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

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

Shuren Chou^1#, Bin Chen²*^#, Jing Chen^3,4*, Miaomiao Wang^2,5, Shaoqiang Wang^2,5,6, Holly Croft⁷, Qin Shi⁸

¹Space Security Center, Space Engineering University, Beijing 101416, China;

²Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China;

³School of Geographical Sciences, Fujian Normal University, Fuzhou, 350117, China

⁴Department of Geography and Planning, University of Toronto, Toronto, Canada

⁵College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, China

⁶College of Geography and Information Engineering, China University of Geosciences, Wuhan, China

⁷Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, U.K.

⁸Institute of Botany, Jiangsu Province and Chinese Academy of Sciences, Nanjing 210014, China;

Abstract: 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 (Chl_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 ^oC) 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 (PRI_{Leaf_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 (R² = 0.89 and 0.87, respectively), which were better than N_leaf (R² = 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 (R² = 0.95 to 0.96). Also, the product of leaf chlorophyll a and Car_Leaf was a good proxy for V_cmax25 (R² = 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 PRI_{Leaf_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.

Keywords: seasonal variations; leaf nitrogen content; photosynthetic pigments; leaf maximum carboxylation rate