B008-06
Mechanistic drivers of canopy-scale spatial patterns in solar induced fluorescence from boreal forests

Monday, 7 December 2020: 07:20
Virtual
Andrew Maguire1, Jan Eitel1, Troy Magney2, Christian Frankenberg3, Erica Orcutt2, Nicholas Parazoo4, Ryan Pavlick5, Zoe Pierrat6 and Philip A Townsend7, (1)University of Idaho, Moscow, ID, United States, (2)University of California Davis, Plant Sciences, Davis, CA, United States, (3)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (4)University of California Los Angeles, JIFRESSE, Los Angeles, CA, United States, (5)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (6)University of California Los Angeles, Los Angeles, CA, United States, (7)University of Wisconsin, Department of Forest and Wildlife Ecology, Madison, WI, United States
Recorded Presentation
Abstract:
Solar induced chlorophyll fluorescence (SIF) tracks the light reactions of photosynthesis and is useful for remotely sensing plant productivity. However, the structural complexity of evergreen forests precludes interpretation of canopy-scale SIF as a direct proxy of photosynthesis. Here we examine mid-summer canopy-scale SIF observations by NASA’s airborne Chlorophyll Fluorescence Imaging Spectrometer (CFIS) of boreal forest landscapes in Alaska coupled with hyperspectral observations by AVIRIS-ng. Our objectives are to (1) examine mechanisms driving spatial patterns in canopy-scale SIF using hyperspectral proxies; and (2) determine the degree to which sub-pixel variance in proxies of light use efficiency are manifested in canopy-scale SIF. Regression modeling showed that near infrared reflectance of vegetation (NIRv, a measure of canopy structure; standardized slope = 0.54) and the photochemical reflectance index (PRI, indicative of light use efficiency; standardized slope = -0.23) were the strongest predictors of variation in relative SIF, a proxy for SIFyield (R2 = 0.43, p < 0.001 for both variables). These results suggest a strong mechanistic linkage between observed SIF and canopy structure as well as pigment-driven light use efficiency. Interestingly, the strength of this relationship was dependent on forest canopy cover: whereas in densely forested landscapes the relationship was strong, in sparsely forested landscapes the relationship deteriorated. Contemporaneous field observations of sub-canopy scale PRI demonstrate that considerable within-pixel heterogeneity in light use efficiency occurs at sparsely forested landscapes, driven in part by strong shading effects characteristic of high latitude forest systems. Continued analyses include efforts to parse the effect of forest canopy from understory tundra vegetation on SIF observations in mixed pixels. We discuss the implications of these findings in the context of interpreting snapshot observations of canopy-scale SIF from structurally complex ecoregions toward understanding ecosystem productivity.
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