In nature, fluctuations in light intensity (FL) are tightly coupled to rapid changes in leaf temperature (Tleaf), yet the short-term physiological effects of these concurrent drivers remain largely unresolved. Here, we combined rapid infrared induced Tleaf fluctuations with controlled step changes in light intensity for leaf gas exchange measurements to disentangle how each factor, and their interaction, affects stomatal conductance (gs) and net CO2 assimilation (A) in cucumber plants grown under constant light or FL. Modest but rapid increases in Tleaf (~3°C) alone triggered a pronounced wrong‑way-like stomatal response, leaf movements due to change in epidermal cell turgor, and transient (but long-lasting) decrease in A. This transient decrease in A disappeared under low O₂, indicating a photorespiratory origin. When Tleaf and light increased simultaneously, both gs and A responded faster and more strongly than to light alone, with cumulative enhancement across successive cycles. Plants acclimated to FL displayed larger transient increases in A and maintained higher integrated carbon gain under combined fluctuations. Our findings demonstrate that realistic, rapid Tleaf dynamics exert strong biomechanical and biochemical influences on dynamic gas exchange that are distinct from steady-state responses and should be explicitly considered in experimental design and dynamic photosynthesis models.
Shrestha et al. (Thu,) studied this question.