Optimization of Vegetation Photosynthesis and Respiration Model Parameters for the CO2 Flux Simulation in the Pearl River Delta

Abstract The Vegetation Photosynthesis and Respiration Model (VPRM) is a promising tool that provides reliable patterns of surface CO 2 flux for fine-scale inversions. However, the distribution of its parameters in terrestrial ecosystems of China remains to be elucidated. The parameters of the VPRM were optimized and validated across various growth seasons and weather conditions using 2010–2012 CO 2 flux observations from the tree-crop mixed ecosystems in the Pearl River Delta region of China. The optimum maximum quantum yield ( λ ) of 0.16 was consistent with the mean value (0.17) for C3 plants. The optimized photosynthetically active radiation at half-saturation of photosynthesis (PAR 0 ) was 351.27 μmol m −2 s −1 , and the respiration parameters α and β were 0.06 μmol CO 2 m −2 s −1 °C −1 and 1.34 μmol CO 2 m −2 s −1 , respectively. Using the mean of the optimized parameters, the VPRM accurately simulated net ecosystem exchange (NEE) in tree–crop mixed ecosystems in the Pearl River Delta region. The mean error of the simulated 30-min NEE decreased to − 0.24 μmol m −2 s −1 compared with the value of 2.20 μmol m −2 s −1 using the default parameters in the Weather Research and Forecasting model coupled with the VPRM (WRF-VPRM). The mean errors of the NEE simulation were 0.80 and 0.42 μmol m −2 s −1 in the peak and non-peak growth seasons, respectively. The VPRM using optimized parameters could accurately simulate the carbon flux under clear and cloudy conditions, but there was still uncertainty in the calculation of respiration. In future work, the respiratory flux module of the VPRM will be improved with nonlinear models or segmentation functions to decrease the uncertainty in the carbon sink and source simulation. Graphical Abstract