The Styrax L. genus contains ≈130 species distributed in Asia, the Mediterranean, South America, and North America (Fritsch, 1999). Two species from Asia, Styrax japonicus Sieb. & Zucc. (Japanese snowbell) and Styrax obassia Sieb. & Zucc. (fragrant snowbell), are the most frequently planted members of the genus in landscapes in the United States. Styrax americanus Lam. (American snowbell) is rarely cultivated (Dirr, 1978) but forms attractive shrubs or small trees up to 4 m tall that occur in nature at moist sites alongside streams, near swamp margins, and in floodplains (Gonsoulin, 1974). The species blooms in late spring, producing dainty inflorescences of white fragrant flowers with reflexed petals. In fall, hard drupes adorn the branches, and striped bark adds ornamental interest.
Styrax americanus occurs throughout much of the southeastern United States and is distributed continuously as far north as southeastern Virginia and southern Illinois. We are particularly interested in the northern limit of the distribution, which is a disjunct population located in the Momence Wetlands of northern Illinois, ≈500 km north of the closest populations to the south (Phillippe et al., 2003). Numerous factors, including its resistance to environmental stressors, must be examined before the potential for S. americanus as a species for the nursery and landscape industries is understood. Low temperatures restrict where many woody species can be used, and little is known about the cold tolerance of S. americanus. Therefore, we investigated midwinter-hardiness and deacclimation patterns of populations of S. americanus from northern and southern locations within its natural distribution.
Cold acclimation is the accrual of cold-hardiness in response to lengthening nights and declining temperatures. Deacclimation is the loss of cold-hardiness in response to environmental and phenological changes (Kalberer et al., 2006). Increasing temperatures, rather than lengthening photoperiods, principally govern the deacclimation process (Beck et al., 2004). The capacity of a woody species to resist deacclimation when exposed to unseasonably warm temperatures in late winter and early spring is an important trait to consider when specifying taxa for placement in horticultural landscapes (Taulavuori et al., 2004; Wolf and Cook, 1992). Our objectives were to determine if plants from the northernmost disjunct population of S. americanus are more cold-tolerant than plants from other populations and to compare plants from different provenances for their resistance to deacclimation and their chilling requirement. Our results provide needed information about variation in tolerance to low temperature among provenances of this North American species.
Arora, R., Rowland, L.J., Ogen, E.L., Dhanaraj, A.L., Marian, C.O., Ehlenfeldt, M.K. & Vinyard, B. 2004 Dehardening kinetics, bud development, and dehydrin metabolism in blueberry cultivars during deacclimation at constant, warm temperatures J. Amer. Soc. Hort. Sci. 129 667 674
Beck, E.H., Heim, R. & Hansen, J. 2004 Plant resistance to cold stress: Mechanisms and environmental signals triggering frost hardening and dehardening J. Biosci. 29 449 459
Ehlenfeldt, M.K., Ogden, E.L. & Rowland, L.J. 2006 Evaluation of midwinter cold hardiness among 25 rabbiteye blueberry cultivars HortScience 41 579 581
Fritsch, P.W. 1999 Phylogeny of Styrax based on morphological characters, with implications for biogeography and infrageneric classification Syst. Bot. 24 356 378
Graves, W.R., Schrader, J.A. & Sharma, J. 2006 Cold hardiness of the rare Dirca occidentalis: Comparisons to Dirca palustris from disparate provenances J. Environ. Hort. 24 169 172
Harrison, L.C., Weiser, C.J. & Burke, M.J. 1978 Freezing of water in red-osier dogwood stems in relation to cold hardiness Plant Physiol. 62 899 901
Kalberer, S., Arora, R., Leyva-Estrada, N. & Krebs, S.L. 2007a Cold hardiness of floral buds of deciduous azaleas: Dehardening, rehardening, and endodormancy in late winter J. Amer. Soc. Hort. Sci. 132 73 79
Kalberer, S.R., Leyva-Estrada, N., Krebs, S.L. & Arora, R. 2007b Frost dehardening and rehardening of floral buds of deciduous azaleas are influenced by genotypic biogeography Environ. Exp. Bot. 59 264 275
Kalberer, S.R., Wisniewski, M. & Arora, R. 2006 Deacclimation and reacclimation of cold-hardy plants: Current understanding and emerging concepts Plant Sci. 171 3 16
Karlson, D.T., Zeng, Y., Stirm, V.E., Joly, R.J. & Ashworth, E.N. 2003 Photoperiodic regulation of a 24-kD dehydrin-like protein in red-osier dogwood (Cornus sericea L.) in relation to freeze-tolerance Plant Cell Physiol. 44 25 34
Lennartsson, M. & Ogren, E. 2002 Causes of variation in cold hardiness among fast-growing willows (Salix spp.) with particular reference to their inherent rates of cold hardening Plant Cell Environ. 25 1279 1288
Lim, C.C., Krebs, S.L. & Arora, R. 1999 A 25-kDa dehydrin associated with genotype- and age-dependent leaf freezing-tolerance in Rhododendron: A genetic marker for cold hardiness? Theor. Appl. Genet. 99 912 920
Phillippe, L.R., Handel, W.C., Horn, S.L., Harty, F.M. & Ebinger, J.E. 2003 Vascular flora of Momence wetlands, Kankakee County, Illinois Trans. Ill. State Acad. Sci. 96 271 294
Powell, A., Himelrick, D., Dozier, W. & Williams, D. 1999 Fruit culture in Alabama: Winter chilling requirements Alabama Coop. Ext. System ANR-53-D
R Development Core Team 2009 R: A language and environment for statistical computing R Foundation for Statistical Computing Vienna, Austria 3 Aug. 2009 <http://www.R-project.org>.
Rowland, L.J., Ogden, E.L., Ehlenfeldt, M.K. & Vinyard, B. 2005 Deacclimation kinetics, and bud development among 12 diverse blueberry genotypes under field conditions J. Amer. Soc. Hort. Sci. 130 508 514
Schrader, J.A. & Graves, W.R. 2003 Phenology and depth of cold acclimation in the three subspecies of Alnus maritima J. Amer. Soc. Hort. Sci. 128 330 336
Taulavuori, K.M.J., Taulavuori, E.B., Skre, O., Nilsen, J., Igeland, B. & Laine, K.M. 2004 Dehardening of mountain birch ecotypes at elevated winter temperatures New Phytol. 162 427 436
The Weather Channel 2009 Oct. 2009 <http://www.weather.com>.
Wolf, T.K. & Cook, M.K. 1992 Seasonal deacclimation patterns of three grape cultivars at constant warm temperature Amer. J. Enol. Viticult. 43 171 179
Zimmerman, E.M., Jull, L.G. & Shirazi, A.M. 2005 Effects of salinity and freezing on Acer platanoides, Tilia cordata, and Viburnum lantana J. Environ. Hort. 23 138 144