14 Percival and Barnes: Influence of Ca and N Fertilization on Freezing and Salinity Tolerance significantly higher SPAD regression values as a measure of leaf chlorophyll concentration and overall plant dry weights were recorded (Tables 3 through 7). Leaf nitrogen status has been shown to be highly correlated with leaf chlorophyll concentration (i.e., “green- ness”) and yield in a range of plants (Evans 1983; Seemann et al. 1987; Hoel 1998). Higher leaf nitrogen content as a result of N:P:K (24:7:7) fertilization in both evergreen oak and holly may account for the improved leaf color and total plant dry weights recorded. Consequently, results of this investigation indicate that although application of a N:P:K (24:7:7) fertilizer induced no significant freezing and salinity protectant properties in evergreen oak and holly, leaf color and overall growth were significantly (P < 0.05) better in both species compared to nonfertilized controls. Similar results have been obtained elsewhere using pear (Pyrus spp.) as a test species (Raese 1997). In conclusion, previous investigations have shown that calcium fertilization can improve the salinity and freezing tolerance of apple and pear trees cultivated under orchard conditions (Raese 1996); trees used in urban landscapes such as hornbeam (Carpinus spp.), and white poplar (Populus alba) (Percival et al. 1999); fruit and vegetables such as beans, potatoes, avocados, mangoes, cherries; and various grass species (Akhavankharazian et al. 1991; Anderson and Campbell 1995; Palta 1996). The present study offers further evidence in this respect. Acknowledgments. The authors are grateful for funding from the TREE Fund (John Z. Duling grant program). LITERATURE CITED Akhavankharazian, M., W.F. Campbell, J.J. Jurinak, and L.M. Dudley. 1991. Calcium amelioration of NaCl effects on plant growth, chlorophyll, and ion concentration in Phaseolus vulgaris. Arid Soil Res. Rehabil. 5:9–19. Anderson, J.L., and W.F. Campbell. 1995. Calcium transport and ATPase activity in microsomal vesicle fraction from ‘Montmorency’ sour cherry fruit. Acta Hortic. 398:47–57. Berbezy, P., L. Legendre, and A. Maujean. 1996. Purification and characterisation of alpha-amylase from vine shoot inter-nodes. Plant Physiol. Biochem. 34(3):353–361. Biggs, M.P. 1996. Low temperature acclimation and associated physiological changes in species of Rhododendron. Ph.D. thesis. University of Strathclyde, in association with SAC Auchincruive. Cameron, R.W.F., and G.R. Dixon. 1997. Air temperature, humidity and rooting volume affecting freezing injury to Rhododendron and other perennials. J. Hortic. Sci. Biotechnol. 72(4):553–562. Cannel, M.G.R., and R.I. Smith. 1986. Climatic warming, spring budburst and frost damage on trees. J. Appl. Ecol. 23:177–191. ©2005 International Society of Arboriculture Dehaynes, D.H., M.A. Ingle, and C.E. White. 1998. Nitrogen fertilization enhances cold tolerance of red spruce seedlings. Can J. For. Res. 19:1037–1043. Dobson, M.C. 1991. De-icing salt damage to trees and shrubs. For. Commiss. Bull. 101. Edgerton, I. J. 1957. Effects of nitrogen fertilization on cold hardiness of apple trees. Proc. Am. Soc. Hortic. Sci. 70:40–45. Evans, J.T. 1983. Nitrogen and photosynthesis in the flag leaf of wheat. Plant Physiol. 72:297–302. Greaves, J.A., and J.M. Wilson. 1987. Chlorophyll fluorescence analysis—An aid to plant breeders. Biologist 34(4):209–214. Hoel, B.O. 1998. Use of a handheld chlorophyll meter in winter wheat: Evaluation of different measuring positions on the leaf. Acta Agric. Scand. 48:222–228. Legge, R.L., E. Thompson, J.E. Baker, and M. Lieberman. 1982. The effect of calcium on the fluidity and phase properties of microsomal membranes isolated from postclimacteric Golden Delicious apples. Plant Cell Physiol. 23:161–169. Lichtenthaler, H.K., and A.R. Wellburn. 1983. Determinations of total carotenoids and chlorophylls a and b of leaf extracts in different solvents. Biochem. Soc. Transcr. 11:591–593. McKay, H. 1992. Electrolyte leakage from fine roots of conifer seedlings: A rapid index of plant vitality following cold storage. Can. J. For. Res. 22:1371–1377. Meinander, O., S. Somersalo, T. Holopainen, and R.J. Strasser. 1996. Scots pine after exposure to elevated ozone and carbon dioxide probed by reflectance spectra and chlorophyll a fluorescence transients. J. Plant Physiol. 148:229–236. Monroy, A.F., F. Sarhan, and R.S. Dhindsa. 1993. Cold- induced changes in freezing tolerance, protein phosphorylation, and gene expression. Plant Physiol. 102:1227–1235. Palta, J.P. 1996. Role of calcium in plant responses to stresses: Linking basic research to the solution of practical problems. HortScience 31(1):51–57. Pellet, N.E., and D.B. White. 1969. Effects of soil nitrogen and soil moisture levels on cold acclimation of container- grown Juniperus chinensis ‘Hetsi’. J. Am. Soc. Hortic. Sci. 94:457–459. Percival, G.C., and G.A. Fraser. 2001. Measurement of the salinity and freezing tolerance of Crataegus genotypes using chlorophyll fluorescence. J. Arboric. 27(5):233– 245. Percival, G.C., and A. Galloway. 1999. The potential of chlorophyll fluorescence measurements to detect salt and waterlogging stress in urban trees. Acta Hortic. 496:253–259.
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