Biochemical versus stomatal acclimation of dynamic photosynthetic gas exchange to elevated CO 2 in three horticultural species with contrasting stomatal morphology.

Understanding photosynthetic acclimation to elevated CO ₂ (eCO ₂ ) is important for predicting plant physiology and optimizing management decisions under global climate change, but is underexplored in important horticultural crops. We grew three crops differing in stomatal density-namely chrysanthemum, tomato, and cucumber-at near-ambient CO ₂ (450 μmol mol ^-1 ) and eCO ₂ (900 μmol mol ^-1 ) for 6 weeks. Steady-state and dynamic photosynthetic and stomatal conductance (g _s ) responses were quantified by gas exchange measurements. Opening and closure of individual stomata were imaged in situ, using a novel custom-made microscope. The three crop species acclimated to eCO ₂ with very different strategies: Cucumber (with the highest stomatal density) acclimated to eCO ₂ mostly via dynamic g _s responses, whereas chrysanthemum (with the lowest stomatal density) acclimated to eCO ₂ mostly via photosynthetic biochemistry. Tomato exhibited acclimation in both photosynthesis and g _s kinetics. eCO ₂ acclimation in individual stomatal pore movement increased rates of pore aperture changes in chrysanthemum, but such acclimation responses resulted in no changes in g _s responses. Although eCO ₂ acclimation occurred in all three crops, photosynthesis under fluctuating irradiance was hardly affected. Our study stresses the importance of quantifying eCO ₂ acclimatory responses at different integration levels to understand photosynthetic performance under future eCO ₂ environments.
(© 2024 The Author(s). Plant, Cell & Environment published by John Wiley & Sons Ltd.)