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Abstract. Global warming may enhance soil organic carbon (SOC) turnover and CO2 release, potentially accelerating further warming in a positive feedback loop. The temperature sensitivity (TS) of soil respiration is a key determinant for the climate feedback of soils. However, it is uncertain how TS may change under continued warming due to potential microbial thermal acclimation and changes in substrate quality and availability. We examined TS in an incubation experiment using intact soil cores that had undergone 13 years (decadal) of in situ geothermal warming spanning a broad warming gradient of +0 °C to +75 °C. The observed loss of SOC stock (medians ± SE, kg C m-2) compared to ambient had increased with decadal warming, from -4.9 ± 2.4 % at +1–3 °C to -19.3 ± 1.5 % at +7–10 °C. Across incubation temperatures from 5 to 35 °C in the lab experiment, area-based TS generally declined with decadal warming intensity while SOC-normalized TS was similar across treatments. This suggests that SOC depletion rather than microbial thermal acclimation was the dominant control for reduced respiration rates with warming. TS showed variation with temperature range and was generally lower between the 5–15 °C and 25–35 °C incubation temperature changes and markedly higher in the 15–25 °C change. Best-fit standard field models for soil respiration (Van’t Hoff and Lloyd & Taylor models, R2 = 0.842–0.929) failed to capture these shifts in TS, while a sigmoidal function closely captured the observed TS dynamics (R² = 0.970–0.998). Our study suggests that using fixed Q10 TS values to upscale C budgets is inadequate. Although area-based respiration rates declined with warming, the observed decline in soil respiration with warming suggests a latent reduction of further SOC loss over time following prolonged exposure to warming.

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