Vegetation photosynthesis and ecosystem respiration model: Improved estimation of diurnal, seasonal and interannual dynamics of carbon fluxes at eddy covariance tower sites

Reliable quantification of diurnal, seasonal and interannual dynamics of gross primary production (GPP), ecosystem respiration (ER) and net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) is essential for advancing our understanding of terrestrial carbon cycle. In this study, we developed the Vegetation Photosynthesis and Ecosystem Respiration Model (VPERM, v1.0) that estimates half-hourly GPP, ER, and NEE. VPERM incorporates (1) a new GPP module that considers the saturation of light absorption by chlorophyll and (2) a new ER module that considers respiration of live plants and microbes, decomposition of newly dead plant and microbes, and decomposition of soil organic carbon. Driven by satellite images (MODIS) and climate data, VPERM was applied to 112 eddy covariance tower sites (EC) across nine vegetation types. The results showed that the temporal dynamics of GPP VPERM , ER VPERM and NEE VPERM from VPERM simulations agreed reasonably well with GPP EC , ER EC and NEE EC from EC tower sites in terms of diurnal (half-hourly data), seasonal (daily data), and interannual (annual data) dynamics. The linear regression results also show that the slopes between GPP VPERM and GPP EC are 1.02, 1.07, 1.08 at half-hourly, daily and annual scales; the slopes between ER VPERM and ER EC are 0.96, 0.97, and 1.00; and the slopes between NEE VPERM and NEE EC are 0.97, 0.96, 1.03. VPERM provides a simple and efficient way to estimate half-hourly GPP, ER and NEE over the EC tower sites, which has the potential to be used and evaluated across the scales from local to regional and globe.