Seed Germination Ecology Research Articles

Germination ecology of heteromorphic seeds of bur clover (Medicago denticulata willd.)

Bur clover (Medicago denticulata Willd.) is a winter annual weed commonly found in wheat fields of Punjab, India. We observed it produces heteromorphic seeds varying in seed coat colour -cream and brownish-black. The information on germination ecology of M. denticulata seeds varying in seed coat colour is lacking. So, the present study was undertaken under laboratory conditions to study the effect of seed coat colour on germination characteristics of M. denticulata seeds in relation to various environmental variables. Germination of both cream and brownish-black seeds was independent of light. Cream seeds germinated in the wide temperature range of 15/5 to 30/20°C; while, brownish-black seeds germinated in a narrow temperature range of 15/5 to 25/15°C. Cream seeds were able to withstand greater salinity stress as some seeds (10%) were able to germinate under NaCl concentration of 200 mM; whereas germination of brownish-black seeds was completely inhibited at 200 mM NaCl. The NaCl concentration required for 50% inhibition of maximum germination for cream and brownish-black seeds was 100 and 70.6 mM NaCl, respectively. The osmotic potential required for 50% inhibition of the maximum germination of cream and brownish-black seeds was -0.37 and -0.32 MPa, respectively. These results indicated a greater ability of cream seeds to tolerate either salinity or osmotic stress. Both seeds germinated under acidic and alkaline pH with >40% germination in pH range 3-10. The highest emergence of cream and brownish-black seeds was recorded when seeds placed on the soil surface.

Seed germination ecology of Conyza stricta Willd. and implications for management.

Numerous cropping systems of the world are experiencing the emergence of new weed species in response to conservation agriculture. Conyza stricta Willd. is being a newly emerging weed of barley-based cropping systems in response to conservational tillage practices. Seed germination ecology of four populations (irrigated, rainfed, abandoned and ruderal habitats) was studied in laboratory and greenhouse experiments. The presence/absence of seed dormancy was inferred first, which indicated seeds were non-dormant. Seed germination was then recorded under various photoperiods, constant and alternating day/night temperatures, and pH, salinity and osmotic potential levels. Seedling emergence was observed from various seed burial depths. Seeds of all populations proved photoblastic and required 12-hour light/dark period for germination. Seeds of all populations germinated under 5–30°C constant temperature; however, peak germination was recorded under 17.22–18.11°C. Nonetheless, the highest germination was noted under 20/15°C alternating day/night temperature. Ruderal and irrigated populations better tolerated salinity and germinated under 0–500 mM salinity. Similarly, rainfed population proved more tolerant to osmotic potential than other populations. Seeds of all populations required neutral pH for the highest germination, whereas decline was noted in germination under basic and alkaline pH. Seedling emergence was retarded for seeds buried >2 cm depth and no emergence was recorded from >4 cm depth. These results add valuable information towards our understanding of seed germination ecology of C. stricta. Seed germination ability of different populations under diverse environmental conditions suspects that the species can present severe challenges in future if not managed. Deep seed burial along with effective management of the emerging seedlings seems a pragmatic option to manage the species in cultivated fields. However, immediate management strategies are needed for rest of the habitats.

Implications of seed germination ecology for conservation of Camptotheca acuminata, a rare, endemic, and endangered species in China

Seed germination and seedling recruitment are among the most critical stages for plant population persistence and development, which may be influenced by habitat fragmentation and resulting microhabitat changes. We conducted laboratory and field experiments using seeds of Camptotheca acuminata, a rare, endemic, and endangered species in China, to investigate the effects of temperature change and water availability on seed viability and germination. The seeds were sensitive to high temperature and water stress. Germination percentages > 60% occurred only between 20–35 °C and water potentials > − 0.6 MPa. Heating at 75 °C and above for 30 min, continuous heating at 40 °C for 20 days, or desiccation following 120 h imbibition killed nearly all seeds. These seed traits made none of the five microhabitats investigated suitable for regeneration. In the understory plot, most seeds germinated, but the resultant seedlings survived only a short time, depending on reserve food supply from the seeds. Sensitivity to high temperature and water stress inhibited germination in the other plots and most seeds died in the hydration-dehydration cycles. We concluded that efficient natural regeneration could occur only in very special habitats: cool, with stable moist soil but ample sunlight, most likely in suitable gaps in continuous forests. In addition to habitat loss and over-exploitation, difficulties in natural seed germination and seedling recruitment are primary reasons for the current status of C. acuminata. For population recovery of C. acuminata, understory microhabitat protection and artificial support for germination and seedling recruitment are required.

Dry-storage and light exposure reduce dormancy of Arabian desert legumes more than temperature

Propagation and conservation of desert plants are assisted by improved understanding of seed germination ecology. The effects of dry-storage on dormancy and germination were studied in seven desert legumes. Mature seeds were collected in summer 2017 and germinated within one week of collection (fresh) and after six months (dry-storage) under two temperature and two light regimes. Seed weight of two species increased 22-55% within 24 hours of water imbibition but others increased ≤ 7%. Germination ranged from 0-32% in fresh and 2-92% in dry-stored seeds, indicating a mix of non- and physically-dormant seeds at maturity. Dry-storage at ambient room temperature was effective at relieving dormancy, though the extent was species-dependent. Germination percentage increased in response to light exposure during incubation, while the effect of temperature was species-dependent. This variable response to dormancy alleviation may assist to spread the population risk of seedling survival in the harsh and variable environment of the Arabian desert.

Seed germination ecology of Viola calaminaria, an endangered metallophyte with a narrow distribution

AbstractViola calaminaria is an endangered metallophyte endemic to a small area close to the border between Belgium, Germany and the Netherlands, where it grows on rock outcrops rich in heavy metals (zinc, lead and cadmium). Because V. calaminaria reproduces mainly by seeds, it is of crucial importance to understand its germination requirements. Germination percentage and speed at constant (11–25°C) and alternating (23/09°C) temperatures were investigated in five large populations. Germination percentage was positively correlated to seed weight. Germination was low (<25%) at 11 and 16°C, intermediate (around 65%) between 20 and 25°C and the highest (93%) at the alternating temperature regime (23/09°C). V. calaminaria is a slow germinator requiring 41 days on average to germinate at 23/09°C and considerably more at 20 to 25°C (105 days on average). Our results also highlighted that the species is desiccation tolerant and can therefore be safely conserved under standard seed bank conditions.

Overcoming germination barriers in four native Malvaceae shrub species of Reunion island to improve restoration in arid habitats

Islands are well-known to house an incredible biodiversity, higher level of threatened species and extinctions than mainlands. Because of human activities and climate change, these endangered regions required advanced conservation and restoration strategies.In this study, we investigated seed germination ecology of four native Malvaceae species (Dombeya acutangula, Dombeya populnea, Ruizia cordata and Thespesia populneoides) of degraded dry lowlands of Reunion Island. We measured seed imbibition, investigated the dormancy class of seeds, determined light requirements for germination and identified treatments to improve germination of these species. For this purpose, germination tests were performed over 32 days and two photoperiods (12 h/12 h or 0 h/24 h), by using seeds treated with H2O2, gibberellic acid and smoke water. Mechanical and chemical scarifications as well as heat treatment were also carried out. Germination percentages were analyzed by fitting generalized linear models (GLMs) with a logit link function.For the four species, a significant mass increase is detected for scarified seeds after a week imbibition (>60% mass increase). Germination percentages of seeds treated with H2O2, GA3 and smoke water were not significantly different from control seed. On the contrary, scarified seeds exhibited significantly higher germination percentages than control seeds. In addition, germination speed was also significantly higher for scarified seeds. These results are congruent with a physical dormancy phenomenon of seeds of the four Malvaceae shrubs. In addition, no particular light requirement was observed for germination. Artificial methods to break dormancy and stimulate germination described in this study could improve establishment success in arid habitats.

Seed germination ecology of Ageratum houstonianum: A major invasive weed in Nepal.

In recent years, spread of invasive alien plant species (IAPS) has been a major concern in Nepal. One such IAPS is Ageratum houstonianum, an Asteraceae, that is a prolific seed producer and difficult-to-control in farmland and various ecological regions causing crop yield and biodiversity losses. However, very little information is available on the germination biology and ecology of this species. Therefore, experiments were conducted to assess the effect of water stress, pH level, and light requirement on seed germination, and the effect of seed burial depth on seedling emergence. Water stress was simulated by polyethylene glycol solutions ranging from 0–5.56 MPa and pH solutions ranging from 4 to 9 were prepared using hydrochloric acid and sodium hydroxide. Germination tests were conducted in petri dishes lined with filter paper and placed in a controlled environment chamber set at 20° C. Light requirement comparisons were made by having petri dishes wrapped with aluminum foil or left unwrapped. Seedling emergence was evaluated by placing seeds at depths ranging from 0 to 20 mm in the soil. Results indicated that this species was moderately drought-tolerant because germination ceased beyond 0.51 MPa. Greater germination occurred at neutral to acidic than at alkaline pH levels. The seeds were positively photoblastic because no germination occurred under dark condition. No seedlings emerged from seeds placed more than 2 mm deep in the soil, indicating that this is a primarily surface germinating species. These findings will help predict future invasions and in development of management strategies for this IAPS.

Seed germination ecology of Bidens pilosa and its implications for weed management

It is now widely recognized that Bidens pilosa has become a problematic broadleaf weed in many ecosystems across the world and, particularly in the light of recent climate change conditions, closer management strategies are required to curtail its impact on agricultural cropping. In this investigation, experiments were conducted to evaluate the effect of environmental factors on the germination and emergence of B. pilosa, and also on the response of this weed to commonly available post-emergence herbicides in Australia. The environmental factors of particular interest to this current work were the effect of light and temperature, salinity, burial depth and moisture on B. pilosa since these are key management issues in Australian agriculture. In addition, the effects of a number of commonly used herbicides were examined, because of concerns regarding emerging herbicide resistance. In the tested light/dark regimes, germination was found to be higher at fluctuating day/night temperatures of 25/15 °C and 30/20 °C (92–93%) than at 35/25 °C (79%), whilst across the different temperature ranges, germination was higher in the light/dark regime (79–93%) than in complete darkness (22–38%). The standard five-minute temperature pretreatment required for 50% inhibition of maximum germination was found to be 160 °C, and it was further shown that no seeds germinated at temperatures higher than 240 °C. With regard to salinity, some B. pilosa seeds germinated (3%) in 200 mM sodium chloride (NaCl) but all failed to germinate at 250 mM NaCl. Germination declined from 89% to 2% as the external osmotic potential decreased from 0 to −0.6 MPa, and germination ceased at −0.8 MPa. Seeding emergence of B. pilosa was maximum (71%) for seeds placed on the soil surface and it was found that no seedlings emerged from a depth of 8 cm or greater. A depth of 3.75 cm was required to inhibit the seeds to 50% of the maximum emergence. In this study, application of glufosinate, glyphosate and paraquat provided commercially acceptable control levels (generally accepted as >90%) when applied at the four-leaf stage of B. pilosa. However, none of the herbicide treatments involved in this study provided this level of control when applied at the six-leaf stage. In summary, B. pilosa germination has been clearly shown to be stimulated by light and thus its emergence was greatest from the soil surface. This suggests that infestation from this weed will remain as a problem in no-till conservation agriculture systems, the use of which is increasing now throughout the world. It is intended that information generated from this study be used to develop more effective integrated management programs for B. pilosa and similar weeds in commercial agricultural environments which are tending toward conservation approaches.

Effects of salinity and temperature on seed germination and seedling establishment in the endangered seagrass Zostera japonica Asch. & Graebn. in northern China

Seagrass meadows are recognized as critical and among the most vulnerable habitats on the planet. As a worldwide concern, there is an urgent need to develop techniques to restore and preserve these vital coastal ecosystems due to their alarming decline rate. To effectively preserve and restore seagrasses, more research is required on the germination ecology of seeds. The seagrass Zostera japonica Asch. & Graebn is an endangered species in its native range, the Northwestern Pacific Coast. The present study investigated the germination and seedling establishment in Z. japonica seeds (collected from northern China) under different temperature and salinity conditions to explore suitable seed germination and establishment conditions, as well as the seedling formation process. Results showed that salinity had a more significant influence on seed germination rate. Germination rate decreased with an increase in salinity, and seeds did not germinate when salinity was higher than 40 psu. Temperature was more likely to influence germination speed, which increased with an increase in temperature, with high germination rates and the most rapid germination speed observed at 30 °C. Therefore, the optimal culture conditions were 10 psu salinity at 30 °C for germination and 10–20 psu salinity at 20 °C for seedling establishment, with a seed germination rate of 45.6% after 6 days of germination culture and a seedling establishment rate of 14.3% after 6 days of seedling culture, respectively. A new seedling raising method with low salinity (5 psu) germination and high salinity (20 psu) seedling establishment was proposed and a flow chart of seedling formation of Z. japonica was created. The results provide insight into the seed germination and seedling establishment in Z. japonica, and will facilitate future large-scale seedling culture and field restoration activities for this seagrass species.

Seed germination ecology and salt stress response in eight Mediterranean populations of Sarcopoterium spinosum (L.) Spach

AbstractThis study aims to deepen the analysis of seed germination ecology and salinity tolerance of Sarcopoterium spinosum (Rosaceae).Germination tests were conducted to evaluate the effect of the fruit’s spongy tissue and the intraspecific variability in seed germination among eight populations of the species on responses to light and total darkness, constant and alternating temperatures, salt stress and germination recovery. The effect of the presence of the spongy tissue varied among populations, with significant results for seed germination. For all populations, optimum germination temperatures were observed in the range of 10–20°C, indicating that S. spinosum and its germination in the field might occur preferably in the period between autumn and early spring. The high water availability due to rainfall during this period could be a considerable advantage for the seed germination of this species. Seeds of S. spinosum showed the ability to germinate in up to 250 mM NaCl in the substrate, and their ability to recover after salt exposure may be interpreted as adaptation to the coastal habitats in which they generally grow. These results give this species a halo‐tolerant character. Great inter‐population variability is detected in this study in several aspects, which indicated that the Mediterranean populations of S. spinosum differ considerably and are adapted to their local conditions. This study provides new information about S. spinosum seed ecology, which could help to preserve and apply effective conservation measures for this species, which in several areas of its distribution range is endangered.

A Comparative Study of Seed Germination And Seedling Emergence of Two Wild Edible Allium Species Endemic to Zagros Areas

Allium L. is one of the largest and most diversified monocotyledonous genera worldwide. These taxa have wide geographical distribution range mainly occurred in the northern hemisphere with an important center of diversity in the Mediterranean and Irano-Anatolian regions. They include an important number of taxa of high economic values (wild edible, cultivated, medicinal, ornamentals, etc.). These geophytes species exhibit diversified adaptation strategies that permit them to persist under harsh environmental conditions. The present experimental study was designed to understanding better the environmental factors that control the natural regeneration of the two wild edible Allium (A. calocephalum and A. notabile) species endemic to Zagros areas via evaluating the effect of different (i) pre-sowing treatments on seed germination rate and (ii) soil depth on seedling emergence timing. The results of the present study confirmed relatively high seed and bulbs viabilities under the different pre-sowing treatments. In general, both Allium species have a relatively similar germination trend (around 80% without treatments) and seedling emergence (from bulbs at 5 cm) patterns. The high rate of seed germination for A. calocephalum was found under cold stratification for 1 month and soak in water for 3 days and GA3 1500 ppm with 83%, 86%, and 85%, respectively. The different germination pattern was found for A. notabile with 83%, 85%, 84% for soaking water for 2 and 3 days and GA3 1000 ppm, respectively. Whoever, these two threatened species from different taxonomical groups and habitats have different adaptation strategy. A. notabile is Mediterranean species exhibiting an optimum seedling emergence in autumn-early winter with summer underground organ dormancy to avoid the hot-dry conditions; While, A. calocephalum is IranoAnatolian species exhibiting an optimum seedling in late winter-early spring permitting it to persist thanks to its avoidance strategy of the harsh winter climatic conditions. The results of this research support the idea that Allium species from different habitats exhibit different seed germination and seedling emergency strategies allowing it to persist. The evidence of this experimental study enriches our understanding of the diversified adaptation strategy of the plants. In this context, further experimental investigations are needed to evaluate the crucial rule of the seed germination ecology and bulbs dormancy strategies on the population dynamic and persistence.

Seed germination ecology of Alexandra palm (Archontophoenix alexandrae) and its implication on invasiveness

Biological invasions are occurring worldwide, causing enormous economic and ecological damage. Early detection and prediction of invasiveness are the most effective measures to reduce its damage. The Alexandra palm (Archontophoenix alexandrae) is a prolific seeder and an alien species widely planted in tropical China. To help understand the invasion risks posed by this species, lab and field experiments on seed germination were conducted. Results show that the seeds only germinate within a temperature range of 20–30 °C and are sensitive to desiccation and high temperature, with seedling inhibition at 35 °C and −0.8 MPa. Complete viability loss was observed after desiccation to water content of 0.17–0.21 g/g or heat treatment for 30 minutes at 60 °C and above. However, appropriate habitats such as the rainforest understory, forest gaps, forest edges, and a rubber plantation are present in Xishuangbanna. Seeds are also frequently consumed by animals; therefore, there is a high potential for Alexandra palm to become an invasive species in Xishuangbanna. Currently, the main barrier to invasion in Xishuangbanna is likely to be the need for seed dispersal into suitable moist, partly shaded, habitats. Understanding the requirements for germination of the Alexandra palm can better inform management strategies for the control of this species.

Seed-germination ecology of glyphosate-resistant and glyphosate-susceptible biotypes of Echinochloa colona in Australia

Echinochloa colona L. (Link) (awnless barnyard grass) is one of the top three most problematic weeds of summer crops in Australia. This weed has evolved resistance to glyphosate. A study was conducted to evaluate the effect of environmental factors on the germination and seedling emergence of a glyphosate-resistant (GR) and a glyphosate-susceptible (GS) biotype of E. colona. The two biotypes had similar germination and emergence responses to light and temperature conditions, water stress, solution pH, sorghum residue cover and seed burial depth. Light stimulated germination more than dark conditions, and seeds germinated at a wide range of alternating day/night temperatures, from 20°C/10°C to 35°C/25°C, whereas no seeds germinated at 15°C/5°C. These results suggest that E. colona can emerge in spring, summer and autumn in Queensland. The sodium chloride concentration required to inhibit 50% germination was greater for the GR biotype (209 mm) than the GS biotype (174 mm). Seed germination was not affected by pH in the range 4–10. Water stress reduced germination by 50% at an osmotic potential of –0.44 MPa. In a shade-house study, retention of sorghum residue cover on the soil surface reduced the seedling emergence of E. colona. Emergence was 70% in the absence of crop residue, whereas a residue amount of 8 t ha–1 reduced emergence to 47%. Emergence was greatest for seeds placed on the soil surface and declined linearly with increasing burial depth; no seedlings emerged from 8 cm depth. The GR biotype had higher germination than the GS biotype under high sodium chloride concentrations; therefore, this biotype may be highly competitive with crops under highly saline conditions. Because germination was high on the soil surface and was stimulated by light, this weed will remain problematic under no-till farming systems in Australia.

Soil Physics Involvement in the Germination Ecology of Buried Weed Seeds.

Trials were performed to test the germination ecology of buried weed seeds as a function of physical soil conditions such as of burial depth, texture, and compaction. Indeed, these ecological conditions, due to the adopted agronomic practices, play a crucial role in modulating the seed bank germination dynamics. Experiments were carried out in open fields in confined soils (polypropylene pipes), and in the laboratory in Petri dishes. Sowing depth strongly inhibited the seed germination of the three weed species selected. This inhibition was found to be inversely proportional to the size of the soil particles. Compaction strongly increased the depth-mediated inhibition, especially in soils that were rich in clay particles, and was inversely proportional to the seed size. The physiological nature of the dormancy imposed by burial was investigated. In addition, ungerminated seeds, re-exhumed after deep-sowing for six months, were found to be in deep dormancy, especially after burial in compacted clay soil. This dormancy induction was more pronounced in weed species characterized by small seeds. Critical issues are discussed regarding weed seed bank ecophysiology and their management in sustainable agricultural cropping systems.

Alleviation of morphophysiological dormancy in seeds of the Australian arid-zone endemic shrub, Hibbertia glaberrima F. Muell. (Dilleniaceae)

AbstractMorphophysiological dormancy (MPD) is predominantly found in seeds of temperate regions and is uncommon in arid biomes. MPD has been reported in a number of Hibbertia (Dilleniaceae) species of temperate Australia, and in a single species of the arid zone, H. glaberrima. This study aimed to examine the dormancy and germination ecology of seeds of H. glaberrima. Seeds were subjected to temperature stratification treatments designed to mimic summer and autumn conditions in the Pilbara region of Western Australia. Seed germination and embryo growth were measured. We also tested the interaction between temperature stratification and cycles of drying and wetting designed to mimic sporadic rainfall events. All temperature and moisture treatments were tested in combination (+/–) with the smoke-derived chemical karrikinolide (KAR1). Exposing dormant seeds to temperatures suitable for warm stratification (35°C) for ≥ 8 weeks, followed by incubation at 25°C, resulted in significantly higher germination compared with non-stratified seeds. Exposing seeds to dry/wet cycling in conjunction with temperature stratification did not significantly increase germination. Exposure to KAR1 increased germination under most conditions. Once seeds are shed during October to December, they are exposed to hot and sporadically wet conditions over summer, allowing MPD to be overcome in a proportion of the seed population. Seeds may germinate in autumn (March to April), in conjunction with cooler temperatures. More deeply dormant individuals may require more than one summer to overcome dormancy. Similar to other species occurring in fire-prone ecosystems, fire also plays a crucial role in the germination ecology of H. glaberrima.

Overcoming dormancy and light requirements in seeds of Heteropogon contortus, a target species for savanna restoration

As observed at a world scale, in Reunion Island Heteropogon contortus savannas face major pressure and need to be preserved and restored. However, the use of this species in restoration projects is hampered by the limited knowledge about the seed germination ecology and more specifically about dormancy and light requirements. Dormancy state and light requirements for germination of H. contortus seeds were assessed over a 3-year after-ripening period (i.e. storage). Dormancy loss was observed after one year of storage. Between one and two years of after-ripening, H. contortus seeds exhibit significantly higher mean germination percentages in daily light than in darkness, demonstrating their positive photoblasty (i.e. requires light for germination). Smoke solutions significantly enhanced germination in both daily light and darkness during the first two years of dry storage. This study also demonstrated that smoke-infused water with beekeeping smoker fuel could be an efficient method to enhance germination of H. contortus seeds. Overall, this method could be adopted for large scale restoration projects due to its efficiency, its low cost and its reproducibility.

SEED GERMINATION ECOLOGY AND SEEDLING EMERGENCE OF SIXTEEN TREE SPECIES AUTUMN SOWN

In nature, the regeneration and the seed germination ecology of tree species is varied due to divers’ environmental factors and evolution process. As a consequence, understanding the factors controlling the seed germination and seedling emergence in the time and the space. In most nurseries, tree seeds are usually sown in spring or rarely in autumn and, they are often pretreated to increase the seed germination where the germination timing is selective sieve that a plant experiences throughout its life history. However, in most nursery of Kurdistan region, the managers have not a good knowledge about the seeds sowing timing and seedling emergency of native tree species. Therefore, the main aim of this study is to investigate seed germination phenology with providing new data and determine optimal ways of seed sowing time that will permit a best seedling establishment of sixteen native and introduced tree species. The results showed, the seed sowing timing and seedling emergence of these tree species. In addition, these species exhibit significant divergence in term sowing timing and seedling establishment. Thereby, our results have a high value for managers of Kurdistan governmental and private nurseries as a suggestion which exact time is better for sowing seeds and which seeds need pre-treatment before sowing in order to obtain better regeneration.

Seed germination ecology in Trapa natans L., a widely distributed freshwater macrophyte

Trapa natans is an aquatic annual plant that grows in stagnant water and occupies an extremely wide, yet discontinuous native range across temperate Europe, Asia, and Africa, and is naturalized in North America and Australia. Despite its wide distribution and invasion success, its seed germination ecology is poorly known. We hypothesized that, due to its wide distribution range, T. natans seeds should germinate under a broad spectrum of environmental conditions. In the present study, freshly matured seeds were cold stratified and tested for germination over a range of temperatures in light/dark, and dark under aerobic and hypoxia conditions. Seed and seedling tolerance to freezing and desiccation also were determined. Freshly matured seeds were physiologically dormant, requiring 9 weeks of cold stratification to overcome the dormancy. Seeds tolerated freezing down to −14 °C, whereas those with an emerged hypocotyl exhibited a high sensitivity to freezing down to −4 °C. The non-dormant seeds germinated (75–100%) under almost all environmental conditions, i.e. constant 22 °C and alternating temperature of 14/6 °C to 30/22 °C and 30/10 °C, light and darkness, oxic and hypoxia, thus supporting our proposed hypothesis. Finally, seeds were found to be highly desiccation-sensitive, even at high relative humidity. Our findings suggest that the wide germination niche could help explain its broad distribution and invasion success at local and global scales.

Seed Dormancy and Germination Ecology ofCalycanthus floridusL., a Species with Threatened Status in Kentucky

Abstract The seed germination ecology of Calycanthus floridus (Eastern Sweetshrub) has not been formally investigated. The purposes of this study were to determine the type of seed dormancy found in the species, the most effective method of breaking this dormancy, and the environmental conditions producing maximum germination. We employed a variety of standard treatments to determine the specific type(s) of dormancy present, as well as treatments to determine effective dormancy-breaking mechanisms. We determined that seeds possessed physical dormancy (PY) imposed by a water-impermeable seed coat. Mechanical scarification was the most effective method of breaking PY; submersion in acid was also moderately effective. Seed germination following scarification can occur over a wide range of temperatures. There is no light requirement for seed germination. This study represents the first case of physical dormancy reported for the genus and only the second for the family.

Seeds of Halopeplis perfoliata display plastic responses to various abiotic factors during germination

Halopeplis perfoliata is a coastal marsh halophyte with several ecological and economic usages. Information about seed germination ecology of Halopeplis species is limited. Germination and recovery responses to NaCl (0, 0.1–0.6molL−1), light (12h light/12h dark and 24h dark), alternating temperature regimes (10/20, 15/25, 20/30 and 25/35°C), NaCl exposure time (20, 40 and 60days) and dormancy regulating chemicals (DRCs) were therefore studied. Fresh seeds were non-dormant and showed highest germination (≈90%) in distilled water, irrespective of incubation temperature. Seeds germinated better in 12h photoperiod than 24h dark. Salinity increment decreased germination; however some seeds could germinate in 0.6molL−1 NaCl under 12h photoperiod. High salinity (≥0.3molL−1 NaCl) and 24h dark enforced dormancy in seeds and they showed high recovery when transferred to distilled water and to light respectively. Seeds showed enforced dormancy under hyper-salinity (up to 2.0molL−1 NaCl) at all temperature regimes except at 25/35°C where seed mortality was high. All DRCs (except proline) alleviated enforced dormancy due to dark but were generally ineffective in reversing inhibitory effects of salinity. Our data indicate that seeds of H. perfoliata are sensitive to variations in different abiotic factors, which may thus act as possible cue for germination in its habitats. Results of DRC application indicate that germination inhibition under high salinity and dark might be due to osmotic and biochemical reasons respectively.