Seed ecology of the geophyte Conopodium majus (Apiaceae), indicator species of ancient woodland understories and oligotrophic meadows

• Conopodium majus is a geophyte with pseudomonocotyly, distributed in Atlantic Europe. It is an indicator of two declining European habitats: ancient woodland understories and oligotrophic hay meadows. Attempts to reintroduce it by seed have been hindered by scarce seedling emergence and limited knowledge of its seed biology.
• Micro‐CT scanning was used to assess pseudomonocotyly. Embryo growth and germination were studied in the laboratory and the field, using dissection and image analysis. The effects of temperature, light, nitrate and GA₃ on germination were tested. Seed desiccation tolerance was investigated by storage at different RHs and by drying seeds at different stages of embryo growth.
• Seeds possess morphological but not physiological dormancy. Embryo growth and germination were promoted by temperatures between 0 and 5 °C, arrested above 10 °C, and indifferent to alternating temperatures, light, nitrate and GA₃. Pseudomonocotyly appears to result from cotyledon fusion. While seeds tolerated drying to 15% RH and storage for 1 year at 20 °C, viability was lost when storage was at 60% RH. Seeds imbibed at 5 °C for 84 days had significant internal embryo growth but were still able to tolerate drying to 15% RH.
• Reproduction by seed in C. majus follows a strategy shared by geophytes adapted to deciduous temperate forests. The evolution of fused cotyledons may enable the radicle and the hypocotyl to reach deeper into the soil where a tuber can develop. The embryo is capable of growth within the seed at low temperatures so that germination is timed for early spring.

     

Dissecting seed dormancy and germination in Aquilegia barbaricina,through thermal kinetics of embryo growth

• Threshold‐based thermal time models provide insight into the physiological switch from the dormant to the non‐dormant germinating seed.
• This approach was used to quantify the different growth responses of the embryo of seeds purported to have morphophysiological dormancy (MPD) through the complex phases of dormancy release and germination. Aquilegia barbaricina seeds were incubated at constant temperatures (10–25 °C) and 25/10 °C, without pre‐treatment, after warm+cold stratification (W+C) and GA₃ treatment. Embryo growth was assessed and the time of testa and endosperm rupture scored. Base temperatures (T_b) and thermal times for 50% (θ₅₀) of embryo growth and seed germination were calculated.
• W+C enabled slow embryo growth. W+C and GA₃ promoted rapid embryo growth and subsequent radicle emergence. The embryo internal growth base temperature (T_be) was ca. 5 °C for W+C and GA₃‐treated seeds. GA₃ treatment also resulted in similar T_b estimates for radicle emergence. The thermal times for embryo growth (θ_e50) and germination (θ_g50) were four‐ to six‐fold longer in the presence of GA₃ compared to W+C.
• A. barbaricina is characterised by a multi‐step seed germination. The slow embryo growth during W+C reflects continuation of the maternal programme of development, whilst the thermal kinetics of both embryo and radicle growth after the removal of physiological dormancy are distinctly different. The effects of W+C on the multiphasic germination response in MPD seeds are only partially mimicked by 250 mg·l^?1 GA₃. The thermal time approach could be a valid tool to model thermal kinetics of embryo growth and radicle protrusion.

     

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.

     

Interpopulation variability on embryo growth,seed dormancy break,and germination in the endangered Iberian daffodil Narcissus eugeniae (Amaryllidaceae)

The main goal of the study was to assess germination requirements in a threatened daffodil to elaborate a detailed protocol for plant production from seeds, a key tool for conservation. Experiments were carried out both in the laboratory and outdoor conditions. In Pseudonarcissi section, endemic Iberian species of Narcissus studied heretofore have different levels of morphophysiological dormancy (MPD). Embryo length, radicle emergence, and shoot emergence were analyzed to determine the level of MPD. Both interpopulational variability and seed storage duration were also studied. Mean embryo length in fresh seeds was 1.32 mm and the embryo had to grow until it reached at least 2.00 mm to germinate. Embryo growth occurs during warm stratification, after which the radicle emerges when temperatures go down. Seed dormancy was broken in the laboratory at 28/14°C in darkness followed by 15/4°C, but the germination percentage varies depending on the population. In outdoor conditions, seed dispersal occurs in June, the embryo grows during the summer and then the radicle emerges in autumn. The radicle system continues to grow during the winter months, but the shoot does not emerge until the beginning of the spring because it is physiologically dormant and requires a cold period to break dormancy. Early cold temperatures interrupt embryo growth and induce dormancy in seeds with an advanced embryo development. Seeds of N. eugeniae have deep simple epicotyl MPD. In addition, we found that embryo growth and germination were improved by seed storage duration.     

Sensitivity cycling in physically dormant seeds of the Neotropical tree Senna multijuga (Fabaceae)

• Cycling of sensitivity to physical dormancy (PY) break has been documented in herbaceous species. However, it has not been reported in tree seeds, nor has the effect of seed size on sensitivity to PY‐breaking been evaluated in any species. Thus, the aims of this study were to investigate how PY is broken in seeds of the tropical legume tree Senna multijuga, if seeds exhibit sensitivity cycling and if seed size affects induction into sensitivity.
• Dormancy and germination were evaluated in intact and scarified seeds from two collections of S. multijuga. The effects of temperature, moisture and seed size on induction of sensitivity to dormancy‐breaking were assessed, and seasonal changes in germination and persistence of buried seeds were determined. Reversal of sensitivity was also investigated.
• Fresh seeds were insensitive to dormancy break at wet–high temperatures, and an increase in sensitivity occurred in buried seeds after they experienced low temperatures during winter (dry season). Temperatures ≤20 °C increased sensitivity, whereas temperatures ≥30 °C decreased it regardless of moisture conditions. Dormancy was broken in sensitive seeds by incubating them at 35 °C. Sensitivity could be reversed, and large seeds were more sensitive than small seeds to sensitivity induction.
• Seeds of S. multijuga exhibit sensitivity cycling to PY‐breaking. Seeds become sensitive during winter and can germinate with the onset of the spring–summer rainy season in Brazil. Small seeds are slower to become sensitive than large ones, and this may be a mechanism by which germination is spread over time. Sensitive seeds that fail to germinate become insensitive during exposure to drought during summer. This is the first report of sensitivity cycling in a tree species.

     

Deep and intermediate complex morphophysiological dormancy in seeds of Ferula gummosa (Apiaceae)

We tested the hypothesis that seeds of the monocarpic perennial Ferula gummosa from the Mediterranean area and central Asia have deep complex morphophysiological dormancy. We determined the water permeability of seeds, embryo morphology, temperature requirements for embryo growth and seed germination and responses of seeds to warm and cold stratification and to different concentrations of GA₃. The embryo has differentiated organs, but it is small (underdeveloped) and must grow inside the seed, reaching a critical embryo length, seed length ratio of 0.65–0.7, before the seed can germinate. Seeds required 9 weeks of cold stratification at <10°C for embryo growth, dormancy break and germination to occur. Thus, seeds have morphophysiological dormancy (MPD). Furthermore, GA₃ improved the germination percentage and rate at 5°C and promoted 20 and 5% germination of seeds incubated at 15 and 20°C, respectively. Thus, about 20% of the seeds had intermediate complex MPD. For the other seeds in the seed lot, cold stratification (5°C) was the only requirement for dormancy break and germination and GA₃ could not substitute for cold stratification. Thus, about 80% of the seeds had deep complex MPD.     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

Seed germination ecology of the threatened endemic Iberian <Emphasis Type="Italic">Delphinium fissum</Emphasis> subsp. <Emphasis Type="Italic">sordidum</Emphasis> (Ranunculaceae)

Seeds of Delphinium fissum subsp. sordidum are physiologically dormant at maturity, with underdeveloped embryos; thus they have morphophysiological dormancy (MPD). The aims of this study were to determine the requirements for embryo growth, dormancy break and germination, to characterise the type of seed dormancy and to evaluate the effects of light, seed age, pollination mechanism, and inter-annual and inter-population variability on germinative ability. After 3 months of incubation at 5°C (cold stratification) in darkness conditions, the mean embryo length increased from 5.6 to 2.07 mm, with 76% of seeds germinating. Conversely, embryos of seeds incubated during 3 months at 20/7 or 28/14°C hardly grew and no germination was recorded. Since cold stratification was the only requirement for the loss of MPD, and both dry storage in laboratory conditions and warm stratification prior to cold stratification shortened the cold stratification period required for germination, it could be concluded that D. fissum subsp. sordidum seeds have intermediate complex MPD. Cold stratification and incubation in darkness conditions promoted higher germination percentages than those in light. In addition, germinative ability increased with seed age up to 8 months (reaching 96% at 5°C in darkness), showed a pronounced inter-annual and inter-population variability, as well as a significant decrease in seeds coming from pollination by geitonogamy. High temperatures (25/10 or 28/14°C) induced seeds to secondary dormancy, so seedling emergence in the greenhouse was restricted to February–March. The requirements for dormancy break and germination reflect an adaptation to trigger germination in late winter. This study is the first one to document a gradual increase in germination percentage with seed age for plant species with intermediate complex MPD.     

Annual dormancy cycles in buried seeds of shrub species: germination ecology of Sideritis serrata (Labiatae)

The germination ecology of Sideritis serrata was investigated in order to improve ex‐situ propagation techniques and management of their habitat. Specifically, we analysed: (i) influence of temperature, light conditions and seed age on germination patterns; (ii) phenology of germination; (iii) germinative response of buried seeds to seasonal temperature changes; (iv) temperature requirements for induction and breaking of secondary dormancy; (v) ability to form persistent soil seed banks; and (vi) seed bank dynamics. Freshly matured seeds showed conditional physiological dormancy, germinating at low and cool temperatures but not at high ones (28/14 and 32/18 °C). Germination ability increased with time of dry storage, suggesting the existence of non‐deep physiological dormancy. Under unheated shade‐house conditions, germination was concentrated in the first autumn. S. serrata seeds buried and exposed to natural seasonal temperature variations in the shade‐house, exhibited an annual conditional dormancy/non‐dormancy cycle, coming out of conditional dormancy in summer and re‐entering it in winter. Non‐dormant seeds were clearly induced into dormancy when stratified at 5 or 15/4 °C for 8 weeks. Dormant seeds, stratified at 28/14 or 32/18 °C for 16 weeks, became non‐dormant if they were subsequently incubated over a temperature range from 15/4 to 32/18 °C. S. serrata is able to form small persistent soil seed banks. The maximum seed life span in the soil was 4 years, decreasing with burial depth. This is the second report of an annual conditional dormancy/non‐dormancy cycle in seeds of shrub species.     

Seed dormancy and germination in Jeffersonia dubia (Berberidaceae) as affected by temperature and gibberellic acid

The genus Jeffersonia, which contains only two species, has a trans‐Atlantic disjunct distribution. The aims of this study were to determine the requirements for breaking dormancy and germination of J. dubia seeds and to compare its dormancy characteristics with those of the congener in eastern North America. Ripe seeds of J. dubia contain an underdeveloped embryo and were permeable to water. In nature, seeds were dispersed in May, while embryos began to grow in September, and were fully elongated by late November. Germination started in March of the next year, and seeds emerged as seedlings soon after germination. In laboratory experiments, incubation at high temperatures (25 °C, 25/15 °C) for at least 8 weeks was required to initiate embryo growth, while a transfer to moderate temperatures (20/10 °C, 15/6 °C) was needed for the completion of embryo growth. At least 8 weeks at 5 °C was effective in overcoming physiological dormancy and for germination in seeds after the embryos had fully elongated. Thus, both high and low temperatures were essential to break dormancy. Gibberellic acid (GA₃) treatment could substitute for the high temperature requirement, but not for the low temperature requirement. Based on the dormancy‐breaking requirements, it is confirmed that the seeds have deep simple morphophysiological dormancy. This dormancy type is similar to that of seeds of the eastern North American species J. diphylla. Although seeds require 10–11 months from seed dispersal to germination in nature, under controlled conditions they required only 3 months after treatment with 1000 mg·l^?1 GA₃, followed by incubation at 15/6 °C. This represents practical knowledge for propagation of these plants from seed.     

Seed germination and dormancy traits of forbs and shrubs important for restoration of North American dryland ecosystems

• In degraded dryland systems, native plant community re‐establishment following disturbance is almost exclusively carried out using seeds, but these efforts commonly fail. Much of this failure can be attributed to the limited understanding of seed dormancy and germination traits.
• We undertook a systematic classification of seed dormancy of 26 species of annual and perennial forbs and shrubs that represent key, dominant genera used in restoration of the Great Basin ecosystem in the western United States. We examined germination across a wide thermal profile to depict species‐specific characteristics and assessed the potential of gibberellic acid (GA₃) and karrikinolide (KAR₁) to expand the thermal germination envelope of fresh seeds.
• Of the tested species, 81% produce seeds that are dormant at maturity. The largest proportion (62%) exhibited physiological (PD), followed by physical (PY, 8%), combinational (PY + PD, 8%) and morphophysiological (MPD, 4%) dormancy classes. The effects of chemical stimulants were temperature‐ and species‐mediated. In general, mean germination across the thermal profile was improved by GA₃ and KAR₁ for 11 and five species, respectively. We detected a strong germination response to temperature in freshly collected seeds of 20 species. Temperatures below 10 °C limited the germination of all except Agoseris heterophylla, suggesting that in their dormant state, the majority of these species are thermally restricted.
• Our findings demonstrate the utility of dormancy classification as a foundation for understanding the critical regenerative traits in these ecologically important species and highlight its importance in restoration planning.

     

Impacts of fire cues on germination of Brassica napus L. seeds with high and low secondary dormancy

• Agricultural burning is used in farm management operations; however, information about the impact of fire cues on the release and/or induction of secondary dormancy in crop seeds is scarce.
• Seeds from two oilseed rape cultivars were induced for high (HD) or low (LD) secondary dormancy using polyethyleneglycol (PEG) pre‐treatment, and their germination after exposure to various fire cues was compared to control PEG pre‐treated and non‐dormant seeds.
• Non‐dormant seed germination was unaffected by various fire cues. Low doses of aerosol smoke released secondary dormancy in HD seeds, while higher doses increased dormancy of LD seeds. Dilute smoke water also released HD seed secondary dormancy, but concentrated smke water enhanced dormancy in both LD and HD seeds. The concentrated aqueous extracts from charred oilseed rape straw only promoted germination of HD seeds, while dilution inhibited LD seed germination. Heat shock (80 °C, 5 min) released secondary dormancy in HD seeds; however, higher temperatures and/or increased exposure time was associated with seed death. GC‐MS analyses of smoke water revealed two butenolides and an array of monoaromatic hydroxybenzene compounds with potential germination inhibitor or promoter activity.
• The extent of secondary dormancy induction in seeds affects their subsequent responses to fire cues. Both aerosol smoke and smoke water have both germination promoter and inhibitor activity. Lacking any butenolides, aqueous extracts of charred straw contain a potential germination stimulating steroid, i.e. ergosterol. The significance of fire‐derived cues on behaviour of oilseed rape seeds in the soil seed bank is discussed.

     

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.

     

The impact of global warming on germination and seedling emergence in Alliaria petiolata,a woodland species with dormancy loss dependent on low temperature

• The impact of global warming on seed dormancy loss and germination was investigated in Alliaria petiolata (garlic mustard), a common woodland/hedgerow plant in Eurasia, considered invasive in North America. Increased temperature may have serious implications, since seeds of this species germinate and emerge at low temperatures early in spring to establish and grow before canopy development of competing species.
• Dormancy was evaluated in seeds buried in field soils. Seedling emergence was also investigated in the field, and in a thermogradient tunnel under global warming scenarios representing predicted UK air temperatures through to 2080.
• Dormancy was simple, and its relief required the accumulation of low temperature chilling time. Under a global warming scenario, dormancy relief and seedling emergence declined and seed mortality increased as soil temperature increased along a thermal gradient. Seedling emergence advanced with soil temperature, peaking 8 days earlier under 2080 conditions.
• The results indicate that as mean temperature increases due to global warming, the chilling requirement for dormancy relief may not be fully satisfied, but seedling emergence will continue from low dormancy seeds in the population. Adaptation resulting from selection of this low dormancy proportion is likely to reduce the overall population chilling requirement. Seedling emergence is also likely to keep pace with the advancement of biological spring, enabling A. petiolata to maintain its strategy of establishment before the woodland canopy closes. However, this potential for adaptation may be countered by increased seed mortality in the seed bank as soils warm.

     

Hydrothermal thresholds for seed germination in winter annual forbs from old‐field Mediterranean landscapes

• Under Mediterranean climates with dry‐hot summers and cool‐wet winters, many forbs with potential for habitat restoration are winter annuals, but there is little information about their germination.
• We performed laboratory germination experiments on 13 ruderal dicots native to Andalusia (southern Spain). We measured the germination of recently harvested seeds from natural populations across nine temperature treatments (from 5 to 35 °C, constant and alternate); two storage periods; and eight water stress treatments (from 0 to ?1.0 MPa). We then calculated the hydrothermal thresholds for seed germination.
• Final germination ranged from 0–100% and results were mixed in response to temperature. Base temperature was below 6 °C, optimal temperature was around 14 °C and the ceiling temperature around 23 °C. For five species, 10 months of storage improved total germination, indicating a dormancy‐breaking effect, but the other species did not respond or had their germination reduced. All species were relatively tolerant to water stress, with base water potential ranging from ?0.8 to ?1.8 MPa.
• Our results suggest that hydrothermal germination thresholds, rather than physiological dormancy, are the main drivers of germination phenology in annual forbs from Mediterranean semi‐dry environments. The variation in germination responses of these forb species differs from winter annual grasses, but their seeds are all suitable for being stored before restoration.

     

Hormonal and temperature regulation of seed dormancy and germination in <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Fluctuating temperature plays a critical role in determining the timing of seed germination in many plant species. However, the physiological and biochemical mechanisms underlying such a response have been paid little attention. The present study investigated the effect of plant growth regulators and cold stratification in regulating Leymus chinensis seed germination and dormancy response to temperature. Results showed that seed germination was less than 2 % at all constant temperatures while fluctuating temperature significantly increased germination percentage. The highest germination was 71 % at 20/30 °C. Removal of the embryo enclosing material of L. chinensis seed germinated to 74 %, and replaced the requirement for fluctuating temperature to germinate, by increasing embryo growth potential. Applications of GA₄₊₇ significantly increased seed germination at constant temperature. Also, inhibition of GA biosynthesis significantly decreased seed germination at fluctuating temperatures depending upon paclobutrazol concentration. This implied GA was necessary for non-dormant seed germination and played an important role in regulating seed germination response to temperature. Inhibition of ABA biosynthesis during imbibition completely released seed dormancy at 20/30 °C, but showed no effect on seed germination at constant temperature, suggesting ABA biosynthesis was important for seed dormancy maintenance but may not involve in seed germination response to temperature. Cold stratification with water or GA₃ induced seed into secondary dormancy, but this effect was reversed by exogenous FL, suggesting ABA biosynthesis during cold stratification was involved in secondary dormancy. Also, cold stratification with FL entirely replaced the requirement of fluctuating temperature for germination with seeds having 73 % germination at constant temperature. This appears to be attributed to inhibition of ABA biosynthesis and an increase of GA biosynthesis during cold stratification, leading to an increased embryo growth potential. We suggest that fluctuating temperature promotes seed germination by increasing embryo growth potential, mainly attributed to GA biosynthesis during imbibitions. ABA is important for seed dormancy maintenance and induction but showed less effect on non-dormant seed germination response to temperature.     

Seed traits and germination behaviour of four Sardinian populations of Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) along an altitudinal gradient

• Helichrysum microphyllum subsp. tyrrhenicum (Asteraceae) is an endemic taxon of Sardinia and Corsica, where it grows at different altitudes. The objective of this study was to investigate the seed traits and germination behaviour of four Sardinian populations of this taxon located at different altitudes.
• Seed traits were evaluated, and germination tests were carried out by incubating seeds at a range of constant (5–30 °C) and alternating (25/10 °C) temperatures. The dry after‐ripening (DAR) pre‐treatment was also applied by storing seed in dry conditions for 3 months at 25 °C. Seed traits and germination behaviour data were statistically analysed to identify if there was a correlation with altitude.
• Differences in seed size, area and mass among populations were recorded, however, no relationship was found with altitude. High germination percentages were obtained in all populations, both in untreated and DAR seeds, and were positively affected by alternating temperatures. The final germination percentage and time required to reach 50% final germination (T₅₀) showed no relationship with altitude.
• The differences in seed traits and germination detected among the studied populations of H. microphyllum subsp. tyrrhenicum were not correlated with altitude. This study provides new and important knowledge for this taxon. H. microphyllum subsp. tyrrhenicum is characterised by high germination percentages and low T₅₀ values and does not seem to require any dormancy‐breaking treatment. This species represents a high‐potential native plant species that should be considered within environmental management plans.

     

Effect of Temperatures on Dormancy and Germination in Three Species in the Lamiaceae Occurring in Northern Wetlands

In the temperate region temperature is the main factor influencing the germination period of plant species. The purpose of this study was to examine effects of constant and fluctuating temperatures on dormancy and germination under laboratory and field conditions in the three wetland species Lycopus europaeus, Mentha aquatica and Stachys palustris. The results should give indications if the temperature-dependent regulation of dormancy and germination is phylogenetically constrained. Tests for germination requirements showed a minimum temperature for germination of 9 °C in Mentha and 12 °C in Lycopus and Stachys, and a maximum temperature of 33 °C for Lycopus and 36 °C for Mentha and Stachys. Fluctuating temperatures promoted germination in all three species but the amplitude required for high germination (>50%) differed: it was 8 °C in Mentha, 10 °C in Stachys and 14 °C in Lycopus (mean temperature 22 °C). The effect of temperatures on the level of dormancy was examined in the laboratory by imbibing seeds at temperatures between 3 °C and 18 °C for periods between 2 and 28 weeks, as well as by a 30-month burial period, followed by germination tests at various temperatures, in light and darkness. In the laboratory only low temperatures (≤12 °C) relieved primary dormancy in seeds of Lycopus, while in Mentha and Stachys also higher temperatures lead to an increase of germination. Dormancy was only induced in Lycopus seeds after prolonged imbibition at 12 °C in the laboratory. Buried seeds of all species exhibited annual dormancy cycles with lower germination in summer and higher germination from autumn to spring. Exhumed seeds, however, showed considerable differences in periods of germination success. Dormancy was relieved when ambient temperatures were below 12 °C. Ambient temperatures that caused an induction of dormancy varied depending on species and test condition, but even low temperatures (8 °C) were effective. At high test temperatures (25 °C) in light, exhumed seeds of all three species showed high germination throughout the year. The three species showed various differences in the effects of temperatures on dormancy and germination. Similarities in dormancy and germination found among the species are in common with other spring-germinating species occurring in wetlands, so it seems that the temperature dependent regulation of dormancy and germination are related to habitat and not to phylogenetic relatedness.     

Diversity of epicotyl dormancy among tropical montane forest species in Sri Lanka

• Fruiting season of many Sri Lankan tropical montane species is not synchronised and may not occur when conditions are favourable for seedling establishment. We hypothesised that species with different fruiting seasons have different seed dormancy mechanisms to synchronise timing of germination with a favourable season for establishment. Using six species with different fruiting seasons, we tested this hypothesis.
• Germination and imbibition of intact and manually scarified seeds were studied. Effect of GA₃ on germination was examined. Embryo length:seed length (E:S) ratio of freshly matured seeds and of those with a split seed coat was determined. Time taken for radicle and plumule emergence and morphological changes of the embryos were recorded.
• The radicle emerged from Ardisia missionis, Bheza nitidissima and Gaetnera walkeri seeds within 30 days, whereas it took >30 days in other species. Embryos grew in seeds of B. nitidissima and G. walkeri prior to radicle emergence but not in Microtropis wallichiana, Nothapodytes nimmoniana and Symplocos cochinchinensis. A considerable delay was observed between radicle and plumule emergence in all six species. Warm stratification and/or GA₃ promoted germination of all species.
• All the tested species have epicotyl dormancy. Seeds of B. nitidissima and G. walkeri have non‐deep simple morphophysiological epicotyl dormancy, and the other four species have non‐deep physiological epicotyl dormancy. Differences in radicle and epicotyl dormancy promote synchronisation of germination to a favourable time for seedling development. Therefore, information on dormancy‐breaking and germination requirements of both radicle and epicotyl are needed to determine the kind of dormancy of a particular species.

     

Understanding biological and ecological factors affecting seed germination of the multipurpose tree Anogeissus leiocarpa

• Anogeissus leiocarpa (DC.) Guill. & Perr. (Combretaceae) has important economic and cultural value in West Africa as source of wood, dye and medicine. Although this tree is in high demand by local communities, its planting remains limited due to its very low propagation via seed.
• In this study, X‐rays were used to select filled fruits in order to characterise their morphology and seed germination responses to treatment with sulphuric acid and different incubation temperatures.
• Morphological observations highlighted a straight orthotropous seed structure. The increase in mass detected for both intact and scarified fruits through imbibition tests, as well as morphological observations of fruits soaked in methylene blue solution, confirmed that they are water‐permeable, although acid‐scarified fruits reached significantly higher mass increment values than intact ones. Acid scarification (10 min soaking in 98% H₂SO₄) positively affected seed germination rate but not final germination proportions. When intact fruits where incubated at a range of temperatures, no seeds germinated at 10 °C, while maximum seed germination (ca. 80%) was reached at 20 °C. T₅₀ values ranged from a minimum of ca. 12 days at 25 °C to a maximum of ca. 34 days at 15 and 35 °C. A theoretical base temperature for germination (T_b) of ca. 10 °C and a thermal requirement for 50% germination (S) of ca. 195 °Cd were also identified for intact fruits.
• The results of this study revealed the seed germination characteristics driven by fruit and seed morphology of this species, which will help in its wider propagation in plantations.