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U.S. Department of Energy Office of Biological and Environmental Research

PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Measuring Photosynthesis via the Glow of Plants

Lianhong Gu

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16 October 2017

Novel observations suggest a great potential of measuring global gross primary production via solar-induced fluorescence.

The Science  
When energized by photons of sunlight, chlorophyll molecules in plant leaves emit a faint red light—solar-induced fluorescence (SIF). SIF originates directly from the core of the photosynthetic machinery and is produced concurrently with carbon fixation. Orbiting Carbon Observatory-2 (OCO-2) is capable of monitoring SIF at high spatial resolution. After validating OCO-2’s SIF measurements against ground measurements, the team related OCO-2 SIF to gross primary production (GPP) estimated from AmeriFlux sites under the OCO-2’s orbital tracks. A significant linear relationship is obtained between these two variables across different vegetation types.

The Impact
Photosynthesis is the foundation of life and civilization on Earth. Yet scientists' current ability to measure photosynthesis at large scales is extremely limited. The team shows that SIF is a direct proxy of photosynthesis and the relationship is consistent across biomes. This research opens up a new direction for photosynthesis observations at multiple scales. It also shows how ground-based observations such as those from AmeriFlux can be integrated with satellite remote sensing to advance photosynthesis research at local, regional, and global scales.

Summary
Quantifying GPP remains a major challenge in global carbon cycle research. Space-borne monitoring of solar-induced chlorophyll fluorescence (SIF), an integrative photosynthetic signal of molecular origin, can assist in terrestrial GPP monitoring. However, the extent to which SIF tracks spatiotemporal variations in GPP remains unresolved. The OCO-2 SIF data acquisition and fine spatial resolution permit direct validation against ground and airborne observations. Empirical orthogonal function analysis shows consistent spatiotemporal correspondence between OCO-2 SIF and GPP globally. A linear SIF-GPP relationship is also obtained at eddy-flux sites covering diverse biomes, setting the stage for future investigations of the robustness of such a relationship across more biomes. Team findings support the central importance of high-quality satellite SIF for studying terrestrial carbon cycle dynamics.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigators
Lianhong Gu, Distinguished Scientist
Oak Ridge National Laboratory
Oak Ridge, TN 37831
lianhong-gu@ornl.gov (865-241-5925)

Jeff Wood, Assistant Research Professor
University of Missouri
Columbia, MO 65211
woodjd@missouri.edu (573-883-3295)

Funding
U.S. National Aeronautics and Space Administration (NASA)
Office of Biological and Environmental Research within the U.S. Department of Energy Office of Science
The Academy of Finland
The European Union

Publications
Sun, Y. et al. “OCO-2 advances photosynthesis observation from space via solar-induced chlorophyll fluorescence.” Science 358(6360), 189 (2017). [DOI:10.1126/science.aam5747]

Related Links
http://science.sciencemag.org/content/358/6360/eaam5747

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