Enhancement of photosynthetic performance, water use efficiency and grain yield during long-term growth under elevated CO2 in wheat and rye is growth temperature and cultivar dependent

- Cold acclimation stimulates photosynthesis.
- Cold acclimation increases water use efficiency.
- Cold acclimation enhances biomass.
- Cold acclimation enhances seed yield.
- We compared CA and NA winter and spring wheat and rye at either ambient or elevated CO2.
- CA winter cereals exhibited a 30-40% increase in light and CO2-saturated rates of photosynthesis at both ambient and elevated CO2 relative to NA counterparts.
- Biomass increased by 28-46% and grain yield per plant by 60% in CA versus NA winter cereals.
- In contrast, both CA spring cultivars exhibited a 45-60% inhibition of light- and CO2-saturated rates of photosynthesis at ambient CO2 as well as growth at elevated CO2 relative to NA controls.
- Biomass accumulation was reduced by about 25% in CA versus NA spring cultivars at elevated CO2.
- We conclude that the potential for enhancement of photosynthetic performance, water use efficiency and grain yield of cereals grown at elevated CO2 is both growth temperature and cultivar dependent.

The effects of long-term elevated CO2 on photosynthetic performance of winter (cv Musketeer) and spring (cv SR4A) rye (Secale cereale) and winter (cv Norstar) and spring (cv Katepwa) wheat (Triticum aestivum) grown at either 20/16 °C (non-acclimated (NA)) or 5/5 °C (cold acclimated (CA) and at either ambient (380 μmol C mol−1) or elevated (700 μmol C mol−1) CO2 were studied. Compared to NA counterparts, CA winter cereals exhibited a 30-40% increase in light and CO2-saturated rates of photosynthesis at both ambient and elevated CO2. This was accompanied by a 35-50% decrease in excitation pressure and non-photochemical energy dissipation. Concomitantly, biomass increased by 28-46% and grain yield per plant by 60%. In contrast, both CA spring cultivars exhibited a 45-60% inhibition of light- and CO2-saturated rates of photosynthesis at ambient CO2 as well as growth at elevated CO2 relative to NA controls. This inhibition was specific for photosynthesis since cold acclimation stimulated rates of respiration by 22-47% in all cultivars tested. This was accompanied by a 58% increase in excitation pressure and a 17% increase in non-photochemical energy dissipation in the cold acclimated spring rye and spring wheat. Consequently, biomass accumulation was reduced by about 25% in CA versus NA spring cultivars at elevated CO2. We conclude that the potential for enhancement of photosynthetic performance, water use efficiency and grain yield of cereals grown at elevated CO2 is both growth temperature and cultivar dependent.