Global Distribution Patterns of Light Use Efficiency Model Parameters

Abstract:

In the context of modeling global biogeochemical cycles, the spatialization of ecosystem-level parameters in land surface schemes is a major challenge which has been relying on generalizations based on plant functional types. In these models, the parameters represent either the response of biological, or ecosystem, processes to environmental constraints, or the biophysical variables themselves. Based on the principles of biological evolution, adaptation and acclimation, it is reasonable to hypothesize that several of these parameters follow large bioclimatic patterns, hence linking to patterns in plant biophysical traits. To test the hypothesis, our study aims to explore the parameter spatial distribution patterns in light use efficiency (LUE) models with the climate and vegetation properties, and use it to understand the regional sensitivities of photosynthesis to climate. As such, a general LUE model that simulates gross primary productivity (GPP) was selected based on eddy covariance data. The same model was parameterized globally against Sun-Induced Fluorescence assuming a linear relationship with GPP to analyze the global distribution patterns in the model parameters. Our current results show that three, out of twelve, parameters show a spatial pattern along with the spatial patterns in mean seasonal cycle temperature globally. One parameter changed with the mean seasonal cycle of precipitation while two parameters could be set as constant. These results corroborate, at least partly, a strong link between climatological traits and parameter spatial variability. According to the average climate sensitivity functions, the temperature exerts a strong control on productivity in cold and mostly moist regions, showing few effects in hot climate, or warm and dry climates. These latter seem to be rather controlled by vapor pressure deficits. Interestingly, the cloudiness controls on modeled SIF show a robust North-South gradient in North America, but an East-West pattern in Eurasia. A high unexplained variance of SIF observations in the wet tropics suggests the need to further explore different SIF and climate products, alongside with improved model structures, to investigate the ecosystem level sensitivity of primary productivity to climate.