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 CO 2 uptake when assimilating nitrogen de novo via the photorespiratory pathway by fixing carbon as amino acids in addition to carbohydrates. Plants fed NO 3 − had higher rates of CO 2 assimilation under photorespiratory than low-photorespiratory conditions, while plants lacking NO 3 − nutrition exhibited lower stimulation of CO 2 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 CO 2 uptake and of rates of photosynthetic electron transport. The results highlight how photorespiration can improve photosynthetic performance despite reducing the efficiency of Rubisco carboxylation. Photorespiration was considered to be wasteful because it reduces photosynthetic efficiency. However, here a modified photosynthesis model, which incorporates photorespiratory nitrogen assimilation, suggests that photorespiration also has beneficial effects on carbon uptake.