Solar‐induced chlorophyll fluorescence is strongly correlated with terrestrial photosynthesis for a wide variety of biomes: First global analysis based on OCO‐2 and flux tower observations |
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| Authors: | Xing Li Jingfeng Xiao Binbin He M Altaf Arain Jason Beringer Ankur R Desai Carmen Emmel David Y Hollinger Alisa Krasnova Ivan Mammarella Steffen M Noe Penélope Serrano Ortiz A Camilo Rey‐Sanchez Adrian V Rocha Andrej Varlagin |
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| Institution: | 1. Earth Systems Research Center, Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire;2. School of Resources and Environment, University of Electronic Science and Technology of China, Chengdu, China;3. Center for Information Geoscience, University of Electronic Science and Technology of China, Chengdu, China;4. McMaster Centre for Climate Change and School of Geography and Earth Sciences, McMaster University, Hamilton, ON, Canada;5. The UWA school of Agriculture and Environment, The University of Western Australia, Crawley, WA, Australia;6. Department of Atmospheric and Oceanic Sciences, University of Wisconsin‐Madison, Madison, Wisconsin;7. Department of Environmental Systems Science, Institute of Agricultural Sciences, ETH Zurich, Zurich, Switzerland;8. Northern Research Station, USDA Forest Service, Durham, New Hampshire;9. Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Tartu, Estonia;10. Faculty of Science, Institute for Atmosphere and Earth System Research/Physics, University of Helsinki, Helsinki, Finland;11. Instituto Interuniversitario de Investigación del Sistema Tierra en Andalucía (IISTA‐CEAMA), Universidad de Granada, Granada, Spain;12. Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, Ohio;13. Department of Biological Sciences and the Environmental Change Initiative, University of Notre Dame, Notre Dame, Indiana;14. A.N. Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia |
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| Abstract: | Solar‐induced chlorophyll fluorescence (SIF) has been increasingly used as a proxy for terrestrial gross primary productivity (GPP). Previous work mainly evaluated the relationship between satellite‐observed SIF and gridded GPP products both based on coarse spatial resolutions. Finer resolution SIF (1.3 km × 2.25 km) measured from the Orbiting Carbon Observatory‐2 (OCO‐2) provides the first opportunity to examine the SIF–GPP relationship at the ecosystem scale using flux tower GPP data. However, it remains unclear how strong the relationship is for each biome and whether a robust, universal relationship exists across a variety of biomes. Here we conducted the first global analysis of the relationship between OCO‐2 SIF and tower GPP for a total of 64 flux sites across the globe encompassing eight major biomes. OCO‐2 SIF showed strong correlations with tower GPP at both midday and daily timescales, with the strongest relationship observed for daily SIF at the 757 nm (R2 = 0.72, p < 0.0001). Strong linear relationships between SIF and GPP were consistently found for all biomes (R2 = 0.57–0.79, p < 0.0001) except evergreen broadleaf forests (R2 = 0.16, p < 0.05) at the daily timescale. A higher slope was found for C4 grasslands and croplands than for C3 ecosystems. The generally consistent slope of the relationship among biomes suggests a nearly universal rather than biome‐specific SIF–GPP relationship, and this finding is an important distinction and simplification compared to previous results. SIF was mainly driven by absorbed photosynthetically active radiation and was also influenced by environmental stresses (temperature and water stresses) that determine photosynthetic light use efficiency. OCO‐2 SIF generally had a better performance for predicting GPP than satellite‐derived vegetation indices and a light use efficiency model. The universal SIF–GPP relationship can potentially lead to more accurate GPP estimates regionally or globally. Our findings revealed the remarkable ability of finer resolution SIF observations from OCO‐2 and other new or future missions (e.g., TROPOMI, FLEX) for estimating terrestrial photosynthesis across a wide variety of biomes and identified their potential and limitations for ecosystem functioning and carbon cycle studies. |
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| Keywords: | carbon cycle carbon flux chlorophyll fluorescence eddy covariance gross primary productivity MODIS OCO‐2 vegetation type |
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