A simulation model to predict seed dormancy loss in the field for Bromus tectorum L

Bromus tectorum L. (cheatgrass) is an invasive winterannual whose seeds lose dormancy through dry after-ripening. In this papera thermal after-ripening time model for simulating seed dormancy loss ofB. tectorum in the field is presented. The modelemploys the hydrothermal time parameter mean base water potential(b(50)) as an index of dormancy status. Other parameters of thehydrothermal time equation (the hydrothermal time constant HT,the standard deviation of base water potentials b, andthe base temperature Tb) are held constant, whileb(50) is allowed to vary and accounts for changes in germinationtime-course curves due to stage of after-ripening or incubationtemperature. To obtain hydrothermal time parameters for each of fourcollections, seeds were stored dry at 20Cfor different intervals, then incubated in water (O MPA) or polyethyleneglycol (PEG) solutions (-0.5, -1.0, -1.5 MPa) at 15 and 25C. Germination data for the thermal after-ripeningtime model were obtained from seeds stored dry in the laboratory at 10, 15,20, 30, 40, and 50°C for 0 to 42 weeks, then incubated at twoalternating temperatures in water. Change in b(50) wascharacterized for each collection and incubation temperature as a linearfunction of thermal time in storage. Measurements of seed zone temperatureat a field site were combined with equations describing changes inb(50) during after-ripening to make predictions of seed dormancyloss in the field. Model predictions were compared with values derived fromincubation of seeds retrieved weekly from the field site. Predictions ofchanges in b(50) were generally close to observed values,suggesting the model is useful for simulating seed dormancy loss duringafter-ripening in the field.