Partitioning net ecosystem carbon exchange with isotopic fluxes of CO2

David R. Bowling, Pieter P. Tans, Russell Monson

Research output: Contribution to journalArticle

158 Citations (Scopus)

Abstract

Because biological and physical processes alter the stable isotopic composition of atmospheric CO2, variations in isotopic content can be used to investigate those processes. Isotopic flux measurements of 13CO2 above terrestrial ecosystems can potentially be used to separate net ecosystem CO2 exchange (NEE) into its component fluxes, net photosynthetic assimilation (FA) and ecosystem respiration (FR). In this paper theory is developed to partition measured NEE into FA and FR, using measurements of fluxes of CO2 and 13CO2, and isotopic composition of respired CO2 and forest air. The theory is then applied to fluxes measured (or estimated, for 13CO2) in a temperate deciduous forest in eastern Tennessee (Walker Branch Watershed). It appears that there is indeed enough additional information in 13CO2 fluxes to partition NEE into its photosynthetic and respiratory components. Diurnal patterns in FA and FR were obtained, which are consistent in magnitude and shape with patterns obtained from NEE measurements and an exponential regression between night-time NEE and temperature (a standard technique which provides alternate estimates of FR and FA). The light response curve for photosynthesis (FA vs. PAR) was weakly nonlinear, indicating potential for saturation at high light intensities. Assimilation-weighted discrimination against 13CO2 for this forest during July 1999 was 16.8-17.1%, depending on canopy conductance. The greatest uncertainties in this approach lie in the evaluation of canopy conductance and its effect on whole-canopy photosynthetic discrimination, and thus the indirect methods used to estimate isotopic fluxes. Direct eddy covariance measurements of 13CO2 flux are needed to assess the validity of the assumptions used and provide defensible isotope-based estimates of the component fluxes of net ecosystem exchange.

Original languageEnglish (US)
Pages (from-to)127-145
Number of pages19
JournalGlobal Change Biology
Volume7
Issue number2
DOIs
StatePublished - 2001
Externally publishedYes

Fingerprint

Ecosystems
Carbon
partitioning
Fluxes
ecosystem
carbon
canopy
isotopic composition
net ecosystem exchange
eddy covariance
High intensity light
flux measurement
photosynthetically active radiation
temperate forest
deciduous forest
terrestrial ecosystem
light intensity
biological processes
Photosynthesis
photosynthesis

Keywords

  • Canopy conductance
  • Carbon dioxide
  • Eddy covariance
  • Forest micrometeorology
  • Net ecosystem exchange
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology
  • Global and Planetary Change
  • Environmental Science(all)
  • Environmental Chemistry

Cite this

Partitioning net ecosystem carbon exchange with isotopic fluxes of CO2. / Bowling, David R.; Tans, Pieter P.; Monson, Russell.

In: Global Change Biology, Vol. 7, No. 2, 2001, p. 127-145.

Research output: Contribution to journalArticle

Bowling, David R. ; Tans, Pieter P. ; Monson, Russell. / Partitioning net ecosystem carbon exchange with isotopic fluxes of CO2. In: Global Change Biology. 2001 ; Vol. 7, No. 2. pp. 127-145.
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