Allergenic potential of ornamental Cupressales species and its consequences for urban planting

Cupressales species are widely planted in urban landscapes, where their pollen represents a growing source of biological air pollution and contributes to seasonal allergies. Linking their flowering dynamics with atmospheric allergen loads is essential for understanding ecological flows of airborne particles in cities. We aimed to quantify interspecific differences in allergenic potential among common urban Cupressales taxa and to determine how flowering periods and pollen production shape airborne allergen levels. We specifically assessed variation in Cup a 1 homolog abundance to evaluate its relevance for landscape-scale allergy risk. The study was conducted in Poznań (Poland) during the 2023-2024 pollen seasons. Phenological observations, aerobiological monitoring, and immunoenzymatic assays were combined to relate flowering timing, atmospheric pollen concentrations, and allergen content across ten Cupressales species. Species differed substantially in flowering phenology, pollen output, and allergen levels. Taxus baccata, Thuja occidentalis, and Th. plicata released large amounts of pollen but contained low levels of Cup a 1 homologs. Conversely, Juniperus taxa and Callitropsis nootkatensis showed consistently high allergenicity, contributing disproportionately to peak atmospheric allergen loads despite moderate pollen release. These patterns indicate that allergen exposure risk is driven not only by pollen abundance but also by species-specific allergen potency. Urban planting dominated by high-allergenicity taxa may therefore intensify allergy symptoms at the neighbourhood scale. Our findings demonstrate that allergenicity metrics can inform urban vegetation planning. Selecting species with favourable phenological and allergenic profiles may help reduce airborne allergens and support healthier, more resilient urban landscapes.