The Asteraceae with up to 30,000 species occurs on all continents except Antarctica and in all major vegetation zones on earth. Our primary aim was to consider cypselae dormancy-break and germination of Asteraceae in relation to ecology, vegetation zones and evolution. Cypselae are desiccation-tolerant and in various tribes, genera, species and life forms of Asteraceae are either non-dormant (ND) or have non-deep physiological dormancy (PD) at maturity. All six types of non-deep PD are found among the Asteraceae, and dormancy is broken by cold or warm stratification or by afterripening. Soil cypselae banks may be formed but mostly are short-lived. Much within-species variation in dormancy-break and germination has been found. Using data compiled for 1192 species in 373 genera and 35 tribes of Asteraceae, we considered ND and PD in relation to life form, vegetation zone and tribe. Senecioneae and Astereae had the best representation across the vegetation zones on earth. In evergreen and semi-evergreen rainforests, more species have ND than PD, but in all other vegetation zones, except alpine/high-latitude tundra (where ND and PD are equal), more species have PD than ND. Tribes in the basal and central grades and those in the Heliantheae Alliance have both ND and PD. The high diversity and lability of non-deep PD may have enhanced the rate of species diversification by promoting the survival of new species and/or species in new habitats that became available following globally disruptive events since the origin of the Asteraceae in the Late Cretaceous.

Germination ecology was investigated in a natural population of Xyris longiscapa, a perennial herbaceous species endemic to the Brazilian campo rupestre. Seeds were collected over four consecutive years (2014 to 2017) to evaluate germination responses to a range of temperatures (from 15 to 30°C). The light requirement was evaluated in seeds collected in 2014. Seeds collected in 2014 were also buried in soil in the natural habitat of the species to evaluate changes in germinability at different temperatures over the time. Seeds showed an absolute light requirement for germination. Seed germination was affected by temperature, collection year and the interaction between these two factors. Seeds collected in 2014 showed a narrower temperature range for germination (15–20°C), compared with the seeds collected in 2015, 2016 and 2017 that germinated in a temperature range of 15–25°C. Buried seeds remained viable in soil for at least 14 months and exhibited seasonal dormancy cycling. Secondary dormancy was induced during the rainy season and alleviated during the dry season, following a conditional dormancy/dormancy cycle. The degree of primary dormancy appeared to be influenced by the environmental conditions experienced by seeds during maturation. Primary dormancy (when present), seed persistence in soil and seasonal dormancy cycles are strategies of X. longiscapa to enhance regeneration success in the harsh environment of the Brazilian campo rupestre.

The genus Aegilops belongs to the secondary gene pool of wheat and has great importance for wheat cultivar improvement. As a genus with only annual species, regeneration from seeds in Aegilops is crucial. In several species in Aegilops, spikes produce different seed morphs, both in size and germination patterns. However, little is known about the ecology of seed germination, nor about the seed longevity in this genus. Here we investigated the germination phenology of Ae. neglecta under laboratory and field conditions and assessed longevity of different seed morphs of five additional Aegilops species using controlled ageing tests. Large seeds were short-lived and germinated faster than small seeds in most of the species. Field experiments with Ae. neglecta showed that large seeds of the dimorphic pair germinated 3 months after dispersal in contrast to 14 months for smaller seeds. Differences in longevity were detected not only in dimorphic seed pairs, but also among seeds from different positions on the spike. Our results indicate that different longevities in seed morphs of Aegilops may reflect a different soil seed bank persistence, with smaller seeds able to maintain a higher viability after dispersal than larger ones, thereby spreading seedling emergence over two years. Differences of seed germination and longevities between seed morphs in Aegilops may have important implications for ex situ seed conservation and reinforce the hypothesis of a bet-hedging strategy in the germination ecology of this genus.

We assessed inter-seasonal dynamics of seed banks, dormancy and seed germination in three endemic Chihuahuan Desert succulent species, under simulated soil warming conditions. Hexagonal open top-chambers (OTCs) were used to increase soil temperature. Seeds of Echinocactus platyacanthus (Cactaceae), Yucca filifera and Agave striata (Asparagaceae) were collected and buried within and outside OTCs. During the course of one year, at the end of each season, seed batches were exhumed to test viability and germination. Soil temperature in OTCs was higher than in control plots. Yucca filifera seeds always had high germination independently of warming treatment and season. Agave striata seeds from OTCs had higher germination than those from control plots. Agave striata exhibited low germination in fresh seeds, but high germination in spring. Seeds from this species lost viability throughout the experimental timeframe, and had no viable seeds remaining in the soil. Echinocactus platyacanthus showed high germination in fresh seeds and displayed dormancy cycling, leading to high germination in spring, low germination in summer and autumn, and high germination in winter. Germination of this species was also higher in seeds from OTCs than those from control plots. Echinocactus platyacanthus formed soil seed banks and its cycle of inter-seasonal dormancy/germination could be an efficient physiological mechanism in a climate change scenario. Under global warming projections, our results suggest that future temperatures may still fall within the three studied species’ thermal germination range. However, higher germination for A. striata and E. platyacanthus at warmer temperatures may reduce the number of seeds retained in the seed bank, and this could be interpreted as limiting their ability to spread risk over time. This is the first experimental study projecting an increase in soil temperature to assess population traits of succulent plants under a climate change scenario for American deserts.

The pattern of seed dispersal in time and space can affect plant fitness and the soil seed bank, and thus information is needed on this aspect of the seed biology of a species before it is selected for use in habitat restoration projects. Zygophyllum xanthoxylon is a super-xerophilous shrub that is a potential pioneer species for use in revegetating highly disturbed areas of the cold deserts of northwest China. We studied fruit release and soil seed banks of Z. xanthoxylon for 3 years in two cold desert habitats characterized by different degrees of drought and wind velocity. In our study, fruit (a three-winged capsule) release began in summer (June 2010, August 2011, July 2012) and extended for 9–10 months, but plants can be found in the population with previous- and current-year fruits attached to them. More than 50% of the fruits were released in the first 3–4 months after maturity, while the others were released gradually over a 7–8 month period. The temporal pattern of fruit dispersal varied with habitat but not with amount of precipitation during summer. The pattern of fruit deposition on the soil surface was affected by neighbouring plants, wind velocity, wind direction and topography. In both habitats, >90% of the fruits were deposited beside large and small clusters of plants, mainly Ephedra przewalskii. To facilitate plant community development, we suggest that E. przewalskii should be planted (as a wind break) together with Z. xanthoxylon when native pioneer species are used for restoration of cold desert shrublands.

Seed longevity is dependent on seed traits and storage conditions. This study evaluated the seed longevity and physical dormancy (PY)-break of two species of Dimorphandra endemic to Brazilian biodiversity hotspots. Longevity was tested in situ, by burying seeds in their natural habitats (12 months), and ex situ, by storage in a cold chamber (5°C; 24 months). Seeds were taken at regular intervals to assess germinability at 30°C (12 h photoperiod) using intact and scarified seeds. Intact seeds (freshly collected, and after 12 months storage) were analysed using scanning electron microscopy. The germinability of freshly collected seeds of both species reached approximately 10% for intact seeds and >85% for scarified seeds. Cold storage maintained seed viability in both species, and broke dormancy for 35% of D. wilsonii seeds. After 12 months, only 55% (for D. exaltata) and 41% (for D. wilsonii) of the buried seeds were recovered; more than 90% of which remained viable in both species. Seeds gradually overcame PY during burial, with a higher germination increase for D. wilsonii (71%) than D. exaltata (32%). Dimorphandra exaltata seeds did not show clear structural changes after cold storage although D. wilsonii seeds evidently experience an increase in the depth of fracture lines. Burial promoted deep seed coat changes in both species, more intense in D. wilsonii, indicating that temperature and humidity variations throughout the year are among the main factors releasing Dimorphandra seeds from PY. The seeds of both studied species overcame PY during burial and are able to form small persistent soil seed banks.

Seed of 41 economically important weed species of the Great Plains region of the United States were buried 20 cm deep in soil in eastern and western Nebraska in 1976. The 41 species consisted of 11 annual grass, 14 annual broadleaf, 4 biennial broadleaf, and 12 perennial broadleaf species. Weed seeds were exhumed annually for germination tests the first 9 yr, then after 12 and 17 yr. Germination percentages at the two burial locations averaged over 0, 1 to 4, 5 to 8, and 9 to 17 yr of burial were 57, 28, 9, and 4% for annual grass; 47, 26, 16, and 11 % for annual broadleaf; 52, 49, 44, and 30 % for biennial broadleaf; 36, 18, 13, and 8% for perennial broadleaf; and 47, 26, 16, and 10% for all 41 weed species, respectively. Biennial broadleaf weeds showed the greatest seed germination over years. Annual grass weeds showed less seed germinability over 17 yr of burial than annual broadleaf weeds and perennial broadleaf weed species were intermediate. Weed seed germinability in soil was greater in the reduced rainfall and more moderate soil temperatures of western Nebraska than in the greater rainfall and more fluctuating soil temperatures of eastern Nebraska. The greatest seed survival among the 41 weed species was shown by common mullein, which had 95% germination after 17 yr of burial in western Nebraska. Decay rates of individual weed species in soil will be of most value to weed scientists, agriculturalists, and modelers evaluating past or designing future weed management systems.

An elutriation system was developed to estimate weed seed densities in soil. The system provided reliable estimates of seed densities for weed species with a broad range of seed weights (0.06 to 9.80 mg) and had no effect on seed viability of three weed species tested. Elutriation of soil samples (up to 60 g) taken from a cultivated field took approximately 15 min. Separating, classifying, and counting seeds is time consuming (20 to 30 min per sample) but provides an accurate estimate of seed densities for weeds with a diameter of 0.5 mm or more.

Studies were conducted to compare changes in germinability and/or viability of yellow starthistle achenes buried (in packets) in soil or stored dry in the laboratory, and to determine the rate of achene depletion from a soil seed bank. In one study, after 72 mo, 0 to 96% germinable achenes remained in packets buried 5 cm deep, and a mean above 99% after dry storage. In another study, total live (germinable plus viable) achenes declined from 100% at harvest to 77.6% after 24 mo of burial. Germinable pappus-bearing achenes remaining in packets increased with depth of burial. After 12 mo of burial, maximum survival of achenes occurred at depths of 5 cm or more. The density of yellow starthistle achenes and seedlings in a natural soil seed bank declined, when achene rain was prevented, to 3.9 and 1.1% of initial density, respectively, after 36 mo. Decline was attributed primarily to seedling emergence and achene death. Achene density in the upper 2.5 cm of soil appeared to be a good predictor of seedling emergence after autumn rains.

Postemergence herbicides alone and in combination were evaluated for Venice mallow control in corn and onion in Colorado during 1986 and 1987. Season-long control of 88 to 98% in corn was obtained with bromoxynil plus cyanazine or atrazine; 2,4-D amine plus dicamba or bromoxynil; or linuron, bromoxynil, or dicamba applied alone. Oxyfluorfen plus bromoxynil in a split application controlled Venice mallow 80 to 99% all season in onions. Uncontrolled Venice mallow caused higher yield reductions in onions than in corn.

Flax is a minor oilseed crop in Canada largely exported to the European Union for use as a source of industrial oil and feed ingredient. While flax could be genetically engineered (GE) to enhance nutritional value, the adoption of transgenic technologies threatens conventional flax market acceptability. Harvest seed loss of GE crops and the persistence of GE crop volunteers in the seed bank are major factors influencing transgene persistence. Ten commercial fields in Alberta, Canada, were sampled after harvesting conventional flax in 2006 and 2007, and flax seed density and viability were determined. Additionally, artificial seed banks were established at two locations in Alberta in 2005 and 2006 to quantify persistence of five conventional flax cultivars with variability in seed coat color (yellow or brown) and α-linolenic acid (ALA, 18:3cisΔ9,13,15) content (3 to 55%) at three soil depths (0, 3, or 10 cm). Harvest methods influenced seed loss and distribution, > 10-fold more seed was distributed beneath windrows than between them. Direct harvested fields had more uniform seed distribution but generally higher seed losses. The maximum yield loss was 44 kg ha−1 or 2.3% of the estimated crop yield. Seed loss and the viability of flax seed were significantly influenced by year, presumably because weather conditions prior to harvest influenced the timing and type of harvest operations. In artificial seed bank studies, seed coat color or ALA content did not influence persistence. Flax seed viability rapidly declined in the year following burial with < 1% remaining midsummer in the year following burial but there were significant differences between years. In three of four locations, there was a trend of longer seed persistence at the deepest burial depth (10 cm). The current study predicts that seed-mediated gene flow may be a significant factor in transgene persistence and a source of adventitious presence.

Japanese stiltgrass is a nonnative invasive grass occupying a range of habitats in the eastern United States. Conventional management recommendations include hand-removal, mowing, or a nonselective herbicide application in autumn prior to flowering. However, no study has directly compared the ecological impacts of long-term management strategies on Japanese stiltgrass populations or recruitment and establishment of native flora. An experiment was initiated in 2002 and continued for three growing seasons in mixed pine-hardwood forests in central North Carolina. Conventional treatments included hand-removal, mowing, or an application of glyphosate (1.1 kg ai/ha) once in autumn, and selective removal by hand or fenoxaprop-P (0.19 kg ai/ha) season-long as needed. All treatments were compared to nontreated plots. Percent vegetation cover by species was recorded twice annually. Data were aggregated into five classes; Japanese stiltgrass, other exotic plants, native forbs, native monocots, and native woody plants. The soil seed bank of all species was estimated annually by extracting soil cores and documenting seedling emergence. All Japanese stiltgrass management treatments significantly reduced Japanese stiltgrass cover and seed bank over time compared to no management. However, recruitment and reestablishment of native plants and overall species richness were greater with selective Japanese stiltgrass management treatments including both hand-removal and fenoxaprop-P. Relative cover of other exotic plants decreased 2% to 49% after 3 yr with all Japanese stiltgrass management treatments except season-long hand-removal, which increased relative cover of other exotic plants 51%.

Buffalobur is an invasive summer annual species in Xinjiang Province, China. Our purpose was to investigate certain aspects of the seed biology of this weedy species that might be useful in controlling it. In contrast to a previous report that fresh seeds have physical (water-impermeable seed coat) plus physiological (low growth potential of embryo) dormancy, our results, along with those of others, verify that the seeds have only physiological dormancy. The seed's coat is water-permeable, the embryo is fully developed at seed maturity, and dormancy can be broken by cold stratification in the field during winter and early spring. Fifty-five percent of seeds buried in the soil in autumn germinated in the soil the following May, and 53% of the remaining nongerminated seeds germinated when tested in light in the laboratory. Thus, about 20% of the seeds did not germinate but were viable, demonstrating that the species forms at least a short-lived persistent seed bank. This information will be useful in planning a management strategy for this highly invasive species in northwest China.

A study was initiated in 2001at four locations in western Canada to investigate an integrated approach to managing wild oat, the region's worst weed. The study examined the effects of combining semidwarf or tall barley cultivars with normal or twice-normal barley seeding rates in either continuous barley or a barley–canola–barley–field pea–barley rotation. Herbicides were applied at 25, 50, and 100% of recommended rates. The first phase of the study was completed in 2005. This paper reports on the second phase, which was continued for four more years at two of the locations, Beaverlodge and Fort Vermilion, AB, Canada. The objective was to determine the long-term impact of the treatments on wild oat seed in the soil seed bank. In 2009 (final year), the diverse rotation combined with the higher barley seeding rate (optimal cultural practice) resulted in higher barley yields and reduced wild oat biomass compared to continuous barley and lower barley seeding rate (suboptimal cultural practice). In contrast to the first phase, barley yield was higher with the semidwarf cultivar, and cultivar had no effect on wild oat management. Wild oat seed in the soil seed bank decreased with increasing herbicide rate, but amounts were often lower with the optimal cultural practice. For example, at the recommended herbicide rate at Beaverlodge, an approximate 40-fold reduction in wild oat seed occurred with the optimal compared to the suboptimal cultural practice. The results indicate that combining optimal cultural practices with herbicides will reduce the amount of wild oat seed in the soil seed bank, and result in higher barley yields. Optimal cultural practices may also compensate for reduced herbicidal effects in terms of reducing wild oat seed accumulation in the soil seed bank and increasing barley yield. The results have implications for mitigating the evolution of herbicide resistance in wild oat.

Trials were carried out to investigate the effects of seed burial depth on seedling emergence rate of 20 weed species. Marked depth-mediated variation in emergence ability of the different species was observed, together with a general pattern of decreasing emergence with increasing soil depth. At 10 cm, only johnsongrass, velvetleaf, catchweed bedstraw, and cutleaf geranium emerged, albeit only in limited numbers. Species most severely inhibited by burial depth were buckhorn plantain, large crabgrass, common purslane, chickweed, and corn spurry, none of which emerged from beyond 6 cm. In all species, depth-mediated inhibition was found to be sigmoidal (polynomial regression). In addition, the number of seedlings and rate of seedling emergence decreased when depth of burial increased. The depth at which the number of emerged seedlings was halved varied by species and ranged from 3.6 cm for common purslane and chickweed to 7 cm for velvetleaf and catchweed bedstraw. Excessive burial depth generally induced dormancy (in roughly 85% of cases) rather than suicide germination. A close inverse relation (second-degree equation) between seed unit weight and depth-mediated inhibition was observed. The physiological involvement of depth inhibition in seed bank ecology is discussed.

Glyphosate-resistant canola was seeded at Vegreville, Alberta, in 1997 and 1999 and barley in rotation with the canola in 1998 at three seeding rates. The effects, at each crop seeding rate, of variable glyphosate (canola) and tralkoxydim plus bromoxynil plus MCPA (barley) rates on crop yield, net economic return and seed production by wild oat, wild mustard, and wild buckwheat, and the amount of weed seed in the soil seed bank was determined. Crop seeding rate influenced the response of canola and barley yield and weed seed production to herbicide rate. At the lowest crop seeding rates, yield responses tended to be parabolic with yields increasing up to one-half and three-quarters of the recommended herbicide rates and trends toward reduced yields at the full rates. This response was not evident at the higher crop seeding rates, where, in most cases the yield reached a maximum between one-half and the full recommended rate. The effects of the herbicides on weed seed production, especially at the lowest rate, were often superior at the higher crop seeding rates. The results indicate that seeding canola and barley at relatively high rates may reduce risk associated with lower crop yields and increased weed seed production at lower than recommended herbicide rates. However, the current cost of herbicide-resistant canola seed may preclude the adoption of this integrated weed management practice by growers.

Wild oat is the most important weed in Argentine barley and one of the worst weeds in wheat and barley worldwide. During 1997 and 1998, field experiments were performed to determine the response of wild oat to N fertilizer at planting and at early tillering at 55 kg ha−1 with and without the use of diclofop-methyl. Seedling emergence and survival rate, individual fecundity, and preharvest seed dispersal rate of wild oat were assessed. The effect on the individual growth of wild oat was also studied. N fertilizer increased both wild oat seedling survival rate and fecundity, especially when it was applied at early tillering. However, the effect of N fertilization was negligible with diclofop-methyl treatment. In addition, the application of N fertilizer reduced the seed dispersal rate immediately before crop harvest. Quantification of the effects of each agronomic practice, such as N fertilization, is useful to develop simulation models that predict the population dynamics. When N was applied at sowing, the annual growth rate of the wild oat population was almost 25% lower than when applied at early tillering.

In fire-prone ecosystems, many species regenerate after fire from persistent soil seed banks. Species with physically dormant (PY) seeds have dormancy broken by fire-related heat. The magnitude of post-fire recruitment, to predict response to varying fire severity, is commonly estimated by testing dormancy-breaking temperature thresholds of fresh PY seeds. However, seeds spend years in the soil during the inter-fire period, and determining whether dormancy-breaking thresholds change over time is essential to accurately predict population persistence. Germination of four south-eastern Australian PY species from the Fabaceae family (Acacia linifolia, Aotus ericoides, Bossiaea heterophylla and Viminaria juncea) were studied. Dormancy-breaking temperature thresholds vary inter-specifically and the species represented either high or low dormancy-breaking threshold classes. Freshly collected seeds, and seeds that had been buried in the field or stored in dry laboratory conditions for 6 and 18 months were subjected to a fire-related range of heat treatments (40–100°C). Seed ageing increased germination response to heat treatments, effectively lowering the dormancy-breaking thresholds of three species. The fourth species, A. linifolia, initially had a relatively large non-dormant fraction which was lost as seeds aged, with older seeds then displaying PY broadly similar to the other study species. Patterns of threshold decay were species-specific, with the thresholds and viability of low-threshold species declining more rapidly than high-threshold species. The non-dormant fraction did not increase over time for any of our study species. Instead of increasing their non-dormant fraction, as is common in other vegetation types, these fire-prone PY species displayed a change of dormancy-breaking temperature thresholds. This is an important distinction, as maintaining dormancy during the inter-fire period is essential for population persistence. While changes in sensitivity to dormancy-breaking treatments have previously been reported as seeds age, our study provides the first test of changes to temperature thresholds, which increases the range of germination response from the seed bank under varying fire severity.

Seeds have evolved to be highly efficient environmental sensors that respond not only to their prevailing environment, but also their environmental history, to regulate dormancy and the initiation of germination. In the present work we investigate the combined impact of a number of environmental signals (temperature, nitrate, light) during seed development on the mother plant, during post-shedding imbibition and during prolonged post-shedding exposure in both dry and imbibed states, simulating time in the soil seed bank. The differing response to these environments was observed in contrasting winter (Cvi, Ler) and summer (Bur) annual Arabidopsis ecotypes. Results presented show that environmental signals both pre- and post-shedding determine the depth of physiological dormancy and therefore the germination response to the ambient environment. The ecotype differences in seed response to ambient germination conditions are greatly enhanced by seed maturation in different environments. Further variation in response develops following shedding when seeds do not receive the full complement of environmental signals required for germination and enter the soil seed bank in either dry or imbibed states. Species seed dormancy characteristics cannot therefore be easily defined, as seed dormancy is a dynamic state subject to within-species adaptation to local environments.

Several studies have compared seed banks of the different morphs of heteromorphic species, but none of them was on an amphi-basicarpic species. Our primary aim was to compare the relative ability of aerial and basal diaspores of an amphi-basicarpic species to form a seed bank. We compared the seed-bank dynamics of basal and aerial diaspores of three populations of the cold-desert annual Ceratocarpus arenarius growing in the Junggar Desert in north-western China. A 2.5-year experimental garden study compared germination phenology and retention of viability in basal (a) and aerial (c and f) morphs. Aerial morphs formed a modified Thompson and Grime type III seed bank (small proportion of seeds carried over to next year) and the basal morph a modified type IV seed bank (large proportion of seeds carried over to next year). Seeds germinated only in spring, and cumulative germination percentages were f>c>a (year 1), f = c>a (year 2) and f = c = a (year 3). The relationship between length of germination period, retention of viability during burial and relative ability to form a persistent seed bank was basal morph > aerial morphs. The results of this seed-bank study on C. arenarius are in full agreement with those published previously on seed dispersal and dormancy in this species. Thus, strong additional support is provided for a high risk–low risk germination strategy in this cold-desert annual.