Loss Of Dormancy Research Articles

An Update on the Role of NCED and CYP707A ABA Metabolism Genes in Seed Dormancy Induction and the Response to After-Ripening and Nitrate

The molecular mechanisms underlying the regulation of seed dormancy and sensu stricto germination once dormancy is removed are still largely unknown. The hormone abscisic acid (ABA), through a complex crosstalk with other plant hormones, transcription factors and cellular signals belonging to the development program, directly controls the induction and maintenance of primary seed dormancy. A working hypothesis is that loss of primary dormancy and induction of germination requires that the severe control exercised by ABA during seed maturation is down-modulated and is replaced by different signaling pathways. Therefore, it is reasonable to speculate that both ABA metabolism and/or a decrease in ABA sensitivity is operative. The ABA-metabolic NCED and CYP707A gene families are considered key for several developmental plant processes that are ABA-controlled, including seed development and sensu stricto germination. Hence, we propose that ABA metabolism and sensitivity are involved in the mechanisms of action of after-ripening (AR), a process which overcomes the seed primary dormancy status. This review summarizes the current knowledge in the last decade on the controlling role of the NCED and CYP707A gene families as well as changes in ABA sensitivity during the seed life cycle. The expression of ABA-metabolic genes and seed sensitivity to ABA during AR and in the presence of nitrate are also considered.

Inter- and intra-specific variability in seed dormancy loss and germination requirements in the Lavatera triloba aggregate (Malvaceae)

Background and aims – The genus Lavatera is comprised of perennial and annual species that grow in different ecosystems such as coastal cliffs, plains, endorheic lagoons and ditches. In this study, we compared the seed germination ecology of three phylogenetically related taxa: L. agrigentina, L. triloba subsp. pallescens and L. triloba subsp. triloba, all of which belong to the L. triloba aggregate (section Glandulosae) and grow on chalky plains, limestone cliffs and endorheic lagoons with clayey sediments. Methods – For each taxon, the effects of seed scarification and dry after-ripening (90 days at 25°C) on seed dormancy loss and of light and temperature (constant 5 to 25°C and alternating 25/10°C) on seed germination were evaluated. Key results – Scarification allowed water imbibition and subsequent seed germination, indicating physical dormancy (PY) for all three investigated taxa. In addition, dry after-ripening positively affected seed germination in L. agrigentina, thus, seeds of this species have combinational dormancy [physical (PY) + physiological (PD)]. Light did not affect the final germination in any of the taxa. The germination response to incubation temperatures varied among the taxa, suggesting ecological adaptations, with the highest germination in the range of 10–20°C for L. agrigentina and L. triloba and 5–15°C for L. pallescens. Interpopulation variability in final germination was detected for both L. agrigentina and L. triloba subsp. triloba and in germination rate only for L. agrigentina. Conclusions – The three Lavatera taxa differed in their germination requirements, and these could be related to the habitat/ecology of each taxon. Our results suggest that seeds of the three taxa can germinate in the field from autumn to spring, when conditions are favourable for seedling establishment in the Mediterranean climate.

Storage Humidity and Temperature Affect Dormancy Loss and Viability of Tanglehead (Heteropogon contortus) Seeds

Tanglehead (Heteropogon contortus) is a drought- and fire-tolerant native Hawaiian grass that possesses seed dormancy on shedding. Although a dry after-ripening period is known to break dormancy, specific storage conditions to optimize this are not known. This study examined the effects of storage temperature and equilibrium relative humidity (eRH) on tanglehead seed dormancy loss and viability. Fresh seeds harvested in Mar. and Oct. 2011 were stored for 30 days in three eRH levels (12%, 50%, and 75%) and then incubated for 0, 1, 3, 6, 9, and 12 months at three temperatures [10, 20 (ambient in laboratory), and 30 °C]. The eRHs were maintained during incubation by sealing seeds in airtight packages. Seed germination and tetrazolium tests were conducted after each incubation period to determine dormancy loss and seed viability. Analysis of germination and seed viability data indicated a significant interaction among eRH, storage temperature, incubation period, and seed harvest month. Storage at 12% eRH and 30 °C for 12 months optimized dormancy loss of tanglehead seeds. Seeds remained viable in all eRH and temperature combinations except those stored at either 75% eRH and 20 °C or 75% eRH and 30 °C. In these treatment combinations, significant seed deterioration and loss of viability were recorded. Harvest time (i.e., harvest month) within the year also affected the rate of dormancy loss of seeds. March-harvested seeds achieved maximum dormancy loss 3 months earlier than seeds harvested in October.

Thermal time model ofSolanum sarrachoidesgermination

AbstractA population-based modelling approach was used to predict the occurrence of germination inSolanum sarrachoides(SOLSA) for different treatments. Seeds collected in Toledo (Spain) were exposed to constant temperatures, to temperatures alternating between 10 and 30°C and to gibberellins (GAs; 0, 50, 100, 150 and 1000 ppm) during a 24-h imbibition period. The following parameters were measured: base temperature (Tb), mean thermal time (θT(50)) and the standard deviation of thermal time (σθT). The SOLSA seeds only germinated at constant temperatures when the highest GA concentration was applied. The thermal model suggests that the induction and loss of physiological dormancy following seed dispersal is achieved when temperatures vary and when a mean thermal time of 66 growing degree-days (d°C) and aTbvalue of 16°C are achieved when no GA treatment was added. The concentration of GA applied under conditions of alternating temperatures has an additive effect, reducing θT(50) up to threefold, from basal level (66 d°C) to 19.40 d°C, when the 1000 ppm GA treatment was applied. In this last case, the germination was accelerated by reducingTbto 14°C. A 5–10°C change in temperature and a range of average temperatures of 20–27.5°C promoted the germination of SOLSA seeds to the greatest extent in the absence of GA. However, these conditions are not frequently encountered in the irrigated areas of the studied region; this finding could explain the limited ability of SOLSA to expand its range within this area.

Dormancy-breaking and germination requirements for seeds of Acacia papyrocarpa, Acacia oswaldii and Senna artemisioides ssp.×coriacea, three Australian arid-zone Fabaceae species

Physical dormancy is common in seeds of arid-land legumes. Improved understanding of germination requirements of hard-seeded species will further our understanding of arid lands and aid restoration projects. We studied the germination responses of Acacia papyrocarpa (Benth.), A. oswaldii (F.Muell) and Senna artemisioides (Gaudich. ex DC.) Randell ssp. × coriacea (Benth.) Randell from a chenopod shrubland in South Australia. Imbibition testing indicated that all three species had physical dormancy, but the proportion of dormant seeds was lower in A. oswaldii. This corresponded to a thinner testa in this species. Mechanisms tested to scarify seeds included mechanical scarification and different durations of wet or dry heat. Mechanically scarified seeds germinated readily, reaching maximum numbers in 10–15 days, independently of incubation temperatures, with the exception of S. artemisioides seeds, which germinated at a slower rate in cooler temperatures. Overall, wet heat was more effective than dry heat to alleviate physical dormancy, whereas dry heat in some cases resulted in seed mortality. On the basis of these results, it is recommended that seeds of A. papyrocarpa and S. artemisoides be pretreated with wet heat in future restoration programs. No pre-treatment is required for dormancy loss in A. oswaldii seeds. The different responses of seeds of these species suggest that their populations have varying strategies for persistence in this unpredictable environment.

Tumor dormancy and the neuroendocrine system: an undisclosed connection?

Tumor dormancy is a poorly understood phenomenon conceptualized as a protracted quiescent state during which cancer cells are present but clinical disease is not apparent, a condition referred to as "cancer without disease" by Folkman. Examples include the incidental detection of occult in situ tumors in post-mortem organ analysis and cancer recurrence after long disease-free periods. Lack of angiogenic competency has been proposed as a major determinant of the fate of dormant tumors. Other proposed processes include establishment of homeostatic equilibrium between tumor cells and the host's immune system response and a non-permissive microenvironment for tumor growth. Recent cellular and molecular studies suggest that neuroendocrine mediators regulate the biology of tumor progression and act as endogenous modulators of angiogenesis, inflammation, and other molecular processes involved in tumor reactivation from dormancy. We review experimental and clinical evidence and propose that neuroendocrine dynamics of the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis might contribute to the loss of tumor dormancy.

CHANGES IN ABA LEVELS IN VEGETATIVE AND FLOWER BUDS DURING DORMANCY IN CAMELLIA

Camellia japonica L. is an evergreen acidophilic perennial, member of Theaceae Mirb. (Theales), that includes more than 3,000 named cultivars of great ornamental value. Bud dormancy is a key adaptive trait during the annual cycle of overwintering temperate woody plants and is present in Camellia. There is sufficient evidence that abscisic acid (ABA) is responsible for the initiation and, in a number of species, also for the maintenance of endodormancy. Increase of endogenous ABA is generally observed at the onset of endodormancy, while loss of bud dormancy is linked to declining ABA levels. To deepen our understanding of the role of ABA in C. japonica during dormancy, both vegetative and flower buds were studied. In a first experiment, we assessed the seasonal dynamics of ABA in vegetative buds from the onset of dormancy to its release. In this case, the results described a complex type of response, with several peaks of ABA in the middle of dormancy, and a major peak followed by a drastic reduction right before dormancy release of the vegetative bud. The second experiment concerned the quantification of ABA in flower buds during a cold treatment (7°C) performed after dormancy onset. Here, the results indicated a clear downward trend of flower buds ABA levels in response to increasing periods at constant low temperatures. Overall, morphological and physiological data confirmed the critical role of cold in the release of endodormancy in camellia. Future studies concerning the release of bud dormancy and correlated ABA levels in response to cold should focus on a wide range of C. japonica cultivars. This could allow selection of genotypes that bloom later in spring on the one hand (garden camellias) or genotypes that can be easily forced in flowering (flowering pot plants) on the other hand. This knowledge could also be exploited in breeding programs.

Seed Dormancy and Seedling Recruitment in Smooth Barley (Hordeum murinum ssp. glaucum) Populations in Southern Australia

Weedy barley species have emerged as important weeds in southern Australia, where they can be particularly difficult to control in cereal crops. Knowledge of seed dormancy mechanisms, germination ecology, and recruitment behavior in the field would facilitate development of effective weed-control programs for these weed species. Based on somatic chromosome number, smooth barley was identified as the species infesting all the sites sampled in South Australia. Smooth barley populations from cropping fields and noncrop habitats showed large differences in their pattern of dormancy loss. Noncrop populations (EP2, EP3, and MN2) rapidly lost dormancy during dry after-ripening and showed 70 to 95% germination at 3 mo after maturity. Five populations collected from cropping fields (EP1, EP4, EP5, MN1, and MN3), on the other hand, showed < 30% germination, even at 8 mo after maturity, when germination was assessed at 20/12 C day/night temperatures. These dormant, smooth barley populations from cropping fields were found to be highly responsive to cold stratification, with germination increasing in response to the duration of the treatment. Germination of dormant, smooth barley populations increased with the addition of gibberellic acid (0.001 M GA3), but only when lemma and palea had been removed. Recruitment behavior of smooth barley in the field was influenced by the population and the tillage system. A nondormant population, collected from a long-term pasture (MN2), showed high seedling emergence (> 90%) during autumn, which was well before planting of the winter crop (lentil). In contrast, the other three populations sampled from cropping fields showed very little seedling establishment (< 10%) before crop planting, which would make them difficult to control in cereals because there are no selective herbicides available for the control of weedy barley species. There was a significant seeding system by emergence time interaction (P < 0.001), which was reflected in greater in-crop, smooth barley plant densities under zero-till than under conventional tillage and no-till systems.

Ecophysiology of embryo development and seed germination of the European woodland herbaceous perennial Corydalis cava (L.) Schweigg. & Körte subsp. cava (Fumariaceae)

AbstractIn this study we examined the germination ecology with special reference to the temperature requirements for embryo development and germination of Corydalis cava subsp. cava, under both outdoor and laboratory conditions. Corydalis cava is a spring flowering woodland tuberous geophyte widely distributed across Europe. Germination phenology, including embryo development and radicle and cotyledon emergence, was investigated in a population growing in northern Italy. Immediately after harvest, seeds of C. cava were sown both in the laboratory under simulated seasonal temperatures and naturally. Embryos, undifferentiated at the time of seed dispersal, grew during summer and autumn conditions, culminating in radicle emergence in winter, when temperatures fell to ca 5°C. Cotyledon emergence also occurred at ca 5°C, but first emergence was delayed until late winter and early spring. Laboratory experiments showed that high (summer) followed by medium (autumn) and low temperatures (winter) are needed for physiological dormancy loss, embryo development and germination respectively. Unlike seeds of C. cava that germinated in winter, in other Corydalis species radicle emergence occurred in autumn (C. flavula) or did not depend on a period of high summer temperature to break dormancy (C. solida). Our results suggest that subtle differences in dormancy and germination behavior between Corydalis species could be related to differences in their geographical distribution.

CLINAL VARIATION IN SEED TRAITS INFLUENCING LIFE CYCLE TIMING INARABIDOPSIS THALIANA

Early life-history transitions are crucial determinants of lifetime survival and fecundity. Adaptive evolution in early life-history traits involves a complex interplay between the developing plant and its current and future environments. We examined the plant's earliest life-history traits, dissecting an integrated suite of pregermination processes: primary dormancy, thermal induction of secondary dormancy, and seasonal germination response. We examined genetic variation in the three processes, genetic correlations among the processes, and the scaling of germination phenology with the source populations' climates. A spring annual life history was associated with genetic propensities toward both strong primary dormancy and heat-induced secondary dormancy, alone or in combination. Lineages with similar proportions of winter and spring annual life history have both weak primary dormancy and weak thermal dormancy induction. A genetic bias to adopt a spring annual strategy, mediated by rapid loss of primary dormancy and high thermal dormancy induction, is associated with a climatic gradient characterized by increasing temperature in summer and rainfall in winter. This study highlights the importance of considering combinations of multiple genetically based traits along a climatic gradient as adaptive strategies differentiating annual plant life-history strategies. Despite the genetic-climatic cline, there is polymorphism for life-history strategies within populations, classically interpreted as bet hedging in an unpredictable world.

Seed Dormancy and Adaptive Seedling Emergence Timing in Giant Ragweed (Ambrosia trifida)

Giant ragweed germination is delayed by both a physiological dormancy of the embryo (embryo dormancy) and an inhibitory influence of embryo-covering structures (covering structure-enforced [CSE] dormancy). To clarify the roles of embryo and CSE dormancy in giant ragweed seedling emergence timing, we conducted two experiments to address the following objectives: (1) determine changes in germinability for giant ragweed dispersal units (hereafter “involucres”) and their components under natural burial conditions, and (2) compare embryo and CSE dormancy alleviation and emergence periodicity between successional and agricultural populations. In Experiment 1, involucres were buried in crop fields at Columbus, OH, periodically excavated, and brought to the laboratory for dissection. Involucres, achenes, and embryos were then subjected to germination assays at 20 C. In Experiment 2, temporal patterns of seedling emergence were determined at a common burial site. Reductions in embryo and CSE dormancy were compared with controlled-environment stratification followed by germination assays at 12 and 20 C, temperatures representative of soil conditions in spring and summer. Results indicated that overwinter dormancy loss involved sequential reductions in embryo and CSE dormancy. CSE dormancy, which may limit potential for fatal germination during fall, was caused by the pericarp and/or embryo-covering structures within the pericarp. In Experiment 2, successional populations emerged synchronously in early spring, whereas agricultural populations emerged throughout the growing season. Levels of embryo dormancy were greater in the agricultural populations than the successional populations, but CSE dormancy levels were similar among populations. In 12 C germination assays, embryo dormancy levels were positively correlated with time required to reach 95% cumulative emergence (run 1:r= 0.81, P = 0.03; run 2:r= 0.76, P = 0.05). These results suggest that late-season emergence in giant ragweed involves high levels of embryo dormancy that prevent germination at low temperatures in spring.

The influence of chilling requirement on the southern distribution limit of exotic Russian olive (Elaeagnus angustifolia) in western North America

Russian olive (Elaeagnus angustifolia L.), a Eurasian tree now abundant along rivers in western North America, has an apparent southern distribution limit running through southern California, Arizona, New Mexico and Texas. We used field observations to precisely define this limit in relation to temperature variables. We then investigated whether lack of cold temperatures south of the limit may prevent the accumulation of sufficient chilling, inhibiting dormancy loss of seeds and buds. We found that Russian olive occurrence was more strongly associated with low winter temperatures than with high summer temperatures, and results of controlled seed germination and vegetative bud-break experiments suggest that the chilling requirements for germination and bud-break are partly responsible for the southern range limit. Both seed germination proportion and germination time decreased under conditions simulating those south of the range limit. Similarly, percentage bud break decreased when chilling dropped below values typical of the range limit. In 17–65% of the years from 1980 to 2000, the chilling accumulated at a site near the range limit (El Paso, TX) would lead to a 10% or more decrease in bud-break. The potential decline in growth could have large fitness consequences for Russian olive. If climate change exhibits a warming trend, our results suggest the chilling requirement for bud-break of Russian olive trees will not be met in some years and its southern range limit may retreat northward.

Projected soil temperature increase and seed dormancy response along an altitudinal gradient: implications for seed bank persistence under climate change

Background and aims Understanding the mechanistic effects of climate change on species key life-history stages is essential for predicting ecological responses. In fire-prone regions, long-term seed banks allow post-fire recovery and persistence of plant populations. For physically dormant species, seed bank longevity depends on the maintenance of dormancy which is controlled primarily by temperature. Successful inter-fire recruitment is rare and dormancy loss between fires produces a net loss to the seed bank. We assessed whether temperature increases related to climate change can affect seed dormancy and, potentially, seed bank longevity.

Effects of light conditions and after‐ripening time on seed dormancy loss of Bromus diandrus Roth.

Del Monte JP & Dorado J (2011). Effects of light conditions and after‐ripening time on seed dormancy loss of Bromus diandrus Roth. Weed Research51, 581–590.SummaryBromus diandrus is an emerging problem in barley crops in temperate climates, owing to its ability to adapt to certain farming techniques, as well as the absence of an efficient means of control. The aim of this study was to evaluate the germination of B. diandrus as a function of light conditions, time after ripening, temperature and water potential. Our results indicate that light conditions were the principal factor affecting germination and that seeds had negative photoblastism. Darkness modified the hydrotime parameters of the seeds somewhat, for example, by decreasing the values of Ψb and by favouring dormancy loss. The after‐ripening time significantly modified the hydrotime parameters of the seeds, causing Ψb to drift towards more negative values (greater dormancy loss) as the after‐ripening time increased. The combination of both variables explains the dormancy dynamics of this species in Mediterranean climates that are characterised by two distinct germination flushes, coinciding with two periods when soil humidity and temperature are not limiting. The first and main cohort of seedlings would emerge in autumn, originating from young buried seeds. A second cohort would emerge in the spring, from mature seeds on the surface of the soil.

Progress in research on dry afterripening

AbstractThe transition from the dormant to the non-dormant state of a viable and mature seed can take place at low hydration by exposure to air-dry storage conditions (dry afterripening; AR). The events occurring during this loss of dormancy are of considerable physiological, ecological and agricultural interest. AR may be attributable to increased sensitivity to germination-stimulating factors and a widening of the temperature window for germination. Genetic, –omics and physiological studies on this mode of dormancy breaking provide support for a key role of the balance between gibberellin (GA) and abscisic acid (ABA) metabolism and sensitivity. Recent evidence also supports a possible role for ethylene (ET) in this complex signalling network that is necessary for AR implementation. However, hormone-independent signals, such as reactive oxygen species (ROS), nitrate (NO _{3}^{ - }) or nicotinamide adenine dinucleotide (NAD+), also appear to be involved. The way in which hormone- and non-hormone-signalling pathways affects each other (cross-talk) is still under study. This review provides updated information on the programmes that overcome seed dormancy. Thus, we have reviewed: (1) the –omic status in dry seeds; (2) the relationship between temperature and nitrate signalling and AR; (3) alterations in ABA/GA synthesis and signalling; (4) the action of hormone molecules other than ABA and GA (i.e. ET, salicylic and jasmonic acids); and (5) participation of reactive oxygen species (ROS), NAD+and protein carbonylation. Taken together, the acquisition and implementation of dry AR involve a complex signalling network that is difficult to disentangle.

Detecting karrikinolide responses in seeds of the Poaceae

The smoke-derived chemical karrikinolide commonly triggers seeds in the Brassicaceae, Solanaceae and Asteraceae families to germinate, yet species in the Poaceae – another major understorey and weed family – have responded to the chemical with mixed results. This study aimed to understand why some grass species respond to karrikinolide while others do not. Using a field-based seed-burial trial, dose-response experiment, and stratification experiment, we investigated whether karrikinolide could alleviate dormancy and trigger seeds to germinate for seven global agronomic weeds: Avena fatua L., Lolium rigidum Gaudin, Eragrostis curvula (Schrad.) Nees, Phalaris minor Retz., Hordeum glaucum Steud., Ehrharta calycina Sm. and Bromus diandrus Roth. Seeds of A. fatua were consistently stimulated to germinate with karrikinolide in all experiments, whether seeds were freshly collected or dormancy had been partially alleviated. In contrast, seeds of L. rigidum failed to respond to karrikinolide when the seeds were fresh, after-ripened in the laboratory, and even during natural dormancy loss in the field. Interestingly, although karrikinolide did not stimulate freshly collected E. curvula seeds to germinate, it hastened dormancy loss when applied during stratification. These findings are helpful for understanding the responses of grass species following fire. They also contribute to a growing body of research aimed at using karrikinolide as a tool for triggering uniform germination of seeds for enhancing restoration efforts and depleting the weed seed bank.

Role of relative humidity, temperature, and water status in dormancy alleviation of sunflower seeds during dry after-ripening.

The effect of various combinations of temperature and relative humidity on dormancy alleviation of sunflower seeds during dry after-ripening was investigated. The rate of dormancy alleviation depended on both temperature and embryo moisture content (MC). Below an embryo MC of 0.1 g H2O g−1 dw, dormancy release was faster at 15 °C than at higher temperatures. This suggests that dormancy release at low MC was associated with negative activation energy, supported by Arrhenius plots, and low Q10 values. At higher MC, the rate of dormancy alleviation increased with temperature, correlating well with the temperature dependence of biochemical processes. These findings suggests the involvement of two distinct cellular mechanisms in dormancy release; non-enzymatic below 0.1 g H2O g−1 dw and associated with active metabolism above this value. The effects of temperature on seed dormancy release above the threshold MC were analysed using a population-based thermal time approach and a model predicting the rate of dormancy alleviation is provided. Sunflower embryo dormancy release was effective at temperatures above 8 °C (the base temperature for after-ripening, TbAR, was 8.17 °C), and the higher the after-ripening temperature above this threshold value, the higher was the rate of dormancy loss. Thermodynamic analyses of water sorption isotherms revealed that dormancy release was associated with less bound water and increased molecular mobility within the embryonic axes but not the cotyledons. It is proposed that the changes in water binding properties result from oxidative processes and can, in turn, allow metabolic activities.

A combined physical and physiological dormancy controls seasonal seedling emergence of Geranium robertianum

Temperate forest herbs with seeds exhibiting both a physical and a physiological dormancy mechanism are rare, and knowledge on the factors regulating germination of these species is fragmentary. The biennial Geranium robertianum L. grows mainly in temperate woodlands, but can also be found in exposed habitats. Seedlings of G. robertianum are known to emerge from spring until autumn, but little is known about the environmental factors regulating germination. In this study, phenology of seedling emergence and of physical dormancy loss was examined for seeds buried at shaded or sunny exposed locations. The role of temperature in regulating dormancy and germination was analysed by incubating seeds in temperature sequences simulating temperatures that seeds experience in nature. The results indicate that most seeds of G. robertianum buried in sunny conditions germinate immediately after physical dormancy loss in summer. Seeds buried in shaded conditions also lose physical dormancy mainly during summer, but remain physiologically dormant and do not germinate until late winter or early spring. Besides physical dormancy, seeds of G. robertianum also initially have a high level of physiological dormancy, which is reduced during dry storage. Physiological dormancy is reduced through chilling in winter, thus enabling the seeds to germinate at low temperatures. We conclude that a complex combination of physical and physiological dormancy ensures that G. robertianum seeds germinate in summer at exposed sites and in early spring at shaded sites.

An after‐ripening thermal‐time model for Lithospermum arvense seeds based on changes in population hydrotime parameters

Chantre GR, Sabbatini MR & Orioli GA (2010). An after‐ripening thermal‐time model for Lithospermum arvense seeds based on changes in population hydrotime parameters. Weed Research50, 218–227.Summary Lithospermum arvense seeds show primary physiological dormancy. Changes in population hydrotime parameters during after‐ripening were used to model primary dormancy loss. Lithospermum arvense seeds were dry‐stored at constant temperatures of 5, 15, 24 and 30°C for 180 days. After different storage periods, seeds were incubated at 10°C at a range of water potentials (0 to −1.2 MPa). Experimentally obtained cumulative–germination curves were analysed by repeated probit regressions to obtain seed population hydrotime parameters. The population mean base water potential (Ψb(50)) showed a progressive decrease as after‐ripening time progressed and the dormancy release rate was positively related to storage temperature. The hydrotime constant (θH) and the SD of the base water potential (σΨb) were unaffected by after‐ripening time or storage temperature. To account for the effect of after‐ripening time and temperature on dormancy release, an after‐ripening thermal‐time model was developed. The model consisted of the description of Ψb(50) changes as a function of an after‐ripening thermal‐time index (θAT). An exponential decay function accurately described (R2 = 0.92) the decrease pattern of Ψb(50) as function of θAT. Model evaluation under fluctuating soil water regimes showed a good correlation between observed and predicted data (r = 0.94 and 0.96). This indicated that the after‐ripening process could be adequately described as a thermal‐time response, further suggesting the potential applicability of the model to predict L. arvense emergence in the field.

Predicting changes in dormancy level in natural seed soil banks

The possibility of accurately predicting timing and extent of seedling emergence from natural seed soil banks has long been an objective of both ecologist and agriculturalist. However, as dormancy is a common attribute of many wild seed populations, we should first be able to predict dormancy changes if we intend to predict seedling emergence in the field. In this paper, we discuss the most relevant environmental factors affecting seed dormancy of natural seed soil banks, and present a conceptual framework as an attempt to understand how these factors affect seed-bank dormancy level. Based on this conceptual framework we show approaches that can be used to establish quantitative functional relationship between environmental factors regulating dormancy and changes in the seed-bank dormancy status. Finally, we briefly explain how we can utilize population-based threshold models as a framework to characterize and quantify changes in seed sensitivity to environmental factors as a consequence of dormancy loss and/or induction.