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Abstract Tropical forest canopies cycle vast amounts of carbon, yet we still have a limited understanding of how these critical ecosystems will respond to climate warming. We implemented in situ leaf‐level + 3°C experimental warming from the understory to the upper canopy of two Puerto Rican tropical tree species,Guarea guidoniaandOcotea sintenisii. After approximately 1 month of continuous warming, we assessed adjustments in photosynthesis, chlorophyll fluorescence, stomatal conductance, leaf traits and foliar respiration. Warming did not alter net photosynthetic temperature response for either species; however, the optimum temperature ofOcoteaunderstory leaf photosynthetic electron transport shifted upward. There was noOcotearespiratory treatment effect, whileGuarearespiratory temperature sensitivity (Q10) was down‐regulated in heated leaves. The optimum temperatures for photosynthesis (Topt) decreased 3–5°C from understory to the highest canopy position, perhaps due to upper canopy stomatal conductance limitations.Guareaupper canopyToptwas similar to the mean daytime temperatures, whileOcoteacanopy leaves often operated aboveTopt. With minimal acclimation to warmer temperatures in the upper canopy, further warming could put these forests at risk of reduced CO2uptake, which could weaken the overall carbon sink strength of this tropical forest.
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Thermal sensitivity across forest vertical profiles: patterns, mechanisms, and ecological implications
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 (Tleaf), 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 canopyTleaf. 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 damagingTleafthan their smaller counterparts, particularly under climate change. By contrast, understory trees experience fewer extreme highTleaf'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.
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- PAR ID:
- 10384694
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- New Phytologist
- Volume:
- 237
- Issue:
- 1
- ISSN:
- 0028-646X
- Format(s):
- Medium: X Size: p. 22-47
- Size(s):
- p. 22-47
- Sponsoring Org:
- National Science Foundation
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