Exponential or Unimodal Relationships Between Nighttime Ecosystem Respiration and Temperature at the Eddy Covariance Flux Tower Sites

ABSTRACT Ecosystem respiration is a key flux in the terrestrial carbon cycle and is affected substantially by temperature. This work analysed the time series data of nighttime net ecosystem exchange of carbon dioxide (NEE night ) from 196 FLUXNET2015 sites to re‐evaluate the relationships between NEE night and temperature. A total of 93 sites (48%) were identified to have a unimodal relationship between NEE night and temperature. Site‐specific apparent optimum temperature parameters were then estimated at these sites. We further assessed the impacts of using exponential or unimodal equations on NEE night predictions. The predicted NEE night values at high temperatures were substantially higher from the exponential‐type equations (mean: ~200%) than from the unimodal equation (mean: ~30%), compared to the observed NEE night . This study calls for using a unimodal equation to predict NEE night (often considered as nighttime ecosystem respiration, ER night ), which could substantially improve the accuracy and reduce uncertainty in ER estimates, in particular under the scenario of global warming.