Interspecific differences in the Air Pollution Tolerance Index (APTI) of plants in an urban roadside environment: relationships with biochemical indicator profiles.

Urban roadside plants can differ in their leaf biochemical profiles even when they grow along the same transect. The Air Pollution Tolerance Index (APTI) brings together several of these traits and offers a way to compare species within a shared setting. This study examined eight commonly planted species along Huaxia Road in Luoyang, China. Leaves were sampled monthly from June to August 2023, with three site-level composite samples for each species in each month. Leaf ascorbic acid (AsA), total chlorophyll content (TCC), extract pH, and relative water content (RWC) were measured and used to calculate APTI. Statistical comparisons focused on differences among species within each month; patterns across months were described from the observed values. All eight species fell within the sensitive category under the applied APTI thresholds, although their index values differed. The highest 3-month mean values were found in Prunus cerasifera (9.842) and Nerium oleander (9.570), while Paeonia suffruticosa (8.983) and Eriobotrya japonica (8.414) had the lowest. Prunus cerasifera ranked first in June and July, whereas Nandina domestica had the highest value in August. Eriobotrya japonica remained lowest in all 3 months. Individual leaf traits did not consistently follow the overall APTI ranking: Paeonia suffruticosa had high AsA despite its low mean APTI, and Photinia serratifolia showed comparatively high TCC while remaining in the sensitive category. RWC was positively correlated with APTI in every month, partly reflecting its inclusion in the index. Prunus cerasifera and Nerium oleander had the highest relative APTI among the eight species examined.