Germination biology and seedling growth of Clusia hilariana Schltdl., a dominant CAM-tree of drought-prone sandy coastal plains

The spatial and temporal fluctuations of water availability can be an obstacle for recruitment of many species in the restinga and might restrict seed germination and seedling growth in specific regeneration safe-sites. Clusia hilariana is one of the most dominant species of Restinga de Jurubatiba. This species has a high proportion of seedling establishment occurring inside the tanks of soil bromeliads underneath vegetation patches. Given the thin seed coats, the fast germination time and seed dispersal of C. hilariana during the dry season, we hypothesized that their major regeneration niche (the tanks of soil bromeliads) is related to susceptibility of seed germination and also seedling growth to low water availability. To test this hypothesis, seeds were germinated under decreasing water potentials using PEG 6000 solutions and seedlings were grown under varying water regimes. The percentage of seed germination progressively decreased at lower water potentials. After 38 days in ?1.0 MPa no seeds germinated. However, approximately 90% of seeds germinated when transferred to Ψ = 0 MPa. The relative growth rates of seedlings of C. hilariana did not differ between water treatments. Thus, the major regeneration niche of C. hilariana is not a consequence of a high sensitivity of seeds and seedlings to water shortage. Nonetheless, C. hilariana showed an array of seed and seedling traits that may help to overcome establishment constraints of the harsh environment of restingas.     

Seed dispersal in the mycoheterotrophic orchid Yoania japonica: Further evidence for endozoochory by camel crickets

• Although orthopterans are rarely considered to be effective seed dispersal agents, the large flightless crickets known as ‘weta’ have been suggested to function as ecological replacements for small mammals in New Zealand, where such mammals are absent. In addition, a recent study reported that camel crickets mediate seed dispersal of several heterotrophic plants, including Yoania amagiensis in Japan.
• I investigated the seed dispersal mechanism of Yoania japonica because the fruit morphology is similar to Y. amagiensis. Specifically, I aimed to determine whether Y. japonica fruits are consumed by camel crickets and, if so, whether the seeds defecated by camel crickets remains intact, by checking seed viability with TTC staining, and whether germination rate is different between seeds collected directly from fruits and defecated seeds by comparing in situ seed germinability.
• The present study provides evidence that camel crickets function as seed dispersal agents of Y. japonica. Camel crickets were important consumers of Y. japonica fruits, and a substantial portion of the consumed seeds remained viable after passing through the digestive tract. In situ seed germination experiments revealed that the seeds defecated by camel crickets actually germinated in the field. In addition, the germination rate of defecated seeds was even higher than that of intact seeds, although the difference was not significant.
• Taken together with recent reports of insect‐mediated endozoochory, such a seed dispersal system may be common in plants with fleshy indehiscent fruits and small seeds, even in locations where other seed dispersal agents are present.

     

Differences in reward removal efficiency and its consequences for seed germination in the ant-dispersed sedge <Emphasis Type="Italic">Carex tristachya</Emphasis> (Cyperaceae)

Reward removal is an essential step for seed dispersal mutualism because residual rewards inhibit germination. Nevertheless, variation in the reward removal efficiency (RRE) among dispersers and its consequences for germination have rarely been reported. In this study, we compared the RREs of two sympatric seed-dispersing ants, Formica japonica and Pheidole noda, using seeds of the ant-dispersed sedge Carex tristachya. Then, we conducted seed sowing experiments in a non-heated glasshouse to evaluate the effect of RRE on the percentage and speed of germination. The majority (85%) of seeds handled by F. japonica had residual elaiosomes, while elaiosomes were completely removed from all seeds handled by P. noda, demonstrating that P. noda has much higher RRE than F. japonica. The seed sowing experiments revealed that RRE, defined by the presence or absence of residual elaiosomes, was not associated with the percentage germination within a year. However, high RRE seeds with no residual elaiosomes germinated significantly faster than low RRE seeds with residual elaiosomes. Similarly, artificial removal of elaiosomes from C. tristachya seeds accelerated germination speed without affecting germination percentage. These results suggest that RRE is one of the most important parameters determining the effectiveness of a seed dispersal agent.     

Experimental Seed Predator Removal Reveals Shifting Importance of Predation and Dispersal Limitation in Early Life History Stages of Tropical Forest Trees

Recruitment limitation of trees in tropical forests can occur because of high rates of seed predation or low rates of seed dispersal, but the degree to which limitation is influenced by variation in seed predator abundance, and hence variation in seed predation and dispersal, is not well understood. We experimentally reduced the density of a granivorous small mammal (Heteromys desmarestianus) by 90 % to assess the degree to which its rates of seed predation and dispersal limit seed to seedling survival of nine species of trees in a Neotropical lowland forest. Overall, the proportion of seeds that germinated was influenced more by high rates of predation than by limited dispersal. Reduction in density of H. desmarestianus resulted in an order of magnitude decrease in fruit removal rates and an order of magnitude increase in both the absolute and relative numbers of seeds that germinated. However, the proportion of seeds that were cached remained relatively constant across all periods and between control grids and removal plots. In removal plots, H. desmarestianus dispersed and cached about 10 % of the fruits they handled, of which approximately 25 % germinated. This was 2 to 3 times greater than the germination rates of undispersed seeds, and for two species dispersed seeds were the only ones that germinated. The results suggest the simultaneous occurrence of both seed predation and dispersal limitation for trees with animal-dispersed seeds, but there may also be a hierarchy of importance in the relative strength of these two mechanisms that is determined by the dynamics of seed predator populations.     

Dispersal of Camellia japonica seeds by Apodemus speciosus revealed by maternity analysis of plants and behavioral observation of animal vectors

Seed dispersal determines a plant’s reproductive success, range expansion, and population genetic structures. Camellia japonica, a common evergreen tree in Japan, has been the subject of recent genetic studies of population structure, but its mode of seed dispersal has been assumed, without detailed study, to be barochory. The morphological and physiological features of C. japonica seeds, which are large and nutritious, suggest zoochorous dispersal, however. We compared actual distances between mother trees and seedlings with distances attributable to gravity dispersion only, to test the zoochory hypothesis of C. japonica. The animals that transport the seeds for caching were identified experimentally. We also examined the extent to which seed dispersal is affected by the behavior of animal vectors. Seed dispersal by Apodemus speciosus was confirmed by taking photographs of animals that were consuming seeds experimentally deposited on the ground. Camellia seeds hoarded by the rodents under the litter or soil were protected from drying. On the basis of microsatellite analysis of maternal tissue from the seed coat, the mother trees of 28 seedlings were identified. Maternity analysis revealed the average seed-dispersal distance from mother trees was 5.8 m±6.0 SD, a distance greater than initial dispersal by gravity alone. These results indicate that C. japonica is a zoochorous species dispersed by A. speciosus. Fifty percent of the seed dispersal occurred from mature evergreen forests to dwarf bamboo thickets. This directional seed dispersal would contribute to range expansion of C. japonica. Home range sizes of A. speciosus were 0.85 ha at most and covered with different types of vegetation, from evergreen forests to grassland. This low specificity of their microhabitat use might enhance seed dispersal to different types of vegetation.All animal experiments complied with Japanese laws.     

Germination and water dispersal of seeds from a threatened plant species Penthorum chinense

To conserve a threatened plant species (Penthorum chinense Pursh) in Japan, seed germination responses to pretreatment (imbibition and/or chilled), temperature and light, and seed dispersal by water were examined. The seeds collected from abandoned paddy fields in a warm temperate region, central Japan, germinated in light (14 h photoperiod; light 22°C, dark 21°C) after a moist-chilled treatment. After this pretreatment, the seeds germinated well at 10–25°C (optimum temperature 15°C), but did not germinate in darkness even at the optimum temperature. Most of the seeds floated on distilled water, but 20–60% of the seeds that were collected from several populations sank in distilled water, indicating dimorphism in seed dispersal by water. The floating and sunken seeds did not show significant differences in weight and germination rate within a population. The addition of a surface-active agent in distilled water submerged the seeds, indicating that the buoyancy of the seeds is attributable to an oil coating on the seed surface that enhances the interfacial tension on the seeds. Three times the number of seeds sank in river water collected from a rural area than in distilled water. A greater number of seeds also sank in water that had increasing concentrations of linear alkylbenzenesulfonate, which is a major component of synthetic detergents. This suggests that the water dispersal of this species is suppressed by surface-active agents, including detergents, in river water.     

Role of trichomes and pericarp in the seed biology of the desert annual Lachnoloma lehmannii (Brassicaceae)

In many angiosperms, the fruit rather than the seed is the dispersal/germination unit, and this is the case with Lachnoloma lehmannii, a desert annual ephemeral in central southwestern Asia with indehiscent nonmucilaginuous silicles covered with trichomes. The primary aim of this study was to assess the role of trichomes and pericarp in dispersal, anchorage of diaspores, and seed germination of this species. Mature silicles are dispersed by wind and gravity, and trichomes not only significantly increased their dispersal distance, adherence to sandy soil particles, mass of water imbibed and moisture content, but also decreased the rate of water loss and moisture content of seeds. A significantly higher percentage of seeds within silicles than of isolated seeds retained viability after exposure to 60 °C for 24 h. Seed dormancy is due to the pericarp and to nondeep physiological dormancy, as shown by the increase in germination percentage of isolated seeds following dry storage and treatment with GA₃. Removal of pericarp increased germination of 6-month-old seeds from 0 to 80–90 %, and leachate from both pericarp and trichomes significantly inhibited germination of isolated seeds. Ninety-five percent of seeds within silicles buried in soil for 2 years were viable, but only 28 % of them germinated in light at 15/2 °C; thus L. lehmannii forms a persistent soil seed bank. The pericarp and its trichomes may maximize plant fitness by determining the settlement location of silicles, thus helping to ensure that seeds germinate during the cool season for seedling survival in the desert environment.     

Fruit and seed heteromorphism in the cold desert annual ephemeral Diptychocarpus strictus (Brassicaceae) and possible adaptive significance

Background and Aims

Diptychocarpus strictus is an annual ephemeral in the cold desert of northwest China that produces heteromorphic fruits and seeds. The primary aims of this study were to characterize the morphology and anatomy of fruits and seeds of this species and compare the role of fruit and seed hetermorphism in dispersal and germination.

Methods

Shape, size, mass and dispersal of siliques and seeds and the thickness of the mucilage layer on seeds were measured, and the anatomy of siliques and seeds, the role of seed mucilage in water absorption/dehydration, germination and adherence of seeds to soil particles, the role of pericarp of lower siliques in seed dormancy and seed after-ripening and germination phenology were studied using standard procedures.

Key Results

Plants produce dehiscent upper siliques with a thin pericarp containing seeds with large wings and a thick mucilage layer and indehiscent lower siliques with a thick pericarp containing nearly wingless seeds with a thin mucilage layer. The dispersal ability of seeds from the upper siliques was much greater than that of intact lower siliques. Mucilage increased the amount of water absorbed by seeds and decreased the rate of dehydration. Seeds with a thick mucilage layer adhered to soil particles much better than those with a thin mucilage layer or those from which mucilage had been removed. Fresh seeds were physiologically dormant and after-ripened during summer. Non-dormant seeds germinated to high percentages in light and in darkness. Germination of seeds from upper siliques is delayed until spring primarily by drought in summer and autumn, whereas the thick, indehiscent pericarp prevents germination for >1 year of seeds retained in lower siliques.

Conclusions

The life cycle of D. strictus is morphologically and physiologically adapted to the cold desert environment in time and space via a combination of characters associated with fruit and seed heteromorphism.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

Effects of disperser abundance, seed type, and interspecific seed availability on dispersal distance

Seed dispersal distance is influenced by a variety of seed properties and functional responses of dispersers. However, to our knowledge, how and why seed dispersal distances are determined remains poorly understood. In the present study, seeds of sympatric tree species, Pinus koraiensis, Corylus mandshurica, Corylus heterophylla, and Quercus mongolica were released to investigate the effects of rodent abundance, seed type, and seed availability on seed dispersal. Our results showed that seeds of P. koraiensis were dispersed further than those of C. heterophylla and C. mandshurica regardless of the ambient rodent and seed abundances, reflecting a consistent effect of seed type on seed dispersal distances. Seed dispersal distance was greatly facilitated by lower per-capita seed abundance (the ratio of seeds to rodents); however, seed caching and cache survival were benefited from higher per-capita seed abundance. Although seed dispersal and seed caching of a particular tree species can be enhanced by its own seed availability, no consistent influence was detected at interspecific levels, reflecting different interspecific effects of seed availability on seed dispersal of sympatric seed species. Our results provide evidences that the effect of seed availability on seed dispersal should be evaluated in terms of per-capita seed abundance and interspecific effects, rather than the independent influence of seed or disperser abundances.     

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.     

The salinity preference of members of the genus Macroplea (Coleoptera, Chrysomelidae, Donaciinae), fully aquatic leaf beetles that occur in brackish water

Reed beetles (Donaciinae) of the genus Macroplea Samouelle, 1819 live permanently submerged. Literature indicates that Macroplea mutica occurs in brackish water, whereas Macroplea appendiculata is restricted to freshwater. The salinity preference of these two species was tested in a linear and a circular device that offered a continuous salinity gradient. The distribution of animals in the devices was monitored over at least 3 h in each of the 21 experiments. Both species preferred freshwater (salinity 0) over brackish water (salinity 10). In particular, this holds true for specimens collected in brackish water. Likewise, immediate reactions could be observed when during such experiments the direction of the gradient was reversed. While M. mutica can be regarded as a truly marine insect, this marine environment does not strictly reflect its fundamental niche with respect to salinity preference. This is in line with accumulating evidence that M. mutica can be found in freshwater habitats (and M. appendiculata in brackish water). This indicates that the species’ distribution might be influenced by other factors like host plant preference or dispersal mechanisms. It is discussed if—in spite of similar fundamental niches—differences in salinity tolerance (and hence performance in brackish water) may have contributed to speciation in the genus Macroplea.     

A water drop-shaped slingshot in plants: geometry and mechanics in the explosive seed dispersal of Orixa japonica (Rutaceae)

Background and AimsIn angiosperms, many species disperse their seeds autonomously by rapid movement of the pericarp. The fruits of these species often have long rod- or long plate-shaped pericarps, which are suitable for ejecting seeds during fruit dehiscence by bending or coiling. However, here we show that fruit with a completely different shape can also rely on pericarp movement to disperse seeds explosively, as in Orixa japonica.MethodsFruit morphology was observed by hard tissue sectioning, scanning electron microscopy and micro-computed tomography, and the seed dispersal process was analysed using a high-speed camera. Comparisons were made of the geometric characteristics of pericarps before and after fruit dehiscence, and the mechanical process of pericarp movement was simulated with the aid of the finite element model.Key ResultsDuring fruit dehydration, the water drop-shaped endocarp of O. japonica with sandwich structure produced two-way bending deformation and cracking, and its width increased more than three-fold before opening. Meanwhile the same shaped exocarp with uniform structure could only produce small passive deformation under relatively large external forces. The endocarp forced the exocarp to open by hygroscopic movement before seed launching, and the exocarp provided the acceleration for seed launching through a reaction force.ConclusionsTwo layers of water drop-shaped pericarp in O. japonica form a structure similar to a slingshot, which launches the seed at high speed during fruit dehiscence. The results suggest that plants with explosive seed dispersal appear to have a wide variety of fruit morphology, and through a combination of different external shapes and internal structures, they are able to move rapidly using many sophisticated mechanisms.     

Variation in temperature and light but not salinity invokes antioxidant enzyme activities in germinating seeds of Salsola drummondii

Seeds with efficient antioxidant defence system show higher germination under stress conditions; however, such information is limited for the halophyte seeds. We therefore studied lipid peroxidation and antioxidant responses of a leaf-succulent halophyte Salsola drummondii during seed germination under different salinity levels (0, 200 and 800 mM NaCl), temperature (10/20, 20/30 and 25/35°C) and light regimes. Seeds absorbed water and germinated in less than 1 h in non-saline control while increases in salinity decreased the rate of water uptake as well as seed germination. Non-optimal temperatures (10/20 and 25/35°C) and complete dark condition reduced seed germination in comparison to those seeds germinated under optimal temperature (20/30°C) and 12-h photoperiod, respectively. Generally, higher lipid peroxidation and antioxidant enzyme activities were observed in seeds at non-optimal temperature and in those seeds germinated in dark. Decrease in reduced ascorbic acid content was found in highest salinity and temperature treatments, while reduced glutathione content did not change significantly with changes in salinity, temperature and light regimes. These results indicate variation in temperature and light but not salinity enhances antioxidant enzyme activities in germinating seeds of Salsola drummondii.     

Predicted potential distribution of Sydowia japonica in Japan

Sydowia japonica, a dothidealean fungus, is a parasite that is specific to the male strobili of Japanese cedar. The fungus is a candidate for the control of Japanese cedar pollen dispersal, which is a cause of pollinosis. To evaluate S. japonica for bioherbicidal applications, it is necessary to characterise its potential distribution and environmental niche. Here, we predicted the distribution of S. japonica in Japan using field surveys and a maximum entropy model, and identified the environmental variables that influence its distribution. We identified S. japonica from a total of 87 localities in Japan through field surveys. Based on presence data and associated environmental variables, our model predicted that S. japonica is widely distributed in Japan, but concentrated in the Hokuriku and Kinki areas along the Sea of Japan. The model also predicted that the most important environmental variables influencing fungal distribution were sunshine duration in the winter and precipitation in the summer. This new information will contribute to the development of bioherbicidal applications for S. japonica.     

Dispersal of yellow phase Japanese eels <Emphasis Type="Italic">Anguilla japonica</Emphasis> after recruitment in the Kojima Bay-Asahi River system,Japan

The density, size and age distribution were investigated for 233 eels, Anguilla japonica, sampled in fresh and brackish water areas of the Kojima Bay-Asahi River system, Okayama, Japan, to evaluate the possible patterns of dispersal of eels that recruit to this area. Migratory histories of 183 eels were categorized into 5 types depending on the Sr and Ca concentrations in their otoliths: (1) brackish water residents (74 fish, 40.4%), which settled in saline water and remained until capture; (2) freshwater residents (46 fish, 25.1%), which settled in freshwater and remained until capture; (3) upstream shifters (3 fish, 1.6%), which settled in saline water and moved upstream into freshwater; (4) downstream shifters (53 fish, 29.0%), which settled in freshwater and moved downstream into saline water; (5) multiple habitat shifters (7 fish, 3.8%), which shifted their habitats between freshwater and saline water more than twice. For eels captured in the brackish water area, fish density decreased with distance in the downstream direction, while the size and age of eels increased. For eels captured in the freshwater area, size and age were greater than those in the upper-most brackish site. These observations suggest that eels in this system initially accumulate in the lower reaches of the river and then disperse in both upstream and downstream directions following their growth.     

The effects of shrub patch sizes on the colonization of pioneer plants on the volcano Mount Koma,northern Japan

Vegetation recovery on Mount Koma, Hokkaido, Japan, has been slow after the catastrophic eruption in 1929, due to undeveloped soil and limited plant colonization. Nowadays, the seedling establishment is supported mostly by a nurse plant, Salix reinii forming shrub patches, facilitates the plant colonization. Although the effects of shrub patches should differ with patch sizes, the size effects have not been examined well. To examine the size effects, seed-sowing experiments were conducted on two common pioneer herbaceous species, Miscanthus sinensis and Polygonum sachalinense, in the field. The seed germination and seedling survival were monitored by the seeds sown into S. reinii patches (0.97 m²–4.12 m² in area) for 4 months during snow-free periods. Microenvironments altered by the patches were measured. Lab-experiments were performed to characterize the seed germination and seedling growth.Larger patches decreased light intensity and temperature more and increased litter and water content. The large patches promoted the seed germination of the two species. Interspecific interactions, examined by a seed mixture experiment, showed that the interaction increased the seed germination on M. sinensis and decreased that on P. sachalinense. On the lab-experiments at three temperatures (15, 20 and 25 °C), M. sinensis seeds germinated more at higher temperatures and obtained higher seedlings biomass. P. sachalinense germinated the seeds more at 20 °C and grew faster at lower temperatures. The total biomass of the two species was reduced by shade that intercepted 50% of light intensity. The seed germination and seedling growth of these two species became higher on litter with 2 cm in depth than on no litter. Soil water supported seed germination when the seeds of these two species were mixed while the water reduced the growth of P. sachalinense seedlings. Therefore, the dry soils were suitable for their growths. In all the treatments, P. sachalinense seedlings showed higher mortalities than M. sinensis.In conclusion, the large patches facilitated more to the colonization of pioneer plants via seed germination and growth. Large patches acted as a nursery supporting the natural regeneration in the disturbed area by improving litter accumulation, maintaining soil water, reducing strong light and/or protecting from heat.     

The novel ethylene antagonist, 3-cyclopropyl-1-enyl-propanoic acid sodium salt (CPAS), increases grain yield in wheat by delaying leaf senescence

Orchid is a major floral crop around the world and Dendrobium hybrids are considered to be one of the most popular orchids. In vitro germination of hybrid seeds is a common practice among orchid growers, however, in many cross pollinations the embryos may not develop to maturity, leading to poor seed germination. The effect of seed maturity and sucrose concentration were investigated via asymbiotic germination of nobile Dendrobium hybrids. Capsules were harvested from two hybrids (Den. Lucky Girl × Den. Second Love ‘Kirameki’ and Den. Lucky Girl × Den. Hamana Lake ‘Kumi’) and one selfing of Den. Second Love ‘Kirameki’ at 2, 3, 4, and 5 months after pollination and immature seeds were taken. Immature seeds from 3- to 5-month old capsules could be successfully germinated on Hyponex based medium. Immature seeds from 4-month old capsules showed greatest germination rate of tested treatments, whereas 3-month old immature seeds showed the least germination. After 6 weeks of in vitro culture, protocorms derived from embryos developed on every concentration of sucrose, but germination was greater at lower concentrations. Greater concentration of sucrose decreased normal-developed protocorms.     

Suitable water temperature for seed storage of Zostera japonica for subtropical seagrass bed restoration

Restoration of Zostera japonica is needed. Laboratory culture experiments to know the germination characteristics might be helpful for implementation of actual restoration. As a part of germination experiments, we explored suitable water temperature for long-term storage of Z. japonica seeds. This work was based on earlier reports of Zostera marina, which presumably has similar physiological properties to Z. japonica. This study consisted of two experiments: (1) preservation experiments to investigate the fate of stored Z. japonica seeds and (2) germination experiments to investigate the germination potential of the stored seeds. The results of the preservation experiments suggested that seed condition, that is, germinated, degraded, unstable, stable, etc., showed variations between the seeds stored at 4 and 23 °C. The majority of the seeds stored at 4 °C were germinated, while those at 23 °C seemed to be degraded, presumably by bacteria and mold. The germination experiments suggested high germination potential of seeds stored at 4 °C even after 302 days had elapsed. In conclusion, including previously reported results on Z. marina, low temperature was suitable for the preservation of seeds to maintain germination potential.     

Differential dispersal of Chamaesyce maculata seeds by two ant species in Japan

Seed dispersal by ants (myrmecochory) is a widely distributed plant–animal interaction in many ecosystems, and it has been regarded as a generalized (multiple species) interaction in which specialization on specific ant partners is uncommon. In this paper, we demonstrate species-specific seed dispersal of spotted spurge (Chamaesyce maculata) by ants in Japan. C. maculata produces seeds from summer to autumn in Japan. The seeds produced in autumn are carried by two ant species, Tetramorium tsushimae and Pheidole noda. We performed laboratory experiments to investigate the fate of C. maculata seeds in the nests of T. tsushimae and P. noda. P. noda consumed the seeds in the nest and rarely carried seeds out of the nest, while T. tsushimae consumed only the seed coat, and subsequently carried the seeds out of the nest. Removal of the seed coat by T. tsushimae may increase seed survival by reducing their susceptibility to infection by fungi. We also observed ant responses to filter paper soaked with an aqueous extract of the seed coat. P. noda did not react to the filter paper, but T. tsushimae carried the filter paper into their nest. Analysis by high-pressure liquid chromatography revealed that the aqueous extract contained at least four sugars and one unknown substance. Myrmecochory has been regarded as a generalized interaction with specialization for specific ant partners uncommon. However, our study suggests there is a species-specific interaction in seed dispersal by ants in autumn-flowering individuals of C. maculata in Japan.