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.

Principal Investigator

Lianhong Gu
Oak Ridge National Laboratory
lianhong-gu@ornl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

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

References