Foliar C/N stoichiometry in urban forest trees on a global scale

Foliar C/N stoichiometry is an indicator of geochemical cycling in forest ecosystems, but the driving changes for its response to urbanization at the wide scale is not clear. In this study, data on tree-leaf C and N stoichiometry were collected in papers from across 105 tree species from 82 genera and 46 families. The foliar C/N of urban forest trees varied among different climate zones and tree taxonomic variation and tended to be higher in trees of urban forests near the equator and in eastern regions, mainly driven by lowered foliar N concentration. Neither the foliar C concentration nor foliar C/N for trees of urban forests was statistically higher than those of rural forests. For variation by taxonomic classification, C4 species Amaranthus retroflexus and Chenopodium ambrosoides (Amaranthaceae) had lower foliar C/N than did other species and families. Myrsine guianensis (Primulaceae) and Myconia fallax (Asteraceae) had the highest foliar C/N. Therefore, urbanization has not caused a significant response in forest trees for foliar C/N. The change in foliar N concentration was globally the main force driving of the differences in foliar C/N for most tree species in urban forests. More work is needed on foliar C/N in trees at cities in polar regions and the Southern Hemisphere.