Annual dormancy cycles in buried seeds of shrub species: germination ecology of Sideritis serrata (Labiatae)

The germination ecology of Sideritis serrata was investigated in order to improve ex‐situ propagation techniques and management of their habitat. Specifically, we analysed: (i) influence of temperature, light conditions and seed age on germination patterns; (ii) phenology of germination; (iii) germinative response of buried seeds to seasonal temperature changes; (iv) temperature requirements for induction and breaking of secondary dormancy; (v) ability to form persistent soil seed banks; and (vi) seed bank dynamics. Freshly matured seeds showed conditional physiological dormancy, germinating at low and cool temperatures but not at high ones (28/14 and 32/18 °C). Germination ability increased with time of dry storage, suggesting the existence of non‐deep physiological dormancy. Under unheated shade‐house conditions, germination was concentrated in the first autumn. S. serrata seeds buried and exposed to natural seasonal temperature variations in the shade‐house, exhibited an annual conditional dormancy/non‐dormancy cycle, coming out of conditional dormancy in summer and re‐entering it in winter. Non‐dormant seeds were clearly induced into dormancy when stratified at 5 or 15/4 °C for 8 weeks. Dormant seeds, stratified at 28/14 or 32/18 °C for 16 weeks, became non‐dormant if they were subsequently incubated over a temperature range from 15/4 to 32/18 °C. S. serrata is able to form small persistent soil seed banks. The maximum seed life span in the soil was 4 years, decreasing with burial depth. This is the second report of an annual conditional dormancy/non‐dormancy cycle in seeds of shrub species.     

Temperature controls seed germination and dormancy in the European woodland herbaceous perennial Erythronium dens-canis (Liliaceae)

We examined the germination ecology and the temperature requirements for germination of Erythronium dens-canis, under both outdoor and laboratory conditions. E. dens-canis is a spring flowering woodland geophyte widely distributed across Europe. Germination phenology, including embryo development and radicle and cotyledon emergence, were investigated in a natural population growing in Northern Italy. Immediately after harvest, seeds of E. dens-canis were either sown on agar in the laboratory under simulated seasonal temperatures or placed in nylon mesh sachets and buried in the wild. Embryos, undifferentiated at the time of seed dispersal, grew during summer and autumn conditions in the laboratory and in the wild, culminating in radicle emergence in winter when temperatures fell to ≈ 5 °C. Emergence of cotyledons did not occur immediately after radicle emergence, but was delayed until the end of winter. Laboratory experiments showed that temperature is the main factor controlling dormancy and germination, with seeds becoming non-dormant only when given warmth, followed by cold stratification. Unlike seeds of E. dens-canis that germinate in winter, in other Erythronium species radicle emergence occurs in autumn, while in some it is delayed until seeds are transferred from winter to spring conditions. Our results suggest that there is genetic and environmental control of the expression of seed dormancy amongst Erythronium species, which is related to local climate.     

Cyclic dormancy,temperature and water availability control germination of Carrichtera annua,an invasive species in chenopod shrublands

Abstract We studied the germination of seeds of Carrichtera annua L. from a single cohort, stored in the field for up to 18 months, when retrieved at different times and subject to different combinations of temperature and water availability. Germination was affected by season of retrieval, and temperature and water availability in a complex interactive way. Germination rates were lowest when seeds were retrieved during summer or spring, but seeds germinated readily when retrieved during autumn and winter, if exposed to temperatures simulating autumn or winter conditions, and provided water equivalent to at least 50% field capacity. High temperatures and low water availability reduced germination substantially. The results indicate that this species has a combination of cyclic dormancy and germination requirements that minimizes the risk of germination during periods when the risk of prereproductive mortality is high. Given the short life of the seeds of this species, these mechanisms may be essential for the persistence of the species in the highly unpredictable arid lands of southern Australia.     

Does cold stratification level out differences in seed germinability between populations?

Populations of seeds can vary greatly in their dormancy-breaking and germination characteristics. The purpose of this study was to determine if such dormancy differences are levelled out by cold stratification. Seeds of 33 annual weed species, each represented by three populations, were tested in light and darkness 7 weeks after harvest and after two stratification treatments: 18 weeks at 3 °C in the laboratory and 19 weeks outdoors in soil during winter. Cold stratification removed population differences in some species, but in several species such differences became apparent only after stratification. This happened either because dormancy became stronger in weakly dormant seeds (winter annuals) or weaker in strongly dormant seeds (summer annuals). In several species, the light requirement for germination increased after stratification. These results clearly indicate that germination tests performed on fresh seeds from a single population may not adequately predict germination percentages in the field.     

The dual role of temperature in the regulation of the seasonal changes in dormancy and germination of seeds of Polygonum persicaria L.

Summary The role of temperature in the regulation of seasonal changes in dormancy and germination was studied in seeds of Polygonum persicaria. Seeds were buried in the field and under controlled conditions. Portions of seeds were exhumed at regular intervals and germination was tested over a range of conditions. Seeds of P. persicaria exhibited a seasonal dormancy pattern that clearly showed the typical features of summer annuals, i.e. dormancy was relieved at low winter temperatures, the germination peak occurred in spring and dormancy was re-induced in summer. The expression of the dormancy pattern was influenced by the temperature at which germination was tested. At 30°C exhumed seeds germinated over a much longer period of the year than at 20° or 10°C. Nitrate added during the germination test occasionally stimulated germination. The seasonal changes in dormancy of buried seeds were regulated by the field temperature. Soil moisture and nitrate content did not influence the changes in dormancy. The fact that, on the one hand, field temperature determined the changes in dormancy and, on the other hand, germination itself was influenced by temperature, was used to describe the seasonal germination pattern of P. persicaria with a model. Germination of exhumed seeds in Petri dishes at field temperature was accurately described with this model. Germination in the field was restricted to the period where the range of temperatures over which germination could proceed (computed with the model) and field temperature overlapped.     

Accumulation of buried seeds and establishment of ruderal therophytic communities in disturbed habitat,central Japan

The establishment and maintenance mechanisms of pioneer communities were investigated in ruderal habitats under two disturbance regimes, frequent and infrequent cutting sites. In the infrequent cutting sites, large perennials dominated through the year and inhibited the invasion of annuals, and the perennial community succeeded to forest stage if the cutting was stopped. In the frequent cutting sites, therophytic communities of winter and summer annuals alternated by season. Fresh seeds of both winter and summer annuals are dormant, but they have different germination times and thus can share the same sites in different seasons. Wind-dispersed biennials and large perennials have nondormant seeds and easily invade the sites; however, they are unable to mature to reproductive phase due to recurrent cuttings. The therophytic species, which can complete their life-cycle in a period between cuttings, accumulate seeds in the soils and are maintained by these buried seeds (seed bank annuals) during recurrent disturbances. The seed bank is compensation for the dispersal inefficiency of seed bank annuals. After abandonment of the frequent cutting sites, the buried seeds of seed bank annuals germinate and become the first-year pioneers. Thus, seed bank annuals are not invasive colonizers but are the remnants of the ruderal weed communities before abandonment.     

Temperature effects on dormancy levels and germination in temperate forest sedges (Carex)

The effects of stratification temperatures and burial in soil on dormancy levels of Carex pendula L. and C. remota L., two spring-germinating perennials occurring in moist forests, were investigated. Seeds buried for 34 months outdoors, and seeds stratified in the laboratory at temperatures between 3 and 18 °C for periods between 2 and 28 weeks, were tested over a range of temperatures. Seeds of the two species responded similarly to stratification treatments, except for an absolute light requirement in C. pendula. Primary dormancy was alleviated at all stratification temperatures, but low temperatures were more effective than higher ones . (≥ 12 °C). Dormancy induction in non-dormant seeds kept at 5 °C occurred when seeds were subsequently exposed to 18 °C. Dormancy was not induced by a transfer to lower temperatures. Buried seeds of both species exhibited seasonal dormancy cycles with high germination from autumn to spring and low germination during summer. Temperatures at which the processes of dormancy relief and of dormancy induction occurred, overlapped to a high degree. Whether, and when, dormancy changes occurred depended on test conditions. The lower temperature limit for germination (> 10%) was 9 °C in C. remota and 15 °C in C. pendula. Germination ceased abruptly above 36 °C. Germination requirements and dormancy patterns suggest regeneration from seed in late spring and summer at disturbed, open sites (forest gaps) and the capability to form long, persistent seed banks in both species.     

Life history traits of the pseudometallophyte Thlaspi caerulescens in natural populations from Northern Europe

We examined recruitment, survival, life cycle and fecundity of two metallicolous (M, on metalliferous calamine soils) and two non-metallicolous (NM, on normal soils) populations of Thlaspi caerulescens in Belgium and Luxemburg. In each population, permanent plots were monitored over two reproductive seasons. In M populations, plots were located in two contrasting environments (grass versus grove) in order to test the influence of vegetation cover on life strategy. Our results show that the monocarpic life cycle is dominant in all populations of T. caerulescens. However the length of the pre-reproductive period varies from several months (winter annuals) to 1 year or more (perennials), and is partly related to plant origin (M versus NM). Most plants growing in metalliferous environments were annuals, whereas NM plants were mostly perennials. These differences in life cycle were related to differences in survival during summer, which was better in NM than in M populations. Within each M population, different survival conditions and life cycles were observed according to vegetation cover. Plants growing in grass areas were mostly annuals and had a low survival rate in summer whereas grove plants were mostly perennials and survived better in summer. Our results suggest the selection of stress avoiders (shortening of life cycle) in M populations of T. caerulescens but only for individuals growing in grass areas. Summer survival seems to play a key role in selection of life strategy in T. caerulescens.     

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

In 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.     

Seed Germination Biology of the Narrowly Endemic Species Lesquerella stonensis (Brassicaceae)

Abstract Lesquerella stonensis (Brassicaceae) is an obligate winter annual endemic to a small portion of Rutherford County in the Central Basin of Tennessee, where it grows in disturbed habitats. This species forms a persistent seed bank, and seeds remain viable in the soil for at least 6 years. Seeds are dormant at maturity in May and are dispersed as soon as they ripen. Some of the seeds produced in the current year, as well as some of those in the persistent seed bank, afterripen during late spring and summer; others do not afterripen and thus remain dormant. Seeds require actual or simulated spring/summer temperatures to come out of dormancy. Germination occurs in September and October. Fully afterripened seeds germinate over a wide range of thermoperiods (15/6–35/20°C) and to a much higher percentage in light (14 h photoperiod) than in darkness. The optimum daily thermoperiod for germination was 30/15°C. Nondormant seeds that do not germinate in autumn are induced back into dormancy (secondary dormancy) by low temperatures (e.g., 5°C) during winter, and those that are dormant do not afterripen; thus seeds cannot germinate in spring. These seed dormancy/ germination characteristics of L. stonensis do not differ from those reported for some geographically widespread, weedy species of winter annuals and thus do not help account for the narrow endemism of this species.     

Seed germination of exotic and native winter annuals differentially responds to temperature and moisture,especially with climate change scenarios

Seeds of winter annuals require a summer after-ripening period for dormancy loss and low autumn temperatures for germination. With current and future changes in moisture and temperature, we tested the effects of warming along a relative humidity (RH) gradient on dormancy loss and effects of decreased diurnal temperature range (DTR) on germination. We further reasoned that the effects of changes in these variables would be disproportionate between the exotic and native winter annuals. Seeds of exotic species (Buglossoides arvensis, Lamium purpureum and Ranunculus parviflorus) and co-occurring native species (Galium aparine, Paysonia stonensis and Plantago virginica) were collected in middle Tennessee. After-ripening occurred over a 15–100% RH gradient at 25 and 30°C and germination was tested at 20/10 and 20/15°C. Niche breadth was calculated using Levins' B. Fresh Ranunculus seeds had high germination and those of other species did not. Germination for these species increased with after-ripening, mostly across the RH gradient irrespective of temperature. A decrease in DTR showed mixed results – the extreme being Ranunculus with no germination at 20/15°C. Most exotic species had wider germination niche breadths than native species. With climate change, we suggest that a decrease in DTR may have a larger effect on germination than increasing moisture or warming on dormancy break. Moreover, there is not a clear-cut winner with climate change when we compare exotic versus native species because the responses of our six species were species specific.     

GERMINATION ECOLOGY OF SEDUM PULCHELLUM MICHX. (CRASSULACEAE)

Factors controlling the timing of seed germination were investigated in the small succulent winter annual Sedum pulchellum Michx. (Crassulaceae) in its natural habitat on unshaded limestone outcrops in northcentral Kentucky. At maturity in early July the dormant seeds are not dispersed but are retained in the fruits on the standing dead plants until September and October. Many, but not all, of the seeds afterripen in the fruits during summer, and at the time of dispersal some of them are dormant and some are nondormant. Germination and annual population establishment occur in September and October from seed reserves that have been in the soil for one or more years and from seeds produced in the current year. Germination of nondormant seeds may be prevented in autumn by lack of the appropriate combination of environmental factors including light, temperature and soil moisture in the seed's microsite. The effect of low winter temperatures on ungerminated seeds in the population is to induce nondormant seeds into secondary dormancy and to prevent afterripening of dormant seeds. Thus, in spring all the seeds in the population's seed reserve are dormant. During spring and summer some of these seeds afterripen, and they germinate in autumn when, and if, germination requirements are fulfilled.     

Dormancy and the fire-centric focus: germination of three Leucopogon species (Ericaceae) from South-eastern Australia

BACKGROUND AND AIMS: Germination studies of species from fire-prone habitats are often focused on the role that fire plays in breaking dormancy. However, for some plant groups in these habitats, such as the genus Leucopogon (Ericaceae), dormancy of fresh seeds is not broken by fire cues. In the field, these same species display a flush of seedling emergence post-fire. Dormancy and germination mechanisms therefore appear complex and mostly unknown. This study aimed to identify these mechanisms by establishing dormancy class and testing the effects of a set of typical germination cues, including those directly related to fire and entirely independent of fire. METHODS: To classify dormancy, we assessed seed permeability and embryo morphology, and conducted germination experiments at seasonal temperatures in incubators. To test the effects of fire cues on germination, factorial combinations of smoke, heat and dark treatments were applied. Ageing treatments, using burial and seasonal incubation, were also tested. Germination phenology was established. KEY RESULTS: Seeds were dormant at release and had underdeveloped embryos. Primary dormancy of the study species was classified as morphophysiological. Seasonal temperature changes overcame primary dormancy and controlled timing of germination. Fire cues did not break primary dormancy, but there was a trend for smoke to enhance germination once this dormancy was overcome. CONCLUSIONS: Despite the fact that fire is a predominant disturbance and that many species display a flush of emergence post-fire, seasonal temperatures broke the primary physiological dormancy of the study species. It is important to distinguish between fire being responsible for breaking dormancy and solely having a role in enhancing levels of post-fire germination for seeds in which dormancy has been overcome by other factors. Biogeographical evidence suggests that morphological and physiological factors, and therefore seasonal temperatures, are likely to be important in controlling the dormancy and patterns of post-fire germination of many species in fire-prone regions.     

Hydrothermal thresholds for seed germination in winter annual forbs from old‐field Mediterranean landscapes

• Under Mediterranean climates with dry‐hot summers and cool‐wet winters, many forbs with potential for habitat restoration are winter annuals, but there is little information about their germination.
• We performed laboratory germination experiments on 13 ruderal dicots native to Andalusia (southern Spain). We measured the germination of recently harvested seeds from natural populations across nine temperature treatments (from 5 to 35 °C, constant and alternate); two storage periods; and eight water stress treatments (from 0 to ?1.0 MPa). We then calculated the hydrothermal thresholds for seed germination.
• Final germination ranged from 0–100% and results were mixed in response to temperature. Base temperature was below 6 °C, optimal temperature was around 14 °C and the ceiling temperature around 23 °C. For five species, 10 months of storage improved total germination, indicating a dormancy‐breaking effect, but the other species did not respond or had their germination reduced. All species were relatively tolerant to water stress, with base water potential ranging from ?0.8 to ?1.8 MPa.
• Our results suggest that hydrothermal germination thresholds, rather than physiological dormancy, are the main drivers of germination phenology in annual forbs from Mediterranean semi‐dry environments. The variation in germination responses of these forb species differs from winter annual grasses, but their seeds are all suitable for being stored before restoration.

     

Vegetation development on deposit soils starting at different seasons

Permanent plots were created in different seasons (autumn and spring) and filled with two substrates: nutrient-rich topsoil and nutrient-poor ruderal soil (n = 5 for each treatment). My objectives were to assess the influence of starting season on initial species composition, whether differences at the start cause divergent or convergent pathways of succession and which mechanisms are operating during vegetation development. Mean species richness (number of species per plot) and mean total cover of herb layer differed significantly between substrates and changed significantly during 10 year succession, but there were no significant differences with respect to starting season. However, seasonal as well as substrate effects were evident for particular dominant species and for the pattern of successional sequences. When succession on topsoil plots started in spring, first summer annuals dominated, then monocarpic and polycarpic perennial herbs, then herbaceous perennials together with woody perennials, and at the end of the decade woody perennials. When succession started in autumn, polycarpic perennial herbs dominated from the beginning, and then were replaced by woody perennials in the second half of the decade. On ruderal soil, there was a less rapid but continuous increase of polycarpic perennial herbs and woody species, both on spring and on autumn plots, whereas short-lived plants were more abundant in the first years and then decreased. Species turnover was very high from the first to the second year for all treatments (except topsoil plots starting in autumn), but slowed down during succession. Priority effects due to starting season caused high dissimilarity at the start on the nutrient-rich substrate, but convergent succession towards the end of the first decade. The main mechanisms during early succession on the nutrient-rich topsoil were tolerance based on different life-history traits and inhibition due to reduced light availability. There was no evidence for obligate facilitation. However, an indirect facilitative effect by annuals, which slowed the development of herbaceous perennials down, and thus facilitated growth of woody species, could be seen on topsoil when succession started in spring.     

The comparative germination ecology of nine Rumex species

The germination requirements, dormancy cycle and longevity of nine Rumexspecies were studied in field conditions and laboratory experiments to show theadaptations of the related species to their specific habitat. Within one genus,rather striking differences were observed in germination ecology. However, theclosely related species, R. acetosa and R.scutatus, are very similar: they fruit in early summer; theirseeds can germinate immediately after dispersal, and they are nondormant andshort-lived. R. acetosella also has fruits insummer, but the seeds do not germinate the first season after dispersal. Theyare long-lived, but buried seeds do not show a dormancy cycle; they mightgerminate in different seasons after exposure to light. Seeds of four species (R. conglomeratus,R. maritimus, R. sanguineus andR. crispus) are long-lived and undergo aseasonal dormancy cycle, with a low level of dormancy in winter and early springand a deep dormancy in summer as was already known for R.obtusifolius. These seeds are shed in the autumn, and they germinatemainly in the spring in consecutive years. R. maritimusalso germinates in summer and autumn on drying muddy soils. The seeds of R. hydrolapathum only germinate onwaterlogged soils, which explains its growth at the edge of streams and ponds.Its seeds are rather short-lived. The seeds of the species on very wetplaces require a higher temperature for germination.     

ENVIRONMENTAL CONTROL OF SEED GERMINATION IN THLASPI ARVENSE (CRUCIFERAE)

The effect of environmental conditions during storage and imbibition on germination was investigated in field pennycress (Thlaspi arvense L.), a weed species that can behave as a winter or a summer annual. Freshly harvested seeds of an inbred line with a cold requirement for flowering exhibited primary dormancy that was rapidly lost following 1 month of afterripening in a dry state. Nondormant seeds were positively photoblastic. The light effect was mediated through phytochrome since germination was promoted by red light and inhibited by far red light. Seedling emergence was also inhibited by light filtered through a canopy of wheat leaves. Germination of field pennycress seeds was considerably more sensitive to moisture stress than two sympatric species, wild oat (Avena fatua L.) and wheat (Triticum aestivum L., cv. ERA). Seeds of the latter two species were chosen in order to compare the effect of water potential on germination in field pennycress with that in sympatric species. It was concluded that the major environmental factor limiting nondormant field pennycress seeds on the soil surface was water availability. Imbibition of fully afterripened seeds at low temperatures (6 C) induced a deep secondary dormancy. In contrast to primary dormancy, cold-induced dormancy was not alleviated by red light, alternating temperatures (21/5 C), or 2 months of dry storage at 6, 15, or 35 C. However, exogenous gibberellin A₃ or 24 weeks of dry storage resulted in germination in cold-induced dormant seeds. Secondary dormancy was not observed in fully afterripened seeds that were preincubated at 21 C for 1 or 2 days prior to the cold treatment. These results may explain the failure in field experiments to observe the cold-induced secondary dormancy that limits spring emergence in other winter annuals (J. Baskin, C. Baskin, Weed Res. 1979 19: 285–292).     

Is Ginkgo biloba (Ginkgoaceae) really an oviparous plant?

Germination of Ginkgo biloba seeds with intact and removed sarcotesta was compared to test the role of the seed coat in germination biology. The presence of an intact sarcotesta significantly reduced total germination percentage when compared to seeds with the sarcotesta removed. Some seeds were also cold stratified. This treatment was not necessary for germination, but it did improve total germination percentage. The seeds were collected during the period of natural abscission. Contrary to the accepted literature, we found that Ginkgo seeds contain well-developed embryos at the time of dispersal. These data demonstrate that the seed coat contributes to winter dormancy of G. biloba, and that the phenology of this species is less primitive than popularly believed.     

Temperature Response Pattern during Afterripening of Achenes of the Winter Annual Krigia oppositifolia (Asteraceae)

Abstract Freshly-matured achenes of Krigia oppositifolia Raf. were buried in soil at near-natural temperatures for 0–35 months and then exhumed and tested in light and darkness at (12/12 hr) daily thermoperiods of 15/6, 20/10, 25/15, 30/15 and 35/20°C. Achenes required light for germination and exhibited an annual dormancy/nondormancy cycle, being dormant in spring and nondormant in autumn. High summer temperatures (30/15, 35/20°C) fully promoted afterripening, whereas low temperatures (5, 15/6°C) prevented it. As buried seeds came out of dormancy in summer, they first germinated at medium temperatures (20/10, 25/15°C), but with additional afterripening the maximum and minimum temperatures for germination increased and decreased, respectively. Thus, during afterripening, achenes exhibit type 3 temperature responses, which otherwise are known only in two perennial Asteraceae and one perennial Liliaceae. The physiological responses of achenes of K. oppositifolia are unlike those of most winter annuals, which have type 1 responses—i.e., the maximum temperature for germination increases during afterripening. Also, they are unlike the majority of Asteraceae, which have type 2 responses—i.e., the minimum temperature for germination decreases during afterripening. Type 1 responses, typical of most winter annuals, have yet to be reported in the Asteraceae.     

Seed dormancy and germination of the European Chaerophyllum temulum (Apiaceae), a member of a trans-Atlantic genus

BACKGROUND AND AIMS: The European Chaerophyllum temulum and two North American Chaerophyllum species have a trans-Atlantic disjunct distribution. This work aimed to resolve requirements for dormancy break and germination of C. temulum seeds and to compare dormancy traits with those of the two North American congeners. METHODS: Phenology of germination and embryo growth was studied by regularly exhuming seeds sown in natural conditions. Temperature requirements for embryo growth, breaking of dormancy and germination were determined by incubating seeds under controlled laboratory conditions. Additionally the effect of GA(3) on germination was tested to determine the specific dormancy type. KEY RESULTS: In natural conditions, embryo growth starts in early winter. Seedlings emerge in late winter shortly after the embryos reached the critical ratio for embryo length to seed length (E : S) of approx. 0.95. Growth of the embryo only occurs during a prolonged incubation period at 5 degrees C. After stratification at 5 degrees C, which breaks physiological and morphological dormancy, seeds can germinate at a wide range of temperatures. GA(3) did not substitute for cold stratification in seeds placed at 23 degrees C. CONCLUSIONS: Chaerophyllum temulum has deep complex morphophysiological dormancy. This dormancy type differs considerably from that of the two North American congeners.