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Plants increase CO2 uptake by assimilating nitrogen via the photorespiratory pathway


Photorespiration is a major bioengineering target for increasing crop yields as it is often considered a wasteful process. Photorespiratory metabolism is integrated into leaf metabolism and thus may have certain benefits. Here, we show that plants can increase their rate of photosynthetic CO2 uptake when assimilating nitrogen de novo via the photorespiratory pathway by fixing carbon as amino acids in addition to carbohydrates. Plants fed NO3 had higher rates of CO2 assimilation under photorespiratory than low-photorespiratory conditions, while plants lacking NO3 nutrition exhibited lower stimulation of CO2 uptake. We modified the widely used Farquhar, von Caemmerer and Berry photosynthesis model to include the carbon and electron requirements for nitrogen assimilation via the photorespiratory pathway. Our modified model improves predictions of photosynthetic CO2 uptake and of rates of photosynthetic electron transport. The results highlight how photorespiration can improve photosynthetic performance despite reducing the efficiency of Rubisco carboxylation.

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We thank M. Holloway-Phillips for assistance with growing the plants. This work was supported by the ARC Centre of Excellence for Translational Photosynthesis and by the Australian Science Industry and Endowment Fund (SIEF grant RP04-122). R.F.S. was supported by Discovery grants 154273-2007 and 154273-2012 from the Natural Science and Engineering Research Council (NSERC) of Canada.

Author information

F.A.B. conceived the study and undertook the experimental work, with input from R.F.S. F.A.B. and G.D.F. carried out the modelling. F.A.B. wrote the manuscript with help from all authors.

Competing interests

The authors declare no competing financial interests.

Correspondence to Florian A. Busch.

Supplementary information

  1. Supplementary Information

    A description of the derivation of expressions for α G and α S, Supplementary Figures 1–4. Supplementary Table 1.

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Fig. 1: Schematic representation of the photosynthetic carbon reduction and photorespiratory cycles.
Fig. 2: Effect of N fertilization on α old.
Fig. 3: The CO2 response of A in KNO3-fertilized plants fitted with the photosynthesis model incorporating N assimilation.
Fig. 4: Modelled CO2 response of A to the chloroplastic CO2 concentration (C c), showing the effect of amino acid export from the photorespiratory pathway as glycine and serine.