Heat Shock Germination Responses of Three Eastern North American Temperate Species

The requirement for heat shock to break physical dormancy of hard seeds is a widely known strategy for recruitment in fire maintained ecosystems. Despite extensive work by fire ecologists in the southeastern United States, heat shock response has been demonstrated for only a few eastern North American temperate species. In this study germination responses to dry and wet heat were investigated for three species with physical dormancy: Galactia regularis (Fabaceae), Lupinus perennis (Fabaceae), and Rhus copallinum (Anacardiaceae). Control, wet heat (I min boiling), and dry heat (10 min at 60, 70, 80, 90, 100, and 110 degrees C) treatments were independently applied in the laboratory. Maximum germination occurred at 80 degrees C for G. regularis and L. perennis and was significantly greater than both control and boiling treatments. For R. copallinum, maximum germination occurred at 90 degrees C for all populations investigated and was significantly greater than the control group in three of four populations. Heat shock germination may play a larger role in post fire recruitment in the flora of the eastern United States than currently recognized.