Plants increase CO2 uptake by assimilating nitrogen via the photorespiratory pathway

Busch FA1, Sage RF2 and Farquhar GD1

  1. Research School of Biology and ARC Centre of Excellence for Translational Photosynthesis, Australian National University, Acton, ACT, Australia.
  2. Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.

Photorespiration is a major bioengineering target for increasing crop yields as it is often considered a wasteful process due to the release of previously fixed CO2. Photorespiratory metabolism is integrated into leaf metabolism and thus may have certain benefits. Using a combination of mathematical modelling and photosynthetic gas exchange measurements, we show that plants can increase their rate of photosynthetic CO2 uptake when assimilating nitrogen de novo via the photorespiratory pathway. Plants achieve this by fixing carbon as amino acids in addition to carbohydrates. When plants were fed nitrate they had higher rates of CO2 assimilation under photorespiratory than low-photorespiratory conditions, while plants lacking nitrate 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.