Evaluation of global maximum carboxylation rate of leaves using remotely sensed leaf chlorophyll content

Wednesday, December 11, 2019 - 09:15
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The maximum carboxylation rate (Vcmax) represents the intrinsic capability of leaves to take up CO2 through photosynthesis. Limited understanding of observed variability in Vcmax is a major source of uncertainty in today’s earth system models simulating global photosynthesis and the global carbon cycle. In recent years, scientists have proposed several ecological theories to derive seasonal- and spatially varying Vcmax, in an attempt to constrain the uncertainty of models. The resulting global Vcmax datasets can generally be categorized into 3 types: nutrient-driven, climate-driven and climate-nutrient-driven. The quality of these Vcmax products has yet to be evaluated. In this study, we aim to evaluate seven different global gridded Vcmax datasets using newly released satellite-derived global leaf chlorophyll content (Chl), based on the hypothesis that the variability of Chl is tightly coupled with Vcmax. Our results show that a climate-driven Vcmax product based on optimality theory has the strongest correlation with Chl for croplands and grasslands, while for forests, the climate-nutrient-driven Vcmax performed slightly better than those driven by climate only. Our study demonstrates a novel approach for testing ecological theories of photosynthetic potential using remote sensing observations, and implies a difference in the mechanisms underlying Vcmax seasonality and heterogeneity between different biomes.

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