The Science

SIF provides critical information about ecosystem functioning and productivity. SIF observations complement eddy covariance (EC) measurements of net fluxes of carbon dioxide and water vapor. Measuring SIF is, however, challenging. There is a need for a system that integrates seamlessly with existing EC systems at flux sites. The Fluorescence Auto-Measurement Equipment (FAME) was designed to provide versatility, extensibility, autonomous operation, and ease of maintenance for acquiring large quantities of high-quality SIF data at flux sites. A prototype FAME has operated continuously at the Missouri Ozark AmeriFlux site since September 2016, providing high-quality measurements in a challenging environment. FAME observed saturation or even slight decrease of canopy SIF at high photosynthetically active radiation (PAR), similar to leaf photosynthesis. Diurnal hysteresis was also observed, with higher SIF in the morning than afternoon despite the same PAR levels. These patterns of SIF emission were likely caused by dynamic adjustments of energy use in photosynthesis in response to changing environmental conditions and by stress-induced movements of chloroplasts and leaves, which affected light interception.

The Impact

The technology and measurement protocol introduced in this study advances the coordinated observation of SIF and EC fluxes. The results obtained at an AmeriFlux site demonstrate that integrated EC/SIF observation enables new science and represents a step change in observational ecosystem research.

Summary

Long-term continuous SIF observations have the potential to greatly advance terrestrial ecosystem science. Realizing this potential, however, requires synergistic implementation of SIF measurements within EC flux networks. The FAME system and SIF measurement protocol were designed to fulfill this purpose. The innovative hardware and software of FAME support plug-and-play integration with existing EC data acquisition systems. A major novel feature of FAME is its synchronized sampling of spectral irradiance and environmental variables, allowing for more precise interpretation of the SIF signal. The continuous operation of FAME at the Missouri Ozark AmeriFlux site indicates that FAME has achieved its design objective. The light saturation response of SIF and asymmetrical diurnal patterns observed by FAME point to new directions in terrestrial ecosystem science that have not been previously explored.

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

Terrestrial Ecosystem Science program of the Office of the Biological and Environmental Research, within the the U.S. Department of Energy Office of Science.

References