Bimodal diel pattern in peatland ecosystem respiration rebuts uniform temperature response

Järvi Järveoja,Mats B Nilsson,Patrick M Crill,Matthias Peichl

doi:10.1038/s41467-020-18027-1

Abstract

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 flux measurement techniques, i.e. eddy covariance and manual chambers, generate empirical ER data during only night- or daytime, respectively, which are extrapolated to the daily scale based on the paradigm that assumes a uniform diel temperature response. Here, using continuous autochamber measurements, we demonstrate a distinct bimodal pattern in diel peatland 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 varying contributions from Rh and Ra. We further find that disregarding these bimodal dynamics causes significant bias in ER estimates across multiple temporal scales. This calls for improved process-based understanding of ER to advance our ability to simulate peatland carbon cycle-climate feedbacks.

Highlights

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
The diel AC ER patterns contrast the unimodal diel ER estimates derived from adjacent (i.e., ~25 m) eddy covariance (EC) measurements which rely on the same modeling procedure (Supplementary Fig. 2a–c), i.e., extrapolating nighttime ER to the daytime assuming a uniform diel temperature response
Our empirical evidence for bimodal diel ER patterns strongly contrasts with the established narrative of diel ER having a unimodal pattern emerging from the assumption of a uniform temperature response[17,26,27]

Summary

Introduction

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. Using continuous autochamber measurements, we demonstrate a distinct bimodal pattern in diel peatland 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 varying contributions from Rh and Ra. We further find that disregarding these bimodal dynamics causes significant bias in ER estimates across multiple temporal scales. An automated dark chamber system provides direct ER estimates (in short-canopy ecosystems) at high temporal resolution (e.g., hourly) throughout the full diel cycle While such systems have previously been used to measure diel respiration fluxes in forests[21,22,23], grasslands[20,24] and croplands[25], similar studies are lacking in northern peatland ecosystems. Our current knowledge of peatland ER dynamics and budgets relies heavily on the conceptual assumptions inherent to the models used for extrapolating semi-continuous diel data to daily and annual scales

Methods

Results

Conclusion