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Space-based vegetation indices have been used to model global photosynthesis for more than two decades.However, vegetation indices are fundamentally linked to leaf optical properties rather than leaf physiology, which limits their utility in regions where changes in photosynthesis are driven by leaf development and demography.Contrary to vegetation indices, solar-induced chlorophyll fluorescence contains information on leaf physiology and has been shown to be synchronous with photosynthetic activity in the tropics.Here we present a novel model of global photosynthesis, ChloFluo, which uses spaceborne chlorophyll fluorescence to estimate the amount of photosynthetically active radiation (PAR) absorbed by chlorophyll (APAR chl ).ChloFluo is unique in that instead of estimating APAR chl as a function of a vegetation index and an ancillary PAR product, we model APAR chl using its empirical relationship with SIF and the proportion of APAR chl that is reemitted as SIF, or ΦF.This empirical, fluorescence-based approach to estimating the amount of sunlight absorbed by chlorophyll accounts for non-linearities between SIF and photosynthesis emerging from seasonality diverging efficiencies in light use.We compare and validate our model using FluxCom, FluxSat, and eddy covariance tower data and find that ChloFluo best matches the seasonality of tower photosynthesis in the Amazon.Thus, ChloFluo has potential for advancing our ability to accurately model photosynthesis in tropical evergreen broadleaf forests, which is responsible for one-third of terrestrial photosynthesis.Potential uses of our model are to investigate and advance our understanding of the timing and magnitude of the uptake of atmospheric carbon dioxide by vegetation, its effect on atmospheric carbon dioxide fluxes, and vegetation response to climate events and change.
Doughty et al. (Sun,) studied this question.