Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology

The Optimal Allocation of Nitrogen Within the C3 Photosynthetic System at Elevated CO2

BE Medlyn

Australian Journal of Plant Physiology 23(5) 593 - 603
Published: 1996


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 unclear.

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 (Jmax : Vcmax) should increase by 40%. In contrast, measurements of Jmax : Vcmax taken from the literature show a slight but non-significant increase in response to an increase in CO2. The discrepancy between predicted and observed Jmax : Vcmax 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.

Keywords: atmospheric CO2 concentration, leaf nitrogen, nitrogen partitioning, optirnisation, photosynthetically active radiation

© CSIRO 1996

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