Bimodal diel pattern in peatland ecosystem respiration rebuts uniform temperature response

Accurate projections of climate change impacts on the vast carbon stores of northern peatlands require detailed knowledge of ecosystem respiration (ER) and its heterotrophic (Rh) and autotrophic (Ra) components. Currently, however, standard measurement techniques (i.e. eddy covariance and manual chambers) generate semi-continuous empirical ER data (i.e. during only night- or daytime, respectively) that are extrapolated to the daily scale based on the paradigm that assumes a uniform diel response to temperature. Here, using continuous autochamber measurements of hourly ER, Rh and Ra in a boreal peatland, we demonstrate a distinct bimodal pattern in diel ER which contrasts the unimodal pattern inherent to the classical assumption. This feature results from divergent temperature dependencies of day- and nighttime ER due to differing contributions from Rh and Ra. We show that the classical approach overestimated daily ER by up to ~2-fold and growing season ER by 16-23%. These findings call for improved process-based understanding of ER to avoid bias in simulations of peatland carbon cycle-climate feedbacks.