PHOTOSYNTHETICA

Photosynthetica X:X | DOI: 10.32615/ps.2026.006

Exploring prediction mechanisms for temperature-induced variation in maximum carboxylation rate from spectral reflectance across 450-850 nm in cucumber leaves

T. SHIBATA¹, H. YAMAGUCHI¹, S. KUBOTA², D. YASUTAKE^{2, 3}, T. HIROTA², G. YOKOYAMA²

¹ Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, 744 Motooka, Nishi-ku, 819-0395 Fukuoka, Japan

² Faculty of Agriculture, Kyushu University, 744 Motooka, Nishi-ku, 819-0395 Fukuoka, Japan

³ IoP Collaborative Creation Center, Kochi University, 200 Otsu, Monobe, Kochi, 783-8502 Nankoku City, Japan

Leaf spectral reflectance across 450-850 nm has been shown to predict maximum carboxylation rate (V_cmax), which varies with leaf temperature (T_leaf). However, the mechanism by which temperature-induced variation in V_cmax is predicted from reflectance remains unclear. The objective of this study was to explore this mechanism using spectral reflectance across 450-850 nm. We measured V_cmax across a range of T_leaf (18-31°C) and reflectance in cucumber (Cucumis sativus L.) leaves. Partial least squares regression models moderately predicted V_cmax (R² = 0.73), whereas T_leaf was weakly predicted (R² = 0.32). When only visible reflectance (450-700 nm) was used, prediction accuracy for both V_cmax and T_leaf declined (R² = 0.59 and 0.17). Because predicting T_leaf from reflectance suggests that temperature-related information may help predict temperature-induced variations in V_cmax, our results indicate that reflectance in 700-850 nm possibly captures temperature-induced variation in V_cmax.

Additional key words: Cucumis sativus L.; leaf temperature; maximum carboxylation rate; partial least squares regression; photosynthesis; reflectance spectroscopy.

Received: December 17, 2025; Revised: March 10, 2026; Accepted: April 1, 2026; Prepublished online: April 13, 2026