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Abstract:
With consistently rising global temperatures and lower rainfall, drought conditions are becoming increasingly severe, and plants are compelled to either migrate, adapt and evolve at an increased pace, or face extinction. Two well-known adaptation strategies to drought are escape, where plants shift their phenology (e.g. earlier flowering) to have important life history events occur before the drought, and avoidance, where plants utilize mechanisms to improve their water use efficiency (WUE) (e.g. stomatal regulation). Previous studies have found that early flowering plants have a lower WUE than late-flowering plants. Ruffley et al. 2022 (unpublished) found that there is a simultaneous selective pull for both drought escape and avoidance traits, although the existence of the tradeoff suggests that the escape and avoidance strategies cannot co-occur. However, unpublished data from Expósito-Alonso et al. 2019 found that Arabidopsis thaliana from a dry climate of origin and grown in drought conditions trends towards having a higher fitness with both early flowering and high WUE. To expand on this study, we grew 47 A. thaliana ecotypes and 47 derived lines using a CRISPR-mediated knockout of their early flowering Flowering Locus C (flc) in three different drought conditions. We measured germination time, flowering time, stomatal indices, and fitness via seed weight to evaluate the escape-avoidance tradeoff, as well as using WUE and flowering time data from previous studies done on the same ecotypes of A. thaliana. Our results show that, in well-watered conditions, earlier-flowering founder plants had a higher fitness than late-flowering plants, and late-flowering plants had greater WUE, as expected. In well-watered conditions, plants with the flc KO had a significant positive correlation between fitness and WUE, as well as between fitness and flowering time. Therefore, we found that there could be selection for both early flowering and high WUE when flowering time is held constant, breaking the escape-avoidance tradeoff. These plants could have both high WUE and flower early, making them models for resisting drought conditions. To expand on this data, we are currently examining flowering time and WUE (through stomatal density and δC13) in a larger field experiment across multiple drought levels. We intend to conduct future experiments with these seed resources in a common garden experiment to help inform this tradeoff in natural conditions. Ultimately, understanding drought strategies and their tradeoffs in the natural world will help inform predictions in plant adaptations and distributions under worsening climate change.
