Comparative responses and variation analysis of leaf traits in plants under contrasting roadside air-pollution...

With the rapid expansion of urbanization and the increasing number of motor vehicles, air pollution along urban roads has become increasingly severe, posing serious challenges to the ecological functions and growth status of roadside vegetation. As important organs directly exposed to the external environment, plant leaves play a crucial role in revealing the response characteristics of plants to polluted environments through variation in their traits. In this study, three major roads in Nanjing were selected as research sites, and six common plant species were investigated. Air pollutant concentrations were monitored simultaneously, and multiple leaf traits-including morphological, anatomical, stomatal, and biochemical characteristics-were measured along the three roads. Two-way analysis of variance (ANOVA), correlation analysis, and principal component analysis (PCA) were employed for the analysis. The results showed that under relatively high-pollution backgrounds, plants generally exhibited decreased specific leaf area (SLA), increased leaf dry matter content (LDMC), and thickened tissue structures, reflecting a tendency toward more conservative leaf trait configurations. Stomatal traits showed a size-density trade-off, reflecting changes in stomatal structural configuration under different pollution backgrounds. Biochemical traits were characterized by changes in osmotic adjustment substances and photosynthetic pigment contents, while antioxidant enzyme activities varied among species. In terms of species responses, among the six plant species examined in this study, Camphora officinarum Nees and Osmanthus fragrans (Thunb.) Lour exhibited relatively stable structural and biochemical trait performance and may serve as trait-based references for future roadside plant selection. PCA further indicated multivariate associations between air pollutants and leaf morphological, structural, and biochemical traits, suggesting that plant responses under roadside ombined-pollution backgrounds were expressed more as combined multi-trait changes than as adjustments of a single trait. This study provides field-based empirical evidence for understanding plant leaf trait responses and interspecific differences under urban air pollution backgrounds, and can provide localized trait-level references for plant selection and green-space configuration optimization under similar roadside pollution backgrounds.