E. Thomas Smiley Deep-Rooted Trees for Urban Environments: Selection and Propagation ............................................................ 184 Abstract. Seedling liners of three tree species (Fraxinus uhdei, Pistacia chinensis, and Zelkova serrata) were planted in the field and grown for 18 months. Pneumatic air excavation followed by digital photography, three-dimensional modeling, and root analysis showed there were significant differences in root architecture among the three species and within each species’ population. Among the three species, Pistacia chinensis had, on average, the deepest, most vertically oriented root systems and Fraxinus uhdei and Zelkova serrata the shallowest; however, there were shallow-rooted and deep-rooted genotypes in each species. Shallow-rooted and deep-rooted genotypes of Fraxinus and Zelkova selected from the seedling popula- tions were propagated vegetatively by cuttings, planted in the field, and grown for 5 to 6 years. On excavation and three-dimensional model creation, the root architecture of the cutting-propagated clones was assessed using liminal angles and individual root angles. Cutting-propagated clones of shallow-rooted parents were shallow-rooted; thus, they maintained the parents’ root architecture. Cutting-propagated clones of deep-rooted par- ents were also shallow-rooted; they did not maintain their parents’ root architecture. Results are discussed in terms of genetic, physiological (e.g., auxin treatment, adventitious root formation), and environmental (e.g., soil moisture) factors that can affect tree root growth and development. Key Words. Arboriculture; Gravitropism; Infrastructure Damage; Liminal Angle; Root Architecture, Root Growth; Root System Genetics; Street Tree; Urban Forestry. Glynn Percival and Sally Barnes Calcium-Induced Freezing and Salinity Tolerance in Evergreen Oak and Apple cv. ‘Golden Crown’.................. 191 Abstract. Greater variability in weather patterns and later spring frosts equate to poor winter hardiness, premature spring budbreak, and greater susceptibility to low-temperature damage and concomitant deicing salt application. A field trial was undertaken to determine the influence of a range of commercially available calcium fertilizers applied as foliar sprays on the freezing and salinity tolerance of two tree species, evergreen oak (Quercus ilex L.) and apple (Malus cv. ‘Golden Crown’). In all cases, application of calcium sprays increased twig, leaf, and root freezing and salt tolerance of both species as measured by leaf chlorophyll fluorescence and tissue electrolyte leakage bioassays. In the case of apple, a hardi- ness gain of 4.3°C (7.74°F) was recorded in twig tissue. In the case of evergreen oak, a hardiness gain of 2.1°C (3.78°F) was recorded in leaf tis- sue. Aſter a –5°C (23°F) (apple) and –6.5°C (20°F) (evergreen oak) freezing stress, root electrolyte leakage values as a measure of cell membrane structural damage were 16% to 27% less in calcium-treated trees compared with noncalcium-treated controls. The salt concentration needed to cause 50% reductions in leaf chlorophyll fluorescence as a measure of photosynthetic efficiency rose by 0.2% to 1.2% in calcium-fertilized trees indicating a positive influence of calcium on enhancing leaf tissue tolerance to salt damage. Differences in the magnitude of freezing and salinity tolerance gained were noticeable between the calcium products used. In general, calcium hydroxide, calcium nitrate borate, and cal- cium metalosate improved twig, leaf, and root freezing and salt tolerance in both tree species to a greater degree than calcium chloride, calcium sulphate, calcium nitrate, and a calcium–magnesium complex. A significant correlation existed between increased freezing tolerance and inter- nal tissue calcium content. Results of this study indicate that calcium sprays during late summer and fall can increase the freezing and salin- ity tolerance of evergreen oak and apple during the winter. This should be considered noteworthy for individuals involved in the management of trees in areas subject to subzero temperature fluctuations and/or concomitant applications of deicing salts in the form of sodium chloride. Key Words. Chlorophyll Fluorescence; Cold Tolerance; Electrolyte Leakage; Fertilizer; Landscape Management; Plant Health Care; Stress. Louis Anella, Thomas C. Hennessey, and Edward M. Lorenzi Research Note Growth of Balled-and-Burlapped versus Bare-Root Trees in Oklahoma, U.S. ......................................................200 ©2008 | International Society of Arboriculture | ISSN:1935-5297
May 2008
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