Estimation of leaf photosynthetic capacity from the photochemical reflectance index and leaf pigments

Leaf chlorophyll content has recently been found to be a better proxy than leaf nitrogen content for leaf photosynthetic capacity in a mixed deciduous broadleaf forest. A key concept underlying the relationship between leaf photosynthetic capacity and leaf chlorophyll content was the coordinate regulation of photosynthetic components (i.e. light harvesting, photochemical, and biochemical components). In order to test this hypothesis, we measured seasonal variations in leaf nitrogen content (N-leaf), leaf photosynthetic pigments (i.e. chlorophyll (Chkl(Leaf), carotenoids (Car(Leaf)) and xanthophyll (Xan(Leaf))) and leaf photosynthetic capacity (i.e. the maximum rate at which ribulose bisphosphate (RuBP) is carboxylated (V-cmax25) and regenerated (J(max25)) at 25 degrees C) at a paddy rice site during the growing season in 2016. We investigated the effectiveness of (N-leaf), leaf photosynthetic pigments, leaf-level photochemical reflectance index at sunny noon (PRILeaf-noon) and their possible combinations for estimating leaf photosynthetic capacities (i.e. V-cmax25 and J(max25)) at a paddy rice site. Chl(Leaf) was highly correlated to V-cmax25 and J(max25) (R-2 = 0.89 and 0.87, respectively), which were better than N-leaf (R-2 = 0.80 and 0.85, respectively). The products of PRI(Leaf-noon )with leaf pigments (i.e. Chl(Leaf), Car(Leaf )and Xan(Leaf)) were also found to be highly correlated with V-cmax25 (R-2 = 0.95-0.96). Also, the product of leaf chlorophyll a and Car(Leaf )was a good proxy for V-cmax25 (R-2 = 0.93). In sum, this study supported the previously findings that leaf chlorophyll content was better correlated with V-cmax25 than leaf nitrogen content. Also, combining PRILeaf-(noon) with leaf pigments (i.e. Chl(Leaf), Car(Leaf) and Xan(Leaf)) offered an additional way to estimate leaf photosynthetic capacity (i.e. V-cmax25). These findings supported the hypothesis of coordinate regulation of photosynthetic components and they would be helpful to estimation of leaf photosynthetic capacity using remote sensing data.