Ozone uptake by adult urban trees based on sap flow measurement

The O-3 uptake in 17 adult trees of six urban species was evaluated by the sap flow-based approach under free atmospheric conditions. The results showed very large species differences in ground area scaled whole-tree ozone uptake (F-O3), with estimates ranging from 0.61 +/- 0.07 nmol m(-2) s(-1) in Robinia pseudoacacia to 4.80 +/- 1.04 nmol m(-2) s(-1) in Magnolia liliiflora. However, average F-O3 by deciduous foliages was not significantly higher than that by evergreen ones (3.13 vs 2.21 nmol m(-2) p = 0.160). Species of high canopy conductance for 03 (G(O3)) took up more 03 than those of low G(O3), but that their sensitivity to vapour pressure deficit (D) were also higher, and their F-O3 decreased faster with increasing D, regardless of species. The responses of F-O3 to D and total radiation led to the relative high flux of O-3 uptake, indicating high ozone risk for urban tree species. (C) 2011 Elsevier Ltd. All rights reserved.