Phase-Asymmetric Thermal Sensitivity Amplifies Respiration Hysteresis in Heatwaves

Area of Science:

• Ecology
• Climate Science
• Biogeochemistry

Background:

• Understanding ecosystem respiration (Re) responses to extreme climate events is crucial for predicting carbon-climate feedbacks.
• Heatwaves significantly impact terrestrial ecosystems, but their effects on Re's temperature sensitivity and thermal hysteresis remain under-quantified.

Purpose of the Study:

• To investigate how heatwaves alter the temperature sensitivity (Q10) and thermal hysteresis of ecosystem respiration.
• To develop a quantitative framework for analyzing phase-specific Q10 indices (Q10,I for warming, Q10,II for cooling) and their role in hysteresis.

Main Methods:

• Combined flux-tower observational data with land surface model simulations.
• Developed a framework using temperature thresholds, seasonal timing, and phase-specific Q10 indices (Q10,I, Q10,II).
• Utilized Principal Component Analysis and Structural Equation Modeling to analyze heatwave impacts.

Main Results:

• Heatwaves amplified thermal hysteresis in Re, driven by asymmetric shifts in temperature sensitivity, particularly a decline in Q10,II.
• The post-heatwave cooling phase (Q10,II) was most affected, accounting for 71% of the total phase-specific Q10 change.
• Heatwave-induced hysteresis was fully mediated by Q10,II decline, influenced by thermal thresholds and seasonal timing.

Conclusions:

• Heatwaves induce a phase-asymmetric temperature sensitivity in ecosystem respiration, amplifying thermal hysteresis.
• This amplified hysteresis, driven by reduced Q10,II, suggests short-term heatwaves can lead to prolonged carbon losses.
• Findings highlight the need to incorporate heatwave impacts and asymmetric respiration responses into climate models for accurate carbon-climate feedback predictions.