Isoprenoid and aromatic compound emissions in relation to leaf structure, plant growth form and species ecology in 45 East-Asian urban subtropical woody species

Abstract

Volatile emissions from urban parks and forests can significantly contribute to local and regional air quality due to biogenic volatile organic compound (BVOC) emissions from vegetation, but the source strength of BVOC of urban habitats is difficult to assess due to a complex mixture of ornamental species with widely varying leaf and whole plant characteristics and taxonomy. Furthermore, there is very limited information of BVOC emission characteristics of subtropical urban sites and overall lack of information of emission capacity of aromatic compounds that are often left out in BVOC screening studies. We investigated BVOC emissions from healthy mature leaves of 45 East-Asian subtropical wide-spread broad-leaved ornamental woody species with contrasting leaf structure and longevity (evergreen vs. deciduous), growth form (shrub vs. tree) and temperature, light and water requirements to characterize the overall frequency of volatile emissions in relation to species characteristics. BVOC emissions were characterized by the share of each compound and compound class in total emissions, absolute emission rates and frequency of emission of different volatiles. Isoprene contributed the greatest share of total emissions (42.6 %), followed by monoterpenes (29.7 %), sesquiterpenes (13.8 %) and aromatic compounds (7.5 %). However, isoprene was emitted only in 20 % of species, whereas the other volatile compound classes were emitted in the majority of species (35.6 %–95.6 %). The overall emission rates were relatively low for isoprene (up to 1.7 nmol m−2 s-1 and for aromatics (up to 0.2 nmol m−2 s-1) and moderately high for terpenes (up to 0.8 nmol m−2 s-1 for both mono- and sesquiterpenes). Isoprenoid and aromatic compound emissions were positively correlated across the species. Multivariate analyses indicated that species taxonomy poorly explained the emission patterns, but for most compound classes, the emissions were higher in species with structurally more robust leaves (higher leaf dry mass per unit area, and lower leaf water content) and in species capable of growing in environments with higher light, higher temperature and lower water availability. In addition, isoprene emissions were more prevalent in deciduous species and aromatic emissions in evergreens. Overall, the study emphasizes that apart from isoprene, urban ornamentals constitute a large source of monoterpenes, sesquiterpenes and aromatic compounds and that planting of stress resistant species that require less maintenance might enhance BVOC emissions.