Changes in the chloroplastic CO2 concentration explain much of the observed Kok effect: a model

Graham D Farquhar, Florian A Busch

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38 Citations (Scopus)


Mitochondrial respiration often appears to be inhibited in the light when compared with measurements in the dark. This inhibition is inferred from the response of the net CO2 assimilation rate (A) to absorbed irradiance (I), changing slope around the light compensation point (Ic ). We suggest a model that provides a plausible mechanistic explanation of this 'Kok effect'.

The model uses the mathematical description of photosynthesis developed by Farquhar, von Caemmerer and Berry; it involves no inhibition of respiration rate in the light. We also describe a fitting technique for quantifying the Kok effect at low I.

Changes in the chloroplastic CO2 partial pressure (Cc ) can explain curvature of A vs I, its diminution in C4 plants and at low oxygen concentrations or high carbon dioxide concentrations in C3 plants, and effects of dark respiration rate and of temperature. It also explains the apparent inhibition of respiration in the light as inferred by the Laisk approach. 
While there are probably other sources of curvature in A vs I, variation in Cc can largely explain the curvature at low irradiance, and suggests that interpretation of day respiration compared with dark respiration of leaves on the basis of the Kok effect needs reassessment.
Original languageEnglish
Pages (from-to)570-584
Number of pages15
JournalNew Phytologist
Issue number2
Early online date20 Mar 2017
Publication statusPublished - Apr 2017

Bibliographical note

© 2017 The Authors. New Phytologist © 2017 New Phytologist Trust.


  • Carbon Dioxide/metabolism
  • Chloroplasts/drug effects
  • Light
  • Models, Biological
  • Oxygen/pharmacology
  • Partial Pressure
  • Photochemical Processes
  • Photosynthesis/drug effects
  • Plant Leaves/drug effects
  • Temperature


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