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Title: Timing and magnitude of C partitioning through a young loblolly pine ( Pinus taeda L.) stand using 13C labeling and shade treatments

The dynamics of rapid changes in carbon (C) partitioning within forest ecosystems are not well understood, which limits improvement of mechanistic models of C cycling. Our objective was to inform model processes by describing relationships between C partitioning and accessible environmental or physiological measurements, with a special emphasis on short-term C flux through a forest ecosystem. We exposed eight 7-year-old loblolly pine ( Pinus taeda L.) trees to air enriched with 13CO 2 and then implemented adjacent light shade (LS) and heavy shade (HS) treatments in order to manipulate C uptake and flux. The impacts of shading on photosynthesis, plant water potential, sap flow, basal area growth, root growth, and soil CO 2 efflux rate (CER) were assessed for each tree over a three-week period. The progression of the 13C label was concurrently tracked from the atmosphere through foliage, phloem, roots, and surface soil CO 2 efflux. The HS treatment significantly reduced C uptake, sap flow, stem growth and fine root standing crop, and resulted in greater residual soil water content to 1 m depth. Sap flow was strongly correlated with CER on the previous day, but not the current day, with no apparent treatment effect on the relationship. Althoughmore » there were apparent reductions in new C flux belowground, the heavy shade treatment did not noticeably reduce the magnitude of belowground autotrophic and heterotrophic respiration based on surface soil CO 2 efflux rate (CER), which was overwhelmingly driven by soil temperature and moisture. The 13C label was immediately detected in foliage on label day (half-life = 0.5 d), progressed through phloem by day 2 (half-life = 4.7 d), roots by day 2-4, and subsequently was evident as respiratory release from soil which peaked between days 3-6. The δ 13C of soil CO 2 efflux was strongly correlated with phloem 13C on the previous day, or two days earlier. While the 13C label was readily tracked through the ecosystem, the fate of root C through respiratory, mycorrhizal or exudative release pathways were not assessed. Lastly, these data detail the timing and relative magnitude of C flux through various components of a young pine stand in relation to environmental conditions.« less
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  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Tree Physiology
Additional Journal Information:
Journal Volume: 32; Journal Issue: 6; Journal ID: ISSN 0829-318X
Oxford University Press
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
60 APPLIED LIFE SCIENCES; carbon allocation; carbon partitioning; 13CO2; loblolly pine; Pinus taeda; respiration; shade; soil CO2 efflux
OSTI Identifier: