scholarly journals A hydrothermal after-ripening time model for seed dormancy loss in Bromus tectorum L.

2006 ◽  
Vol 16 (1) ◽  
pp. 17-28 ◽  
Author(s):  
Necia B. Bair ◽  
Susan E. Meyer ◽  
Phil S. Allen
Keyword(s):  
Water Potential ◽  
Time Course ◽  
Bromus Tectorum ◽  
Base Temperature ◽  
Time Model ◽  
Seed Collection ◽  
Ripening Time ◽  
Water Potentials ◽  
Ripening Rate ◽  
Base Water Potential

After-ripening, the loss of dormancy under dry conditions, is associated with a decrease in mean base water potential for germination ofBromus tectorumL. 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 twoB. tectorumpopulations 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 potential) was calculated from each time course using hydrothermal time equations developed for each seed collection. Seeds stored at −400 MPa did not after-ripen. At water potentials from −400 to −150 MPa, the rate of after-ripening increased approximately linearly with increasing water potential. Between −150 and −80 MPa, there was no further increase in after-ripening rate, while at −40 MPa seeds did not after-ripen 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 after-ripening. 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.

A hydrothermal time model of seed after-ripening in Bromus tectorum L.

1996 ◽  
Vol 6 (4) ◽  
pp. 155-164 ◽  
Author(s):  
Maren Christensen ◽  
Susan E. Meyer ◽  
Phil S. Allen
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Time Course ◽  
Bromus Tectorum ◽  
Incubation Temperature ◽  
Hydrothermal Time ◽  
Germination Time ◽  
Water Potentials ◽  
Incubation Temperatures ◽  
Base Water Potential

AbstractBromus tectorum L. is an invasive winter annual grass with seeds that lose dormancy through the process of dry after-ripening. This paper proposes a model for after-ripening of B. tectorum seeds based on the concept of hydrothermal time. Seed germination time course curves are modelled using five parameters: a hydrothermal time constant, the fraction of viable seeds in the population, base temperature, mean base water potential and the standard deviation of base water potentials in the population. It is considered that only mean base water potential varies as a function of storage duration and incubation temperature following after-ripening. All other parameters are held constant throughout after-ripening and at all incubation temperatures. Data for model development are from seed germination studies carried out at four water potentials (0, −0.5, −1.0 and −1.5 MPa) at each of two constant incubation temperatures (15 and 25°C) following different storage intervals including recently harvested, partially after-ripened (stored for 4, 9 or 16 weeks at 20°C) and fully after-ripened (stored for 14 weeks at 40°C). The model was fitted using a repeated probit regression method, and for the two seed populations studied gave R2 values of 0.898 and 0.829. Germination time course curves predicted by the model generally had a good fit when compared with observed curves at the incubation temperature/water potential treatment combinations for different after-ripening intervals. Changes in germination time course curves during after-ripening of B. tectorum can largely be explained by decreases in the mean base water potential. The simplicity and good fit of the model give it considerable potential for extension to simulation of after-ripening under field conditions.

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

2000 ◽  
Vol 10 (3) ◽  
pp. 213-223 ◽  
Author(s):  
Susan E. Meyer ◽  
Susan B. Debaene-Gill ◽  
Phil S. Allen
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Time Course ◽  
Germination Rate ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Time Model ◽  
Priming Effects ◽  
Elymus Elymoides ◽  
Temperature Regimes

AbstractHydrothermal 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.

Relationship between accumulated hydrothermal time during seed priming and subsequent seed germination rates

1994 ◽  
Vol 4 (2) ◽  
pp. 63-69 ◽  
Author(s):  
Kent J. Bradford ◽  
Anthony M. Haigh
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Seed Priming ◽  
Threshold Temperature ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Time Model ◽  
Radicle Emergence ◽  
The Times ◽  
Base Water Potential

AbstractSeed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimal T and/or reduced ψ are inversely proportional to the amounts by which T exceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimal T and ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even at T or ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentum Mill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin = 7.05°C) and water potential (ψmin = −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb = 11°C; ψb = −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination when T or ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimal T and ψ at which metabolic progress toward radicle emergence is possible.

scholarly journals Germination response of Hylocereus setaceus (Salm-Dyck ex DC: ) Ralf Bauer (Cactaceae) seeds to temperature and reduced water potentials

2010 ◽  
Vol 70 (1) ◽  
pp. 135-144 ◽  
Author(s):  
E. Simão ◽  
M. Takaki ◽  
VJM. Cardoso
Keyword(s):  
Water Potential ◽  
Germination Rate ◽  
Base Temperature ◽  
Temperature Range ◽  
Water Potentials ◽  
Germination Response ◽  
Wide Range ◽  
Optimum Interval ◽  
Time Courses ◽  
Base Water Potential

The germination response of Hylocereus setaceus seeds to isothermic incubation at different water potentials was analysed by using the thermal time and hydrotime models, aiming to describe some germination parameters of the population and to test the validity of the models to describe the response of the seeds to temperature and water potential. Hylocereus setaceus seeds germinated relatively well in a wide range of temperatures and the germination was rate limited from 11 to 20 °C interval and beyond 30 °C until 40 °C, in which the germination rate respectively shifts positively and negatively with temperature. The minimum or base temperature (Tb) for the germination of H. setaceus was 7 °C, and the ceiling temperature varied nearly from 43.5 to 59 °C depending on the percent fraction, with median set on 49.8 °C. The number of degrees day necessary for 50% of the seeds to germinate in the infra-optimum temperature range was 39.3 °C day, whereas at the supra-optimum interval the value of θ = 77 was assumed to be constant throughout. Germination was sensitive to decreasing values of ψ in the medium, and both the germinability and the germination rate shift negatively with the reduction of ψ, but the rate of reduction changed with temperature. The values of base water potential (ψb) shift to zero with increasing temperatures and such variation reflects in the relatively greater effect of low ψ on germination in supra optimum range of T. In general, the model described better the germination time courses at lower than at higher water potentials. The analysis also suggest that Tb may not be independent of ψ and that ψb(g) may change as a function of temperature at the infra-otimum temperature range.

Hydrothermal time analysis of tomato seed germination at suboptimal temperature and reduced water potential

1994 ◽  
Vol 4 (2) ◽  
pp. 71-80 ◽  
Author(s):  
Peetambar Dahal ◽  
Kent J. Bradford
Keyword(s):  
Seed Germination ◽  
Water Potential ◽  
Time Course ◽  
Hydrothermal Time ◽  
Tomato Seed ◽  
Time Model ◽  
Germination Time ◽  
Radicle Emergence ◽  
Time Courses ◽  
Hydrotime Model

AbstractBoth temperature (T) and water potential (ψ) have consistent and quantifiable effects on the rate and extent of seed germination (radicle emergence). Germination at suboptimal T can be characterized on the basis of thermal time, or the T in excess of a base (Tb) multiplied by the time to a given percentage germination (tg). Similarly, germination at reduced ψ can be characterized on a hydrotime basis, or the ψ in excess of a base (ψb) multiplied by tg. Within a seed population, the variation in thermal times to germination for a specific percentage (g) is based upon the normal distribution of ψb values among seeds (ψb(g)). Germination responses across a range of suboptimal T and ψ might be accounted for by a general hydrothermal time model incorporating both T and ψ components. We tested this hypothesis for tomato (Lycopersicon esculentum Mill.) seeds of two genotypes differing in germination rates and tolerance of suboptimal T and ψ. For combinations of T (10−25°C) and ψ (0 to −0.9 MPa), a general hydrothermal time model accounted for approximately 75% of the variation in times to germination within the seed populations of both genotypes, and over 96% of the variation in median germination rates. However, ψb(g) distributions were sensitive to both the T and ψ of imbibition, resulting in a poor fit of the model to specific time course data. Analysis of germination timing separately for low and high ψ ranges within a given T resulted in specific models accounting for 88−99% of the variation in individual germination times and >99% of the variation in madian germination rates. Thus, for a given T and ψ range, the hydrotime model closely matched tomato seed germination time courses. Accumulated hydrothermal time accounted well for germination rates at ψ> −0.5 MPa across suboptimal T if ψb(g) was allowed to vary with T. Germination did not show a consistent response to T at ψ < −0.5 MPa, and estimated Tb values varied over different T ranges. Generalization of the hydrothermal time model across the entire range of suboptimal T and ψ was limited by physiological adjustments of the seeds to their current environment. The hydrothermal time model detected and quantified these adjustment processes that would otherwise not be evident from inspection of germination time courses. Temperature and water potential influence the time to germination via physiological mechanisms that reciprocally interact.

Hydropriming accelerates seed germination of Medicago sativa under stressful conditions: A thermal and hydrotime model approach

2017 ◽  
Author(s):  
Rong Li ◽  
Dandan Min ◽  
Lijun Chen ◽  
Chunyang Chen ◽  
Xiaowen Hu
Keyword(s):  
Water Potential ◽  
Germination Rate ◽  
High Water ◽  
Nacl Stress ◽  
Base Temperature ◽  
Severe Water Stress ◽  
Hydrotime Model ◽  
Response To Temperature ◽  
Base Water Potential ◽  
Temperature Water

This study determined the effects of priming on germination in response to temperature, water potential and NaCl. Thermal and hydrotime models were utilized to evaluate changes in parameters of the model after priming. Priming reduced the amount of thermal time in both cultivars, but slightly increased the base temperature for germination from 1.0 to 3.5°C in “Longdong”. Priming significantly increased germination rate at high water potential but had no effect at low water potential. Further, priming reduced the hydrotime constant but made the median base water potential value slightly more positive in both cultivars. Thus, priming increased germination rate in water but decrease it under severe water stress. Germination rate was significantly increased in both cultivars under salinity (NaCl) stress. Moreover, priming improved seedling growth in response to temperature, water and salinity stress in both cultivars.

Ecological aspects of seed dormancy loss

1998 ◽  
Vol 8 (2) ◽  
pp. 183-192 ◽  
Author(s):  
Phil S. Allen ◽  
Susan E. Meyer
Keyword(s):  
Water Potential ◽  
Seed Dormancy ◽  
Laboratory Data ◽  
Simulation Models ◽  
Base Temperature ◽  
Hydrothermal Time ◽  
Seed Biology ◽  
Seed Population ◽  
Germination Timing ◽  
Base Water Potential

AbstractAdvances in seed biology include progress in understanding the ecological significance of seed dormancy mechanisms. This knowledge is being used to make more accurate predictions of germination timing in the field. For several wild species whose seedlings establish in spring, seed populations show relevant variation that can be correlated with habitat conditions. Populations from severe winter sites, where the major risk to seedlings is frost, tend to have long chilling requirements or to germinate very slowly at low temperatures. Populations from warmer sites, where the major risk is drought, are non-dormant and germinate very rapidly under these same conditions. Seed populations from intermediate sites exhibit variation in dormancy levels, both among and within plants, which spreads germination across a considerable time period. For grasses that undergo dry after-ripening, seed dormancy loss can be successfully modelled using hydrothermal time. Dormancy loss for a seed population is associated with a progressive downward shift in the mean base water potential, i.e., the water potential below which half of the seeds will not germinate. Other parameters (hydrothermal time requirement, base temperature and standard deviation of base water potentials) tend to be constant through time. Simulation models for predicting dormancy loss in the field can be created by combining measurements of seed zone temperatures with equations that describe changes in mean base water potential as a function of temperature. Successful validation of these and other models demonstrates that equations based on laboratory data can be used to predict dormancy loss under widely fluctuating field conditions. Future progress may allow prediction of germination timing based on knowledge of intrinsic dormancy characteristics of a seed population and long-term weather patterns in the field.

scholarly journals Temperature but not moisture response of germination shows phylogenetic constraints while both interact with seed mass and lifespan

2017 ◽  
Vol 27 (2) ◽  
pp. 110-120 ◽  
Author(s):  
Fabien Arène ◽  
Laurence Affre ◽  
Aggeliki Doxa ◽  
Arne Saatkamp
Keyword(s):  
Water Potential ◽  
Seed Size ◽  
Phylogenetic Signal ◽  
Seed Mass ◽  
Base Temperature ◽  
Data Set ◽  
Negative Relation ◽  
Germination Timing ◽  
Germination Traits ◽  
Base Water Potential

AbstractUnderstanding how plant traits interact with climate to determine plant niches is decisive for predicting climate change impacts. While lifespan and seed size modify the importance of germination timing, germination traits such as base temperature and base water potential directly translate climatic conditions into germination timing, impacting performance in later life stages. Yet we do not know how base temperature, base water potential, seed mass, lifespan and climate are related. We tested the relationships between base temperature and base water potential for germination, seed size and lifespan while controlling for bioclimatic regions. We also quantified the phylogenetic signal in germination traits and seed size using Pagel's λ. We used a worldwide data set of germination responses to temperature and moisture, seed size and lifespan of 240 seed plants from 49 families. Both germination temperature and moisture are negatively related to seed size. Annual plants show a negative relation between seed size and base water potential, whereas perennials display a negative relation between base temperature and seed mass. Pagel's λ highlighted the slow evolution of base temperature for germination, comparable to seed mass while base water potential was revealed to be labile. In the future, base water potential and seed mass can be used when moisture niches of plants are to be predicted. Lifespan, seed size and base temperature should be taken into account when analysing thermal limits of species distributions.

scholarly journals Germination Parameters of Selected Summer Weeds: Transferring of the AlertInf Model to Other Geographical Regions

Agronomy ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 292
Author(s):  
Valentina Šoštarčić ◽  
Roberta Masin ◽  
Donato Loddo ◽  
Ema Brijačak ◽  
Maja Šćepanović
Keyword(s):  
Weed Management ◽  
Field Experiments ◽  
Chenopodium Album ◽  
Seedling Emergence ◽  
Amaranthus Retroflexus ◽  
Base Temperature ◽  
Time Model ◽  
Emergence Patterns ◽  
Geographical Regions ◽  
Base Water Potential

Effective weed management depends on correct control timing, which depends on seedling emergence dynamics. Since soil temperature and soil moisture are the two main factors that determine weed germination, the hydrothermal time model can be used to predict their emergence. The aim of this study was to estimate the base temperature (Tb) and base water potential (Ψb) for the germination of Chenopodium album, Amaranthus retroflexus, Setaria pumila, and Panicum capillare collected from fields in continental Croatia and then to compare these values with those of Italian populations embedded in the AlertInf model. Germination tests were performed at seven constant temperatures (ranging from 4 to 27 °C) and eight water potentials (0.00–1.00 MPa). The estimated Tb and Ψb were 3.4 °C and −1.38 MPa for C. album, 13.9 °C and −0.36 MPa for A. retroflexus, 6.6 °C and −0.71 MPa for S. pumila, and 11.0 °C and −0.87 MPa for P. capillare, respectively. According to the criterion of overlap of the 95% confidence intervals, only the Tb of C. album and the Ψb of A. retroflexus of the Croatian and Italian populations were similar. Further field experiments should be conducted to monitor the weed emergence patterns of C. album and calibrate the AlerInf equation parameters.

scholarly journals Base water potential for germination of radiata pine and buddleia seeds adjusts in response to time, seed-bed water potential and supra-optimal temperatures

2010 ◽  
Vol 14 ◽  
pp. 113-118
Author(s):  
M. Bloomberg ◽  
M.S. Watt
Keyword(s):  
Water Potential ◽  
Pinus Radiata ◽  
Radiata Pine ◽  
Time Model ◽  
Bed Temperature ◽  
Proposed Model ◽  
Ecological Implications ◽  
Asymptotic Function ◽  
Buddleia Davidii ◽  
Base Water Potential

Hydrothermal germination models are mathematical models which predict germination time of seeds for a specified seed-bed temperature (T) and water potential (Ψ). In this paper, the commonly observed decline in seed germination at supra-optimal temperatures is investigated by fitting a hydrothermal time model to germination data from two unrelated plant species (Buddleia davidii and Pinus radiata). For both these species, reduced germination rates and germination percentages above optimum temperatures (20°C and 25°C for P. radiata and B. davidii, respectively) were successfully modelled by an upward shift in the seeds' base water potential (Ψb) during germination. The upwards shift in Ψb was shown to be an asymptotic function of time to germination, but with the rate increased by higher temperatures and moister seed-bed conditions. The physiological and ecological implications of this proposed model of the observed decline in germination at supraoptimal temperatures are discussed. Keywords: hydrothermal, model, Pinus radiata, Buddleia davidii

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