The optimal allocation of nitrogen within the C3 photosynthetic system at elevated CO2

Belinda E. Medlyn*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

70 Citations (Scopus)


The distribution of nitrogen among compounds involved in photosynthesis varies in response to changes in environmental conditions such as photon flux density. However, the extent to which the nitrogen distribution within leaves adjusts in response to increased atmospheric CO2 is unclean. A model was used to determine the nitrogen distribution which maximises photosynthesis under realistic light regimes at both current and elevated levels of CO2, and a comparison was made with observed leaf nitrogen distributions reported in the literature. The model accurately predicted the distribution of nitrogen within the photosynthetic system for leaves grown at current levels of CO2, except at very high leaf nitrogen contents. The model predicted that, under a doubling of CO2 concentration from its current level, the ratio of electron transport capacity to Rubisco activity (J(max):V(cmax)) should increase by 40%. In contrast, measurements of J(max):V(cmax) taken from the literature show a slight but non-significant increase in response to an increase in CO2. The discrepancy between predicted and observed J(max):V(cmax) suggests that leaf nitrogen distribution does not acclimate optimally to elevated CO2. Alternatively, the discrepancy may be due to effects of CO2 which the model fails to take into account, such as a possible decrease in the conductance to CO2 transfer between the intercellular spaces and the sites of carboxylation at elevated CO2.

Original languageEnglish
Pages (from-to)593-603
Number of pages11
JournalAustralian Journal of Plant Physiology
Issue number5
Publication statusPublished - 1996
Externally publishedYes


  • atmospheric CO concentration
  • leaf nitrogen
  • nitrogen partitioning
  • optimisation
  • photosynthetically active radiation


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