Trait-based responses of seven annual crops to elevated CO₂ and water limitation
2018
McGranahan, Devan Allen | Poling, Brittany N.
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].
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