After-ripening, the loss of dormancy under dry conditions, is associated with a decrease in mean base water potential for germination of Bromus tectorum L. seeds. After-ripening rate is a linear function of temperature above a base temperature, so that dormancy loss can be quantified using a thermal after-ripening time (TAR) model. To incorporate storage water potential into TAR, we created a hydrothermal after-ripening time (HTAR) model. Seeds from two B. tectorum populations were stored under controlled temperatures (20 or 30 �C) and water potentials (?400 to ?40 MPa). Subsamples were periodically removed from each storage treatment and incubated at 15 or 25 �C to determine germination time courses. Dormancy status (mean base water [...]
