Plant responses to elevated atmospheric carbon dioxide (eCO2) have been hypothesized as a key mechanism that may ameliorate the impact of future drought. Yet, despite decades of experiments, the question of whether eCO2 reduces plant water use, yielding ‘water savings’ that can be used to maintain plant function during periods of water stress, remains unresolved. In this Viewpoint, we identify the experimental challenges and limitations to our understanding of plant responses to drought under eCO2. In particular, we argue that future studies need to move beyond exploring whether eCO2 played ‘a role’ or ‘no role’ in responses to drought, but instead more carefully consider the timescales and conditions that would induce an influence. We also argue that considering emergent differences in soil water content may be an insufficient means of assessing the impact of eCO2. We identify eCO2 impact during severe drought (e.g. to the point of mortality), interactions with future changes in vapour pressure deficit and uncertainty about changes in leaf area as key gaps in our current understanding. New insights into CO2 × drought interactions are essential to better constrain model theory that governs future climate model projections of land–atmosphere interactions during periods of water stress.
Bibliographical noteFunding Information:
MGDK acknowledges support from the Australian Research Council (ARC) Centre of Excellence for Climate Extremes (CE170100023), the ARC Discovery Grants (DP190101823, DP190102025) and the NSW Research Attraction and Acceleration Program. BEM acknowledges support from the ARC Laureate Fellowship FL190100003. DTT acknowledges support from ARC Linkage Grant LP140100232. All data analysis and plots were generated using the Python language and the Matplotlib library. We all acknowledge the Editor and four anonymous reviewers for their constructive comments.
© 2021 The Authors New Phytologist © 2021 New Phytologist Foundation.
- drought mortality
- elevated CO
- water savings