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    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 8C) and water potentials (2400 to 240 MPa). Subsamples were periodically removed from each storage treatment and incubated at 15 or 25 8C to determine germination time courses. Dormancy status (mean base water potential) was calculated from each time course using hydrothermal time equations developed for each seed collection. Seeds stored at 2400MPa did not afterripen. At water potentials from2400 to 2150 MPa, the rate of after-ripening increased approximately linearly with increasing water potential. Between 2150 and 280 MPa, there was no further increase in afterripening rate, while at 240MPa seeds did not afterripen and showed loss of vigour. These results suggest that the concept of critical water potential thresholds, previously shown to be associated with metabolic activity and desiccation damage in partially hydrated seeds, is also relevant to the process of afterripening. The HTAR model generally improved field predictions of dormancy loss when the soil was very dry. Reduced after-ripening rate under such conditions provides an ecologically relevant explanation of how seeds prolong dormancy at high summer soil temperatures.

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    Bair, Necia B.; Meyer, Susan E.; Allen, Phil S. 2006. A hydrothermal after-ripening time model for seed dormancy loss in Bromus tectorum L. Seed Science Research. 16: 17-28.


    after-ripening, Bromus tectorum, dormancy loss, hydrothermal after-ripening time, hydrothermal time, modelling, water potential

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