Urban habitats have a complex suite of abiotic factors (e.g. elevated temperatures, increased air pollution, elevated CO2) while impervious surface area and compacted soils decrease soil water availability. Therefore, urban trees have limited water availability and can be more vulnerable to xylem cavitation. Leaves account for ~30% of resistance in the whole-plant hydraulic pathway, thus leaf hydraulic conductance (Kleaf) is an important trait for understanding plant hydraulic behavior. However, our understanding of hydraulic behavior in urban trees is still limited and very few studies have explored leaf hydraulic responses in urban settings. The purpose of this study was to quantify interspecific and intraspecific variation in leaf hydraulics for trees occurring in an urban and a rural site. Study sites consisted of Lakeview cemetery in Cleveland, Ohio and rural Secrest Arboretum in Wooster, Ohio. Maximum Kleaf and turgor loss point (TLP, a drought tolerance proxy) were measured in early and late summer on 15 trees (3 per species) at each location using the evaporative flux method and vapor pressure osmometer, respectively. Finally, we generated CO2 response curves for individuals in August to assess photosynthetic capacity.
Results/Conclusions
NOAA climate data revealed that the average daily maximum temperature at the rural site was ~0.5 °C higher than the urban site but ~2 °C lower at night. Trees at the rural location had more negative TLP than the urban location (F=8.71, p < 0.01), indicating a higher drought tolerance. There was a significant interactive effect of location*season (p<0.05) on Kleaf such that species tended to show an increase in Kleaf through the season at the urban site while many species decreased Kleaf later in the season at the rural site. Higher photosynthetic capacity in the urban trees suggest several possibilities: higher nitrogen content, deeper rooting, or lower temperatures were beneficial to urban trees. These data indicate that differences in overall climate and/or site-specific differences, rather than urban and rural factors, could be driving hydraulic and drought tolerance differences between trees at these locations. Further work will include analyses of soil density to better understand how urban and rural trees are differently impacted by land use history, climate, and urbanization.