Effect of salinity on seed germination and seedling growth of the halophyte Suaeda japonica Makino

Seed germination and seedling growth of the annual halophyte species Suaeda japonica Makino were investigated in response to variable salinity of sediment pore water. The germination percentage of S. japonica’s soft brown seeds, which are dominant among dimorphic seeds, decreased with an increase in salinity, although germination was still observed at 1200‐mM NaCl concentration. The germination percentage and germination speed observed in April were higher than those observed in December when treated with sediment water with 400–1200 mM of NaCl concentrations. These data suggest that S. japonica seedlings could be established on sediments that experience high temperatures. Germination recovery of S. japonica seeds transferred from 600‐mM NaCl containing sediment (seawater equivalent) was lowest among 0–1200‐mM NaCl treatments, implying the low tolerance of seawater conditions of S. japonica seeds. Seeds germinated in 900‐ to 1200‐mM NaCl medium showed poor growth, but survived, in hypersaline conditions, and exhibited improvement in growth upon transfer to lower salinity.     

Fine-scale spatial heterogeneity and seed size determine early seedling survival in a desert perennial shrub (<Emphasis Type="Italic">Ericameria nauseosa:</Emphasis> Asteraceae)

In heterogenous landscapes, seeds settle in some microsites more readily than others, independently of whether those microsites are suitable for germination and subsequent growth, and survival of seedlings. Wild seeds and seedlings of Ericameria nauseosa var. oreophila in the sand-dune ecosystem near Mono Lake, California show both concordance and conflict in where seeds are retained and where seedlings flourish. Using a field experiment, we followed performance of seeds and seedlings (i.e., the rate of germination and successful emergence, initial seedling size, seedling growth and survival over first growing season), by planting seeds of known sizes in pre-identified microsites (windward and lee aspects of interspaces between shrubs, under shrub canopies, and under snag canopies, respectively). Heavier seeds were more likely to germinate and emerge successfully and resulted in initially larger seedlings than lighter seeds. These initially larger seedlings subsequently remained larger over the growing season and lived longer than initially smaller seedlings. Independent of seed and initial seedling size, seedlings that germinated under the canopy of adult shrubs grew larger and survived longer than seedlings that germinated in interspaces (open space with little or no vegetation) or under snags (dead adult shrubs). Seedlings grown under the canopy of adult shrubs experienced significantly less solar radiation and wind-deposited sand than seedlings grown in interspace or snag microsites. Sand burial more than 1 cm was lethal for seedlings. The two variables of seed size and microsite type had by far greater impact on eventual growth and survival of seedlings than did aspect, and the effects of the former two variables were independent of each other. This study amplifies the body of work on E. nauseosa at this site demonstrating that the earliest events in the life history of this long-lived perennial shrub appear to persist through time despite the harsh and variable environment.     

Vivipary in Ophiorrhiza mungos L. – a rare phenomenon in angiosperms

Vivipary, the precocious germination of seeds within the parent plant, is a specialised feature of evolutionary and biological importance that ensures survival of a plant. Reports on vivipary in angiosperms are rare, accounting for <0.1% of flowering plants. Here, we report a remarkable case of occurrence of vivipary in Ophiorrhiza mungos. A study was conducted to collect information on the morphology of the capsules that support vivipary, environmental factors that induce vivipary, survival mode and the survival of viviparous seedlings. The hydroscopic movement of the cup‐shaped capsules of O. mungos was found to help in viviparous germination during the rainy season. Of the total seeds in a capsule, 70% showed viviparous germination. The seedlings remaining inside the capsule attain a height of 0.98 ± 0.4 cm and reach the ground when the capsule falls. On the ground, seedlings obtain easy anchorage to the substratum since they have already germinated. Vivipary appears to be an adaptation of O. mungos to the rainy season for ensuring viable offspring. This suggests that vivipary in this species might be artificially induced by continuous spraying with water to rescue seeds in all seasons for use in large‐scale propagation to meet increasing market demand and conservation of this valuable anticancer medicinal herb.     

Interacting effects of grass height and herbivores on the establishment of an encroaching savanna shrub

Shrub encroachment is a widely observed problem in Southern African savannas. Although the effects of herbivory and grass height on woody species recruitment have been studied individually, little information exists about how these factors interact. In this study seeds and seedlings of the encroaching shrub Dichrostachys cinerea were planted in clipped and unclipped grass plots, with and without large herbivores present. Seed germination, seedling survival and seedling predation were monitored for 8 months. Germination started earlier in plots where herbivores were excluded. Overall, the earlier the seeds germinated, the longer the seedlings survived. Clipping positively affected the number of germinated seeds, seedling growth and survival but effects varied among herbivore exclusion treatments and sites. Invertebrates caused the majority of the seedling damage. We conclude the recruitment of D. cinerea is influenced by the interplay of grass height and herbivory. In this study, the presence of large herbivores early in the wet season, and the absence of simulated grazing later on, affected the regeneration of D. cinerea negatively. However, differences in effects among sites suggest that the mechanisms found here may work differently in other habitats.      

Stress-associated factors increase after desiccation of germinated seeds of <Emphasis Type="Italic">Tabebuia impetiginosa</Emphasis> Mart.

Improved re-establishment of desiccation tolerance was studied in germinated seeds of Tabebuia impetiginosa Mart. by exposing to a polyethylene glycol solution prior to desiccation. The effects of different osmotic potentials and drying rates were studied. In addition, temporary temperature stress and exogenous abscisic acid were applied to evaluate their effect on desiccation tolerance of the protruded radicle. An osmotic potential of −1.7 MPa at 5°C followed by slow drying was most effective in the re-establishment of desiccation tolerance in protruded radicles with a length up to 3 mm. An osmotic potential of −1.4 or −2.0 MPa was less effective. Fast drying completely prevented the re-induction of desiccation tolerance. Cold shock or heat shock prior to osmotic treatment as well as abscisic acid added to the osmotic solution improved desiccation tolerance of protruded radicles. Surprisingly, survival of the germinated seed did not depend on re-establishment of desiccation tolerance in the protruded radicle. Even after the protruded radicle became necrotic and died, the production of adventitious roots from the hypocotyls allowed for survival and the development of high quality seedlings. Thus, T. impetiginosa appeared to be well adapted to the seasonally dry biome in which the species thrives via mechanisms that offer protection against desiccation in the young seedling stage.     

Habitat choice and seed–seedling conflict of Spartina alterniflora on the coast of China

To elucidate the seed–seedling conflict and the process of habitat choices during the expansion of S. alterniflora, densities of seeds and seedlings in three different habitats, foreland, Spartina meadow, and canopy gap patch, were measured. Statistical analyses of these measurements were performed to investigate the interaction between seeds or seedlings and environmental factors. Also, the process of habitat choice during the expansion of S. alterniflora was explored. The results show that, in the upper soil seed bank (0–5 cm), both the ratio of germinated seeds and the ratio of survival seedlings to total seeds do not differ significantly among the three habitats. However, in the lower soil seed bank (5–10 cm), these ratios differ significantly, suggesting the seed–seedling conflict of S. alterniflora generally occurs in the lower soil seed bank. The remarkable conflict occurs in the meadow habitat. Greenhouse experiments indicate that the germination rate decreases significantly and the mortality of pre-emerged seedlings increases significantly with increasing burial depth. The maximal burial depth of emerged seedlings varies with sediment types. Comparisons of burial depth effects on seedling height, mesocotyl length, coleoptile length, and root length show that the major responses of S. alterniflora pre-emerged seedlings to the burial treatments are the elongation of coleoptiles and mesocotyls, which favor seedling survival by enhancing aeration and accelerating emergence. These results suggest that burial treatment is a key selection factor, which leads to the seed–seedling conflict in recruitment of S. alterniflora population, and directly affects the expansion rate and the area infected by S. alterniflora. Handling editor: S. M. Thomaz Ziwang Deng: co-first author.     

Ecology of seed germination of eight non-pioneer tree species from a tropical seasonal rain forest in southwest China

We compared various aspects of the seed biology of eight non-pioneer tree species from a tropical seasonal rain forest in Xishuangbanna, SW China, that differ in time of dispersal, size and fresh seed moisture content (MC). Seeds were tested for germination under laboratory conditions after dehydration to different moisture levels and under 3.5, 10 and 30% solar irradiances in neutral-shade houses. For six species, germination was also compared in forest understory (3.5% light) and center of a forest gap (32.5% light). Under continuous dehydration over activated silica gel, 100% of seeds of four species had lost the ability to germinate after 48 h, and those of all species except Castanopsis hystrix (decreased from >90 to 30% germination) had lost the ability to germinate after 120 h. Four species did not differ in final germination percentages at the three irradiances (i.e. uniform germination). However, final germination percentages of Horsfieldia pandurifolia and Litsea pierrei var. szemaois were significantly lower in 30% than in 10 or 3.5% light, and seeds of Antiaris toxicaria and C. hystrix germinated to higher percentages in 30 and 10% than in 3.5% light. Mean time to germination (MTG) of the eight species (forest and shade house data combined) ranged from 5–5 days for Pometia tomentosa to 72–207days for L. pierrei; MTG for four species was ≤21 days. There was no obvious relationship between relative desiccation resistance and either time of dispersal, MTG or uniformity of germination at the three light levels, or between seed size and MC or MTG. However, the relationship between seed MC at maturity (25–60% fresh mass basis) and MC at 50% loss of seed viability (12.4–42.5%) was significant. Seven of the species fit Garwood’s (Ecol Monogr 53:159–181, 1983) rapid-rainy germination syndrome and one, L. pierrei, either her delayed-rainy or intermediate-dry germination syndrome. However, fresh, non-dehydrated seeds of all eight species germinated in ≤30 days at constant 30°C in light.     

<Emphasis Type="Italic">In vitro</Emphasis> germination and micropropagation of <Emphasis Type="Italic">Givotia rottleriformis</Emphasis> Griff.

The propagation of Givotia rottleriformis Griff. is difficult as a result of long seed dormancy associated with poor seed germination. The present study was undertaken to develop a protocol to overcome seed dormancy by culture of zygotic embryo axes and then develop an efficient method for micropropagation of Givotia. Best germination frequency (78.3%) was achieved from mature zygotic embryo axes isolated from acid-scarified fresh seeds when cultured on Murashige and Skoog (MS) medium (half-strength major salts) with 28.9 μM gibberellic acid (GA₃). Efficient plant conversion was achieved by transfer of 10-d-old germinated embryos to MS medium (half-strength major salts) supplemented with 1.2 μM kinetin (KN) and 0.5 μM indole-3-butyric acid (IBA). However, acid scarification of 1-yr-old seeds decreased the germination frequency of zygotic embryo axes in comparison to those obtained from non-acid-scarified seeds which germinated (96.2%) and converted into plants (80.3%) on MS basal (half-strength major salts) medium. Multiple shoot bud induction was achieved by culture of shoot tips derived from in vitro germinated seedlings on MS medium with 0.5 μM thidiazuron for 4 wk, and the shoots elongated after transfer to a secondary medium with 1.2 μM KN. A maximum number of 7.8 shoots per explant with an average shoot length of 3.2 cm was achieved after two subcultures on this medium. The in vitro regenerated shoots rooted (41.5%) on half-strength MS medium with 0.5 μM IBA. The in vitro generated seedlings and micropropagated plants were established in soil with a survival frequency of 70% and 60%, respectively.     

THE EFFECT OF SEED DIMORPHISM ON THE GERMINATION AND SURVIVAL OF SALICORNIA EUROPAEA L. POPULATIONS

Seed dimorphism influenced the germination behavior of Salicornia europaea L., with small seeds being more dormant and less salt tolerant than large seeds. All of the large less dormant seeds of S. europaea germinated prior to May, and all seedlings produced after this time were from small seeds. A persistent seed bank was maintained by the small dormant seeds. Survivorship was relatively constant during the normal germination season, but increasing salinity stress at any time during the spring reduces the chance of seedling survival. Little germination occurred from July through September because of the high surface soil salinities during this period.     

In vitro propagation of the endangered orchid Laelia speciosa

Laelia speciosa is an endangered epiphytic orchid. The effects of various media components on germination of L. speciosa were evaluated. Pods were collected at 4, 7, and 9 months following hand-pollination, and seeds were germinated on Murashige and Skoog (MS) media with 30 g l⁻¹ sucrose and five concentrations (0.0, 0.04, 0.22, 0.44, and 2.22 μM) of benzyladenine (BA) under light and dark conditions. Gibberellic acid (GA₃; 0.0, 0.29, 1.44, 2.89, 14. 43 and 28.87 μM) with naphthaleneacetic acid (NAA; 0.0, 0.54, 1.34, 2.69, and 5.37 μM) were evaluated for in vitro subcultivation. MS medium with 30 g l⁻¹ sucrose was effective for germination. The effects of BA and light on germination of L. speciosa seeds differed with pod maturity. All mature seeds germinated using 0.44 μM BA and light. The highest frequency of germinated seedlings (60%) was obtained using mature seeds grown on MS medium without BA and under light conditions. For subculture, MS with 30 g l⁻¹ sucrose, 2.69 μM NAA, and 0.29 μM GA₃ was effective. Plantlets of 5 cm in length were transplanted to the greenhouse, and a 77.5% of survival rate was obtained. A successful protocol for micropropagation by seed germination will contribute to the development of a sustainable management program for L. speciosa.     

Comparison of seed and seedling functional traits in native Helianthus species and the crop H. annuus (sunflower)

• Seed functional traits of native Helianthus species contribute towards ecosystem services but limitations to their use in managed programmes exist. Many perennial Helianthus possess seed dormancy. The ability for germination to occur under different temperature and drought conditions, as well as the capacity of germinated seeds to convert into normal seedlings is rarely considered. Our aim was to identify and quantify these constraints through functional trait analyses.
• In five seed lots of native Helianthus (four perennial and one annual) and five genotypes of sunflower (H. annuus) for comparison, dormancy, thermal and hydro thresholds and times, morphology, mass, oil content and conversion into normal seedlings were quantified. The influence of the seed collection site environment on these traits was also explored.
• Seed dormancy of the perennial species was overcome by scarification followed by germination in 5 mm GA₃. Thermal and hydro‐time analyses revealed slower germination for the native seed lots (>1350 °Ch) in comparison to the sunflower genotypes (<829.9 °Ch). However, native seed lots had a higher capacity to convert into normal seedlings at high temperatures and low water potentials than sunflower genotypes. For the native seed lots, the average monthly temperature of the collection site was negatively correlated with thermal time.
• Variability in seed functional traits of native Helianthus and greater capacity for germinated seeds to convert into normal seedlings suggests they are better equipped to cope with high temperature and drought scenarios than sunflower. Effective dormancy alleviation is required to facilitate the use of native Helianthus species.

     

Germination of stored and scarified seeds of Passiflora caerulea L. (Passifloraceae)

Abstract

This work evaluates the influence of storage and scarification in the germination of Passiflora caerulea L., in order to acquire the necessary knowledge to cultivate this economically important species. Seeds stored one month under different conditions (no storage, fermentation, desiccation) were submitted to various pre‐treatments (aril removal, mechanical and chemical scarification or combinations of these). Emergence was recorded periodically for 11 months in a greenhouse. Germination time, germination percentage and germination speed were calculated. Histochemical tests were applied to seeds maintained under the three storage conditions, for observing possible changes in the integument and storage tissue. Viability was maintained at least for the storage period tested, as germination occurred after that time. Because the seeds stored under desiccation germinated, the species is orthodox. Chemical scarification prevented germination in most cases. Although germination levels were low, they were higher in stored seeds (fermented and desiccated) than in fresh ones. Fermented seeds (which exhibited no storage tissue and less lignin in the integument) devoid of the aril germinated earlier, faster and in greater quantity. The type of dormancy of this species is discussed.     

The “Trojan horse” strategy: Seed fungal endophyte symbiosis helps to explain the invasion success of the grass,Poa annua,in Maritime Antarctica

Aim

Poa annua L. (annual bluegrass) is presently the sole invasive vascular plant species to have successfully established in Maritime Antarctica, where it poses a significant conservation threat to native plant species. However, the reasons for its success in the region have yet to be established. Here, we determined whether the invasiveness of P. annua, and its competitiveness with the native Antarctic hairgrass Deschampsia antarctica, is influenced by symbioses formed with seed fungal endophytes, and whether plants derived from seeds from four global regions differ in their performance.

Locations

Four regions (Maritime Antarctica, sub-Antarctica, South America and Europe).

Methods

Endophyte frequency was measured in P. annua seeds collected from the four regions. The germination, survival, biomass accumulation, flowering and competitiveness with D. antarctica of P. annua plants grown from endophyte-uncolonised and uncolonised seeds was determined in the laboratory. The effects of endophytes on P. annua seed germination and survival and seedling osmoprotection were also assessed in the Maritime Antarctic natural environment using locally-sourced seeds.

Results

Endophytes were at least twice as frequent in seeds from Maritime Antarctica than in those from other regions. A higher proportion of endophyte-colonized seeds germinated and survived than did uncolonised seeds, but only when they originated from Maritime Antarctica. Seed endophytes increased the competitiveness of P. annua with D. antarctica, but only for plants grown from Maritime Antarctic seeds. In the field, endophyte-colonized seeds from Maritime Antarctica germinated and survived more frequently than uncolonised seeds, and osmoprotection was higher in seedlings grown from colonized seed.

Main Conclusions

The findings indicate beneficial effects of seed endophytes on invasion-related traits of P. annua, such as survival, germination success and flowering. Together with vegetative and reproductive traits facilitating the colonization process, the seed-fungal endophyte symbiosis can be invoked as an important factor explaining the invasiveness of P. annua in Maritime Antarctica.     

Rapid germination and development of <Emphasis Type="Italic">Taxus baccata</Emphasis> L. by <Emphasis Type="Italic">in vitro</Emphasis> embryo culture and hydroponic growth of seedlings

A highly promising procedure to obtain seedlings of Taxus baccata L. has been developed, which involves a combination of in vitro embryo culture and growth under hydroponic conditions. Embryos isolated from freshly collected seeds were 100% sterile, even though the seeds were not treated with acid or soaked in water prior to culturing. The embryo germination level of non-leached seeds was slightly lower (85%) than those leached in running water for 7 d (100%). The leached embryos germinated with extended roots while the non-leached embryos had abnormal shapes. The embryos cultured on media supplemented with an absorbent (PVP or activated charcoal) had extended roots and shoots and were a larger size without any browning, as compared to those grown without the supplement; activated charcoal gave better results. There were no significant differences in germination rates of T. baccata embryos between the media with differing strengths of macronutrients; however, for further development of the shoot, it was necessary to sub-culture the seedlings in MS in the light. To obtain seedlings with longer roots, they had to be maintained in one-half strength MS in darkness. Approximately 90% of the plants survived when grown hydroponically for 2 mo. The surviving plants showed well-extended roots and were a good starting material for genomic, proteomic, and conservational studies as well as Taxol permeabilization investigations.     

Factors limiting the distribution of the annual legumeKummerowia striata in a river floodplain

The annual legumeKummerowia striata often predominates in river floodplains forming a large population, but it is rare in gravelly areas adjacent to it. In order to clarify the factors limiting the distribution ofK. striata, its distribution pattern, germination and survival of seeds sown artificially were studied in the floodplain of the Ohta River. There was a positive correlation between the cover value ofK. striata and the percentage of fine particles (<0.2 mm) in the soil. In the winter season, there was a number of seeds (up to 47 seeds 20 cm⁻²) on the ground where aK. striata population had existed in the previous year, but they were very sparse in areas apart from the population. Only a small proportion of seeds sown in the gravelly area germinated. Many of the germinated individuals died before the first leaf unfolded, but the rest survived to maturity despite repeated floodings. Plants germinated in the gravelly area and those inoculated with soil from the gravelly area bore nodules, showing the presence ofRhizobium in the gravelly area. It was concluded that the colonization ofK. striata in the gravelly area was limited by slow dispersal, and by a low percentage of germination and high mortality in the early stage of establishment.     

Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert

• Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality.
• Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C.
• Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR‐rich light.
• This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource‐limited conditions.

     

Effect of Salinity on Seed Germination,Growth, and Ion Accumulation of Atriplex patula (Chenopodiaceae)

Seeds and seedlings of the halophyte Atriplex patula were exposed to 0–2% NaCl to determine the effect of salt stress on germination and growth. Seeds germinated and plants survived and grew in solutions of up to 2.0% NaCl. Both seed germination and dry mass production were negatively affected by increased salinity. Dry mass production declined to 1% of controls and seed germination to 17% of controls in the 2% NaCl treatments, indicating that seeds were less inhibited than growing plants. Also, recovery treatments indicated that high salinity did not permanently injure seeds. Percent ash, and Na⁺ and Cl⁻ ions increased in shoots with each salt increment, while the K⁺ ion content decreased sharply. Atriplex patula is a facultative halophyte, and is limited to low and moderately saline sites because both seed germination and growth are severely reduced at salinities > 1% NaCl.     

Dihydroquercetin protects barley seeds against mold and increases seedling adaptive potential under soil flooding

Barley (Hordeum vulgare L.) seeds were soaked in aqueous 10⁻⁴ M dihydroquercetin (DHQ) to examine its influence on seed germination and further growth of seedlings under optimal soil watering and flooding conditions. The adaptive potential of the plants was estimated by the content of thiobarbituric acid reactive substances (TBARs) and the activity of ascorbate peroxidase (AsP). High-grade seeds were germinated evenly under (−DHQ)- and (+DHQ)-treatments. Low-grade seeds soaked in DHQ, showed no mold and twofold germination rate in comparison with the same seeds soaked in water. The seedlings grown from the similarly germinated seeds did not differ from each other in the shoot growth, independent of the DHQ-pretreatment. The root growth was higher in DHQ-pretreated plants. Soil flooding suppressed the shoot and root growth rates in non-pretreated and DHQ-pretreated plants, however TBARs content was lower in the roots and leaves of (+DHQ)-seedlings as compared to the (−DHQ)-ones. The activity of AsP increased more significantly in the (+DHQ)-plants. The ratio between TBARs content and the AsP activity was lower in the leaves of (+DHQ)-plants both under optimal soil conditions and flooding. Thus, the treatment of low-grade barley seeds with DHQ protects the seeds against mold and increases adaptive potential of the seedlings.     

Factors affecting the population dynamics of Suaeda maritima at initial stages of development

This study describes life history and population dynamics of the annual halophyte Suaeda maritima, at initial stages of seedling development, in salt-marshes of the Mont-Saint-Michel Bay. Effects of salinity on seed germination and seedling development were studied both in the laboratory and in the field. Salinity was measured as sediment electrical conductivity. Experiments in the laboratory showed that Suaeda maritima was relatively tolerant to salinity during the germination stage. In the field, germination occurred when soil salinity was minimal. Almost all seeds germinated in the field; this may explain the absence of a persistent seed bank. Salinity did not seem to affect the growth of seedlings either. Mortality in the field was attributed to physical factors such as anoxia during temporary immersion, burial by sediment and tidal uprooting. The intensity of these effects varied according to the location of Suaeda maritima seedlings: in hollows, along the edge of tidal creeks, in gaps among dense vegetation cover, or in pattern with Puccinellia maritima. Perennial vegetation did not restrict Suaeda maritima germination. In contrast, perennials such as Puccinellia maritima and Halimione portulacoides limited the development of Suaeda maritima seedlings since only a small number of this annual emerged beneath their canopies. The fate of seedlings depended to a great extent on the permeability of the perennial canopy to light. Thus, disturbance resulting in bare patches inside the perennial vegetation seemed essential for the development of this annual species. Suaeda maritima can grow in the presence of Puccinellia maritima so long as the latter present as an open matrix. Suaeda maritima may also benefit from protection against desiccation and tidal action where this occurs.     

Burial of canopy-stored seeds in the annual psammophyte Agriophyllum squarrosum Moq. (Chenopodiaceae) and its ecological significance

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45–80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes.