Using hydrothermal time concepts to model seed germination response to temperature, dormancy loss, and priming effects in Elymus elymoides

Abstract

Hydrothermal time (HTT) describes progress toward seed germination under various combinations of incubation water potential ( ) and temperature (T). To examine changes in HTT parameters during dormancy loss, seeds from two populations of the bunchgrass Elymus elymoides were incubated under seven temperature regimes following dry storage at 10, 20 and 30°C for intervals from 0 to 16 weeks. Fully after-ripened seeds were primed for 1 week at a range of s. Data on germination rate during priming were used to obtain a HTT equation for each seed population, while data obtained following transfer to water were used to calculate HTT accumulation during priming. HTT equations accurately predicted germination time course curves if mean base water potential, b(50), was allowed to vary with temperature. b(50) values increased linearly with temperature, explaining why germination rate does not increase with temperature in this species. b(50) showed a linear decrease as a function of thermal time in storage. Slopes for the T × b(50) relationship did not change during after-ripening. This thermal after-ripening time model was characterized by a single base temperature and a constant slope across temperatures for each collection. Because the difference between initial and final b(50)s was uniform across tempera-tures, the thermal after-ripening requirement was also a constant. When seeds were primed for 1 week at −4 to −20 MPa, accumulation of HTT was a uniform 20% of the total HTT requirement. When primed at 0 to −4 MPa, HTT accumulation decreased linearly with decreasing priming potential, and a hydrothermal priming time model using a constant minimum priming potential adequately described priming effects. Use of these simple HTT relationships will facilitate modelling of germination phenology in the field.

Variation in Thermal time model Parameters Between Two Contrasting Chickpea (<i>Cicer arietinum</i>) cultivars

“…The reason that T b was often considered as a constant may be for the ease of modeling [29]. Similar to this experiment, [30] reported that base temperature in the thermal time did not appear stable for wild species due to distinct genetic variability within the population. The variation in base temperature between seed size classes of chickpea may favor large seeds, allowing rapid germination and establishment.…”

“…The variation in base temperature between seed size classes of chickpea may favor large seeds, allowing rapid germination and establishment. Poor emergence at low temperature is sometimes attributed to low seed quality, genotypes, disease resistance, and high thermal requirement [30]. According to the results of this study we recommend to introduce kabuli-types (the cultivar "Shendi") in Northern Sudan, and sowing should be done in the early winter (September-October) when temperature is around 20˚C -25˚C to …”

Factors affecting seed germination and seedling establishment of a long-lived desert shrub (Coleogyne ramosissima: Rosaceae)

“…When the slopes of the lines representing rate of dormancy loss at each temperature were plotted as a function of temperature, a linear relationship was obtained (after-ripening rate (months À1 ) = 0.0000522 (storage temperature) + 0.0136, df = 1, R 2 = 0.989, p < 0.10), lending support to the hypothesis that dormancy loss rate increases as a function of temperature for C. ramosissima seeds, as it does for seeds of other species (Bauer et al 1998;Meyer et al 2000).…”

“…We used seed collections from a series of C. ramosissima populations, including those populations used in the field establishment study. The laboratory storage experiment was designed to tell us whether C. ramosissima seeds lose dormancy under dry conditions (i.e., afterripen), and whether the rate of dormancy loss varies as a function of temperature or seed origin (Bauer et al 1998;Meyer et al 2000). In the factorial experiment, we tested the hypothesis that seeds would integrate sequences of time spent at different temperatures and water contents in a way that would tend to be normalizing, so that the ability to germinate at the time when probability of survival for the resulting seedlings is greatest would not be compromised.…”

The effects of temperature on the dormancy and germination of Cirsium arvense (L.) Scop. seeds

“…In the seeds of most species the mean base water potential progressively decreased with storage time, whereas a lower stratification temperature and higher afterripening temperature accelerated dormancy release (Christensen et al 1996;Christensen Bauer et al 1998;Meyer et al 2000;Batlla and Benech-Arnold 2004;Alvarado and Bradford 2005;Bair et al 2006). Seeds of scentless mayweed, a species with a plastic life strategy, released the primary dormancy at both low and high stratification temperatures, even though at low temperatures the process took place fast and lasted for a short time, and at high temperatures was slow but long.…”