A large fraction of tree species forming persistent soil seed-banks and with dormant seeds are expected to be found in strongly seasonal ecosystems such as Neotropical savannas, where seedling recruitment could be highly variable. In the savannas of Central Brazil, we studied seed characteristics (type of dormancy, longevity and moisture content) of 14 representative woody species differing in seed dispersal season. We also studied the dynamics of soil seed-banks and similarity patterns in woody species composition among seed rain, soil seed-bank, seedling bank and standing vegetation along shallow topographic gradients that differ in canopy cover. Woody species composition of the soil seed-bank largely differed from the standing vegetation, the seed rain and the seedling bank species composition, suggesting low recruitment of woody species from the soil seed-bank. Seeds of the 14 woody species remained viable for less than 16 months in laboratory dry-storage conditions. Of those, most seeds dispersed in the dry season were dormant and exhibited low moisture content, while most seeds dispersed in the wet season were non-dormant and exhibited high moisture content. Longevity of these seeds dispersed in the dry and the wet seasons did not differ significantly. This study shows that both timing of seed dispersal and dormancy appear to control timing of seed germination and seedling recruitment of most Neotropical savanna woody species, which did not form persistent soil seed-banks. This study contributes to the understanding of tree/grass coexistence and tree density variations along topographic gradients in tropical savannas.

The ecophysiology of germination in Pinus brutia and P. halepensis was studied in seeds collected from different areas of Greece. In regard to the temperature range of germination, both P. halepensis and the southern provenance (Lasithi, Crete) of the East Mediterranean pine, P. brutia, follow a typical Mediterranean pattern. In the latter species, dramatic differences in the degree of dormancy were noted among the three provenances investigated; in all seed lots however, 20°C was clearly the optimal temperature for germination. Stratification resulted in a considerable promotion of P. brutia seed germination. Nevertheless, the inductive effect of stratification was shown to differ among the three provenances used, escalating from a simple increase of germination rate (in the southern seed lot from Lasithi, Crete) through a broadening of the temperature range of germination (in the intermediate lot from Thasos Island) to, finally, a dramatic release from a particularly deep dormancy (in the northern lot from Soufli). These deeply dormant seeds of the latter provenance displayed an absolute stratification requirement; prolonged illumination or seed coat scarification could not substitute for the promotive effect of prechilling. A considerable interaction between far-red light and stratification was revealed in the dormant seeds of P. brutia (Soufli provenance); far-red pulses during stratification could either cancel or diminish the germination promotion induced by low temperatures. The differences observed in the germination behaviour among the various P. brutia provenances may be attributed to a variable ecophysiological strategy in regard to the temporal pattern of seedling emergence and establishment. According to the variants of this strategy, seed germination is timed to occur during either spring (in regions with relatively cold and moist climates), or autumn and early winter (in southern, mild and dry areas) or both (in intermediate conditions).

After-ripening, the loss of dormancy under dry conditions, is associated with a decrease in mean base water potential for germination of Bromus tectorum L. seeds. After-ripening rate is a linear function of temperature above a base temperature, so that dormancy loss can be quantified using a thermal after-ripening time (TAR) model. To incorporate storage water potential into TAR, we created a hydrothermal after-ripening time (HTAR) model. Seeds from two B. tectorum populations were stored under controlled temperatures (20 or 30 °C) and water potentials (−400 to −40 MPa). Subsamples were periodically removed from each storage treatment and incubated at 15 or 25 °C to determine germination time courses. Dormancy status (mean base water potential) was calculated from each time course using hydrothermal time equations developed for each seed collection. Seeds stored at −400 MPa did not after-ripen. At water potentials from −400 to −150 MPa, the rate of after-ripening increased approximately linearly with increasing water potential. Between −150 and −80 MPa, there was no further increase in after-ripening rate, while at −40 MPa seeds did not after-ripen and showed loss of vigour. These results suggest that the concept of critical water potential thresholds, previously shown to be associated with metabolic activity and desiccation damage in partially hydrated seeds, is also relevant to the process of after-ripening. The HTAR model generally improved field predictions of dormancy loss when the soil was very dry. Reduced after-ripening rate under such conditions provides an ecologically relevant explanation of how seeds prolong dormancy at high summer soil temperatures.

Palm diaspores are reported to have various kinds of dormancy. However, (1) the embryo is underdeveloped; (2) the endocarp is water permeable; and (3) the diaspores take a long time to germinate. Thus, we conclude that the diaspores of the majority of palm species have morphophysiological dormancy (MPD). The ones that do not have MPD are morphologically dormant.

Hydrothermal 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.

Secondary dormancy is predominantly associated with seed behaviour in soil seed banks. Periodic changes in secondary dormancy may explain seasonal emergence of weedy species. Temperature and possibly soil water potential appear to be the predominant factors that determine the annual cycling of dormancy. Dormancy cycling is paralleled by modulations of germination responsiveness to germination stimulants, such as light and nitrate and to the width of the germination temperature window. Membranes have been proposed to be the primary target for the perception of temperature. It is hypothesized that alterations in properties of cellular membranes are involved in the regulation of dormancy. Possible mechanisms are discussed.

Seed size and shape, measured as the variance of the three main dimensions, have been proposed as good indicators for predicting seed persistence. We tested whether these variables were robust predictors of seed persistence in the soil for 58 abundant herbaceous species, primarily annuals, in grass and scrubland of central Spain. Seed persistence was estimated from data on germinable seed banks, while seed weight and shape were measured using fresh seeds collected in the study area. There was a significant tendency for species with persistent seeds to have smaller seeds than species with transient seeds. Seed shape was not, however, related to persistence and we did not find any clear seed weight/shape threshold for predicting persistence. The binary logistic model of seed bank type as a function of seed weight was significant and explained 67% of total variability. Supplementary information about dormancy, environmental conditions of habitat, predation and attack by pathogens has to be used to elaborate more accurate general predictive models of seed persistence.

Nitrate promotes seed germination at low concentrations in many plant species, and functions as both a nutrient and a signal. As a nutrient, it is assimilated via nitrite to ammonium, which is then incorporated into amino acids. Nitrate reductase (NR) catalyses the reduction of nitrate to nitrite, the committed step in the assimilation. Seed sensitivity to nitrate is affected by other environmental factors, such as light and after-ripening, and by genotypes. Mode of nitrate action in seed germination has been well documented in Arabidopsis thaliana and the hedge mustard Sisymbrium officinale. In these species nitrate promotes seed germination independent of its assimilation by NR, suggesting that it acts as a signal to stimulate germination. In Arabidopsis, maternally applied nitrate affects the degree of primary dormancy in both wild-type and mutants defective in NR. This indicates that nitrate acts not only during germination, but also during seed development to negatively regulate primary dormancy. Functional genomics studies in Arabidopsis have revealed that nitrate elicits downstream events similar to other germination stimulators, such as after-ripening, light and stratification, suggesting that these distinct environmental signals share the same target(s). In Arabidopsis, the NIN-like protein 8 (NLP8) transcription factor, which acts downstream of nitrate signalling, induces nitrate-dependent gene expression. In particular, a gene encoding the abscisic acid (ABA) catabolic enzyme CYP707A2 is directly regulated by NLP8. This regulation triggers a nitrate-induced ABA decrease that permits seed germination. This review article summarizes an update of our current understanding of the regulation of seed dormancy and germination by nitrate.

This study investigated the effects of 3-methyl-2H-furo[2,3-c]pyran-2-one, a germination active butenolide present in plant-derived smoke, gibberellic acid and smoke water on seeds of Australian Asteraceae exposed to different light regimes. Seeds of all species required light, with maximum germination occurring under white light, or light dominated by 640 nm. Compared to untreated seeds, butenolide increased germination of Angianthus tomentosus, Gnephosis tenuissima, Myriocephalus guerinae, Podolepis canescens and Rhodanthe citrina at suboptimal light wavelengths and in the dark to a level equal to, or greater than, smoke water. Germination of Erymophyllum glossanthus and Gnephosis acicularis was not promoted by butenolide or smoke water under any light regime. The action of gibberellic acid was compared to that of butenolide for three species (Angianthus tomentosus, Myriocephalus guerinae and Podolepis canescens), and both compounds were found to stimulate germination. This study provides evidence that butenolide can act in a similar fashion as gibberellic acid in promoting seed germination of light-sensitive seeds. The ecological significance of these findings is discussed.

Species with physically dormant (PY) seeds make up over 25% of plant species in a number of ecologically important ecosystems around the globe, such as savannah and Mediterranean shrublands. Many of these ecosystems are subject to temporally stochastic events, such as fire and drought; but are in areas projected to experience some of the most extreme climatic changes in the future. Given the importance of PY in controlling germination timing for successful recruitment, we ask how plastic the PY trait is, and if changes to the maternal environment from climate change could alter recruitment. This review focuses on: (1) the evidence for inter- and intraspecific variation in PY; (2) the genetic, maternal and environmental controls involved; and (3) the ecological consequences of (1) and (2) above. Evidence for (within-community) interspecific variation in conditions required to break PY is strong, but for intraspecific variation evidence is contradictory and limited by a paucity of studies. Identifying controllers of variation in PY is complex, there is some suggestion that conditions of the maternal environment may be important, but no consensus on the nature of effects. The implications of PY plasticity for the persistence of seed banks, species and communities under climate change are discussed. We highlight a number of key knowledge gaps, such as a lack of research estimating the components of variation in non-agricultural species, and identify a suite of seed attributes relevant to understanding the potential impacts of climate change on the population dynamics of PY species in the future.

Ecophysiological aspects of seed germination were investigated in four Mediterranean geophytes of the genus Muscari (Liliaceae): M. comosum (tassel hyacinth), M. neglectum (common grape hyacinth), M. commutatum and M. weissii. Experiments were performed at constant temperatures in the dark and under temperature and light conditions simulating those prevailing in nature during November–January, i.e. well into the rainy season of the Mediterranean climate. In all species, no primary dormancy was revealed, and germination occurred in a rather narrow range of cool temperatures (optimum at 10 or 15°C) and at a remarkably slow rate; both germination characteristics seem to be associated with autumn/winter seed germination and seedling establishment. Such a postulated strategy is ecologically advantageous within an unpredictable rainfall regime, known to prevail during the start of the rainy period of the Mediterranean climate. This strategy may also explain the spread of germination of M. comosum seeds over two consecutive years, observed by Theophrastus. Far-red light, simulating light conditions under a dense canopy, resulted in only a slight delay of germination compared to dark controls. Diurnal white light, qualitatively simulating natural daylight, caused a significant decrease of the germination rate in all four species studied. Moreover, white light was found to suppress considerably final seed germination (photoinhibition) in M. weissii and M. neglectum; in the latter species, prolonged imbibition under white light also led to the induction of secondary dormancy.

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

Seeds of papaya (Carica papaya L.) stored for 12 months at 15°C with 7.9–9.4% moisture content maintained their original germination. In contrast, many seeds stored cooler or drier lost viability, the losses occurring more rapidly at −20°C than at either 0°C or 15°C. The results are not compatible with the definitions of either orthodox or recalcitrant seed storage behaviour.

The drying rate of whole seeds of Ekebergia capensis (Meliaceae) was shown to influence the response to desiccation, with rapidly dried seeds surviving to lower water contents. Short-term rapid drying (to water contents higher than those leading to viability loss) actually increased the rate of germination. The form of the time course of decline of axis water content varied with drying rate; slow drying could be described by an exponential function, whereas with rapid drying initial water loss was faster than predicted by an exponential function. These observations suggest that slow drying brought about homogeneous dehydration and that the rapid drying was uneven across the tissue. This raised the possibility that the different responses to dehydration were a function of different distributions of water in the axis tissue under the two drying regimes. However, ultrastructural observations indicated that different deleterious processes may be occurring under the different drying treatments. It was tentatively concluded that a major cause of viability loss in slowly dried material was likely to be a consequence of aqueous-based processes leading to considerable membrane degradation. Uneven distribution of tissue water could not be rejected as a contributory cause of the survival of rapidly dried seeds to low bulk water contents. The differential response to dehydration at different drying rates implies that it is not possible to determine a ‘critical water content’ for viability loss by recalcitrant seeds.

Desiccation-tolerant (DT) plant germplasm (i.e. seeds, pollen and spores) survive drying to low moisture contents, when cytoplasm solidifies, forming a glass, and chemical reactions are slowed. DT germplasm may survive for long periods in this state, though inter-specific and intra-specific variation occurs and is not currently explained. Such variability has consequences for agriculture, forestry and biodiversity conservation. Longevity was previously considered in the context of morphological features, cellular constituents or habitat characteristics. We suggest, however, that a biophysical perspective, which considers the molecular organization – or structure – within dried cytoplasm, can provide a more integrated understanding of the fundamental mechanisms that control ageing rates, hence the variation of longevity among species and cell types. Based on biochemical composition and physical–chemical properties of dried materials, we explore three types of the interplay between structural conformations of dried cytoplasm and ageing: (1) cells that lack chlorophyll and contain few storage lipids may exhibit long shelf life, with ageing probably occurring through slow autoxidative processes within the glassy matrix as it relaxes; (2) cells with active chlorophyll may die quickly, possibly because they are prone to oxidative stress promoted by the photosynthetic pigments in the absence of metabolic water and (3) cells that lack chloroplasts but contain high storage lipids may die quickly during storage at −20°C, possibly because lipids crystallize and destabilize the glassy matrix. Understanding the complex variation in structural conformation in space and time may help to design strategies that increase longevity in germplasm with generally poor shelf life.

Growers expect high-quality, genetically pure seed. As a result, seed companies maintain quality control programmes that monitor seed from harvest to purchase. An array of ‘traditional’ seed quality tests, including mechanical tests and tests of genetic purity, seed germination and vigour, and seed health tests, is used, and seed quality assessment techniques continue to evolve. Advances in molecular genetics are allowing the release of new varieties differing essentially in one gene. New molecular biology approaches offer the potential to identify these subtle genetic differences. Advances in seed enhancements, such as pelleting, priming and pregermination, require increased scrutiny of seed quality before and after the enhancement process. New developments in computer imaging for improved purity and germination/vigour analyses are being developed. These novel approaches to seed quality assessment become important as new genetic improvements are conveyed in the seed at increased cost to the grower.

Seed development and changes in germination ability and longevity were monitored in two spring and two winter cultivars of each of barley (Hordeum vulgare L.) and wheat(Triticum aestivum L.). Physiological maturity (end of the seed-filling period) occurred between 31 and 41 d after 50% anthesis in the eight cultivars, at which time seed moisture contents had declined naturally to 40–49% (wet basis). Most seeds were able to germinate (in 28 d tests at 10°C) following enforced desiccation at this time (normal germination varied from 83% in one cultivar of winter wheat to 97% in one of spring wheat).Potential seed longevity continued to increase after physiological maturity. The intervalbetween physiological maturity and the time when seeds attained maximum potential longevity varied between 3 and 21 d; maturation drying had reduced seed moisture contents to 16–28% (wb) at this time. The results for all eight cultivars contradict the hypothesis that maximum seed quality is attained at physiological maturity and thereafter declines. The term physiological maturity is potentially misleading, therefore; mass maturity is more appropriate to describe this developmental stage. It is shown that the results of accelerated ageing or controlled deterioration tests may provide misleading conclusions in seed quality development studies if the single storage treatment chosen is inappropriate.

We studied changes in dormancy (as imposed by the different structures surrounding the embryo, namely, endosperm, pericarp and glumellae) and its relationship with changes in embryonic ABA levels and sensitivity, in developing grains of two commercial barley cultivars: B 1215 and Quilmes Palomar, which have, respectively, a low and high dormancy level at harvest and, consequently, a contrasting sprouting behaviour in rainy years. Dormancy imposed by endosperm plus pericarp was gradually and similarly alleviated throughout development in both cultivars. The presence of the hull (glumellae), in contrast, completely inhibited germination of grains from both cultivars until physiological maturity (PM). From there on, hull-imposed dormancy was removed abruptly in B 1215 grains, while in Q. Palomar ones, it was removed at a much lower rate. This difference determined the contrasting sprouting behaviour of these two cultivars within the ‘time window’ going from PM to crop harvest. Embryonic ABA content and sensitivity were similar in the two cultivars throughout development until PM. From there on, ABA content and sensitivity in B 1215 embryos declined dramatically coinciding with the abrupt termination of hull-imposed dormancy observed in this cultivar. In contrast, ABA levels in Q. Palomar embryos remained high for longer and sensitivity to ABA declined at a much slower rate. This correlation suggests that hull-imposed dormancy in barley might be regulated by embryonic ABA levels and / or sensitivity. Inhibition of GA synthesis with paclobutrazol applied after anthesis lowered the germination capacity of grains from both cultivars without altering that of the naked caryopses, thus further suggesting that hull-imposed dormancy is under hormonal control.

Seed longevity of plant species is an important topic in restoration management, and little is known about the effects of environmental conditions on seed survival and longevity under natural conditions. Therefore, the effect of groundwater level on the survival of seeds in the soil seed bank of a natural grassland community was investigated. Large soil cores, mesocosms, were sampled from a grassland site and transferred to two basins under a glass roof. The mesocosms were subjected to different groundwater-level treatments (high and low, respectively 5 and 30 cm below the soil surface) for nearly three years. After that period the soil seed bank of the mesocosms was sampled. In total 15 789 seeds of 38 taxa emerged from the experiment. Significant differences between the number of viable seeds that emerged in the two treatments were found for several species. More seeds of Glyceria fluitans, Cardamine pratensis and Myosotis palustris germinated in the high water-level treatment, whereas fewer seeds of Juncus spp., Cerastium fontanum and Stellaria media were found in this treatment than in the low water-level treatment. The experiment showed that the anoxic conditions prevailing in the high water-level treatment were beneficial to the survival of seeds of species of wet grassland communities. Species of dry grasslands, although represented by only two species, survived better under aerobic conditions.

Epizoochory is widely recognized as an effective long-distance seed dispersal mechanism. Nevertheless, few studies have focused on the investigation of its influencing factors. One of the key aspects of epizoochory is the adhesive interaction between seeds and furs. We describe a new method to quantify experimentally and standardize the adhesivity of seeds to animal fur, as a measure of epizoochorous dispersal potential. The method excludes the impact of animal behaviour and environmental factors, and allows the ranking of species according to their adhesivity score. We measured adhesivity scores for 66 species on the furs of seven mammals. Deep furs with long, rough, undulated hairs implanted at a large angle were most suited for seed adhesion, while seeds adhered less well to shallow furs with short, smooth, straight hairs implanted at small angles. Seeds with specialized adhesive appendages had higher adhesivity scores than seeds with unspecialized appendages and seeds without appendages. However, an interaction effect between certain seed and fur types exists. Although seed morphology is a good predictor for seed adhesivity on fur, less well-adhering seed types often still have relatively high adhesivity scores. Therefore, it is likely that nearly all species are, to some extent, able to disperse epizoochorously.