The relationship between spectral and integrated sun-induced chlorophyll fluorescence and its implication for photosynthesis estimation using fluorescence observations

Ji Li; Lianhong Gu; Jing M. Chen; Yongguang Zhang

doi:10.1016/j.rse.2025.115113

The relationship between spectral and integrated sun-induced chlorophyll fluorescence and its implication for photosynthesis estimation using fluorescence observations

Ji Li
, Lianhong Gu
, Jing M. Chen
, Yongguang Zhang

Ecosystem Processes

Research output: Contribution to journal › Article › peer-review

1 Scopus citations

Abstract

Chlorophyll fluorescence (ChlF) is tightly linked to photosynthetic electron transport and informs gross primary productivity (GPP) across scales. Sun-induced ChlF (SIF) is typically retrieved at specific wavelengths (e.g., Fraunhofer lines, oxygen absorption bands) within a narrow field of view (solid angle), and given in power units. This spectral SIF radiance, denoted SIF_λ , is not directly photosynthetically relevant, rather, it is the integrated radiant exitance, SIF_int , expressed in molar units and integrated over 660–800 nm and the full angular domain, that corresponds mechanistically to photosynthesis. It is generally assumed that the SIF_λ is proportional to SIF_int and that this proportionality is spatially and temporally invariant. Here we tested this assumption with spectrally resolved SIF measured in three crop and six tree species at the leaf level. We found that while SIF_λ is significantly related to SIF_int at individual Fraunhofer lines, this relationship varies with wavelength and leaf chlorophyll content (LCC). We therefore developed a model to predict SIF_int from SIF_λ using wavelength and LCC as inputs. The model performed well across the ChlF emission band, particularly in the far-red region, enabling accurate conversion from observed SIF_λ to mechanistically relevant SIF_int . As an exploratory extension, the model was applied at the canopy scale for C3 and C4 crops with the Mechanistic Light Response model, yielding encouraging agreement between modeled and observed GPP. The core contribution of this work is establishing the SIF_λ –SIF_int relationship and a transfer model at the leaf scale, while the canopy application serves as an exploratory extension illustrating its scaling potential. Together, these findings provide a more mechanistically consistent basis for SIF-based GPP estimation and strengthen the application of fluorescence observations in carbon cycle research.

Original language	English
Article number	115113
Journal	Remote Sensing of Environment
Volume	333
DOIs	https://doi.org/10.1016/j.rse.2025.115113
State	Published - Jan 15 2026

Funding

This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).This research was supported by the National Natural Science Foundation of China (42125105 and 42305129) and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University (2024QNXZ01). We would also thank Dr. Zhongyang Li, Dr. Hezhou Wang, Dr. Pengju Wu, and other researchers from the National Shangqiu station of Farmland Irrigation Research Institute of Chinese Academy of Agricultural Sciences for the field measurements. LG is supported by the U.S. Department of Energy (DOE), Office of Science, Biological and Environmental Research Program. ORNL is managed by UT-Battelle, LLC, for DOE under contract DE-AC05-00OR22725. This research was supported by the National Natural Science Foundation of China ( 42125105 and 42305129 ) and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University ( 2024QNXZ01 ). We would also thank Dr. Zhongyang Li, Dr. Hezhou Wang, Dr. Pengju Wu, and other researchers from the National Shangqiu station of Farmland Irrigation Research Institute of Chinese Academy of Agricultural Sciences for the field measurements. LG is supported by the U.S. Department of Energy (DOE), Office of Science , Biological and Environmental Research Program . ORNL is managed by UT-Battelle , LLC , for DOE under contract DE-AC05-00OR22725 . This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the US Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).

Keywords

Conversion model
Energy units
Integrated SIF
Molar units
Spectral SIF
Sun-induced chlorophyll fluorescence (SIF)

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10.1016/j.rse.2025.115113

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title = "The relationship between spectral and integrated sun-induced chlorophyll fluorescence and its implication for photosynthesis estimation using fluorescence observations",

abstract = "Chlorophyll fluorescence (ChlF) is tightly linked to photosynthetic electron transport and informs gross primary productivity (GPP) across scales. Sun-induced ChlF (SIF) is typically retrieved at specific wavelengths (e.g., Fraunhofer lines, oxygen absorption bands) within a narrow field of view (solid angle), and given in power units. This spectral SIF radiance, denoted SIFλ , is not directly photosynthetically relevant, rather, it is the integrated radiant exitance, SIFint , expressed in molar units and integrated over 660–800 nm and the full angular domain, that corresponds mechanistically to photosynthesis. It is generally assumed that the SIFλ is proportional to SIFint and that this proportionality is spatially and temporally invariant. Here we tested this assumption with spectrally resolved SIF measured in three crop and six tree species at the leaf level. We found that while SIFλ is significantly related to SIFint at individual Fraunhofer lines, this relationship varies with wavelength and leaf chlorophyll content (LCC). We therefore developed a model to predict SIFint from SIFλ using wavelength and LCC as inputs. The model performed well across the ChlF emission band, particularly in the far-red region, enabling accurate conversion from observed SIFλ to mechanistically relevant SIFint . As an exploratory extension, the model was applied at the canopy scale for C3 and C4 crops with the Mechanistic Light Response model, yielding encouraging agreement between modeled and observed GPP. The core contribution of this work is establishing the SIFλ –SIFint relationship and a transfer model at the leaf scale, while the canopy application serves as an exploratory extension illustrating its scaling potential. Together, these findings provide a more mechanistically consistent basis for SIF-based GPP estimation and strengthen the application of fluorescence observations in carbon cycle research.",

keywords = "Conversion model, Energy units, Integrated SIF, Molar units, Spectral SIF, Sun-induced chlorophyll fluorescence (SIF)",

author = "Ji Li and Lianhong Gu and Chen, \{Jing M.\} and Yongguang Zhang",

note = "Publisher Copyright: {\textcopyright} 2025 Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.",

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T1 - The relationship between spectral and integrated sun-induced chlorophyll fluorescence and its implication for photosynthesis estimation using fluorescence observations

AU - Li, Ji

AU - Gu, Lianhong

AU - Chen, Jing M.

AU - Zhang, Yongguang

PY - 2026/1/15

Y1 - 2026/1/15

N2 - Chlorophyll fluorescence (ChlF) is tightly linked to photosynthetic electron transport and informs gross primary productivity (GPP) across scales. Sun-induced ChlF (SIF) is typically retrieved at specific wavelengths (e.g., Fraunhofer lines, oxygen absorption bands) within a narrow field of view (solid angle), and given in power units. This spectral SIF radiance, denoted SIFλ , is not directly photosynthetically relevant, rather, it is the integrated radiant exitance, SIFint , expressed in molar units and integrated over 660–800 nm and the full angular domain, that corresponds mechanistically to photosynthesis. It is generally assumed that the SIFλ is proportional to SIFint and that this proportionality is spatially and temporally invariant. Here we tested this assumption with spectrally resolved SIF measured in three crop and six tree species at the leaf level. We found that while SIFλ is significantly related to SIFint at individual Fraunhofer lines, this relationship varies with wavelength and leaf chlorophyll content (LCC). We therefore developed a model to predict SIFint from SIFλ using wavelength and LCC as inputs. The model performed well across the ChlF emission band, particularly in the far-red region, enabling accurate conversion from observed SIFλ to mechanistically relevant SIFint . As an exploratory extension, the model was applied at the canopy scale for C3 and C4 crops with the Mechanistic Light Response model, yielding encouraging agreement between modeled and observed GPP. The core contribution of this work is establishing the SIFλ –SIFint relationship and a transfer model at the leaf scale, while the canopy application serves as an exploratory extension illustrating its scaling potential. Together, these findings provide a more mechanistically consistent basis for SIF-based GPP estimation and strengthen the application of fluorescence observations in carbon cycle research.

AB - Chlorophyll fluorescence (ChlF) is tightly linked to photosynthetic electron transport and informs gross primary productivity (GPP) across scales. Sun-induced ChlF (SIF) is typically retrieved at specific wavelengths (e.g., Fraunhofer lines, oxygen absorption bands) within a narrow field of view (solid angle), and given in power units. This spectral SIF radiance, denoted SIFλ , is not directly photosynthetically relevant, rather, it is the integrated radiant exitance, SIFint , expressed in molar units and integrated over 660–800 nm and the full angular domain, that corresponds mechanistically to photosynthesis. It is generally assumed that the SIFλ is proportional to SIFint and that this proportionality is spatially and temporally invariant. Here we tested this assumption with spectrally resolved SIF measured in three crop and six tree species at the leaf level. We found that while SIFλ is significantly related to SIFint at individual Fraunhofer lines, this relationship varies with wavelength and leaf chlorophyll content (LCC). We therefore developed a model to predict SIFint from SIFλ using wavelength and LCC as inputs. The model performed well across the ChlF emission band, particularly in the far-red region, enabling accurate conversion from observed SIFλ to mechanistically relevant SIFint . As an exploratory extension, the model was applied at the canopy scale for C3 and C4 crops with the Mechanistic Light Response model, yielding encouraging agreement between modeled and observed GPP. The core contribution of this work is establishing the SIFλ –SIFint relationship and a transfer model at the leaf scale, while the canopy application serves as an exploratory extension illustrating its scaling potential. Together, these findings provide a more mechanistically consistent basis for SIF-based GPP estimation and strengthen the application of fluorescence observations in carbon cycle research.

KW - Conversion model

KW - Energy units

KW - Integrated SIF

KW - Molar units

KW - Spectral SIF

KW - Sun-induced chlorophyll fluorescence (SIF)

UR - https://www.scopus.com/pages/publications/105023831722

U2 - 10.1016/j.rse.2025.115113

DO - 10.1016/j.rse.2025.115113

M3 - Article

AN - SCOPUS:105023831722

SN - 0034-4257

VL - 333

JO - Remote Sensing of Environment

JF - Remote Sensing of Environment

M1 - 115113

ER -

The relationship between spectral and integrated sun-induced chlorophyll fluorescence and its implication for photosynthesis estimation using fluorescence observations

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Keywords

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