Preprints
https://doi.org/10.5194/egusphere-2022-34
https://doi.org/10.5194/egusphere-2022-34
 
09 Mar 2022
09 Mar 2022

Ideas and perspectives: Allocation of carbon from Net Primary Production in models is inconsistent with observations of the age of respired carbon

Carlos A. Sierra1,2, Verónika Ceballos-Núñez3, Henrik Hartmann1, David Herrera-Ramírez1, and Holger Metzler2 Carlos A. Sierra et al.
  • 1Max Planck Institute for Biogeochemistry, 07745 Jena, Germany
  • 2Swedish University of Agricultural Sciences, 75651 Uppsala, Sweden
  • 3Leipzig University, 04103 Leipzig, Germany

Abstract. Carbon allocation in vegetation is an important process in the terrestrial carbon cycle; it determines the fate of photo-assimilates and it has an impact on the time carbon spends in the terrestrial biosphere. Although previous studies have highlighted important conceptual issues in the definition and metrics used to assess carbon allocation, very little emphasis has been placed on the distinction between allocation of carbon from gross primary production (GPP) versus allocation from net primary production (NPP). An important number of simulation models and conceptual frameworks are based on the concept that C is allocated from NPP, which implies that C is respired immediately after photosynthetic assimilation. However, empirical work that estimates the age of respired CO2 from vegetation tissue (foliage, stems, roots) shows that it may take from years to decades to respire previously produced photosynthates. The transit time distribution of carbon in vegetation and ecosystems, a metric that provides an estimate of the age of respired carbon, indicates that vegetation pools respire carbon of a wide range of ages, on timescales that are in conflict with the assumption that autotrophic respiration only consumes recently fixed carbon. In this contribution, we attempt to provide compelling evidence based on recent research on the age of respired carbon and the theory of timescales of carbon in ecosystems, with the aim to promote a change in the predominant paradigm implemented in ecosystem models where carbon allocation is based on NPP. In addition, we highlight some implications for understanding and modeling carbon dynamics in terrestrial ecosystems.

Carlos A. Sierra et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-34', Yingping Wang, 26 Mar 2022
    • AC1: 'Reply on RC1', Carlos Sierra, 03 May 2022
  • RC2: 'Comment on egusphere-2022-34', Anonymous Referee #2, 19 Apr 2022
    • AC2: 'Reply on RC2', Carlos Sierra, 03 May 2022

Carlos A. Sierra et al.

Carlos A. Sierra et al.

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Short summary
Empirical work that estimates the age of respired CO2 from vegetation tissue shows that it may take from years to decades to respire previously produced photosynthates. However, many ecosystem models represent respiration processes in a form that cannot reproduce these observations. In this contribution, we attempt to provide compelling evidence based on recent research, with the aim to promote a change in the predominant paradigm implemented in ecosystem models.