Plants increase CO2 uptake by assimilating nitrogen via the photorespiratory pathway

Abstract

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 uptake when assimilating nitrogen de novo via the photorespiratory pathway by fixing carbon as amino acids in addition to carbohydrates. Plants fed NO had higher rates of CO assimilation under photorespiratory than low-photorespiratory conditions, while plants lacking NO nutrition exhibited lower stimulation of CO 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 uptake and of rates of photosynthetic electron transport. The results highlight how photorespiration can improve photosynthetic performance despite reducing the efficiency of Rubisco carboxylation.

Plant carbon metabolism and climate change: elevated CO2 and temperature impacts on photosynthesis, photorespiration and respiration

“…Additionally, photorespiration is intimately connected with plant nitrogen cycling, as NH 2 is used to produce glycine and ammonium is then produced during the formation of serine. Photorespiration has been linked to increased nitrogen uptake capacity (Rachmilevitch et al ., ; Bloom et al ., , , ; Dellero et al ., ; Busch et al ., ), particularly nitrate, posing the question of whether rising CO 2 may reduce plant nitrogen uptake when nitrate is the main nitrogen source available. This is particularly relevant for crop yield, because nitrate is the dominant soil nitrogen source for most crop plants in cultivated aerated soils (Crawford & Glass, ; Hawkesford et al ., ); by reducing nitrate assimilation, rising CO 2 concentrations may also threaten food quality by depleting crop protein concentrations (Bloom, ; Carlisle et al ., ).…”

Rubisco is not really so bad

“…Although the inability to deal with 2‐phosphoglycolate (even at low photorespiratory rates) is an obvious reason, further evidence suggests that photorespiration could be under positive selection because its metabolism represents a sink for excess reducing equivalents (André, and references therein). In C 3 plants, where the photorespiratory pathway has evolved to carry large fluxes, its suppression could also destabilize plant cell metabolism due to perturbations in flux control properties of photosynthates production and consequences for N and S assimilation (Cornish‐Bowden, , Abadie, Boex‐Fontvieille, Carroll, & Tcherkez, , Eisenhut et al, , Busch, Sage, & Farquhar, , see also below). In other words, the cost/benefit ratio for photorespiration is probably not as large as often assumed and depends on a complex combination of environmental drivers (temperature, CO 2 concentration, and precipitation), as recent insights in the ecology of C 4 plants suggest (Christin & Osborne, ; Urban, Nelson, Street‐Perrott, Verschuren, & Hu, ).…”

Optimizing photorespiration for improved crop productivity

“…Modelling manipulations to photorespiration also can provide unexpected results, such as how changes in photorespiration could affect nitrogen use, which is integral to the role of photorespiration in maintaining photosynthetic efficiency during NH 3 re‐assimilation. Indeed, large scale computational modelling projects have been created to better design next generation crops (Zhu et al ; Marshall‐Colon et al ; Busch et al ).…”

“…In addition, decreased rates of photorespiration, facilitated by growth at elevated CO 2 , have been reported to exhibit a negative feedback on nitrogen assimilation. Indeed, plants can increase their rates of photosynthetic CO 2 uptake when assimilating nitrogen, de novo , via the photorespiratory pathway by fixing carbon as amino acids in addition to carbohydrates (Bloom et al ; Busch et al ).…”