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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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This content will become publicly available on November 21, 2025
Nutrient enrichment can increase the thermal performance of Galápagos seaweeds
Thermal sensitivity in ectothermic organisms is often contingent upon environmental factors. Nutrient availability in particular is believed to influence the physiological responses of primary producers to global warming and is thus relevant to consider when forecasting the structure and functioning of future marine ecosystems. This study measured the effect of nutrient enrichment on the thermal sensitivity of 4 genera of Galápagos seaweeds (Ulva,Caulerpa,Padina, andOchtodes), estimated as the thermal optimum (Topt), performance maximum (Pmax), activation energy, and deactivation energy. These parameters were quantified by modeling thermal performance curves for net photosynthesis under ambient and nutrient-enriched conditions. Our findings revealed variation inToptamong genera, ranging from 27.6° to 36.0°C. Nutrient additions enhancedToptby ~2°C for 2 (PadinaandCaulerpa) of the 4 taxa and also significantly increasedPmaxinPadina, suggesting the ability for warming-induced ocean stratification and associated effects (i.e. decreasing nutrient availability) to reduce the capacities of these populations to maintain and support new growth. No significant differences inToptorPmaxwere observed for eitherUlvaorOchtodeswith enrichment. Ambient net photosynthesis and respiration rates were also compared across genera;Pmaxrates for net photosynthesis were consistently higher than those for respiration (i.e. until just beyondTopt); however, photosyntheticToptvalues were lower. Thus, this study suggests that further warming could reduce overall net primary productivity, with potentially far-reaching implications for marine food webs.
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- Award ID(s):
- 2128592
- PAR ID:
- 10583114
- Publisher / Repository:
- Marine Ecology Progress Series
- Date Published:
- Journal Name:
- Marine ecology Progress series
- Volume:
- 749
- ISSN:
- 1616-1599
- Page Range / eLocation ID:
- 57 to 69
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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