Arboriculture & Urban Forestry 34(3): May 2008 Arboriculture & Urban Forestry 2008. 34(3):191–199. 191 Calcium-Induced Freezing and Salinity Tolerance in Evergreen Oak and Apple cv. ‘Golden Crown’ Glynn Percival and Sally Barnes 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 hardiness 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 tissue. After 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 calcium 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 internal tissue calcium content. Results of this study indicate that calcium sprays during late summer and fall can increase the freezing and salinity 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. Aesthetic criteria is an important influence regarding selection of trees for planting within an urban environment with planting schemes along roads, in town centers, car parks, and streets often stylized by distinct forms and preferred flowering and foliage qualities (Percival and Hitchmough 1995). Consequently, trees selected for planting are located outside their normal climatic zones and may not be fully adapted to the climate in which they are being grown. This lack of fitness to climate may be further exacerbated by changes in weather patterns caused by climate change, which is not only likely to result in more mild winters, but also in more variable weather patterns. Milder winters, greater variability in weather patterns, and later spring frosts equate to poor winter hardiness, premature spring budbreak, and greater susceptibility to low-temperature damage. Late spring frosts are particularly devastating, because young spring growth is unable to acclimate (Cannel and Smith 1986). Pertinent ex- amples include –6°C (20°F) temperatures recorded in early 2007 in California, U.S. causing significant damage to the citrus in- dustry with lemon and orange yield losses greater than 50% predicted (Anon 2007), whereas freezing temperatures less than –20°C (–4°F) experienced in Scotland resulted in significant economic damage to the hardy ornamental woody plant industry (Percival et al. 1999). The application of deicing salts, primarily in the form of so- dium chloride, to maintain safe roadways and pavements is a common practice throughout Europe and the United States. De- spite the benefits for public safety, deicing salts can be a major chemical pollutant in urban landscapes having a detrimental ef- fect on roadside vegetation (Percival et al. 2003). When deicing salts are deposited directly onto twigs, buds, or needles, salt draws moisture out of plant tissue, causing desiccation and ne- crosis. In the case of conifers such as cypress, firs, and spruce, salt spray causes dieback starting at the tips of needles. On deciduous trees, symptoms of salt damage become manifest dur- ing spring and summer when leaf margins typically display ne- crosis or scorch symptoms. Salt spray and excess soil salts can also cause branch dieback, stunted growth of stems and foliage, reduced tree vigor, and death (Dobson 1991). Calcium is a major macronutrient in trees, important to the structural integrity of cell walls and plasma membranes (Ste- ponkus 1984). Calcium has been implicated in resistance to freeze–thaw injury and has been shown to alleviate damage caused by freezing stress to cell membranes (Palta and Li 1980; Palta, 1996). Additionally, low-temperature acclimation can be influenced by the concentration of calcium in the cell cytoplasm (Monroy et al. 1993). Previous research has shown that applica- tions of calcium sprays can improve winter hardiness of fruit trees (Raese 1997) and increase time spent in cold storage of crops such as avocados, mangoes, cherries, and apples (Ander- son and Campbell 1995; Raese 1996). In addition, gypsum (cal- cium sulphate) is widely advocated as a remedial measure to reduce deicing salt injury to plants (Dobson 1991). Commer- cially, a range of fertilizers exist containing different forms of calcium such as calcium nitrate, calcium sulphate, and calcium ©2008 International Society of Arboriculture
May 2008
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
