An empirical method of measuring CO 2 recycling by isotopic enrichment of respired CO 2

Tara Greaver, Leonel Da Silveira Lobo Sternberg, Bruce Schaffer, Tomas Moreno

Research output: Contribution to journalArticlepeer-review

7 Scopus citations


An empirical method to measure respiratory CO 2 recycling using a fast growing agricultural cover crop as a model system was tested and compared with a theoretical method which uses a variation of the Keeling plot. Both methods gave values which were high and similar to each other. The theoretical method gave a value of respiratory based CO 2 recycling of 0.41, while the empirical method gave a value of 0.49. Therefore close to half of the respired CO 2 is refixed during daytime photosynthesis in this densely planted cover crop. Refixation of respired CO 2 during the day should lead to an isotopic enrichment of the remaining respired CO 2 leaving the canopy of the cover crop. Therefore, calculations of gross respiration and photosynthesis using isotopic mass balance equations that do not take this isotopic fractionation into account could be in error. We tested this premise by using isotopic mass balance equations to estimate average gross photosynthesis and respiration in this cover crop under two scenarios: (1) no recycling and (2) recycling of respired CO 2. Values of gross photosynthesis and respiration were unrealistically low when it was assumed that no recycling occurs. On the other hand, realistic values similar to previous publications were observed when recycling was taken into account.

Original languageEnglish (US)
Pages (from-to)67-79
Number of pages13
JournalAgricultural and Forest Meteorology
Issue number1-2
StatePublished - Jan 20 2005


  • Carbon isotope ratios
  • Gross photosynthesis
  • Gross respiration
  • Isotopic mass balance equations
  • Keeling plots
  • Recycling

ASJC Scopus subject areas

  • Forestry
  • Atmospheric Science


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