Water Relations of Sweetgum in an Urban Canyon and Park

Roger K. Kjelgren and James R. Clark

Water use and water relations of sweetgum growing in an urban canyon were investigated. Predawn water potential, dawn-to-dusk stomatal conductance, and leaf morphology were measured over a two-year period at a downtown site in Seattle, Washington. Trees received four hours of direct midsummer sunlight during a midday gap in shade cast by nearby build¬ings. This was compared to similar-aged sweetgum street trees growing in a neighboring park-like setting. Specific leaf area and leaf presentation angle of the canyon trees were character¬istic of shade acclimation. Stomata of the canyon trees quickly opened in response to light during the morning shade period, but closed rapidly in re¬sponse to low humidity during the sunlit period, and remained closed through the afternoon shaded period. Overall lower con¬ductances and leaf temperatures in the canyon trees resulted in calculated transpiration rates that were lower than the park trees. While the park trees re¬ceived supplemental water, the canyon trees did not, but predawn water potential measurements indictated only slightly more water stress. These data suggested that trees growing in urban canyons will deplete soil water less rapidly due to the effects of re¬duced irradiance on tree transpiration

Supporting pdf: Water Relations of Sweetgum in an Urban Canyon and Park