Novel leaf-level measurements of chlorophyll fluorescence for photosynthetic efficiency

Solar induced chlorophyll fluorescence (SIF) from vegetation can now be obtained from satellites as well as ground-based field studies, at select wavelengths associated with atmospheric features. At the leaf level, full spectrum (650-800 nm) chlorophyll emissions (ChlF) can be measured using specialized instrumentation to support interpretation of these SIF observations. We found that ChlF spectra differ for leaf bottoms versus upper leaf surfaces, potentially affecting within-canopy radiative scattering. Our ChlF measurements for leaves of eight tree species (n≥125) obtained during fall 2013 senescence at the Duke Forest in North Carolina, USA and the 2014 growing season (n=72) at the USDA cornfield in Beltsville, MD, USA also demonstrate the benefit of acquiring measurements for both the Red and Far-Red emission peaks. The Red/Far-Red ChlF Ratio was strongly related to both the Photochemical Reflectance Index (PRI) for corn leaves (r≥0.76) and tree leaves (r≥0.89) and to a PSII Photosynthesis Efficiency parameter (r~0.90).