Exploring the scattering and reabsorption of chlorophyll fluorescence: implications for remote sensing of photosynthesis M.P. Cendrero-Mateo 1,2 , Christiaan van der Tol 3 , Karolina Sakowska 4,5 , Marco Celesti 6 , Anke Schickling 1,7 , Giorgio Alberti 8 , Luis Alonso 2 , Andreas Burkart 9 , Sergio Cogliati 6 , Roberto Colombo 6 , Gemini Delle Vedove 8 , Tommaso Julitta 9 , Radosław Juszczak 10 , Jose Moreno 2 , Onno Muller 1 , Cinzia Panigada 6 , Alessandro Peressotti 8 , Patrick Rademske 1 , Micol Rossini 6 , Giulia Tagliabue 6 , Nastassia Vilfan 11 , Peiqi Yang 2 , Franco Miglietta 4,12 , and Uwe Rascher 1 1 Institute of Bio- and Geosciences, IBG-2: Plant Sciences, Forschungszentrum Jülich GmbH, Germany; 2 Image Processing Laboratory, University of Valencia, Spain; 3 University of Twente, Faculty of Geo-Information Science and Earth Observation (ITC), The Netherlands; 4 Institute of BioEconomy (IBE), National Research Council (CNR), Italy; 5 Institute of Ecology, University of Innsbruck, Austria; 6 Department of Earth and Environmental Sciences, University of Milano-Bicocca, Italy; 7 German Aerospace Center, Germany; 8 Department of Agricultural, Food, Environmental and Animal Sciences, University of Udine, Italy; 9 JB Hyperspectral Devices UG, Germany; 10 Laboratory of Bioclimatology, Department of Ecology and Environmental Protection, Poznan University of Life Sciences, Poland; 11 Wageningen University & Research, Business Unit Greenhouse Horticulture, The Netherlands; 12 Foxlab Joint CNR-FEM Initiative, Italy Introduction http://www.walz.com Materials and Methods POT AND FIELD TRIAL UDINE, ITALY 46°02'9.14"N, 13°13'31.63"E Photosynthetic capacity and PAM fluorescence SIF and transmittance, reflectance, absorbance Specific leaf mass Pigments content Nitrogen content fAPPFD LAI NEE Reco CANOPY LEAF CO2 exchange (GPP) Transpiration The principle underlying the use of sun-induced chlorophyll fluorescence (SIF) as a proxy of gross primary productivity (GPP) is based on the fact that the light energy absorbed by chlorophyll molecules can proceed into three different pathways: photochemistry, heat dissipation, and chlorophyll fluorescence. Since these processes directly compete for the same excitation energy, measurements of SIF and non- photochemical quenching (NPQ) are expected to provide information on photosynthetic performance. However, SIF signal measured at the leaf level or beyond is affected by several processes, including wavelength dependent scattering and reabsorption, which may need to be considered when linking SIF data and photosynthetic CO2 assimilation. To address this question, we conducted a multi-scale and multi-technique study that considered two soybean varieties and used the collected data to calibrate the “Soil-Canopy Observation Photosynthesis and Energy fluxes” (SCOPE) model as a tool to investigate the reabsorption and scattering of SIF. Full spectrum active fluorescence SIF and reflectance FLOX MSS VARIANT 1 Top of canopy SIF reabsorption by leaves and canopy VARIANT 2 SIF emitted by photosystems NO reabsorption by leaves and canopy MEASUREMENTS MODEL BIOPHYSICAL PARAMETERS LEAF NET PHOTOSYNTHESIS vs. PPFD ABSORBED BY THE LEAF NDVI MTCI FRACTION OF PHOTOSYNTHETIC PHOTON FLUX DENSITY ABSORBED BY THE CANOPY CANOPY LEVEL SPECTRAL VEGETATION INDICES CANOPY LEVEL SIF and SIF YIELD SIF SIF MEASUREMENT RESULTS Conclusions MODELLING RESULTS Source: © Cendrero-Mateo et al. All rights reserved. Source: © Cendrero-Mateo et al. All rights reserved. NON-PHOTOCHEMICAL QUENCHING Reflected PPFD Transmitted PPFD Photochemistry (P) Chlorophyll fluorescence (SIF) Incident PPFD Absorbed PAR (APAR) 18-98% up to 82% 0.5-2% Heat (NPQ) Eiko < MinnGold 3% < 10% Reflected PPFD • Despite the large difference in Chl content (the ratio of Chl between MinnGold and Eiko was nearly 1:5), similar leaf and canopy photosynthesis rates were maintained in the Chl‐deficient mutant. • This phenomenon wasn’t captured by traditional spectral vegetation indices related to canopy greenness, nor by SIF measured in-situ. • However, the modelling simulations revealed that when correcting for leaf and canopy scattering and reabsorption processes both varieties presented similar SIF yield (SIF/APPFD). • Furthermore, both in-situ and modelled data showed that APPFD and NPQ in MinnGold were lower than in Eiko. • This together explains the similar measured GPP and simulated SIF yield between the two varieties, and indicates that interpretation and application of SIF as a GPP tracer requires understanding and quantification of all these processes. The SCOPE model was used to investigate the reabsoption and scattering of SIF Data source: 1) Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 2) Cendrero-Mateo et al. (in preparation, all rights reserved) Model description: https://doi.org/10.5194/bg-6-3109-2009; https://doi.org/10.1016/j.rse.2016.09.021; https://doi.org/10.1016/j.rse.2018.04.012; https://doi.org/10.1016/j.rse.2019.111292 http://dx.doi.org/10.1016/j.envexpbot.2013.10.009 Legend: N – mesophyll scattering parameter Cx – photochemical reflectance parameter, proxy of NPQ fqe - fluorescence quantum emission efficiency LIDFa, LIDFb - leaf inclination parameters APPFD – the amount of absorbed photosynthetically active photons fAPPFD – fraction of absorbed photosynthetically active photons Source: © Cendrero-Mateo et al. All rights reserved. Top of canopy SIF SIF emitted by photosystems LEAF LIGHT ABSORBANCE AT DIFFERENT WAVELENGTHS Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 GROSS PRIMARY PRODUCTION vs. PPFD ABSORBED BY THE CANOPY Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 Source: © Cendrero-Mateo et al. All rights reserved. Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 Sakowska et al. (2018) https://doi.org/10.1111/pce.13180 Source: © Cendrero-Mateo et al. All rights reserved.