OCT analysis of white clover leaves affected by regional ozone stress

Plants are exposed to atmospheric conditions for extended periods, allowing the observation of their color, texture, and internal structure to infer the surrounding atmospheric conditions. High ozone concentrations, particularly in urban areas, are harmful to plants. Optical coherence tomography (OCT) is a non-destructive method to evaluate samples' internal structure and optical properties, allowing potential measurements without any influence on the sample. This study aimed to estimate the ozone damage on plant leaves by measuring the OCT of white clover (Trifolium repens), an indicator plant of ozone influence, collected from different areas. Initially, to compare the influence of ozone and the impact of transportation from sampling regions, the temporal changes in water transpiration from cutting leaves were evaluated. Next, the leaves of white clover collected from various regions were measured using OCT. Changes on OCT images in light intensity, layer thickness, and texture (contrast, correlation, energy) within the leaves were analyzed to compare the presence or absence of the stresses (ozone and water stresses). The first experiment confirmed that the trends in Energy changes in the OCT images were opposite for ozone and water stress, with ozone increasing Energy due to widespread tissue disruption that blurred texture patterns, and water stress decreasing it due to localized shrinkage. In the second experiment, similar to the first experiment, a decrease in the intensity of the palisade tissue, an increase in thickness, and an increase in Energy were observed in regions with particularly high ozone concentrations. These results confirmed that OCT image analysis could detect specific plant changes due to ozone and water stress. This study demonstrates the potential of in-situ measurements of plants using OCT to infer the environmental conditions to which the plants are exposed.