Germination Phenology Research Articles

Seed Germination Strategies of Species With Restoration Potential in a Fire-Maintained Pine Savanna

Seed germination phenology studies are important tools for determining whether seeds exhibit dormancy and what environmental conditions trigger germination. Within longleaf pine (Pinus palustris Miller) ecosystems of the southeastern United States Coastal Plain, little is known about dormancy patterns and germination cues of the suite of native species composing the diverse fire-maintained ground cover vegetation. We used two methods to determine if several dominant or functionally important herbaceous species were capable of forming a persistent soil seed bank, including: (1) a germination phenology study and (2) a buried seed bag study. Results indicate that within species studied from three common families (Asteraceae, 2 species; Fabaceae, 8 species; and Poaceae, 3 species), species within the Fabaceae family seem most capable of forming long-term persistent seed banks. Although most of the Poaceae and Asteraceae species examined exhibited little dormancy in the germination phenology study, evidence from the buried seed bag study indicates that several species may form transient or even short-term persistent seed banks under favorable conditions. The absence of evidence of persistent seed banking potential for several dominant species examined in this study suggests that seed reintroduction will likely be a necessary component in restoration efforts in longleaf pine ecosystems.

Seed germination and dormancy in the medicinal woodland herbs Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae)

We used a double germination phenology or “move-along” experiment ( sensu Baskin and Baskin, 2003) to characterize seed dormancy in two medicinal woodland herbs, Collinsonia canadensis L. (Lamiaceae) and Dioscorea villosa L. (Dioscoreaceae). Imbibed seeds of both species were moved through the following two sequences of simulated thermoperiods: (a) 30/15 °C→20/10 °C→15/6 °C→5 °C→15/6 °C→20/10 °C→30/15 °C, and (b) 5 °C→15/6 °C→20/10 °C→30/15 °C→20/10 °C→15/6 °C→5 °C. In each sequence, seeds of both species germinated to high rates (>85%) at cool temperatures (15/6 and 20/10 °C) only if seeds were previously exposed to cold temperatures (5 °C). Seeds kept at four control thermoperiods (5, 15/6, 20/10, 30/15 °C) for 30 d showed little or no germination. Seeds of both species, therefore, have physiological dormancy that is broken by 12 weeks of cold (5 °C) stratification. Morphological studies indicated that embryos of C. canadensis have “investing” embryos at maturity (morphological dormancy absent), whereas embryos of D. villosa are undeveloped at maturity (morphological dormancy present). Because warm temperatures are required for embryo growth and cold stratification breaks physiological dormancy, D. villosa seeds have non-deep simple morphophysiological dormancy (MPD). Neither species afterripened in a 6-month dry storage treatment. Cold stratification treatments of 4 and 8 weeks alleviated dormancy in both species but C. canadensis seeds germinated at slower speeds and lower rates compared to seeds given 12 weeks of cold stratification. In their natural habitat, both species disperse seeds in mid- to late autumn and germinate in the spring after cold winter temperatures alleviate endogenous dormancy.

Seeds and seasons: interpreting germination timing in the field

This paper discusses how field and laboratory experiments, using a variety of genetic material, can be combined to investigate the genetic basis of germination under realistic ecological conditions, and it reviews some of our recent work on germination phenology ofArabidopsis thalianain the field. Our results indicate that the genetic basis of germination depends on the environment. In particular, the conditions during seed maturation interact with post-dispersal environmental factors to determine germination phenology, and these interactions have a genetic basis. Therefore genetic studies of germination need to consider carefully the environment – both during seed maturation and after dispersal – in which the experiments are conducted in order to characterize genetic pathways involved with germination in the field. Laboratory studies that explicitly manipulate ecologically relevant environmental factors can be combined with manipulative field studies. These studies can identify the particular environmental cues to which seeds respond in the field and characterize the genetic basis of germination responses to those cues. In addition, a variety of genetic material – including mutant and transgenic lines, intact natural genotypes, recombinant genotypes, and near isogenic lines – can be used in field studies as tools to characterize genetic pathways involved in germination schedules under natural ecological conditions.

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

Long-lived desert shrubs exhibit infrequent, episodic recruitment from seed. In spite of this long time scale, selection on life history attributes that affect seedling recruitment should be strong. We studied factors affecting germination phenology and seedling establishment for Coleogyne ramosissima, a dominant shrub species in the ecotone between warm and cold deserts in western North America. We also examined ecotypic differentiation in establishment strategy in response to selection regimes in two contrasting habitats. We followed patterns of dormancy loss, germination, emergence, and survival in reciprocal field experiments at warm winter Mojave Desert and cold winter Colorado Plateau study sites. Seed germination took place in late winter, under winter rain conditions at the warm desert site and under snow at the cold desert site. Distinctive germination phenologies for the two seed populations at contrasting field sites followed predictions based on laboratory germination experiments. There was no seed bank carryover across years. Seedling survival at the end of three growing seasons was remarkably high (mean survival 54%). Most seedling mortality was due to sprout predation by rodents early the first spring in unprotected caches. Emergence and establishment at each site were significantly higher for seeds from the local population, supporting the idea of ecotypic differentiation in establishment strategy. Establishment success was an order of magnitude greater overall at the Colorado Plateau site, which represents the leading edge of an upward elevational shift in distribution for this species under the current climatic regime. The Mojave Desert site is on the trailing edge of this shift, and recruitment there is apparently a much less frequent occurrence.

Ecophysiology of seed dormancy and germination in the mesic woodland herbaceous perennial Corydalis ambigua (Fumariaceae) in Japan

In Japan, the herbaceous perennial Corydalis ambigua Cham. et Schlecht. occurs in Tohoku and Hokkaido, where it grows in deciduous woodlands. Seeds have an underdeveloped embryo that is physiologically dormant at the time of dispersal in late May. In laboratory experiments, embryos did not grow when kept continuously at 5 °C or at alternating diurnal temperatures of 25/15 °C. However, following warm stratification at 25/15 °C, they grew at 15/5 °C and continued to do so at 0 °C. Radicles emerged after a relatively long period at 0 or 5 °C, following warm stratification at 25/15 °C and then incubation at 15/5 °C. Embryos began to develop in autumn in seeds under near-natural conditions in a metal frame-house, and they had grown to an average of about 90% of their full length by December. Beginning in December, the seed coat split, exposing the endosperm, and in March both the radicle and the cotyledon emerged under the snow or immediately after snow melt. Dormancy in seeds of C. ambigua is the same as that in seeds of Hydrastis canadensis L., which has been described as a special type of deep simple epicotyl morphophysiological dormancy.Key words: Corydalis ambigua, embryo growth, morphophysiological dormancy, seed germination phenology, underdeveloped embryo.

Phenology and life cycle of the annual, Chamaesyce maculata (L.) Small (Euphorbiaceae), with multiple overlapping generations in Japan

AbstractThe phenology of germination, vegetative growth and sexual reproduction in the annual Chamaesyce maculata (L.) Small (Euphorbiaceae) were investigated in a natural population in western Japan. Seedlings emerged from mid‐June to early October, with three peaks: mid‐June, late July and late August. Plants that emerged in June commenced sexual reproduction from late July, and thereafter both vegetative growth and sexual reproduction occurred together until early November, the plants showing no switching from vegetative growth to sexual reproduction. Seedlings that emerged in June and July suffered high mortality, but most seedlings that emerged from August onward survived until the reproductive stage. The minimum size for reproduction was largest for plants that emerged early in the season, and it decreased with a delay in seedling emergence. The late emergence of seedlings that resulted in low reproductive output may be to some extent compensated for by the increased probability of survival in the seedling stage. A transplant experiment clarified that C. maculata can repeat a maximum of three overlapping generations within a year. Multiple generations per year were attained by non‐dormant seeds produced in the first and second generations and clearly resulted in an increased reproductive output per year. The life cycle with multiple overlapping generations may have been acquired in habitats where unpredictable disturbance results in temporally unsuitable conditions for germination, vegetative growth and sexual reproduction of annual plants, but where suitable conditions frequently continue over a period longer than the single generation time of annual plants.

Differences in light and temperature responses determine autumn versus spring germination for seeds of Schoenolirion croceum

Seeds of the southeastern North American Schoenolirion croceum (Michx.) Wood are dormant when dispersed in late spring to early summer. Fresh seeds buried in soil after dispersal germinate in autumn, whereas those sown on the soil surface do so the following late winter – early spring. To understand this difference in germination phenology, we examined the light and temperature requirements for dormancy break and germination. Seeds germinated to high percentages in darkness over 12:12 h thermoperiods ranging from 15:6 to 35:20 °C following warm stratification (25:15 °C) in darkness, whereas no seeds germinated in light following stratification in light. On the other hand, seeds germinated to high percentages in light and in darkness following cold stratification (5 °C) in light or darkness. Seeds exposed to light during autumn germinated in winter–spring regardless of the light regime in summer or winter–spring, whereas those in darkness during autumn germinated in autumn regardless of the light regime in summer. Thus, light conditions during autumn are critical for determining whether seeds will germinate in autumn versus early spring. In contrast with many other species in which germination phenology is mostly temperature controlled, timing of germination for S. croceum depends on the light conditions in relation to temperatures experienced during dormancy release.Key words: dark, germination phenology, Hyacinthaceae, negative photoblastic seeds, photoecology, seed dormancy.

Habitat-correlated variation in blackbrush ( Coleogyne ramosissima: Rosaceae) seed germination response

Blackbrush is a dominant shrub species in the transition zone between North American warm and cold deserts. Its seeds are dormant at dispersal and lose dormancy in response to moist chilling. Seeds from warmer low-elevation habitats have shorter chilling requirements and a higher optimum chilling temperature than those from colder habitats where winter snow regularly occurs. This ecotypic variation functions to time germination optimally in habitats with contrasting chilling regimes. Regulation of germination phenology is an important feature of the life history of this ecotonal species, which must be able to migrate elevationally through recruitment from seed in response to long-term climatic shifts in order to survive.

Germination ecology of seeds of the annual weeds Capsella bursa‐pastoris and Descurainia sophia originating from high northern latitudes

SummaryLow temperatures may inhibit dormancy break in seeds of winter annuals, therefore it was hypothesized that seeds of Capsella bursa‐pastoris and Descurainia sophia that mature at high latitudes in late summer–early autumn would not germinate until they had been exposed to high summer temperatures. Consequently, germination would be delayed until the second autumn. Most freshly matured seeds of both species collected in August and September in southern Sweden were dormant. After 3 weeks of burial at simulated August (20/10°C) and September (15/6°C) temperatures, 28 and 27%, respectively, of the C. bursa‐pastoris and 56 and 59%, respectively, of the D. sophia seeds germinated in light at 15/6°C. In contrast, in germination phenology studies conducted in Sweden, only a few seeds of either species germinated during the first autumn following dispersal. However, there was a peak of germination of both species the following spring, demonstrating that dormancy was lost during exposure to the low habitat temperatures between late summer and early autumn and spring. Nearly 100% of the seeds of both species subjected to simulated annual seasonal temperature changes were viable after 30.5 months of burial. In the burial study, exhumed seeds of C. bursa‐pastoris were capable of germinating to 98–100% in light at the simulated spring–autumn temperature regime (15/6°C) in both spring and autumn, while those of D. sophia did so only in autumn. In early spring, however, seeds of D. sophia germinated to 17–50% at 15/6°C. Thus, most seeds of these two annual weeds that mature in late summer do not germinate in the first autumn, but they may do so the following spring or in some subsequent autumn or spring.

Ecological significance of seed germination characteristics in flood-meadow species

Summary In climate chamber and outdoor experiments we analysed germination traits of 42 vascular plant species typical of floodmeadows of the alliance Cnidion. In Central Europe such flood-meadows and their highly endangered character species are confined to large lowland river corridors with a dry and warm climate. Due to the prevailing ecological conditions, particularl y the extremely high variability in soil moisture potential, it was hypothesised that flood-meadow species exhibit specific strat egies in terms of germination phenology, temperature requirements and primary dormancy to avoid constraints on seedling recruitment imposed by flooding, drought and competition from established vegetation. Furthermore, we expected that germination characteristics could be a key for the causal understanding of range size, confinement to large river corridors, recent rarification processes, seed bank persistence and establishment success in restoration projects. PCA ordination of germination traits reflected a continuous gradient of increasing primary dormancy levels ranging from species with a high capacity for fast and almost complete germination over a wide range of temperatures to those with high and narrow temperature requirements and/or a delayed and asynchronous emergence. Many of the studied species germinated only at relatively high temperature in the year of shedding, but the primary conditional dormancy disappeared in most cases after a period of cold wet stratification. Requirements for chilling and/or high germination temperature were revealed to be the most common strategies for avoidance of harmful autumn and winter germination. The majority of the studied species tends to exploit particularly favourable regeneration niches in early spring. Surprisingly, many species with large long-term persistent soil se ed banks exhibited relatively low dormancy levels in light ; this was correlated with small seed size and a consequent higher probability of burial. We found no relationship between germination characteristics and river corridor confinement or Central European range size. However, there was a significant trend in endangered species towards higher temperature requirements and delayed, asynchronous germination. This is presumably disadvantageous under the environmental conditions of subcontinental flood-meadows.

Multiple mechanisms for seed dormancy regulation in shadscale (Atriplex confertifolia: Chenopodiaceae)

Shadscale (Atriplex confertifolia (Torr. & Frem.) Wats.) is a dominant shrub species of western North American deserts. Its one-seeded utricles are enclosed in bracteoles, and its seeds are highly dormant at dispersal. We examined the role of soluble inhibitors, bracteole effects, after-ripening, and chilling in regulating dormancy for six shadscale populations. Seeds in bracteole-enclosed fruits required chilling to become germinable, and the fraction responsive to chilling was small for recently harvested seeds. This fraction increased during dry storage for 24 weeks, but the rate of increase decreased asymptotically. After-ripening rate was an exponential function of storage temperature over the range 22–50°C. After-ripening models based on these nonlinear relationships for each of four seed populations accounted for 96% of the change in the chilling-responsive fraction during 3 years of laboratory storage. Rate of change in the chilling-responsive fraction during laboratory storage was log-linearly related to the chilling-responsive fraction for recently harvested seeds. Excision of utricles from recently harvested fruits increased the chilling-responsive fraction but did not generally eliminate the chilling requirement. Leaching or dewinging to remove soluble inhibitors increased germination of otherwise nondormant seeds but did not relieve primary dormancy. Knowledge of dormancy loss mechanisms will facilitate prediction of germination phenology and seed bank persistence for shadscale under fluctuating field conditions.Key words: after-ripening, germination, saltbush, soluble inhibitor, stratification, thermal time.

Ecological distribution and phenology of an invasive species, Cardamine hirsuta L., and its native counterpart, Cardamine flexuosa With., in central Japan

Abstract Cardamine hirsuta is a European species that was recently introduced into Japan and its wide distribution has been confirmed in the Kanto district. To understand mechanisms of the recent spread of C. hirsuta in Japan, a comparative study of the alien species and its native congeneric species, C. flexuosa, was conducted. Habitat preferences, phenology and seed germination were examined. Cardamine hirsuta and C. flexuosa showed distinctive habitat‐preferences; the former was most common in open habitats created by recent man‐made constructions, and the latter was common in rice paddy fields and surrounding areas. The results indicate that C. flexuosa is a year‐long annual, with a mixed phenology of summer and winter germination and growth. Seed dormancy during summer was relatively weak for C. flexuosa, and some plants that germinated early in summer reproduced during the same summer–autumn period. Plants that germinated in late summer and autumn behaved as winter annuals. In rice paddy fields, C. flexuosa is a winter annual because germination is prevented by submergence during summer. Plants flower during the following spring and complete their life cycle before the fields are flooded for rice cultivation. Cardamine hirsuta showed strong seed dormancy during summer and behaved as a typical winter annual. Seeds of C. hirsuta were intolerant to submergence in water, a condition that breaks seed dormancy of C. flexuosa. The results explain the absence of C. hirsuta from rice paddy fields. It was concluded that the spread of C. hirsuta is attributable to the recent expansion of urban habitats created by human activity and has occurred without direct competition with C. flexuosa. Considering recent urbanization in many areas, it is suggested that C. hirsuta has been spreading rapidly in Japan.

Propagating framework tree species to restore seasonally dry tropical forest: implications of seasonal seed dispersal and dormancy

One effective approach to forest restoration in degraded tropical forestland is the so-called ‘framework species method’ which involves planting 20–30 indigenous forest tree species to re-establish a basic forest structure that catalyses the recovery of biodiversity. For the seasonally dry tropical forests of Doi Suthep-Pui National Park in northern Thailand, a provisional list of 36 potential framework species was compiled, from 19 different families representing a broad spectrum of the tree flora. This paper examines the seed germination characteristics of these species when grown as a nursery ‘crop’ for planting to restore degraded sites, focussing on germination phenology and dormancy. It considers how such characteristics affect the first stage of nursery production from seed collection to pricking out seedlings in the nursery. Twenty-nine species had a germination percentage of 60% or greater, which is acceptable for nursery production. The median length of dormancy (MLD) ranged from 7 days in the case of Erythrina subumbrans to 219 days for Lithocarpus garrettianus. Germination was defined as rapid if the MLD occurred within 3 weeks, and slow if occurring after 12 weeks. Twelve species germinated rapidly and eight germinated slowly, the remainder being intermediate. Seedling emergence ranged over a period of 7 days in the case of Erythrina stricta and E. subumbrans to 322 days in the case of L. garrettianus.

Dormancy-breaking and germination requirements of seeds of fourLoniceraspecies (Caprifoliaceae) with underdeveloped spatulate embryos

AbstractDormancy-breaking requirements and types of dormancy were determined for seeds ofLonicera fragrantissimaLindl. & Paxt.,L. japonicaThunb.,L. maackii(Rupr.) Maxim. andL. morrowiiA. Gray. Seeds of all four species have underdeveloped spatulate embryos that are about 20–40%fully developed (elongated) when dispersed. Embryos in freshly matured, intact seeds grew better at 25/15°C than at 5°C. Gibberellic acid (GA3) (tested only in the light) was more effective in breaking dormancy inL. maackiiandL. morrowiithan inL. fragrantissimaandL. japonica. Warm- followed by cold stratification was required to break dormancy in seeds ofL. fragrantissima, whereas seeds ofL. japonicarequired cold stratification only. Thus, seeds ofL. fragrantissimahave deep simple morphophysiological dormancy (MPD) and those ofL. japonicanondeep simple MPD. About 50%of the seeds ofL. maackiirequired warm- or cold stratification only to come out of dormancy and 50% of those ofL. morrowiirequired warm stratification only, whereas the other 50% did not require stratification to germinate. Thus, about half of the seeds of the two species has nondeep simple MPD, and the other half has morphological dormancy (MD). In these laboratory tests, seeds ofL. japonica,L. maackii, andL. morrowiigenerally germinated to significantly higher percentages in light than in darkness; seeds ofL. fragrantissimawere not tested in darkness. Peaks of germination for seeds ofL. fragrantissima,L. japonica,L. maackiiandL. morrowiisown on a soil surface and covered withQuercusleaves under near-natural temperature conditions shortly after seed maturity and dispersal in late June 1997, late November 1997, early November 1996 and late June 1998, respectively, occurred in early March 1998, late February 1998, late March 1997 and early October 1998, respectively. The germination phenologies of seeds of the same species and seed lots buried in soil were similar to those of seeds under leaf litter. High percentages of seeds of all four species germinated both under litter (78–96%) and beneath the soil surface (78–97%). These germination patterns correspond closely with the requirements for embryo growth and dormancy break in the fourLoniceraspecies.

Dormancy-breaking and germination requirements for seeds ofDiervilla lonicera(Caprifoliaceae), a species with underdeveloped linear embryos

Dormancy-breaking requirements and type of dormancy were determined for seeds of Diervilla lonicera Mill. Seeds have an underdeveloped linear embryo that is about 35% of the length of the seed at maturity. Embryos (in intact seeds) grew at 25:15°C but not at 5°C. Up to 85% of the freshly matured seeds had morphological dormancy (MD), and thus, they germinated within about 30 days on a moist substrate in light at 30:15°C; a maximum of 3% of the seeds germinated in constant darkness. The other portion of fresh seeds had nondeep simple morphophysiological dormancy (MPD) and required a period of warm stratification or treatment with GA3to break dormancy. These seeds also required light to germinate. In contrast, cold stratification induced dormancy, and dry storage for up to 1 year did not effectively break dormancy. Seeds with MD germinated to significantly higher percentages on soil than on filter paper or on sand. Seeds sown on soil in a non-temperature-controlled greenhouse in mid-November germinated mostly in late May, whereas those sown in mid-April germinated in early May. Apparently, embryos of November-sown seeds were induced into physiological dormancy during winter. Thus, seeds had MPD in spring and needed several weeks of warm temperatures for dormancy break, embryo growth, and germination. This is the first report on seed dormancy in the genus Diervilla.Key words: embryo growth, germination phenology, Diervilla lonicera, morphological seed dormancy, morphophysiological seed dormancy, underdeveloped linear embryo.

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

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.

Seed germination patterns in green dragon (Arisaema dracontium, Araceae)

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as "vulnerable" with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3°C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings.

Ecological genetics of seed germination regulation in Bromus tectorum L. : I. Phenotypic variance among and within populations.

Regulation of seed germination phenology is an important aspect of the life history strategy of invading annual plant species. In the obligately selfing winter annual grass Bromus tectorum, seeds are at least conditionally dormant at dispersal in early summer and lose dormancy through dry-afterripening. Patterns of germination response at dispersal vary among populations and sometimes across years within populations. To assess the relative contribution of genotype and maturation environment to this variation, we grew progeny of ten parental lines from each of six contrasting populations in a common greenhouse environment. We then tested the germination responses of recently harvested seeds of the putative full-sib progeny at five incubation temperatures. Significant germination response differences among populations were observed in greenhouse cultivation, and major differences among full-sib families were evident for some populations and traits. Among-population variation accounted for over 90% of the variance in each trait, while within-family variance accounted for 1% or less. Germination responses of greenhouse-grown progeny were positively correlated with the responses of wild-collected seeds, but there was a tendency for lowered dormancy at higher incubation temperatures. This tendency was more marked in populations from cold desert, foothill, and plains habitats, suggesting a genotype-maturation environment interaction. Differences among populations in the amount of among-family variance were more evident at lower incubation temperatures, while among-family variance was more uniformly low at summer incubation temperatures. Populations from predictable extreme environments (subalpine meadow and warm desert margin) showed significantly less variation among families than populations from less predictable cold desert, foothill, and plains environments. Low among-family variance was not specifically associated with small population size or marginality of habitat, as small marginal populations from unpredictable environments showed variance as high as that of large populations. In populations with high among-family variance for germination traits, germination responses tended to be correlated across incubation temperatures, making it possible to characterize families in terms of their general dormancy status. The results indicate that seed germination regulation in this species is probably under strong genetic control, and that habitats with temporally varying selection are occupied by populations that tend to be more polymorphic in terms of their germination response patterns.

Effects of seed provenance on germination of herbs for agricultural compensation sites

The germination characteristics of European provenances of seven weed and grassland species which are used in agricultural compensation sites in Switzerland, for example on set-asides, were investigated along a W–E gradient (England, Germany, Switzerland, Hungary). In growth chambers the germination increment with temperature was different among the four main species and provenances tested. Consistently, the English provenances were least responsive. The germination rate of Silene alba increased most strongly with temperature, Daucus carota and Leucanthemum vulgare were intermediate, whereas Centaurea cyanus showed the lowest response to temperature. Germination of Daucus was enhanced by alternating temperatures, and this effect was significantly higher for the most distant provenances compared with the Swiss seeds. Also in Leucanthemum and Silene the foreign provenances showed a stronger effect of alternating temperatures, whereas seeds of Centaurea were not affected. In a common garden experiment Cichorium intybus, Daucus, Leucanthemum and Silene, but not Centaurea, revealed a trend towards lower germination with increasing distance of the provenance. Germination phenology of the different provenances varied in the above species and in Hypericum perforatum, except the arable weeds Centaurea and Papaver rhoeas. A principle component analysis confirmed that the overall variability among provenances was lowest in Centaurea, intermediate in Daucus and Leucanthemum, and highest in Silene. The results suggest provenance-specific adaptations which were partly correlated with the climate along the European gradient tested. Such adaptations can be used as an argument against the introduction of foreign seeds for ecological compensation sites.

Seed dormancy cycles and germination phenologies in sedges (Carex) from various habitats

Seeds (nutlets) of four temperate-zone perennialCarex species from various habitats and with different growth forms were investigated to identify seasonal germination patterns. In the first experiment, freshly matured seeds were sown in summer 1994 on the soil surface and at a depth of 1 cm at a sunexposed site and under a leaf canopy in an experimental garden. In the second experiment, seeds were exhumed after various periods of burial (7-cm depth) for up to 30 months and tested for germination in both light and darkness at 15°, 25°, and 22/10°C. In the first experiment, freshly-matured seeds of the four sedges did not germinate during summer or autumn 1994. Almost all surface-sown seeds of the four species germinated from late spring to summer in 1995 at the sun-exposed site. Most buried seeds of three species germinated in the soil, but germinants died prior to emergence. InCarex flacca, however, about 50% of the buried seeds germinated and emerged until 1997, and the ungerminated seeds remained viable. At the shaded site, seeds ofC. acutiformis. andC. flacca did not germinate, whereas a small percentage of the buried and surface-sown seeds ofC. arenaria andC. extensa emerged in the second year. Seeds ofC. acutiformis andC. flacca were dormant, and those ofC. arenaria andC. extensa were conditionally dormant at the beginning of the second experiment. All four species had annual dormancy cycles at 22/10°C in light and in darkness and at 25° and 15° in light. Seeds came out of dormancy in late autumn or winter and re-entered dormancy or conditional dormancy in late spring or early summer. Very few seeds of any of the four species germinated at constant temperatures in darkness. No seeds germinated during burial in soil at a depth of 7 cm. These field germination patterns indicate that the four sedges have the potential to form a persistent seed bank but that losses due to germination in the seed bank are dependent on temperature amplitudes, mean temperatures, and red: far red ratios under a leaf canopy.