Modified photochemical reflectance index to estimate leaf maximum rate of carboxylation based on spectral analysis

The maximum rate of carboxylation in leaves (V_cmax) is an important parameter used to determine the photosynthetic rate. An accurate estimation of V_cmax is important for evaluating the photosynthetic capacity of vegetation productivity and the carbon budget of forest ecosystems. In this study, we measured the light use efficiency (LUE) and V_cmax of leaves and their corresponding spectral characteristics. Spectral analysis was used to find a modified photochemical reflectance index (PRI) of leaves to estimate LUE and thereby estimate leaf V_cmax. The results showed that the precision with which the modified ratio PRI index estimated LUE was significantly increased. The R² of the estimation model was 0.69, and the root mean square error (RMSE) was 0.0024. The R² of the model for estimating leaf V_cmax based on the LUE was 0.72, and the RMSE was 8.439 μmol/m²/s. The V_cmax values of conifer trees (Scots pine, Korean pine, and larch) were higher than those of broadleaf trees (white birch, Manchurian walnut, Siberian elm, Manchurian ash, Mongolian oak, Korean aspen, and Amur linden). This method avoids problem that conventional PRI is not sensitive to high leaf LUE values and provides important parameter data for the quantitative estimation of the gross primary productivity of forest ecosystems.