Effect of Night Temperature on Dehardening in Black Walnut Seedlings
Abstract:Rates of dehardening were measured in seedlings of Juglans nigra L. grown from seed collected in Tippecanoe Co., Indiana, transferred indoors during January, and exposed to warm days plus either warm or cool nights. Five seedlings from both cool and warm night treatments were sampled at 4-day intervals until foliation occurred. Stem sections from each seedling were subjected to test temperatures of +3, -4, -11, -18, -25, or -32°C. Freezing injury was detected visually and by a modified triphenyl tetrazolium chloride test of living bark viability. Eight days elapsed before seedlings exposed to warm nights dehardened to the point that they suffered injury at -18°C. Cool nights delayed similar dehardening by about 16 days but did not prevent it. Absence of injury to living bark at -4°C, even when seedlings were in full leaf, is attributed to the abilitiy of the cell contents to undercool to between -6 and -9°C before ice formed. Seedlings were not highly susceptible to freezing injury due to loss of hardiness by living bark during unusually mild weather in late winter. Forest Sci. 21:313-317.
Document Type: Journal Article
Affiliations: Professor, Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana, U.S.A.
Publication date: 1975-09-01
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