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  • Presentation | B44D: Sun-Induced Chlorophyll Fluorescence: Measurements, Modeling, and Applications from Field, Airborne, and Satellite Platforms II Oral
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  • B44D-04: Drought-induced Photosynthetic Decline and Increased Heat Dissipation Complicate SIF-based Analysis of Amazonian Forests Responses to Climate
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Author(s):
Leonardo Ziccardi, Michigan State University (First Author, Presenting Author)
David Kramer, Michigan State University
Nathan Gonçalves, Michigan State University
Natalia Restrepo-Coupe, University of Arizona
Tyeen Taylor, The Operator’s Manual for the Planet (The OMP LLC)
Bruce Nelson, INPA National Institute of Amazonian Research
Neill Prohaska, University of Arizona
Kleber Campos, University of Western Para-UFOPA
Advanio Siqueira-Silva, Federal University of Western Para
Scott Saleska, University of Arizona
Scott Stark, Michigan State University


Satellite observations often use sun-induced chlorophyll fluorescence (SIF) to estimate how much carbon tropical forests absorb through photosynthesis. This approach works well at large scales, but becomes less accurate at smaller and local scales—especially in structurally complex tropical forests and during droughts—due to how leaves regulate light energy. Recent extreme droughts in Amazonia, usually linked to El Niño events, have increased tree mortality and reduced carbon uptake, but how drought affects the relationship between leaf photosynthesis and SIF at different canopy strata remains unclear. To understand this, we tracked the fates of photons absorbed by leaves across different heights in central Amazonian forests. Using tree climbing techniques, we measured how absorbed sunlight is used in photosynthesis, dissipated as heat, or re-emitted as fluorescence during normal seasons and the 2023–2024 El Niño drought. We found strong photosynthetic reductions in the upper and middle canopy layers during drought linked to increased photoprotective heat dissipation, with minimal changes in fluorescence. This shift changes how well SIF reflects actual photosynthesis during droughts. These findings highlight the need to account for canopy structure and environmental stress when interpreting SIF data to monitor forest health and carbon uptake, especially amid more frequent climate extremes.



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