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Abstract Amazônia is a species-rich region of immense importance to Earth’s water and carbon cycling. Photosynthesis drives the global carbon cycle, so understanding photosynthetic differences across diverse landscapes is a key task of ecophysiology and ecosystem science. Unfortunately, due to physiological and logistical constraints, ground-based photosynthesis data in Amazônia remain scarce and the ‘traditional’ steady-state (SS) method of gas exchange is slow and inefficient. The Dynamic Assimilation™ Technique (DAT) promises a new way to perform A/Ci curves rapidly without requiring SS conditions. Thus far, this technique has only been validated in greenhouse or agricultural-field-grown species and has yet to be tested in forest trees of diverse physiology morphology and environmental adaptation. To test the utility of the DAT in a complex tropical forest ecosystem, we compared the DAT with the SS method in 13 Amazonian trees in situ. We found strong agreement between Vcmax from DAT curves and SS curves, while Jmax was underestimated in DAT curves. We conclude that the DAT provides a robust and rapid estimation of Vcmax. We also identified diverse and unexpected DAT curve shapes among some trees, including the presence of an ‘overshoot’ in assimilation beyond model-derived ribulose-1,5-bisphosphate (RuBP) regeneration limitations. The presence of overshoot may elucidate microclimate and species differences in RuBP regeneration rates and emphasizes the considerable importance of DAT curve protocol specifications, such as the effect of ramp rate and direction on Jmax and TPU. Overall, the DAT saved time relative to the SS method and proved to be an effective and rapid method for quantifying Vcmax in tropical trees. 

Summary Rising temperatures are influencing forests on many scales, with potentially strong variation vertically across forest strata. Using published research and new analyses, we evaluate how microclimate and leaf temperatures, traits, and gas exchange vary vertically in forests, shaping tree, and ecosystem ecology. In closed‐canopy forests, upper canopy leaves are exposed to the highest solar radiation and evaporative demand, which can elevate leaf temperature (T_leaf), particularly when transpirational cooling is curtailed by limited stomatal conductance. However, foliar traits also vary across height or light gradients, partially mitigating and protecting against the elevation of upper canopyT_leaf. Leaf metabolism generally increases with height across the vertical gradient, yet differences in thermal sensitivity across the gradient appear modest. Scaling from leaves to trees, canopy trees have higher absolute metabolic capacity and growth, yet are more vulnerable to drought and damagingT_leafthan their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme highT_leaf's but have fewer cooling mechanisms and thus may be strongly impacted by warming under some conditions, particularly when exposed to a harsher microenvironment through canopy disturbance. As the climate changes, integrating the patterns and mechanisms reviewed here into models will be critical to forecasting forest–climate feedback.