THE CAPTURE OF INCOMING SOLAR RADIATION BY PHOTOSYNTHESIS IS ONE OF THE MOST CRITICAL INPUTS TO THE EARTH SYSTEM AND ONE OF THE MOST DIFFICULT TO MONITOR AND PREDICT ACCURATELY. TRADITIONALLY, THE CHALLENGE HAS BEEN THAT LARGE-SCALE ESTIMATES OF GROSS PRIMARY PRODUCTION (GPP) HAVE BEEN BASED ON MEASUREMENTS OF CARBON DIOXIDE AND THERE IS NO DIRECT WAY TO DIFFERENTIATE BETWEEN THE PHOTOSYNTHETIC CAPTURE AND THE RESPIRATORY RELEASE OF THIS TRACE GAS. IN THE LAST FEW YEARS, IT HAS BECOME CLEAR THAT THE EMERGING SPACEBASED MEASUREMENTS OF SOLAR-INDUCED CHLOROPHYLL FLUORESCENCE (SIF) HAVE THE POTENTIAL TO ENABLE A MAJOR BREAKTHROUGH BECAUSE THEY PROVIDE, FOR THE FIRST TIME, A LARGE-SCALE MEASUREMENT THAT IS UNIQUELY LINKED TO PHOTOSYNTHESIS. THE BASIS OF THIS LINK IS THAT WHEN SOLAR PHOTONS ARE ABSORBED BY THE CHLOROPHYLL PIGMENT, THEY ARE EITHER TRAPPED BY CHEMICAL REACTIONS LINKED TO CARBON DIOXIDE FIXATION, DISSIPATED AS HEAT, OR RE-EMITTED AS FLUORESCENCE. WHILE THIS CREATES A POTENTIALLY POWERFUL OBSERVATIONAL CONSTRAINT, THE CURRENT GENERATION OF PHOTOSYNTHESIS MODELS ARE NOT YET ABLE TO TAKE FULL ADVANTAGE OF IT BECAUSE THEY DO NOT ACCURATELY DEPICT THE PROCESSES THAT LINK LIGHT CAPTURE, CARBON DIOXIDE FIXATION, AND FLUORESCENCE EMISSION. THE OVERALL AIM OF THIS PROPOSAL IS TO DEVELOP A REPRESENTATION OF PHOTOSYNTHESIS WHICH CAPTURES ADVANCES IN PROCESS UNDERSTANDING AND IMPROVES THE SKILL WITH WHICH LAND SURFACE MODELS CAN SIMULATE GPP AND SIF. THE PROPOSED WORK ADDRESSES TWO OBJECTIVES. THE FIRST OBJECTIVE IS TO COMPLETE A NEW LEAF-LEVEL MODEL OF PHOTOSYNTHESIS WITH AN IMPROVED REPRESENTATION OF THE TEMPERATURE RESPONSES OF ELECTRON TRANSPORT, CARBON METABOLISM, AND STOMATAL CONDUCTANCE. PHYSIOLOGICAL EXPERIMENTS WILL BE CONDUCTED WITH AN INSTRUMENT THAT PERMITS PAIRED MEASUREMENTS OF LEAF-LEVEL GAS-EXCHANGE, PULSE AMPLITUDE MODULATED FLUORESCENCE, AND SPECTRALLY RESOLVED FLUORESCENCE AND REFLECTANCE. THE TEMPERATURE RESPONSE FUNCTIONS WILL BE FORMULATED BY IMPLEMENTING THE LEAF-LEVEL MODEL IN AN INVERSION FRAMEWORK WHICH ENABLES DECONVOLUTION OF THE ENVIRONMENTAL, BIOCHEMICAL, AND STRUCTURAL DETERMINANTS OF PHOTOSYNTHETIC PERFORMANCE. THE SECOND OBJECTIVE IS TO DEVELOP A CANOPY-LEVEL MODEL OF PHOTOSYNTHESIS THAT IS CONCEPTUALLY AND QUANTITATIVELY CONSISTENT WITH THE LEAF-LEVEL MODEL. THE DESIGN OF THE CANOPY-LEVEL MODEL WILL BE BASED ON HEMISPHERIC MEASUREMENTS OF SPECTRALLY RESOLVED FLUORESCENCE AND REFLECTANCE THAT ARE PAIRED TO EDDY COVARIANCE MEASUREMENTS OF THE TURBULENT FLUXES. THE CANOPY-LEVEL MODEL WILL BE IMPLEMENTED IN AN INVERSION FRAMEWORK WHICH PERMITS ASSIMILATION OF FLUORESCENCE AND REFLECTANCE MEASUREMENTS, PREDICTION OF THE PHOTOSYNTHETIC CAPACITY OF THE CANOPY WITHIN THE TOWER FOOTPRINT, AND EVALUATION AGAINST THE TURBULENT FLUXES OF HEAT, WATER, AND CARBON DIOXIDE.