Warming Diminishes the Day-Night Discrepancy in the Apparent Temperature Sensitivity of Ecosystem Respiration

Understanding the sensitivity of ecosystem respiration (ER) to increasing temperature is crucial to predict how the terrestrial carbon sink responds to a warming climate. The temperature sensitivity of ER may vary on a diurnal basis but is poorly understood due to the paucity of observational sites documenting real ER during daytime at a global scale. Here, we used an improved flux partitioning approach to estimate the apparent temperature sensitivity of ER during the daytime (E_0,day) and nighttime (E_0,night) derived from multiyear observations of 189 FLUXNET sites. Our results demonstrated that E_0,night is significantly higher than E_0,day across all biomes, with significant seasonal variations in the day-night discrepancy in the temperature sensitivity of ER (ΔE₀ = E_0,night/E_0,day) except for evergreen broadleaf forest and savannas. Such seasonal variations in ΔE₀ mainly result from the effect of temperature and the seasonal amplitude of NDVI. We predict that future warming will decrease ΔE₀ due to the reduced E_0,night by the end of the century in most regions. Moreover, we further find that disregarding the ΔE₀ leads to an overestimation of annual ER by 10~80% globally. Thus, our study highlights that the divergent temperature dependencies between day- and nighttime ER should be incorporated into Earth system models to improve predictions of carbon-climate change feedback under future warming scenarios.