Photosynthetic responses in spring wheat grown under elevated CO 2 concentrations and stress conditions in the European, multiple-site experiment ‘ESPACE-wheat’

Abstract

Spring wheat cv. Minaret crop stands were grown under ambient and elevated CO 2 concentrations at seven sites in Germany, Ireland, the UK, Belgium and the Netherlands. Six of the sites used open-top chambers and one used a controlled environment mimicking field conditions. The effect of elevated CO 2 for a range of N application regimes, O 3 concentrations, and growth temperatures on flag leaf photosynthesis was studied. Before anthesis, flag leaf photosynthesis was stimulated about 50% by 650 compared with 350 μmol mol −1 CO 2 at all sites, regardless of other treatments. Furthermore, there was no evidence of a decrease in photosynthetic capacity of flag leaves due to growth at elevated CO 2 before anthesis, even for low N treatments. However, photosynthetic capacity, particularly carboxylation capacity, of flag leaves was usually decreased by growth at elevated CO 2 after anthesis, especially in low N treatments. Acclimation of photosynthesis to elevated CO 2 therefore appears to occur only slowly, consistent with a response to changes in sink–source relationships, rather than a direct response. Effect of elevated CO 2 on stomatal conductance was much more variable between sites and treatments, but on average was decreased by ~10% at 650 compared with 350 μmol mol −1 CO 2. Carboxylation capacity of flag leaves was decreased by growth at elevated O 3 both before and after anthesis, regardless of CO 2 concentration.