Photosynthetic CO2response characteristics in canopy ofLarix principis-rupprechtiiMayr. tree and practicability of three Models

Abstract

AbstractAccurately predicting the crown photosynthesis of trees is important to understand the tree growth status and carbon circle in terrestrial ecosystem. However, modeling the photosynthetic carbon dioxide (CO2) response curves for individual tree are still challenging due to the complex canopy structure and changeable environmental conditions. Therefore, taking 16-old yearLarix principis-rupprechtii Mayr. as the research material, the dynamic CO2response models of photosynthesis, including rectangular hyperbolic model (RHM), the non-rectangular hyperbolic model (NRHM) and the modified rectangular hyperbolic model (MRHM), were used to simulate CO2response curves of the crown. The fitting accuracy of the models depend on the comparison of determinants coefficients (R2), mean square errors (MSE) and Akaike information criterion (AIC). The results showed that the mean value ofR2(R2=0.9939 ∼ 0.9964) of MRHM was the highest, whereasMSEvalue (MSE=0.2185∼0.2627) andAICvalue (AIC=-13.18∼-8.03) were the lowest. The CO2-saturated gross photosynthetic rate (Amax) and the saturation point (CiSP) obtained by MRHM were closest to the measured value respectively. Therefore, the MRHM fitted the CO2response data well, and calculated the photosynthetic parameters directly and accurately, the fitted result showed α,Amax,CiSP, CiCPandRPwere 0.04, 7.51 μmol·m-2s-1, 938.97 μmol·m-2, 67.54 μmol·m-2and 0.60 μmol·m-2s-1, respectively. In addition, the difference on the photosynthetic CO2response parameters values showed somewhat among different layers and orientations. In all, all data suggested that the modified rectangular hyperbolic model (MRHM) was an ideal model to fit the crown photosynthetic CO2response curve ofLarix principis-rupprechtiiMayr. These results are of great significance for parameter calibration of photosynthetic model and robust prediction of photosynthetic response in forest.