Non-invasive assessment of bamboo leaf optical properties and microstructural changes under light stress using time-domain OCT.

Bamboo is a vital renewable resource in tropical Asia, yet its physiological responses to environmental Bamboo is an ecologically and economically important renewable resource in tropical regions, yet its physiological response to light-induced stress remains poorly characterized under in vivo conditions. In this study, time-domain optical coherence tomography (TD-OCT) was employed as a non-invasive imaging technique to monitor microstructural and optical changes in Bambusa spinosa leaves subjected to controlled light stress. A portable TD-OCT system was used to quantify extinction coefficients and palisade layer thickness following repeated exposure to high-intensity illumination over several days. These measurements were complemented by Vegetation Ratio (VR) index analysis derived from optical microscopy to assess pigment-related changes. The results reveal a systematic decrease in extinction coefficients in both epidermal and mesophyll boundary layers with increasing exposure duration, indicating progressive tissue degradation. Mean extinction coefficients declined from approximately 1.03 mm⁻1 to 0.72 mm⁻1 under prolonged illumination, while palisade layer thickness showed a decreasing trend consistent with stress-induced structural alteration. Variations in VR index values correlated with OCT-derived optical parameters, reflecting concurrent changes in leaf optical properties and physiological condition. The ability of TD-OCT to perform repeated, label-free measurements on intact leaves enables longitudinal monitoring of stress responses. These findings highlight the potential of TD-OCT combined with VR index analysis as a sensitive tool for early stress detection and precision monitoring in sustainable bamboo cultivation and environmental assessment.