Unravelling the Stomatal Phenotype‒Function Relationships in Urban Trees Under Air Pollution Stress: A Multispecies Comparative Study

Urban trees play a vital role in reducing the harmful effects of air pollution, yet their physiological and anatomical responses, especially stomatal plasticity, under long-term urban stress remain poorly understood. This study examined the stomatal phenotype‒function relationships in dominant urban tree species across two contrasting environments in Dhaka: the heavily polluted areas of Motijheel-Sayedabad and the relatively clean National Botanical Garden. We conducted a comparative analysis of key stomatal features, including stomatal density, size, area, perimeter, pore index, and stomatal opening status, across multiple species to assess their adaptive responses to air pollution. Two-way ANOVA showed that most stomatal structural and functional traits of urban plants were strongly affected by species, site, and their interaction, emphasizing distinct species-specific responses to pollution levels. Species such as Polyalthia longifolia , Swietenia mahagoni , and Ficus benghalensis exhibited significant stomatal alterations, indicating potential resilience under environmental stress. Pearson's correlation analysis found significant relationships among various stomatal traits. Principal component analysis of stomatal traits showed that the first two principal components (PC1 and PC2) together explained 69.71% of the total variance. PC1 alone accounted for 44.34%, while PC2 contributed a further 25.37%. This indicates that these two components effectively encapsulate the primary patterns of trait variation. The PCA results demonstrated a clear separation between stomatal morphological traits (e.g., SL, SB, SA, SP) and functional attributes (%OS, %CS), suggesting different physiological mechanisms control them. Overall, this study shows how important stomatal traits are as signs of how well plants can adapt to their environment and also provides useful information for choosing trees in cities for planning green infrastructure.