Annals of Botany 81: 595-602, 1998
© 1998 Annals of Botany Company
Winterfat (Eurotia lanata(Pursh) Moq.) Seedbed Ecology: Low Temperature Exotherms and Cold Hardiness in Hydrated Seeds as Influenced by Imbibition Temperature
,Department of Plant, Soil and Insect Sciences, University of Wyoming, Laramie, WY, 82071, USA USDA, Agricultural Research Service, High Plains Grasslands Research Station, Cheyenne, WY, 82009, USA Department of Crop Science and Plant Ecology, University of Saskatchewan, Saskatoon, Sask., S7N 5A8, Canada
Received: June 27, 1997 ; Returned for revision: September 25, 1997 . Accepted: January 19, 1998 .
Thermal analyses of freezing events in hydrated lettuce (Lactuca sativaL.) seeds show a correlation between low temperature exotherms (LTEs) (evidence of ice crystal formation) and seed death. Yet, weather patterns common to the Northern Great Plains of North America regularly create conditions where non-dormant seeds of native plants hydrate with snow melt and are subsequently exposed to -30 °C or colder conditions. To determine if such weather patterns decimate dispersed seeds, we measured the effects of freezing on fully hydrated winterfat (Eurotia lanata(Pursh) Moq.) seeds harvested from the Northern Plains at two USA and one Canadian location. Survival of hydrated seeds to -30 °C at a cooling rate of 2.5 °C h-1was similar to that of seeds not subjected to cooling, even though both a high temperature exotherm (HTE) and an LTE were observed. Although the LTE was not related to winterfat seed survival, freeze-stressed seeds had reduced germination rates and reduced seedling vigour, particularly for the collection with the lightest seeds. The temperature of LTEs was similar among seed collections with a mean of -17.6 °C, but was warmer when the seeds were imbibed at 0 °C compared to 5, 10 or 20 °C. We found a significant correlation between the HTE and LTE temperatures. The difference and the correlation may be due to the higher moisture content of seeds imbibed at 0 °C. After pericarp removal, only one exotherm in the range of the LTE was observed. This was also true for the naked embryo. We conclude that an LTE indicates ice formation in the embryo, but that it does not signal the death of a winterfat seed.Copyright 1998 Annals of Botany Company
Eurotia lanata(Pursh) Moq.,Krascheninnikovia, Ceratoides,winterfat, exotherm, freezing tolerance, freezing avoidance, seedbed ecology, germination, D50, seedling vigour, seed collection