Do Leaf Characteristics of White Willow (Salix alba L.), Northern Red Oak (Quercus rubra L.), and Scots Pine (Pinus sylvestris L.) Respond Differently to Ambient Air Pollution and Other Environmental Stressors?

This study assessed the effect of ambient air pollution on leaf characteristics of white willow, northern red oak, and Scots pine. Willow, oak, and pine saplings were planted at sixteen locations in Belgium, where nitrogen dioxide (NO2), ozone (O-3), sulfur dioxide (SO2), and particulate matter (PM10) concentrations were continuously measured. The trees were exposed to ambient air during 6 months (April-September 2010), and, thereafter, specific leaf area (SLA), stomatal resistance (R-s), leaf fluctuating asymmetry (FA), drop contact angle (CA), relative chlorophyll content, and chlorophyll fluorescence (F-v/F-m) were measured. Leaf characteristics of willow, oak, and pine were differently related to the ambient air pollution, indicating a species-dependent response. Willow and pine had a higher SLA at measuring stations with higher NO2 and lower O-3 concentrations. Willow had a higher Rs and pine had a higher F-v/F-m at measuring stations with a higher NO2 and lower O-3 concentrations, while oak had a higher F-v/F-m and a lower FA at measuring stations with a higher NO2 and lower O-3 concentrations. FA and R-s of willow, oak, and pine, SLA of oak, and CA of willow were rather an indicator for local adaptation to the micro-environment than an indicator for the ambient air pollution.