Probit-based models relating a proportional response variable to a temporal explanatory variable, assuming that the times to response are normally distributed within the population, have been used in seed biology for describing the rate of loss of viability during seed ageing and the progress of germination over time in response to environmental signals (e.g. water, temperature). These models may be expressed as generalized linear models (GLMs) with a probit (cumulative normal distribution) link function, and, using GLM fitting procedures in current statistical software, parameters of these models are efficiently estimated while taking into account the binomial error distribution of the dependent variable. The fitted parameters can then be used to calculate the ‘traditional’ model parameters, such as the hydro- or hydrothermal time constant, the mean or median response of the seeds (e.g. mean time to death, median base water potential), and the standard deviation of the normal distribution of that response. Furthermore, through consideration of the deviance and residuals, performing model evaluation and modification can lead to improved understanding of the underlying physiological/ecological processes. However, fitting a binomial GLM is not appropriate for the cumulative count data often collected from germination studies, as successive observations are not independent, and time-to-event/survival analysis should be considered instead. This review discusses well-known probit-based models, providing advice on how to collect appropriate data and fit the models to those data, and gives an overview of alternative analysis approaches to improve understanding of the underlying mechanisms of seed dormancy and germination behaviour.

Successful remobilization of seed reserves is the driving force behind seedling establishment for maximum final crop outcomes. The remobilization of stored maize seed phosphorus (P), and its allocation towards growing seedlings is critical for P-autotrophy during early ontogeny. We aimed to (1) evaluate the time frame of the origin of P utilized by maize seedlings, including the heterotrophic, transitional and autotrophic phases; and (2) compare P and carbon (C) dynamics in both seed and seedling compartments during the same phases. Using isotopic signatures (32P), we identified different P fluxes (P-heterotrophy, P-transition and P-autotrophy) and determined the proportion of P fluxes from heterotrophic seed P and external P uptake during 23 d of early ontogeny. The P-heterotrophic growth phase lasted from the first to the fourth day after sowing, when seedlings were entirely made up of heterotrophic P originating from remobilized seed P pool. In our experimental conditions, the P-transitional phase, when growing seedlings were supported by both heterotrophic and autotrophic P, lasted from the fifth to the fifteenth day after sowing. Thereafter, seed P reserves were exhausted and seedlings depended entirely on external P uptake, indicating the P-autotrophic stage. Although seed P reserves were remobilized earlier than C reserves, the length of the three growth phases for P and C was similar in the maize seedlings.

Temperature is a significant factor influencing seed germination and for many species temperature-mediated germination cues are vital for plant persistence. Rising temperatures forecast as a result of anthropogenic climate change may have a substantial influence on the population and range dynamics of plant species. Here, we report on the thermal constraints on seed germination in natural populations of four congeneric Banksia species collected from a longitudinal climate gradient in Western Australia. We investigated whether germination niche: (1) varied between species; (2) varied among populations of each species; and (3) varied in a consistent manner reflecting the climatic gradients of seed origin. We hypothesized that species would differ and that populations from warmer sites would have a broader temperature window for germination than populations from cooler sites. Species differed in the breadth of their germination niche, but temperatures that stimulated the most rapid and complete germination were similar across all species. A sharp reduction in germination percentage occurred above the optimum temperature, which coincided with significant delays in germination relative to the optimum. The temperatures causing these declines varied among populations. Across the species, there was a significant correlation between optimum germination temperature and mean annual temperature at seed source; however, there was no relationship at the population level for individual species. These data provide insight into the vulnerability of Banksia species to climate change, with those populations that require lower temperatures for germination, or have narrower optimal ranges for germination, likely to be most vulnerable to a warming climate.

Germination timing is a key transition of life history. It not only links subsequent life-history traits, such as plant height and flowering time, but also provides a link to the previous generation through the influence of the maternal environment. Environmental factors may mediate these key links, and consequences of this process may influence species regeneration and dispersal. However, little is known about how environmental factors mediate these key links. Here, germination timing under high (natural light) and low light treatments was estimated for 476 angiosperm species of the eastern Tibetan Plateau grasslands. Furthermore, we used standard (std) and phylogenetic (phy) comparative methods to test if germination timing was associated with plant height, flowering time and maternal habitats under both light treatments. Germination timing was positively correlated with plant height only in low light in std-methods. Germination timing was associated with onset of flowering in both light treatments in std-methods, but only in low light when using phy-methods. Germination timing was positively correlated with elevation only in low light when using both comparative methods. Germination timing was correlated with water in maternal habitat only in high light when using both comparative methods. Germination timing was associated with light in maternal habitat in both light treatments in std-methods, but only in high light when using phy-methods. In summary, light-dependent associations of germination timing with subsequent life-history traits and maternal habitats may influence the probability of plant species life-cycle completion and influence distribution and dispersal of plant species in natural plant communities.

Many temperate plant genera, like Sambucus, have species with range disjunctions among North America, Europe and/or Asia. Cold stratification (sometimes in combination with warm stratification) is the primary mechanism to break seed dormancy in these species. For some of these genera showing Northern Hemispheric disjunctions, members also occur in subtropical or tropical regions, mostly confined to higher elevations where climate and vegetation differ from those in northern latitudes. We made two hypotheses concerning germination for the subtropical Taiwanese Sambucus chinensis: (1) seeds from populations exposed to warm temperatures would require warm stratification, and (2) seeds from populations exposed to cold temperatures need cold stratification. We investigated the germination (including embryo growth) of non-stratified seeds over a range of temperatures and tested the effects of cold stratification and of gibberellins GA3 and GA4 on germination. The amount and timing of germination among populations varied substantially in response to temperature treatments. Seeds from all populations of this species required warm temperatures for dormancy break and germination, regardless of environmental conditions. As such, the majority of seeds had non-deep simple morphophysiological dormancy, which, until now, has not been reported in any members of Sambucus. The seed characteristics of the subtropical S. chinensis are different from those of temperate members of the genus in which cold stratification is the predominate treatment to overcome dormancy.

Seeds of Dodonaea viscosa (Sapindaceae) have a water-impermeable seed coat, i.e. physical dormancy (PY). Although mechanical scarification, dry heat, sulphuric acid and hot water treatment make seeds permeable under laboratory conditions, the mechanisms by which dormancy is alleviated in natural environments have not yet been understood completely. The present investigation aims to understand the pattern of dormancy alleviation in D. viscosa seeds using an artificial burial approach for 2 years. Freshly collected seeds held in hydrated soil at 10/20°C, 15/20°C, 15/30°C, 20/35°C and 25°C for 32 weeks germinated to less than 15%, irrespective of storage temperature. Dry storage of seeds at 15, 20, 25 and 30°C for 1 year did not break dormancy. Hot water treatment at 80 and 90°C for 30 s broke dormancy in 90% of the seeds. On the other hand, burying seeds at a depth of 3–5 cm in the natural environment for 2 years increased germination from 7 to 71%. In particular, seeds exhumed after summer in both years showed a significant increase in germination percentage (P< 0.05). However, seeds buried after summer did not germinate to a higher percentage when exhumed prior to summer. We suggest that a high summer temperature, rising above 60°C in the top soil layer of the tropics, is a likely factor breaking dormancy. Most seeds germinated during burial, which indicates that light is not a cue for germination. We conclude that germination of D. viscosa following summer is an adaptive mechanism to tolerate summer droughts, which are common in the dry tropics.

Temperate wetland species often require light and warm temperatures for seed germination. However, recent studies indicate that species which specialize on permanently saturated wetlands that are maintained by groundwater discharge (fens, seeps and mountain springs), rather than wetlands with surface-water-driven hydrologic regimes, diverge from the typical wetland germination niche by germinating at cool temperatures and lacking photoblastic seeds. We conducted laboratory experiments that manipulated stratification conditions (non-stratified versus cold stratification in light and darkness), thermal regime (15/6, 25/15 and 35/20°C), and light (14 h photoperiod versus continuous darkness) to test whether seeds of the North American calcareous fen specialist Parnassia grandifolia diverged from the typical temperate wetland germination niche. After 30 d, fresh seeds were conditionally dormant and could only germinate to high percentages in light at 25/15°C. During 16 weeks of incubation, non-stratified seeds germinated to low percentages ( < 40%) at all thermal regimes in darkness. In contrast, cold-stratified seeds germinated to high percentages in both light and darkness at all thermal regimes, although germination was incomplete (no cotyledon emergence) at 35/20°C. Further, seeds did not require light during cold stratification to germinate to high percentages when incubated in light or darkness. Thus, seeds diverged from the typical temperate wetland germination syndrome in lacking a light and warm temperature requirement for germination. Our results reinforce previous work from European fens and Mediterranean wetlands. This indicates that multiple germination strategies are found in fen wetlands that are maintained by the continuous or near-continuous discharge of cool groundwater.

Whether or not it is time for germination is a dilemma for annuals since they have only a single opportunity to reproduce successfully. This is critical for species living in stressful and unpredictable environments such as Mediterranean habitats. In order to clarify the environmental cues of germination, four annuals of different families, all of them occurring very frequently on gypsum soils, were selected and their germination observed under 14 climate scenarios, mimicking temperature and photoperiod conditions from autumn to spring, at two levels of water availability (continuous irrigation versus an initial single irrigation event followed by a progressive soil desiccation). In spring scenarios, two seed-storage conditions were compared: dry cold and room conditions. In the absence of water limitation, germination decreased from early autumn to late spring. Water scarcity always reduced germination, especially in early spring. Our results suggest a facultative winter germination behaviour and highlight the crucial role of dry cold storage in reducing spring germination. In conclusion, Mediterranean ephemerals showed a very plastic germination response that allows them to take advantage of favourable environmental conditions from autumn to spring. This environmental cueing is combined with the ability to dilute the risk through a variable rate of seed dormancy that, according to bet-hedging strategies, increases from secure autumn to riskier spring.

The role of smoke in fire-stimulated germination in the Mediterranean Basin has often been underestimated. A few records on smoke-enhanced germination are present in Mediterranean Lamiaceae species, but there is still a shortage of information to allow generalizations about this family to be made. To test the hypothesis that smoke enhances germination in Mediterranean Lamiaceae species, we performed a germination experiment, including aqueous smoke treatments in various concentrations (1:1, 1:10 and 1:100) on seven eastern Mediterranean Lamiaceae taxa. Six of the studied taxa (Lavandula stoechas, Origanum onites, Phlomis bourgaei, Stachys cretica ssp. smyrnaea, Satureja thymbra, Teucrium lamiifolium ssp. stachyophyllum) showed significant increments in germination percentage in at least one smoke treatment, as compared to the control. Moreover, L. stoechas, S. thymbra and T. lamiifolium ssp. stachyophyllum displayed faster germination in at least one smoke treatment than in the control. Of the species showing significant increments in germination percentages after aqueous smoke application, at least one single concentration of smoke solution did not stimulate germination, except in L. stoechas and S. thymbra which responded positively to all smoke treatments. Therefore, the concentration of aqueous smoke that improved germination was species-specific. Our results contribute to the current limited knowledge on smoke-enhanced germination in Mediterranean Lamiaceae, and support the idea that smoke is an important germination cue for this family.

Birds are important seed dispersers for fleshy fruits through their transportation of ingested seeds. The seeds of many species germinate faster and in greater proportions after passing through a digestive tract, although the effects of this passage vary amongst bird and plant species. Many factors determine the germination success of ingested seeds, such as seed scarification during the digestion process, the fertilizing effect of droppings and the removal of pulp surrounding the seeds. In central Spain, the great bustard (Otis tarda) may act as a disperser of European black nightshade (Solanum nigrum). We analysed the germination success of ingested and non-ingested S. nigrum seeds. The fertilizing effect of bustard droppings and the disinhibition effect of the removal of Solanum pulp on final germination percentage, germination speed and viability were also assessed. Although ingested seeds germinated faster than non-ingested seeds, the former showed a lower germination percentage than the latter: 80–87% versus 99%. Droppings and fruit pulp showed no effect on germination enhancement, except in one aspect: the germination speed of non-ingested seeds decreased when they were sprayed with a fruit extract. We confirm that seeds ingested by great bustards had lower germination success than non-ingested seeds. Although seed ingestion by great bustards reduced seedling emergence, the number of emerged seedlings was still quite large. Thus, great bustards may play a role as a S. nigrum seed dispersal vector.