145 Water Deficit Stress Responses of Seven Tree Species Used in Urban Landscapes

Abstract

Plant development, leaf morphology, leaf cuticular wax content, and leaf water relations were determined for seven tree species exposed to consecutive cycles of drought. The objective of the experiment was to identify plant taxa suitable for landscapes prone to drought. On the day drought treatments began, plant development traits and leaf morphology varied among species. Leaf cuticular wax content was different among species and ranged from 0.053 mg·cm–2 in California white oak (Quercus lobata Née), to 0.200 mg·cm–2 in Texas red oak (Quercus buckleyi Buckl.). Was content in Bur oak (Quercus macrocarpa Michx.) and Shumard oak (Quercus shumardii Buckl.) averaged 0.105 and 0.11 mg·cm–2, respectively. At harvest, Texas red oak plants treated with drought had the highest root-to-shoot dry weight ratio which averaged 3.1. In contrast, plants of Arizona ash (Fraxinus velutina Torr.) and California white oak that were frequently irrigated had the lowest root-to-shoot dry weight ratio. Drought did not affect stem elongation, total lamina area, leaf dry weight, and specific leaf weight. Abaxial leaf surfaces of Arizona ash were the most pubescent and averaged1836 trichomes/cm2. Drought-stressed plants of golden rain tree (Koelreuteria paniculata Laxm.) had the most negative midday leaf water potential, which averaged –2.5 MPa. Plants of Chinkapin oak (Quercus muehlenbergii Engelm.) that were irrigated frequently had the least negative predawn leaf water potentials. Predawn leaf water potentials tended to be more negative for Arizona ash and golden rain tree than for the oak species. These results suggest that some species of oak might perform well in landscapes prone to drought.