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The size and the age of the metabolically active carbon in tree roots
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  • Boaz Hilman,
  • Jan Muhr,
  • Juliane Helm,
  • Iris Kuhlmann,
  • Erst-Detlef Schulze,
  • Susan Trumbore
Boaz Hilman
Max Planck Institute for Biogeochemistry
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Jan Muhr
University of Goettingen
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Juliane Helm
Max Planck Institute for Biogeochemistry
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Iris Kuhlmann
Max Planck Institute for Biogeochemistry
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Erst-Detlef Schulze
Max Planck Institute for Biogeochemistry
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Susan Trumbore
Max Planck Institute for Biogeochemistry
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Abstract

Little is known about the sources and age of C respired from tree roots. Previous research in tree stems has identified two functional pools of non-structural carbohydrates (NSC): an ‘active’ pool supplied directly from canopy photo-assimilates that supports metabolism and a ‘stored’ pool used when fresh C supplies are limited. We compared the C isotope composition of water soluble NSC and respired CO2 for aspen roots (Populus tremula hybrids) that were cut off fresh C supply via stem-girdling and prolonged incubation of excised roots. We used bomb radiocarbon to estimate the time elapsed since C fixation for respired CO2, water-soluble C, and structural α-cellulose. While freshly excised roots respired CO2 with mean age <1 yr, within a week the age increased to 1.6-2.9 yr. Freshly excised roots from trees girdled ~3 months previously had similar respiration rates and NSC stocks as un-girdled trees, but respired older C (~1.2 yr). We estimate the NSC in girdled roots must be replaced 5-7 times by reserves remobilized from root-external sources. Using a mixing model and observed correlations between Δ14C of water-soluble C and α-cellulose, we estimate ~30% of C is ‘active’ (~5 mg C g-1).

Peer review status:ACCEPTED

15 Mar 2021Submitted to Plant, Cell & Environment
17 Mar 2021Submission Checks Completed
17 Mar 2021Assigned to Editor
09 Apr 2021Reviewer(s) Assigned
11 May 2021Review(s) Completed, Editorial Evaluation Pending
11 May 2021Editorial Decision: Revise Minor
31 May 20211st Revision Received
01 Jun 2021Submission Checks Completed
01 Jun 2021Assigned to Editor
01 Jun 2021Review(s) Completed, Editorial Evaluation Pending
01 Jun 2021Editorial Decision: Accept