Publication Date:
2019-09-28
Description:
On regional to global scales, few constraints exist on gross primary productivity (GPP) and ecosystem respiration (Re) fluxes. Yet constraints on these fluxes are critical for evaluating and improving terrestrial biosphere models. In this study, we evaluate the seasonal cycle of GPP, Re, and net ecosystem exchange (NEE) produced by four terrestrial biosphere models and FLUXCOM, a datadriven model, over northern midlatitude ecosystems. We evaluate the seasonal cycle of GPP and NEE using solarinduced fluorescence retrieved from the Global Ozone Monitoring Experiment2 and columnaveraged dryair mole fractions of CO2 (XCO2) from the Total Carbon Column Observing Network, respectively. We then infer Re by combining constraints on GPP with constraints on NEE from two flux inversions. An ensemble of optimized Re seasonal cycles is generated using five GPP estimates and two NEE estimates. The optimized Re curves generally show high consistency with each other, with the largest differences due to the magnitude of GPP. We find optimized Re exhibits a systematically broader summer maximum than modeled Re, with values lower during JuneJuly and higher during the fall than Re. Further analysis suggests that the differences could be due to seasonal variations in the carbon use efficiency (possibly due to an ecosystemscale Kok effect) and to seasonal variations in the leaf litter and fine root carbon pool. The results suggest that the inclusion of variable carbon use efficiency for autotrophic respiration and carbon pool dependence for heterotrophic respiration is important for accurately simulating Re.
Keywords:
Geophysics
Type:
GSFC-E-DAA-TN63347
,
Journal of Geophysical Research: Biogeosciences (ISSN 2169-8953) (e-ISSN 2169-8961); 123; 9; 2976-2997
Format:
application/pdf
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