Dormancy cycles in buried seeds of three perennial Xyris (Xyridaceae) species from the Brazilian campo rupestre

• Dormancy cycles are an important mechanism for avoiding seed germination under unfavourable periods for seedling establishment. This mechanism has been scarcely studied in tropical species. Here, we studied three tropical and perennial species of Xyris, X. asperula, X. subsetigera and X. trachyphylla, to investigate in situ longevity and the existence of seasonal seed dormancy cycles.
• Seeds of three species of Xyris were buried in their natural habitat, with samples exhumed bimonthly for 18 months. Germination of exhumed seeds was assessed under a 12‐h photoperiod over a broad range of temperatures. Seeds of X. trachyphylla were also subjected to treatments to overcome secondary dormancy.
• Seeds of all species are able to form a persistent seed bank and exhibit seasonal changes in germinability. Secondary dormancy was acquired during the rainy summer and was overcome during the subsequent dry season (autumn/winter). Desiccation partially overcomes secondary dormancy in X. trachyphylla seeds.
• Soil seed bank persistence and synchronisation of seed germination under favourable conditions for seedling establishment contribute to the persistence and regeneration of X. asperula, X. subsetigera and X. trachyphylla in their natural environment.

     

Field fate of Amaranthus patulus seeds subjected to leaf-canopy inhibition of germination

Summary The germination of seeds of Amaranthus patulus Bertol., is known to be sensitive to leaf-transmitted light. Seeds were enclosed in transparent polyester-mesh envelopes and placed horizontally in 10-cm deep soil or on the soil surface, beneath a closed vegetation cover in the field. Changes in the numbers of firm intact seeds and of germinable seeds were traced for up to 3 years by periodical retrievals and germination tests. Rapid loss of germinable seeds, mainly due to germination, was observed in the buried seed population, in which only 20% of seeds maintained their germinability after 1 year, and a negligible number after 3 years. In contrast, the seeds placed on the soil surface maintained germinability relatively well: over 80% of seeds remained germinable after 1 year and a low percentage still preserved their germinability after 3 years. Assuming exponential decay in germinability, the decay rates on and in the soil were calculated from the data of the 1-year experiment to be 0.21 and 0.84 year^-1 respectively. The fate of seeds that were exposed to canopy light on the soil for a month and then buried was shown to be almost the same as that of the seeds which had been continuously in 10-cm deep soil. Correspondingly, the possibility of the induction of secondary (induced) dormancy by exposure to canopy light was excluded in a laboratory experiment, in which it was found that the imbibed seeds suffering leaf-canopy inhibition of germination exuded some diffusible germination inhibitor responsible for apparent dormancy. Estimation of numbers of A. patulus in the seed bank of an early successional field showed that 3,500 seeds/m² remained in the soil to the depth of 10 cm after 3 years' exclusion of the species following the production of 700,000 seeds/m², by a population explosively established after experimental induction of secondary succession.     

Altitudinal and climatic associations of seed dormancy and flowering traits evidence adaptation of annual life cycle timing in Arabidopsis thaliana

The temporal control or timing of the life cycle of annual plants is presumed to provide adaptive strategies to escape harsh environments for survival and reproduction. This is mainly determined by the timing of germination, which is controlled by the level of seed dormancy, and of flowering initiation. However, the environmental factors driving the evolution of plant life cycles remain largely unknown. To address this question we have analysed nine quantitative life history traits, in a native regional collection of 300 wild accessions of Arabidopsis thaliana. Seed dormancy and flowering time were negatively correlated, indicating that these traits have coevolved. In addition, environmental–phenotypic analyses detected strong altitudinal and climatic clines for most life history traits. Overall, accessions showing life cycles with early flowering, small seeds, high seed dormancy and slow germination rate were associated with locations exposed to high temperature, low summer precipitation and high radiation. Furthermore, we analysed the expression level of the positive regulator of seed dormancy DELAY OF GERMINATION 1 (DOG1), finding similar but weaker altitudinal and climatic patterns than seed dormancy. Therefore, DOG1 regulatory mutations are likely to provide a quantitative molecular mechanism for the adaptation of A. thaliana life cycle to altitude and climate.     

Effect of maternal nitrogen and drought stress on seed dormancy and germinability of Amaranthus retroflexus

Amaranthus retroflexus L. is an importunate annual weed in many cropping systems of different countries. The main aim of this study was to investigate the effects of maternal nitrogen and drought stress on the seed dormancy and germinability of A. retroflexus. Field experiment was carried out in a factorial based on randomized complete block design, with four potential levels of soil water (–2, ?6, ?8 and ?10 bar) and three levels of nitrogen (0, 100 and 200 kg/ha). The germination characteristics of the seeds were measured at three different times (1 month, 6 months and 1 year after harvesting). Results showed that drought stress had positive effects on breaking of A. retroflexus seed dormancy until 6 months after seed harvesting. Seeds that were developed under severe water stress exhibited the highest germination percentage and germination rate. The results obtained from this study revealed that application of 100 kg/ha nitrogen during seed development increases germinability of A. retroflexus, whereas application of 200 kg/ha nitrogen induced seed dormancy. Furthermore, 100 kg/ha nitrogen application in the field along with 200 ppm gibberellic‐acid treatment during seed after‐ripening showed the highest germination percentage and germination rate for seeds after 6 months harvesting. Results also indicated that after‐ripening significantly increased seed germination and germination rate of A. retroflexus. These findings indicate that long‐term management of the soil seed bank in this species requires more stringent control due to the changes in germination timing, as detected in this study.     

Seed dormancy and longevity in <Emphasis Type="Italic">Stipa tenacissima</Emphasis> L. (Poaceae)

In the present paper we studied the life history traits related to seed germination of Stipa tenacissima, a key species in semiarid environments of western Mediterranean areas. S. tenacissima is a perennial tussock grass, which has traditionally been considered to expand mainly by vegetative propagation with little or no sexual reproduction. We analysed seed longevity as well as the type of seed dormancy and the role of the seed covers from seeds collected from different populations in SE Spain. We also studied the variation in seed germinability among populations, individuals, and years and the ability of seeds of S. tenacissima to form soil seed banks. There was significant variation in seed germination among individuals, populations and years. Lemma and palea were the main factor controlling these differences since their removal promoted higher and faster germination and eliminated the differences in germination parameters among populations. However, the control of dormancy by lemma and palea was independent of their weight, suggesting that their chemical nature plays a more important role than does size in controlling seed germination. Mechanical scarification treatments (via abrasion with sand) did not affect seed germination. The decay in seed germinability two years after seed collection and the low density of viable seeds in soils one year after seed dispersal indicated that S. tenacissima forms transient soil seed banks.     

Avian gut-passage effects on seed germination of shrubland species in Mediterranean central Chile

Effects of avian gut-passage on seed germination are important to assess the effectiveness of frugivores in woodland regeneration, particularly in biodiversity hotspots that have a high incidence of avian frugivory. We examined the effect of avian gut-passage on seed germination in contrast to seeds that remain uneaten in five shrub species in Mediterranean central Chile and sought to determine the physiological mechanism(s) by which seed germinability is modified. Germination assays were conducted in a glasshouse for five common shrub species of the sub-Andean matorral: Azara dentata (Flacourtiaceae), Schinus polygamus and Schinus molle (Anacardiaceae), Cestrum parqui (Solanaceae), and Maytenus boaria (Celastraceae). We estimated germinability (final percent germination), dormancy length (time from sowing to first germination), mean length of dormancy of all germinated seeds, and contrasted germination rates of defecated versus manually extracted and pulp-enclosed seeds. Avian gut-passage increased seed germinability in four of the five shrub species studied—primarily through deinhibition via pulp removal. Minimum dormancy length was not modified by avian gut-passage for A. dentata, but was significantly shorter for S. molle and C. parqui. Mean dormancy length was significantly shorter in gut-passed seeds of A. dentata, S. molle and M. boaria. Avian gut-passage greatly enhanced the seed germination rates of three species, A. dentata, S. molle and C. parqui. We conclude that the positive effects of birds on seed germination facilitate the regeneration of sub-Andean shrublands, and that bird declines due to landscape change may impair recovery rates of successional or restored areas due to dispersal limitation.     

Patterns of seed persistence in South African fynbos

In fire-prone communities such as fynbos, many species rely on regeneration from seed banks in the soil. Persistent seed banks are particularly important for species with life spans shorter than the average fire cycle, in order to counter local extinction. Persistent seed banks also give potential for restoring ecosystems following disturbances such as alien plant invasion. This study investigated the seed persistence patterns of 25 perennial species, representing several growth forms and life histories, during a three-year burial. Long-term persistence (i.e., seed bank half-life exceeding two years) was found in the hard-seeded Fabaceae and Pelargonium, and the nut-fruited Proteaceae. In this group, germinability was low and dormancy increased further following burial, resulting in a highly viable, dormant seed bank after three-year's burial. A second group with potentially long-term persistent seeds includes four taxa (Pseudopentameris, Passerina, Elegia and Restio) that either have low germinability or develop secondary dormancy following burial. Dormancy in the latter group was partially countered by exposure to smoke-seed primer. Of the small-seeded species, only two Erica species with high initial dormancy had long-term persistent seed banks. The other species mostly displayed high initial germinability and short-term persistent seed banks (i.e., seed bank half-life less than two years). This group included taxa with short to medium life-spans (Syncarpha, Roella) that were expected to have long-term persistent seeds in order to buffer against local extinction following average to long fire-return intervals. We hypothesize that light may play a role in overcoming secondary dormancy in those species, and could have resulted in an underestimate for seed persistence in this study. Alternatively, those short to medium life-span species persist via inter-fire recruitment in gaps or long-distance dispersal (of the smallest seed). No correlations were found between seed persistence and seed mass or variance in seed dimensions. Nor was a correlation found between seed persistence and phenol concentration. In fynbos, seed burial of larger seeds by ants and rodents are major processes that operate in conjunction with passive burial of small seeds. Selection for persistence can be expected to operate across all seed sizes and shapes in fire-prone communities.     

PHYSIOLOGICAL ECOLOGY OF GERMINATION OF VIOLA RAFINESQUII

Seeds of the winter annual Viola rafinesquii Greene exhibit true dormancy at the time of maturity and dispersal in mid to late spring. During the summer rest period the seeds pass from a state of true dormancy to one of relative dormancy and finally to what may be called a state of complete nondormancy. As the seeds enter relative dormancy they will germinate mostly at relatively low temperatures (10, 15, 15/6, and 20/10 C), but as after-ripening continues they gain the ability also to germinate at higher temperatures (20, 25, and 30/15 C). During June, July, and August seeds will not germinate at field temperatures even if kept continuously moist. But by September and October seeds may germinate to high percentages over a wide range of temperatures, including September and October field temperatures. This pattern of germination responses, involving breaking of true dormancy and widening of the temperature range for germination during relative dormancy, appears to be an adaptation of the species to a hot, dry season. Seeds of V. rafinesquii stored on continuously wet soil (field capacity) or on soil that was alternately wet and dried during the summer did not after-ripen at low temperatures (10, 15, 15/6, and 20/10 C) but did after-ripen fully at high temperatures (20, 25, 30/15, and 35/20 C). Thus, the high temperatures that V. rafinesquii “avoids” by passing the summer in the dormant seed stage actually are required to break seed dormancy and, therefore, are essential for completion of its life cycle.     

Dormancy Release,Germination, and Electrolyte Leakage from Apple Embryos during Stratification in the Presence of Sucrose

The dynamics of dormancy release during the stratification of apple (Malus domestica Borkh.) seeds was quantitatively described by three characteristics of seeds germination: the percentage of seeds that germinated by the tenth day, mean germination time, and the sum of seeds germinated in each of ten days (Timson's parameter), which allowed the assessment of the viability, the rate of dormancy release, and seed heterogeneity. We showed that apple seeds were characterized by a combined (physical and physiological) type of dormancy, with the seed coat and the embryo envelope being involved in the maintenance of physical dormancy. The addition of sucrose to the stratification medium accelerated the release of seed dormancy and improved all characteristics that determine seed germinability. Electrolyte leakage from embryos hardly changed during stratification, which agrees with the fact that all seeds remained viable throughout the entire period of dormancy. We assume that the release of seed dormancy is not a single-stage process.     

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.     

Seed germination ecology of the annual grass Leptochloa panicea ssp. mucronata and a comparison with L. panicoides and L. fusca

Leptochloa panicea ssp. mucronata is an annual grass that grows in relatively dry habitats. Requirements for dormancy loss and germination were determined for seeds of this species and compared to those of two species from wet habitats. Seeds of L. panicea were dormant at maturity in autumn, but when exposed to actual or simulated autumn temperatures (e.g. 20/10, 15/6 °C), they entered conditional dormancy and thus germinated to high percentages in light at 35/20 °C. Seeds buried in non-flooded soil exposed to natural seasonal temperature changes in Kentucky (USA) were non-dormant by the following summer and germinated to 80–100 % in light at 25/15, 30/15 and 35/20 °C. Seeds buried in non-flooded soil exhibited an annual conditional dormancy/non-dormancy cycle, with seeds mostly germinating to 80–100 % in light at 30/15 and 35/20 °C throughout the year but to 80–100 % in light at 25/15 °C only in summer. Results for L. panicea were compared to published data for L. panicoides and L. fusca. Whereas seeds of L. panicea buried in flooded soil failed to come out of dormancy, those of L. panicoides, an annual of moist habitats such as mudflats, exhibited an annual conditional dormancy/non-dormancy cycle, and those of L. fusca, a semi-aquatic, required flooding for both dormancy loss and germination. Differences in dormancy breaking and germination responses of seeds of Leptochloa species may help to explain why this genus occupies a wide range of habitats with regard to soil moisture conditions.     

Control of the Germination Responses of Amaranthus retroflexus L. Seeds by their Parental Photothermal Environment

Germination responses of the seeds of Amaranthus retroflexusL. were affected by the photoperiod, temperature, and levelof solar radiation experienced by their parent plants. Seedsfrom parents grown continuously in short days (SD, 8 h) lostpost-harvest dormancy more rapidly and had a higher dark germination,as well as a greater responsiveness (at 30?C) to pretreatmentsat low temperature (5 or 10?C) and to short illuminations, thanseeds from parents grown continuously in long days (LD, 16 h).Dark germination and responsiveness of the seeds to promotivetreatments were both higher when their parents were transferredat flowering from LD to SD than when grown continuously in LD.These responses were lower when their parents were similarlytransferred from SD to LD than when grown continuously in SD.The promotive effects of parental post-flowering SD on darkgermination (at 30?C) were enhanced by reduction of parentaltemperature (from 27/22?C to 22/17?C), but the responsivenessof the seeds to low temperature pretreatment was reduced. Inflorescencesdeveloping in LD produced seed with higher germinability whenfloweringwas not induced (LD throughout) than when it was induced (eitherby SD till flowering, or by three SD cycles when 4–5 leavesappeared). Reduced levels of solar radiation had opposite effectsin the different parental photoperiods: dark germination andthe responsiveness to low temperature pretreatments were reducedin LD, but were increased in SD. Differences in the germination responses resulting from differencesin the parental environment could not be correlated with differencesin seed coat thickness or seed dry weight.     

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.     

Germination dimorphism in Suaeda acuminata: A new combination of dormancy types for heteromorphic seeds

Desert annual Suaeda acuminata produces two morphologically distinct types of seeds on the same plant. The main aims of our study were to compare germination characteristics of the dimorphic seeds, ascertain their dormancy types and give the hormonal explanation. The two seed types of S. acuminata absorbed water at different rates with brown seeds imbibing water faster. Germination percentages of brown seeds were significantly higher than those of black seeds in all temperature and light regimes tested. Eight weeks of cold stratification did not break dormancy of black seeds, whereas exogenous GA₃ promoted germination. Excised embryos of untreated black seeds produced normal seedlings. Contents of ZR, GA₃ and ABA of brown seeds were significantly higher than that of black seeds; while contents of IAA of black seeds were significantly higher than that of brown seeds. Brown seeds of S. acuminata are non-dormant, whereas black seeds have intermediate physiological dormancy (PD). Interaction among ZR, ABA and GA₃ may play an important role in dormancy status of both seed types. This is the first report of non-dormancy and intermediate PD in a heteromorphic species.     

Dormancy cycling and persistence of seeds in soil of a cold desert halophyte shrub

Background and Aims

Formation of seed banks and dormancy cycling are well known in annual species, but not in woody species. In this study it was hypothesized that the long-lived halophytic cold desert shrub Kalidium gracile has a seed bank and dormancy cycling, which help restrict germination to a favourable time for seedling survival.

Methods

Fresh seeds were buried in November 2009 and exhumed and tested for germination monthly from May 2010 to December 2011 over a range of temperatures and salinities. Germination recovery and viability were determined after exposure to salinity and water stress. Seedling emergence and dynamics of the soil seed bank were investigated in the field.

Key Results

Seeds of K. gracile had a soil seed bank of 7030 seeds m⁻² at the beginning of the growing season. About 72 % of the seeds were depleted from the soil seed bank during a growing season, and only 1·4 % of them gave rise to seedlings that germinated early enough to reach a stage of growth at which they could survive to overwinter. About 28 % of the seeds became part of a persistent soil seed bank. Buried seeds exhibited an annual non-dormancy/conditional dormancy (ND/CD) cycle, and germination varied in sensitivity to salinity during the cycle. Dormancy cycling is coordinated with seasonal environmental conditions in such a way that the seeds germinate in summer, when there is sufficient precipitation for seedling establishment.

Conclusions

Kalidium gracile has three life history traits that help ensure persistence at a site: a polycarpic perennial life cycle, a persistent seed bank and dormancy cycling. The annual ND/CD cycle in seeds of K. gracile contributes to seedling establishment of this species in the unpredictable desert environment and to maintenance of a persistent soil seed bank. This is the first report of a seed dormancy cycle in a cold desert shrub.     

Seed germination of three species of <Emphasis Type="Italic">Vallisneria</Emphasis> (Hydrocharitaceae), and the effects of freshwater microalgae

Two experiments were conducted to investigate seed germination under natural temperature and light regimes and to evaluate the influence of freshwater microalgae on seed germination of threeVallisneria species. Seeds exposed to natural seasonal temperature and light changes for 24 months germinated only in spring, perhaps indicating an annual dormancy/non-dormancy cycle. The ecological background of the natural habitat seems to play predominant roles in seed germinability. Mean cumulative seed germination percentages of Vallisneria natans, V. denseserrulata, andV.spinulosa of the first year were 35.2, 19.2, and 11.2%, respectively, and of the second year were 80, 72, and 32.4%, respectively. Germination rates differed significantly among the three Vallisneria species exposed to natural seasonal temperature and light changes in the first year, but differed only between Vallisneria spinulosa and the other two species in the second year. The differences of germination may influence the geographical distribution and thus be related to different survival strategies of the species. Seed germination rates in culture solution inoculated with algae were significantly higher than in solution with no algae. A strong correlation occurred between total biomass of freshwater microalgae and seed germination of the three studied species. Apparently, the extracellular products of freshwater microalgae may play an important role in seed germination. These results support the hypothesis that Vallisneria colonization may be mediated by algae facilitation.     

Seed viability and seed dormancy of non-native Phragmites australis in suburbanized and forested watersheds of the Chesapeake Bay, USA

The non-native, invasive haplotype of Phragmites australis is rapidly invading tidal and non-tidal wetlands across North America. Phragmites has the potential to spread by seeds and rhizomes. Seed viability and dormancy differences were quantified among 18 patches of non-native Phragmites in subestuarine wetlands in developed (i.e., suburbanized) vs. forested watersheds of the Chesapeake Bay. We used tetrazolium and germination assays to assess seed viability and compared germination percentages and rate of germination among fresh seeds, cold–moist treated seeds, and warm–dry treated seeds to evaluate seed dormancy. Seed viability was <1% in most patches but a few patches produced abundant viable seeds (5–21%). Seed viability, however, did not differ significantly between wetlands in forested vs. developed watersheds. Contrary to studies of Phragmites seed dormancy in European populations, some Phragmites seeds were dormant at maturity; cold–moist treated seeds germinated faster and to higher percentages than fresh seeds or warm–dry treated seeds.     

The Role of Chilling in the Germination of some Scottish Montane Species

Summary

Seeds of 32 montane species were collected throughout northern Scotland. Germination responses, particularly the effects of chilling on breaking dormancy, were examined using a serial test incorporating single- and double-chilling treatments, alternating 20°C/10°C incubation temperatures, gibberellic acid and, for some species, nicking of the seed coat. Where practicable, any ungerminated seeds were ultimately dissected to assess their viability. Only three species had an absolute requirement for pre-chilling before seeds germinated. A further eight species required chilling to break the dormancy of 15% or more seeds; otherwise chilling generally increased the extent and rate of germination. Unusually, chilling induced dormancy in the seeds of four species whereas warm conditions induced dormancy which was not broken by subsequent chilling amongst seeds of Draba incana. Germinability and germination rates for nine species were regressed on the altitude, latitude and oceanicity of the plants' origin to assess the relative effects of chilling. These three environmental factors accounted for up to 98% of the variability in the germination parameters but few regressions attained statistical significance. Broad patterns suggest that chilling had a decreasing effect on both the extent and, rate of germination as the altitude of the seed source increased. A similar pattern, but only for germinability, was seen with respect to latitude.     

Relationships between seed germinability of Spergularia marina (Caryophyllaceae) and the formation of zonal communities in an inland salt marsh

BACKGROUND AND AIMS: The formation of zonal communities may be attributed to differences in germination across the community and to timing of germination of seeds present in the seed bank. Our goals were two-fold: (1) to assess the annual germination pattern of Spergularia marina; and (2) to determine whether germination of S. marina differed across zonal communities. METHODS: Fresh seeds were buried in an experimental garden in polyester bags. Bags were harvested monthly for 1 year and exposed to differing 12 h/12 h temperature regimes (5/15 degrees C, 5/25 degrees C, 15/25 degrees C and 20/35 degrees C) with a 12 h dark/12 h light photoperiod. Replicate seeds were exposed to 24 h dark. Seeds were also placed in different zonal communities to assess germinability in the field. KEY RESULTS: Spergularia marina has a primary physiological dormancy. Conditional dormancy occurs from December to May and non-dormancy from June to November. Field germination initiates in the spring when temperatures are cool and salinity is low due to flooding, and ceases in the summer when temperatures exceed germination requirements. Spergularia marina has a light requirement for germination. CONCLUSIONS: If seeds become buried in the field or are light inhibited by Phragmites australis, they will remain dormant until they receive an adequate amount of light for germination. Since S. marina can germinate across all zones in a salt-marsh community, the formation of zonal communities is not determined at the germination stage, but at some later stage of development.