By potentially disrupting crop production, climate change has been implicated as a threat to global food security. We focus on two elements of climate change: elevated atmospheric carbon dioxide concentration, or e[CO2], and reduced water availability, as caused by drought. Both variables have been shown to have effects on crop physiology, although there is considerable evidence of interactions and moderation by species-specific differences. Measuring traits helps scale environmental effects up to functional responses, and we focused on traits connected to photosynthesis, which has a close association with crop yield. We measured the response of four physiological traits—quantum photosynthetic yield, chlorophyll content, root:shoot ratio and leaf area—across a diverse set of seven annual crop species grown under three levels of e[CO2] (450, 575 and 700 ppm) and two levels of water availability (minimum ~45 and ~15% VWC) in a growth chamber. Species included barley, durum wheat, maize, oats, sorghum, pinto bean and sunflower. Our regression analysis focused on testing for interactions between e[CO2] and water limitation and determining relative effect sizes of climate change impacts across species, data that can be used for species-specific modeling or determining appropriate levels of environmental variables in free-air CO2 enrichment studies designed to extend small-scale experimental results to the field. Across all species and all traits, the strongest effect of e[CO2] occurred from 450 to 575 ppm, with only marginal differences from 575 to 700 ppm. We found substantial declines in leaf area across all species as a result of e[CO2] and wide variability in leaf area responses to water limitation. Other traits showed weak and variable responses to both e[CO2] and water limitation. While our data confirm that elements of global change, especially increased atmospheric CO2 concentration, do affect traits related to photosynthesis, we found no discernible pattern to suggest which crops might be more resistant to e[CO2].
