Siti N. Hidayati

Defining transient and persistent seed banks in species with pronounced seasonal dormancy and germination patterns

The most often used time-line for distinguishing a transient seed bank from a persistent seed bank is one calendar year. Thus, species whose seeds live in or on the soil for ,1 year have a transient seed bank, whereas those whose seeds live for

Seed germination ecophysiology of the Asian species Osmorhiza aristata (Apiaceae): comparison with its North American congeners and implications for evolution of types of dormancy

1 year have a persistent seed bank. However, dormancy cycling of seeds buried in soil has not been given due consideration in these models. When dormancy cycling is considered, it is shown that seeds of both autumn-germinators and spring-germinators are in the dormant state when they are 1 year old. Thus, unless the seeds live until at least the second germination season (i.e. usually 16–18 months following dispersal), they are, in effect, part of a transient seed bank, having lived through only one germination season. We propose that for seeds of such species to be considered part of a short-term persistent seed bank, they should remain viable and germinable until at least the second germination season, and to be part of a long-term persistent seed bank, until at least the sixth germination season. Our definitions are applicable to seeds with physiological, physical or morphophysiological dormancy, which often require .1 year after maturity to come out of dormancy in nature. We discuss modifications of the seedling emergence method for detection of a soil seed bank, so that they correspond to our definitions of seed-bank strategies.

Germination ecophysiology of the western North American species Osmorhiza depauperata (Apiaceae): implications of preadaptation and phylogenetic niche conservatism in seed dormancy evolution

Osmorhiza aristata is an herbaceous perennial that grows primarily in Japan, through southern China, to the Himalayas. It closely resembles the eastern North American species O. claytonii and O. longistylis, and, together, the three species are an example of the well-known North American-Asian pattern of disjunction. Requirements for dormancy break and embryo growth were determined for seeds of O. aristata collected in Japan during the summers of 1998-2000. Embryos in fresh seeds were ca. 0.5 mm long, and they had to grow to 9 mm before the radicle emerged from the mericarp. Embryo growth and germination occurred during cold stratification at 5°C, the optimum temperature for germination. Gibberellic acid did not substitute for cold stratification. Thus, O. aristata seeds have deep complex morphophysiological dormancy (MPD). The type of MPD in O. aristata is similar to that in two western North American congeners but different from that in eastern North American congeners (nondeep complex MPD). Mapping the types of MPD onto a phylogeny of the genus suggests that nondeep complex MPD is derived from deep complex MPD. Although eastern North American-Asian disjuncts often exhibit morphological stasis, the taxa may differ greatly in physiological traits, such as seed dormancy.

Sympatric species of Hibbertia (Dilleniaceae) vary in dormancy break and germination requirements: implications for classifying morphophysiological dormancy in Mediterranean biomes.

Requirements for dormancy break and embryo growth were determined for seeds of the western North American species, Osmorhiza depauperata . Seeds were collected in August 2001 from Sandia Crest (3200 m elevation) and Las Huertas (2300 m), New Mexico (USA). Embryos in fresh seeds were c . 0.6 mm long, and they had to grow to c . 9–10 mm before the radicle emerged from the mericarp. Embryo growth occurred at low temperatures (1 and 5°C), and seeds germinated to high percentages at 1°C during 32 weeks of incubation in the light. No seeds germinated at 5, 15/6, 20/10, 25/15 or 30/15°C during 32 weeks of incubation. Although a 4–18 week warm-temperature (25/15°C) pretreatment increased germination rates at 1°C, it was unnecessary for a high percentage of seeds to germinate. Gibberellic acid (GA 3 , 10–1000 mg l –1 ) did not substitute for cold stratification. Seeds from the low-elevation population contained larger embryos and required less time to germinate than those from the high-elevation population. O. depauperata seeds have deep complex morphophysiological dormancy (MPD), which is similar to two other western North American congeners and an Asian congener, but different from two eastern North American congeners. Results from this study suggest that: (1) phylogenetic niche conservatism has played a role in the persistence of deep complex MPD in the three western North American species of Osmorhiza ; and (2) the stimulatory effect from a warm pretreatment in species needing only cold stratification for dormancy break is a preadaptation that initiated the development of an absolute warm requirement in species needing both warm and cold stratification.

Understanding the germination of bulbils from an ecological perspective: a case study on Chinese yam (Dioscorea polystachya)

BACKGROUND AND AIMSnSeveral ecologically important plant families in Mediterranean biomes have seeds with morphophysiological dormancy (MPD) but have been poorly studied. The aim of this study was to understand the seed ecology of these species by focusing on the prominent, yet intractably dormant Australian genus Hibbertia. It was hypothesized that the slow germination in species of this genus is caused by a requirement for embryo growth inside the seed before germination, and that initiation of embryo growth is reliant upon a complex sequence of environmental cues including seasonal fluctuations in temperature and moisture, and an interplay with light and smoke. Using the results, the classification of the MPD level in species of Hibbertia is considered.nnnMETHODSnFour species of Hibbertia in winter rainfall south-western Australia were selected. These species, whilst differing in geographic distributions, are variously sympatric, and all are important understorey components of plant communities. The following aspects related to dormancy break, embryo growth and germination were investigated: temperature and moisture requirements; effects of karrikinolide, gibberellic acid and aerosol smoke; and phenology.nnnKEY RESULTSnFollowing exposure to wet/dry cycles at low or high temperatures, embryo growth and germination occurred, albeit slowly in all species at low temperatures when moisture was unlimited, corresponding to winter in south-west Australia. Photo regime influenced germination only in H. racemosa. Aerosol smoke triggered substantial germination during the 1st germination season in H. huegelii and H. hypericoides.nnnCONCLUSIONSnAlthough the study species are con-generic, sympatric and produce seeds of identical morphology, they possessed different dormancy-break and germination requirements. The physiological component of MPD was non-deep in H. racemosa but varied in the other three species where more deeply dormant seeds required >1 summer to overcome dormancy and, thus, germination was spread over time. Embryos grew during winter, but future studies need to resolve the role of cold versus warm stratification by using constant temperature regimes. To include Mediterranean species with MPD, some modifications to the current seed-dormancy classification system may need consideration: (a) wet/dry conditions for warm stratification and (b) a relatively long period for warm stratification. These outcomes have important implications for improving experimental approaches to resolve the effective use of broadcast seed for ecological restoration.

Evolutionary considerations of the presence of both morphophysiological and physiological seed dormancy in the highly advanced euasterids II order Dipsacales

BACKGROUND AND AIMSnBulbils serve as a means of vegetative reproduction and of dispersal for many plants; this latter aspect making them analogous to seeds. However, germination of bulbils may differ considerably from seeds due to dissimilar anatomical structures and perhaps environmental cue perception. The few laboratory studies done on bulbils suggest that their germination is similar to that of seeds in the same habitats and to vegetative buds of winter-dormant plants. The present study is the first to examine how bulbil germination is controlled in nature in relation to dispersal (before vs. after winter of the same cohort) and to ambient temperatures.nnnMETHODSnUnder laboratory conditions, temperature and light requirements for root and shoot emergences from bulbils of Dioscorea polystachya collected in September, 2005, February, 2006 (produced in 2005) and July, 2006 were determined. Effects of cold stratification and dry storage for releasing dormancy were tested on September and July bulbils. The phenology of dormancy release and of root and shoot emergences and the persistence of bulbils in soil were followed over time under field conditions.nnnKEY RESULTSnAlthough a low percentage of bulbils collected in July or in September produced roots, but no shoots, in the laboratory and field, these roots died within approx. 1 month. Regardless of collection date, cold stratification markedly increased root and shoot emergences. Bulbils sown outdoors in October produced roots and shoots the following March and April, respectively. The soil bulbil bank is short lived.nnnCONCLUSIONSnBulbils of D. polystachya are similar to seeds of many temperate plants being mostly dormant when dispersed in summer or autumn and overcoming dormancy with cold stratification during winter. Adaptively, bulbil germination primarily occurs in spring at the beginning of a favourable period for survivorship and growth.

Seed germination and seedling development ecology in world-wide populations of a circumboreal Tertiary relict.

Although the underdeveloped embryo, and thus morphological (MD) or morphophysiological (MPD) seed dormancy, is basal in angiosperms, it also occurs in advanced groups. A synthesis of the literature, combining phylogeny and the kind of seed dormancy in the highly evolutionarily advanced order Dipsacales , shows that MPD (or MD) occurs throughout all clades except the most advanced one, Valerina . Seeds of taxa in the Valerina clade have fully developed embryos and physiological dormancy (PD) or are non-dormant (ND); thus, PD and ND are derived conditions in Dipsacales . Assuming that types of seed dormancy have not changed since the Early Tertiary, the fossil record suggests that MPD (or MD) was present in extant genera of Dipsacales by the Palaeocene, but PD (or ND) not until the Miocene. Molecular dating indicates that the ages of dipsacalean lineages with MPD and PD are older than those indicated by the fossil evidence.

Germinability of seeds stored in capsules on plants of two myrtaceous shrubs: differences among age cohorts and between species.

Ecological traits of the circumboreal plant Viburnum opulus were examined to improve understanding of the variation of populations occurring in the same biome but on different continents. Seedling development/emergence is shown to be highly similar but some degree of variation was present in other traits, among populations.

A temperate rhamnaceous species with a non-enclosing stone and without physical dormancy

Canopy-stored seed banks are a common trait among members of several plant families in sclerophyllous woodlands of Australia and South Africa, with their fruits usually opening in response to damage or fire. Unknown is whether the degree of dormancy and of germination differs among age cohorts in seeds stored on the mother plant. We examined the extent and speed of germination from two intensely serotinous myrtaceous species, Callistemon glaucus and Calothamnus quadrifidus, for seed held in capsules for up to 9 years. Germination of both species differed significantly among age cohorts (Pu2009<u20090.0001). However, no consistent increase in germination over a range of temperatures with storage was found, suggesting that no after-ripening occurred and that seeds were non-dormant at maturity. Differences among cohorts may be due to pre-conditioning. Significant (Pu2009≤u20090.0214) differences occurred between the small-seeded Callistemon and the large-seeded Calothamnus. Germination was (1) optimum at ≥20°C for Callistemon but at <20°C for Calothamnus, (2) 9–12 days earlier for Callistemon than for Calothamnus, and (3) higher in light than in darkness for Callistemon but equal in both light conditions for Calothamnus. While germination of the species differed in important features, we would expect synchronous germination of all age cohorts to occur following fire and the onset of regular rainfall.

Morphophysiological dormancy in seeds of Convallaria keiskei and a proposal to recognize two types of double dormancy in seed dormancy classification

Department ofBotany, University of Peradeniya, Peradeniya, Sri Lanka(Received 26 March 2012; accepted after revision 16 September 2012)AbstractThe purpose of the present study was to investigatethe dormancy break and germination requirements ofseeds from the rhamnaceous vine Berchemia scandens.The fleshy fruit contains a two-locular stone withan endocarp described as ‘bony, thickish’. Scarifiedand non-scarified stones increased by about 30–50%in mass during imbibition over a 24-h period. Theendocarp of the stone does not completely enclose theseeds and a soft tissue region is present. This regionis the primary area of water entrance to the seed, asshown by dye-tracking and by sealing it. Freshlymatured and overwintered seeds of B. scandensgerminated to low percentages at all temperaturesduring 2 weeks of incubation in light, and theygerminated from moderate to high percentages during12–14 weeks of incubation in light. While coldstratification had a relatively modest effect on thepromotion of total germination across most tempera-tures assessed (if seeds were left for long enough), ithad a somewhat stronger effect on germination rate.Cold-stratified seeds germinated equally well in lightand darkness. The class of dormancy found in seedsof B. scandens would be physiological. The anatomyof the stones readily allows water imbibition, showingthat seeds of B. scandens lack physical dormancy, anuncommon trait in Rhamnaceae.Keywords: Berchemia, endocarp, imbibition test, physicaldormancy, physiological dormancy, Rhamnaceae, stoneIntroductionOf the 51 species in the plant family Rhamnaceaein which the dormancy class has been identified orinferred, 61% have physical dormancy (Baskin andBaskin, 1998, 2003a, b; Baskin et al., 2000, 2007; Turneret al., 2005; Huffman, 2006; Sautu et al., 2006; Haineset al., 2007; Saied et al., 2008; Royal Tasmanian BotanicalGardens, 2009; Maraghni et al., 2010). This type ofdormancy is imposed by a water-impermeable layer ofpalisade or palisade-like cells in the seed or fruit coat.Dormancy break occurs with an opening in aspecialized anatomical structure on the seed or fruit,allowingwaterentrancetotheseed.Forsomemembersof the Rhamnaceae, the seed coat consists of a palisadelayer of macrosclereid cells and the hilar fissure openswith heat (Corner, 1976; Orme and Leege, 1976; Keoghand Bannister, 1994; Baskin et al., 2000; Foroughbakhchet al., 2000; Doweld, 2001). In 22% of the 51 species,physiological dormancy is present in addition tophysical dormancy, i.e. combinational dormancy.Once physical dormancy is broken, seeds still requiresome type of treatment, usually cold stratification inRhamnaceae, for germination to proceed (Baskin andBaskin, 1998). Thus, a water impermeable seed/fruitcoat is a common feature in the Rhamnaceae.However, species with seeds having only physio-logical dormancy (12%) or being non-dormant (6%) arealso reported in the Rhamnaceae (Mugasha andMsanga, 1987; Baskin and Baskin, 1998; Mattana et al.,2009). Some species in this family with physiologicaldormancy or non-dormancy are congeneric withmembers having physical dormancy. In the genusZiziphus, the semi-desert/desert species have physicaldormancy while a semi-evergreen/evergreen rain-forest species may be non-dormant (Baskin andBaskin, 1998; Saied et al., 2008; Maraghni et al., 2010).The pattern of some species having physicaldormancy and others having non-dormancy, particu-larly those growing in tropical/subtropical regions, isa phenomenon seen in other plant families (Baskin and