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Published June 11, 2019 | Published + Supplemental Material
Journal Article Open

Mechanistic evidence for tracking the seasonality of photosynthesis with solar-induced fluorescence

Abstract

Northern hemisphere evergreen forests assimilate a significant fraction of global atmospheric CO_2 but monitoring large-scale changes in gross primary production (GPP) in these systems is challenging. Recent advances in remote sensing allow the detection of solar-induced chlorophyll fluorescence (SIF) emission from vegetation, which has been empirically linked to GPP at large spatial scales. This is particularly important in evergreen forests, where traditional remote-sensing techniques and terrestrial biosphere models fail to reproduce the seasonality of GPP. Here, we examined the mechanistic relationship between SIF retrieved from a canopy spectrometer system and GPP at a winter-dormant conifer forest, which has little seasonal variation in canopy structure, needle chlorophyll content, and absorbed light. Both SIF and GPP track each other in a consistent, dynamic fashion in response to environmental conditions. SIF and GPP are well correlated (R^2 = 0.62–0.92) with an invariant slope over hourly to weekly timescales. Large seasonal variations in SIF yield capture changes in photoprotective pigments and photosystem II operating efficiency associated with winter acclimation, highlighting its unique ability to precisely track the seasonality of photosynthesis. Our results underscore the potential of new satellite-based SIF products (TROPOMI, OCO-2) as proxies for the timing and magnitude of GPP in evergreen forests at an unprecedented spatiotemporal resolution.

Additional Information

© 2019 National Academy of Sciences. Published under the PNAS license. Edited by Gregory P. Asner, Arizona State University, Tempe, AZ, and approved April 26, 2019 (received for review January 7, 2019). Data Availability. The datasets generated and/or analyzed for the current study are available at a data repository hosted at the California Institute of Technology (https://data.caltech.edu/records/1231). The doi associated with this dataset is 10.22002/D1.1231 (71). We thank Dave Eriksson and the support staff at University of Colorado Mountain Research Station for help during field deployment of the canopy access towers and PhotoSpec; Prof. John Lin for enthusiastic support of this research and many helpful discussions; Dr. Greg Ostermann for setting up OCO-2 target selections; Dr. Andrew Richardson for making the PhenoCam data (Fig. 1A) available; and Apogee Instruments for donating quantum sensors. This research was funded by a NASA Postdoctoral Program Fellowship (to T.S.M.); a Langbein Summer Research Fellowship (to S.L.); California Institute of Technology startup funds (to C.F.); the Keck Institute for Space Studies; and NASA Awards NNX16AP33G (to D.R.B.), NNX17AE14G (to C.F.), and NNX15AH95G (to C.F.). Funding for the AmeriFlux core site data (US-NR1/Niwot Ridge; principal investigator, P.D.B.) was supported by the US Department of Energy Office of Science through the AmeriFlux Management Project at Lawrence Berkeley National Laboratory under Award 7094866. The National Center for Atmospheric Research is sponsored by the NSF. These data were produced by the OCO-2 project at the Jet Propulsion Laboratory, California Institute of Technology, and obtained from the OCO-2 data archive maintained at the NASA Goddard Earth Science Data and Information Services Center. This research was carried out, in part, at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. Government sponsorship acknowledged. Copyright 2019. All rights reserved. Author contributions: T.S.M., D.R.B., B.A.L., K.G., J.S., and C.F. designed research; T.S.M., D.R.B., B.A.L., K.G., J.S., P.D.B., S.P.B., M.A.G., S.L., and C.F. performed research; T.S.M., D.R.B., B.A.L., K.G., J.S., S.P.B., R.C., M.A.G., P.K., S.L., N.C.P., B.R., and C.F. analyzed data; and T.S.M., D.R.B., B.A.L., K.G., J.S., P.D.B., S.P.B., P.K., N.C.P., B.R., D.S., and C.F. wrote the paper. The authors declare no conflict of interest. This article is a PNAS Direct Submission. Data deposition: Our data are provided as time series with all of the relevant variables presented in the paper. The data can be found at https://data.caltech.edu/records/1231. The data are saved as a .csv file. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1900278116/-/DCSupplemental.

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Created:
August 22, 2023
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