The use of leaf characteristics of common oak (Quercus robur L.) to monitor ambient ammonia concentrations

Biomonitoring of atmospheric ammonia (NH3) concentrations is generally performed with epi-phytic lichens, using species' abundances and/or nitrogen concentration as monitoring tools. However, the potential of leaf characteristics of trees to monitor the atmospheric NH3 concentration has remained largely unexplored. Therefore, we performed a passive biomonitoring study with common oak (Quercus robur L.) at 34 sampling locations in the near vicinity of livestock farms, located in Flanders (northern Belgium). We aimed at evaluating the potential of specific leaf area, leaf area fluctuating asymmetry, stomatal resistance, and chlorophyll content of common oak to monitor a broad range of NH3 concentrations (four-monthly average of 1.9-29.9 mu gm(-3)). No significant effects of ambient NH3 concentration on the abovementioned leaf characteristics were revealed. Probably, differences in climate, soil characteristics, and concentrations of other air pollutants and/or genotypes confounded the influence of NH3. Consequently, this study demonstrates the inability of using these morphological, anatomical, and physiological common oak leaf characteristics to monitor ambient NH3 concentration

The potential of biomonitoring of air quality using leaf characteristics of white willow (Salix alba L.)

In this study, we assess the potential of white willow (Salix alba L.) as bioindicator for monitoring of air quality. Therefore, shoot biomass, specific leaf area, stomatal density, stomatal pore surface, and stomatal resistance were assessed from leaves of stem cuttings. The stem cuttings were introduced in two regions in Belgium with a relatively high and a relatively low level of air pollution, i.e., Antwerp city and Zoersel, respectively. In each of these regions, nine sampling points were selected. At each sampling point, three stem cuttings of white willow were planted in potting soil. Shoot biomass and specific leaf area were not significantly different between Antwerp city and Zoersel. Microclimatic differences between the sampling points may have been more important to plant growth than differences in air quality. However, stomatal pore surface and stomatal resistance of white willow were significantly different between Zoersel and Antwerp city. Stomatal pore surface was 20% lower in Antwerp city due to a significant reduction in both stomatal length (−11%) and stomatal width (−14%). Stomatal resistance at the adaxial leaf surface was 17% higher in Antwerp city because of the reduction in stomatal pore surface. Based on these results, we conclude that stomatal characteristics of white willow are potentially useful indicators for air quality