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Main Conclusion: Differences in dispersal and dormancy of heteromorphic diaspores of Aegilos tauschii may increase its flexibility to invade/occupy weedy unpredictable habitats by spreading risk in space and time. In plant species that produce dimorphic seeds, there often is a negative relationship between dispersal and dormancy, with high dispersal-low dormancy in one morph and low dispersal-high dormancy in the other, which may function as a bet-hedging strategy that spreads the risk of survival and ensures reproductive success. However, the relationship between dispersal and dormancy and its ecological consequences in invasive annual grasses that produce heteromorphic diaspores is not well studied. We compared dispersal and dormancy responses of diaspores from the basal (proximal) to the distal position on compound spikes of Aegilops tauschii, an invasive grass with heteromorphic diaspores. Dispersal ability increased and degree of dormancy decreased as diaspore position on a spike increased from basal to distal. There was a significant positive correlation between length of awns and dispersal ability, and awn removal significantly promoted seed germination. Germination was positively correlated with GA concentration and negatively correlated with ABA concentration, and the ABA: GA ratio was high in seeds with low germination/high dormancy. Thus, there was a continuous inverse-linear relationship between diaspore dispersal ability and degree of dormancy. This negative relationship between diaspore dispersal and degree of dormancy at different positions on a spike of Aegilops tauschii may facilitate seedling survival in space and time., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s -1 ), while that of diaspores with low wing loading (0.5 mg mm -2 ) and terminal velocity (2.5 m s -1 ) was promoted by relatively high (6 m s -1 ) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community., (© 2022. The Author(s).)

Main Conclusion: Individuals of the annual halophyte Atriplex centralasiatica produce three kinds of diaspores that differ in dispersal, dormancy/germination response and type of seed bank formed, which likely is a bet-hedging strategy in the rainfall-unpredictable environment on the semi-arid, saline Ordos Plateau in Inner Mongolia, China. Seasonal fluctuations in environmental conditions provide germination cues for the establishment of seedlings at the right time and place to ensure plant survival and population regeneration. Diaspore heteromorphism is a phenomenon in which diaspores with stark qualitative differences in morphology and ecology are produced by the same maternal plant. Germination responses and dispersal times of the annual halophyte Atriplex centralasiatica were examined to determine the role of diaspore heteromorphism in its adaptation to salt desert conditions. A. centralasiatica is a tumbleweed that produces three types of diaspores that differ in morphology and ecophysiology. The relative potential dispersal ability and intensity of dormancy of the three diaspore types was type A (fan-shaped diaspores with yellow fruits) < type B (fan-shaped diaspores with black fruits) < type C (globular diaspores with black fruits). In the field, type A retained high germinability, but all of them were depleted from the (transient) soil seedbank in the first growing season. Types B and C cycled between dormancy and nondormancy, and 0 and > 90.0% remained in the soil seedbank 2 years after dispersal, respectively. The dormancy, dispersal and salt tolerance of type B diaspores were intermediate between those of A and C. Type A exhibited low dispersal-nondormancy, type B exhibited intermediate dispersal-intermediate dormancy and type C exhibited high dispersal ability-high dormancy. In the unpredictable salt desert habitat, the functional differences in germination and dispersal of the three diaspores act as a bet-hedging mechanism and ensure population establishment in different years by spreading germination over time and space.

Background and Aims: Several studies have demonstrated trade-offs between depth of seed dormancy and dispersal ability for diaspore-dimorphic species. However, relatively little is known about trade-offs between these two life history traits for a species that produces more than two diaspore morphs. The aim of this study was to investigate the relationship between seed dormancy and dispersal in Ceratocarpus arenarius, an amphi-basicarpic cold desert annual that produces a continuum of dispersal unit morphs., Methods: A comparison was made of dispersal and dormancy breaking/germination responses of dispersal units from ground level (a), the middle of the plant canopy (c) and the top of the plant canopy (f). Various features of the morphology and mass of dispersal units and fruits (utricles) were measured. The role of bracteoles in diaspore dispersal by wind, settlement onto the soil surface and dormancy/germination was determined by comparing responses of intact dispersal units and fruits. Movement of dispersal units by wind and animals, seed after-ripening, germination phenology and the presence of water-soluble germination inhibitors in bracteoles were tested using standard procedures., Key Results: Dispersal units a, c and f differed in morphology and mass; in the majority of cases, extremes were exhibited by a and f, with c being intermediate. Overall, relative dispersal ability was f > c > a, whereas relative intensity of dormancy was a > c > f. Bracteoles increased dispersal distance by wind, enhanced settlement of diaspores onto the soil surface and mechanically inhibited germination., Conclusions: The results provide evidence for a model in which there is a continuous inverse-linear relationship between diaspore dispersal ability and depth of dormancy. Thus, dispersal unit heteromorphism of C. arenarius results in a continuum, from no dispersal ability/high dormancy (dispersal unit a) to high dispersal ability/low dormancy (unit f), which may be a bet-hedging strategy in the cold desert environment.

Post-dispersal seed removal by animals can lead to extensive seed loss and thus is an important factor in structuring plant communities. However, we know much less about post-dispersal seed predation than about other forms of herbivory. Mucilage plays many ecological roles in adaptation of plants to diverse environments; nevertheless, until now the role of mucilage in ant-mediated seed movement remains largely hypothetical. We studied the role of mucilage in seed removal of Artemisia sphaerocephala by ants in Mu Us Sandland in Inner Mongolia, China. Messor aciculatus was the most active seed predator of Artemisia sphaerocephala. Time to first ant collecting (T 1st) of wet intact seeds was longest and significantly different from that for dry intact seeds, wet demucilaged seeds, and dry demucilaged seeds; number of seeds removed to ant nests was lowest for wet intact seeds. After they were collected by ants, 5 % of wet intact seeds were dropped during transport. Our results indicate that seed mucilage of Artemisia sphaerocephala may play a significant role in post-dispersal seed removal by (1) making seeds less attractive to ants, thus resulting in a delay of collection time; (2) forming a strong bond to soil particles, making it difficult for ants to remove seeds; and (3) making seeds more likely to be dropped during transport, thereby allowing them to escape from predation even after collection by ants. This study demonstrates the importance of mucilage in reducing seed removal by ants and thus in anchoring seeds of desert plants in the vicinity of mother plants.

Seed rain and the soil seed bank represent the dispersal of seeds in space and time, respectively, and can be important sources of recruitment of new individuals during plant community regeneration. However, the temporal dynamics of seed rain and the mechanisms by which the seed rain and soil seed bank may play a role in plant community regeneration with increased grazing disturbance remain unclear. Seed rain, soil seed bank, aboveground vegetation, and rodent density were sampled along a grazing gradient in an alpine marsh on the eastern Tibetan Plateau. We described the temporal dynamics of seed dispersal using Bayesian generalized mixed models, and nonmetric multidimensional scaling and the structural equation model were used to examine the effects of grazing disturbance on the relative role of seed rain and soil seed bank on aboveground plant community regeneration. The temporal dynamics of seed rain changed from a unimodal to a bimodal pattern with increased grazing disturbance. Both species diversity and seed density of the seed rain and seed bank increased significantly with increased grazing disturbance. Increased grazing disturbance indirectly increased the similarity of composition between seed rain, seed bank, and aboveground plant community by directly increasing species diversity and abundance of aboveground plant community. However, increased grazing disturbance also indirectly decreased the similarity of seed rain, soil seed bank, and aboveground plant community by directly increasing rodent density. The similarity between seed rain and aboveground plant community was greater than that of the soil seed bank and aboveground plant community with increased grazing disturbance. Grazing disturbance spreads the risk of seed germination and seedling establishment by changing the temporal dynamics of seed dispersal. Plants (positive) and rodents (negative) mediated the role of seed rain and soil seed bank in plant community regeneration. The role of seed rain in plant community regeneration is higher than the seed bank in disturbed alpine marshes. Our findings increase our understanding of the regeneration process of the plant community, and they provide valuable information for the conservation and restoration of alpine marsh ecosystems. [ABSTRACT FROM AUTHOR]

Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana , A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since >90% of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10% moisture content (MC) and >90% of A. nervosa and A. osyrensis seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana , A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana , A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats. [ABSTRACT FROM AUTHOR]

In degraded forest ecosystems, reintroduction of keystone-woody species is an important step for restoration because it provides regeneration niches. However, lack of information on how to propagate species restricts the use of native species; specially in tropical dry forests where seed germination is seasonal and is synchronized with the onset of the wet season. We evaluated the dormancy-breaking and germination requirements of nine keystone-woody species from Dry Chaco Forest. Most fresh viable seeds of the keystone species are nondormant, but viability decreases during dry-cold storage restricting the use of some species. Seeds of three keystone species germinated to higher percentages in light than darkness and those of five species germinated equally well in light and darkness; seeds of Castela coccinea germinated to higher percentages in darkness than in light. Alternating vs. constant temperatures had no effect on germination in seven species. Seeds of Anisocapparis speciosa and Cynophalla retusa were nondormant and remained viable for only 1 month during cold-dry storage; and 62–95% of the seeds of the other seven species were nondormant. Dormancy-break was studied in five of the seven species; seeds of four species had physiological dormancy and one had physical dormancy. Dormancy-breaking was promoted by environmental conditions in the habitat, i.e. warm stratification, after seed dispersal. Castela coccinea, Achatocarpus praecox, Mimosa detinens, and Capparicordis tweedieana are the most suitable keystone species for the restoration of overgrazed areas in the Dry Chaco Forest because their seeds germinate to a high percentage and retain viability during dry storage at low temperatures. Seeds of Mimosa detinens and Capparicordis tweedieana required mechanical scarification and 6-weeks of warm stratification, respectively, for dormancy-break. [ABSTRACT FROM AUTHOR]

Among the diaspores of angiosperms an inflated ovary (IO) is a novel morphological trait, but no studies have evaluated its effects on dispersal. The primary aim of this study was to determine the effect of the IO on diaspore dispersal in three cold desert species (Carex physodes, Calligonum junceum, and Sphaerophysa salsula). Various morphological features and the mass of fruits and seeds of each species were measured. The role of an IO in diaspore dispersal by wind and water was determined by comparing responses of intact (inflated) IOs and flattened fruits and seeds. Mature diaspores of three species were dispersed by wind, and the IO significantly increased dispersal distance in the field and at different wind speeds in the laboratory. The floating time on water was greater for inflated fruits than flattened fruits and seeds. Since the seed remains inside the IO until after dispersal is completed, the IO of the three species enhances diaspore dispersal. This is the first detailed study on how an IO increases diaspore/seed dispersal. Furthermore, after primary dispersal by wind, secondary dispersal can occur via wind or surface runoff of water, and each method is enhanced by the presence of an IO. [ABSTRACT FROM AUTHOR]

Purpose: All secondary dispersal by wind, important for predicting, modeling and regulating diaspore dispersal processes, and for biodiversity conservation and vegetation restoration, is influenced by underlying surface matrix. But little is known about how matrix determines diaspore secondary dispersal. Here we focus on how lift-off velocity, good proxy for secondary dispersal of seeds by wind, is linked to the underlying surface matrix. Methods: We investigated the effect of the underlying surface matrix on diaspore lift-off velocity in a wind tunnel. Our study used 11 matrix types with different particle size, including four pure substrates (loam, aeolian sand, river sand, gravel) and seven mixtures thereof and diaspores of 28 species differing in length, width, height, mass, projected area, shape index, wing loading, and terminal velocity. Results: Diaspores were more easily dispersed from loam, aeolian sand and river sand than from the gravel substrates. For mixed matrices, lift-off velocity was closer to that of the small-sized than of the large-sized component of the substrate. Underlying surface matrix contributed more to diaspore dispersal by wind than diaspore attributes. In addition to wing loading, terminal velocity, and projected area also were important diaspore attributes determining lift-off velocity of the diaspores. Conclusion: Lift-off velocity of diaspores is influenced by particle size of underlying surface matrix during secondary wind dispersal: lift-off velocity is the largest on large-sized particles for pure matrices, and determined by the small-sized component for mixed matrices. [ABSTRACT FROM AUTHOR]

Environmental changes, for example, in rainfall and land use, lead to changes in the environment experienced by subsequent generations of plant species. Environmental conditions of maternal plants can influence the fitness and phenotypes of subsequent generations via non‐genetic mechanisms: transgenerational plasticity (TGP). However, relevant empirical evidence remains scarce and ambiguous. What are the adaptive consequences of TGP for plants in the face of environmental change? For how many generations does the TGP effect remain?We tried to answer these questions by measuring life‐history traits and reproductive characteristics of progeny plants of the diaspore‐heteromorphic annual halophyte Atriplex centralasiatica in a 3‐year TGP experiment covering F0, F1 and F2 and partly F3. Plants from diaspore types A (low dispersal and high germination ability) and C (high dispersal and low germination ability) were grown in favourable versus stressful salinities over three generations in a fully factorial design.Transgenerational plasticity of plants grown in favourable versus stressful salinities decreased from F2 → F1 → F0. Compared to the favourable condition, the stressful condition decreased the length of the vegetative period, increased the length of reproductive time, reproductive allocation and progeny diaspore size. Salinity tolerance and phenotypic plasticity were higher in plants from diaspore A than in those from diaspore C. In the stressful condition, plants produced less plant biomass, larger diaspores, a higher proportion of diaspore C, but lower proportion of diaspore A. Production of the proportion of diaspore C increased with increase in number of previous generations that experienced stress. The stress experience of the great‐great grandmother (F0) continued into the lower A:C ratio of the F3 diaspores.Synthesis. Our findings provide evidence for the 'escape strategy' of A. centralasiatica: TGP could spread the risk of environmental adversity by delaying seed germination temporally and broadening seed dispersal spatially, thus allowing plants to cope with environmental heterogeneity. Specifically, the trade‐off in reproductive allocation between diaspores A and C enables plants to develop divergent strategies. New research should reveal the extent to which wide‐ranging taxa can benefit from TGP and whether even (great)‐great grandmother might be the starting point of TGP. [ABSTRACT FROM AUTHOR]

Why the fruits are retained on dead upright herbaceous plants and how this relates to seed dispersal and timing of germination remain unclear. Stems of the annual Euclidium syriacum (Brassicaceae) with infructescences bearing indehiscent silicles remain upright after plants die in the spring. We investigated the effect of anatomical structures of stem and pedicle and delayed silicle dehiscence on seed dispersal phenology of this species. For comparison, sections were made of the stem of the annual Goldbachia laevigata (Brassicaceae), which has stems that fall over when plants die. Compared to G. laevigata, the stem of E. syriacum has vascular bundles that are closer together, a thicker xylem and phloem, more fibers, a thicker perimedullary zone and a smaller pith diameter:stem diameter ratio. The thickened pedicle did not form an abcission layer. By late October, 5–20% of seeds were dispersed, depending on the position of infructescences on the plant. Snow covered the plants in late autumn and when it melted in mid‐April many of the plants had fallen over, with a high number of seeds germinating in attached silicles; seedlings became rooted in soil. After snowmelt, 14–15% of the silicles on the remaining upright plants contained seeds; all seeds were dispersed by early July. The anatomical structures of the stem and pedicle plus the delayed dehiscence of silicles explain the presence of an aerial seed bank in E. syriacum and delay of germination of many of seeds until spring. Further, pieces of upright plants are broken off and dispersed by wind, which helps to explain the wide distribution of E. syriacum in the cold desert. [ABSTRACT FROM AUTHOR]

The invasive liana Euonymus fortunei (Turcz.) Hand.-Maz. (wintercreeper) is an emerging invader that through monodominance of woodlands can drastically reduce native species diversity and alter nutrient cycling. We studied how the vegetation and soils of invaded (INV), "native" (NAT), and wintercreeper removal (REM) site treatments influenced seed germination and seedling survival of this invader. The effect of aril (with vs. without) was also tested for wintercreeper seeds under field and in vitro conditions as a proxy for gravity vs. animal dispersal of seed, respectively. Germination was significantly delayed for seeds sown with an aril (vs. without), as well as those sown in INV soils (vs. NAT or REM), but neither site nor aril affected total germination. The proportion of germinated seedlings that survived after the first winter was significantly different based on site (p = 0.054) and aril (p = 0.071) treatments, with lower survival resulting from seeds sown without arils, and for seeds sown in INV sites. Magnesium (Mg) concentrations were significantly higher among INV soils (vs. NAT) and provide further support that wintercreeper is a driver of soil nutrient change. Our findings that aril-enclosed (gravity-dispersed) seeds yielded greater survival, despite being locally dispersed within invaded sites (where survival was lowest), support the historically slow rate of spread for this species. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

My purpose is to introduce a special issue of Seed Science Research devoted to papers resulting from material presented at Seed Ecology V held in Caeté, Brazil on 21–25 August 2016. An overview of the field of seed ecology is presented that includes a short summary of what I consider to be the eight basic subcategories of this field, and the five new areas of investigation that have developed as extensions and/or recombinations of basic areas. Seed ecology conferences allow researchers to communicate with each other and build new collaborative relationships. At Seed Ecology V, information was presented that related to each area of seed ecology. The nine papers in this special issue are a small sample of the information presented at the meeting, and each paper is briefly described and placed into one of the subcategories of seed ecology research. [ABSTRACT FROM AUTHOR]

Physical dormancy (PY) in seeds/fruits, which is caused by the water-impermeable palisade layer, has long been considered a mechanism for synchronizing germination to a favourable time for seedling survival and establishment. Recently, a new hypothesis (crypsis hypothesis) was proposed as the main selective factor for the evolution of PY. However, there are some misconceptions in this hypothesis. Our objective is to critically evaluate the crypsis hypothesis and to point out that there are multiple adaptive roles of PY. The fundamental argument in the crypsis hypothesis, that PY evolved as an escape mechanism from predators, is not valid according to the evolutionary theory of Darwin. According to Darwin's hypothesis, variations (dormancy in our case) within a population occur randomly, i.e. there is no direct function of a variation at the time of its origin. Different selection pressures operating in the environment increase or decrease the fitness of individuals with the variation. Water-gap anatomy in seeds/fruits and phylogenetic relationships of species with PY suggest that PY has evolved several times in angiosperms. Thus, we argue that not only predatory pressure but also several other environmental pressures (e.g. proper timing of germination, ultra-drying of seeds, dispersal and pathogens) were involved in increasing the fitness of species producing seeds with PY. The significance of PY in the survival of the species under the above-mentioned environmental pressures and other misconceptions of the crypsis hypothesis are discussed in detail. [ABSTRACT FROM AUTHOR]

* Premise of the study: Many congeneric species are disjunct between eastern Asia and eastern North America. No previous study has compared the seed biology of closely related disjunct taxa of legumes or of a diaspore-heteromorphic species. Our objective was to compare seed dormancy in two such sister species in the genus Amphicarpaea (Fabaceae). * Methods: We investigated the ecology and ecophysiology of aerial and subterranean seeds of the amphicarpic species Amphicarpaea edgeworthii from China and compared the results to those published for its sister species A. bracteata from eastern North America. * Key results: The seed coat of aerial seeds of A. edgeworthii is well developed, whereas the seed coat of subterranean seeds is not. Aerial seeds have combinational dormancy (physical dormancy [PY] + physiological dormancy [PD]) broken by scarification followed by cold stratification or by after-ripening and scarification; whereas subterranean seeds have PD broken by cold stratification. Aerial seeds formed a persistent soil seed bank, and subterranean seeds a transient soil seed bank. Aerial seeds of A. bracteata also have PY+PD and subterranean seeds PD. Subterranean seeds of both species are desiccation intolerant. * Conclusion: Dormancy in neither aerial nor subterranean seeds of both species has diverged over geological time. Compared to subterranean seeds, aerial seeds of both species dispersed over longer distances. Seed dispersal ability and degree of dormancy of neither species fits the high-risk/low-risk (H-H/L-L) strategy found in many diaspore-dimorphic species. Rather, both species have an H-L/L-H strategy for these two life history traits. [ABSTRACT FROM AUTHOR]

Abstract: This study quantified various aspects of the seed biology of 100 tree species native to the seasonal moist tropical forest in the Panama Canal Watershed. Species were selected for study based on their potential for use in reforestation projects in Panama. Seeds of 32, 29, and 33 species were dispersed during the dry (DS, January–March), early rainy (ERS, April–July), and late rainy (LRS, August–December) seasons, respectively. Seed mass was correlated with moisture content (MC) but not with dispersal time, and MC was lowest for seeds dispersed in the DS. Germination of nontreated seeds ranged from 0% (6 species) to 99% and was ≥50% for 46 species. Seeds of Beilschmiedia pendula, Castilla elastica, Diphysa robinioides, Genipa americana, Hura crepitans, Inga spectabilis, Jacaranda copaia, Protium tenuifolium, Pseudobambox septenatum, and Trattinnickia aspera germinated ≥85%. Fresh seeds of 49 (52.1%) of the 94 species that germinated were nondormant and 45 (47.9%) were dormant. Only 12 species had a median length of germination time (MLG)>120 days. MLG for seeds of species dispersed in the LRS was higher than that of those dispersed in the ERS or DS. Forty-eight species had uniform germination (standard deviation of germination time≤14 days). Seed longevity ranged from 0.5 to 36 months, and long-lived (L-L) seeds tended to be larger than short-lived (S-L) or very short-lived (very S-L) ones, but not significantly so. MC increased significantly from L-L to very S-L seeds. The highest proportion of L-L seeds was dispersed in the DS and the lowest in the LRS. Results of this study are used to make recommendations for nursery production of tree seedlings to use in forest restoration projects. [Copyright &y& Elsevier]

• Seeds of Meconopsis integrifolia and M. racemosa have morphophysiological dormancy. • Seeds of both species exhibited annual dormancy cycling in the field. • Dormancy was broken during autumn and winter and reinduced in summer. • Germination occurs in early spring regardless of when seeds are dispersed. Timing of seed germination is critical for seedling establishment and growth of the plant to maturity. Theoretically, then, germination of alpine species should be restricted to a period that ensures seedlings will reach a critical size during the short growing season for overwinter survival. We hypothesized that seeds of two alpine monocarpic perennials of Meconopsis germinate only at the beginning of the growing season in early spring and that dormancy synchronizes the timing of germination to this period. We tested the effects of light, temperature, cold stratification and GA 3 on germination of Meconopsis integrifolia and M. racemosa in the laboratory and germination responses to temperature during two 2-year periods of seed buried at 4450 m a.s.l. on the Tibetan Plateau. Most fresh seeds of both species were dormant, and the embryo underdeveloped, indicating morphophysiological dormancy (MPD). GA 3 promoted embryo growth and germination of seeds. Buried seeds exhibited an annual dormancy cycle. The physiological component of MPD was released gradually in the field during autumn and winter, resulting in embryo growth (release of morphological component of MPD) and germination just after snowmelt in spring. Embryos in seeds that did not germinate the first year remained underdeveloped until the second spring. Delay of seed burial from October until January (simulating a delay in time of seed dispersal) delayed germination for 1 year but did not change the germination season. Thus, our hypothesis that MPD restricts germination to the beginning of the growing season is supported. [ABSTRACT FROM AUTHOR]

Fruit/seed heteromorphic plants have been studied most extensively for differences in dispersal and germination of the morphs. However, fates of the heteromorphic diaspores beginning with seed release and ending with germination/seed death have been documented for relatively few species. Our primary aim was to follow the fates of the two dispersal unit morphs of Diptychocarpus strictus over a several-year period or until they germinated or died. Our hypothesis was that the winged, mucilaginous seeds (dispersal unit) from the dehiscent upper siliques form a short-lived seed bank and the nearly-wingless, nonmucilaginous seeds inside the indehiscent lower siliques (dispersal unit) a long-lived seed bank. Thus, for the two morphs we monitored phenology of seed release in 2010, germination phenology from 2010 to 2014 and germination and survival during burial in soil from 2010 to 2012. All lower siliques had been released from mother plants by late July, whereas seed release of the winged seeds of upper siliques was not completed until late October, after the main stem had become detached (near the base). Most seeds (18%) from upper siliques that did so ( c . 20%) germinated in spring 2011, whereas no seeds in lower siliques germinated until autumn 2011 (0.2%). All seeds from upper siliques had germinated or lost viability by the end of the autumn 2012 germination season, whereas 11% of seeds inside lower siliques germinated in autumn 2014 and a high proportion of the nongerminated seeds was still viable, thus supporting our hypothesis. Buried seeds of both morphs exhibited a 6-mo dormancy cycle in which the nondormant phase coincided with the two germination seasons. Dehiscence of the upper siliques and indehiscence of the lower siliques are required for D. strictus to have a high risk-low risk strategy (H/H-L/L) for diaspore dispersal and dormancy. [ABSTRACT FROM AUTHOR]