In fire-prone ecosystems, many species regenerate after fire from persistent soil seed banks. Species with physically dormant (PY) seeds have dormancy broken by fire-related heat. The magnitude of post-fire recruitment, to predict response to varying fire severity, is commonly estimated by testing dormancy-breaking temperature thresholds of fresh PY seeds. However, seeds spend years in the soil during the inter-fire period, and determining whether dormancy-breaking thresholds change over time is essential to accurately predict population persistence. Germination of four south-eastern Australian PY species from the Fabaceae family (Acacia linifolia, Aotus ericoides, Bossiaea heterophylla and Viminaria juncea) were studied. Dormancy-breaking temperature thresholds vary inter-specifically and the species represented either high or low dormancy-breaking threshold classes. Freshly collected seeds, and seeds that had been buried in the field or stored in dry laboratory conditions for 6 and 18 months were subjected to a fire-related range of heat treatments (40–100°C). Seed ageing increased germination response to heat treatments, effectively lowering the dormancy-breaking thresholds of three species. The fourth species, A. linifolia, initially had a relatively large non-dormant fraction which was lost as seeds aged, with older seeds then displaying PY broadly similar to the other study species. Patterns of threshold decay were species-specific, with the thresholds and viability of low-threshold species declining more rapidly than high-threshold species. The non-dormant fraction did not increase over time for any of our study species. Instead of increasing their non-dormant fraction, as is common in other vegetation types, these fire-prone PY species displayed a change of dormancy-breaking temperature thresholds. This is an important distinction, as maintaining dormancy during the inter-fire period is essential for population persistence. While changes in sensitivity to dormancy-breaking treatments have previously been reported as seeds age, our study provides the first test of changes to temperature thresholds, which increases the range of germination response from the seed bank under varying fire severity.

Seeds of the winter annual Bromus tectorum lose primary dormancy in summer and are poised to germinate rapidly in the autumn. If rainfall is inadequate, seeds remain ungerminated and may enter secondary dormancy under winter conditions. We quantified conditions under which seeds enter secondary dormancy in the laboratory and field and also examined whether contrasting B. tectorum genotypes responded differently to dormancy induction cues. The study also extends previous hydrothermal time models for primary dormancy loss and germination timing in B. tectorum by using similar models to account for induction and loss of secondary dormancy. Maximum secondary dormancy was achieved in the laboratory after 4 weeks at –1.0 MPa and 5°C. Seeds in the field became increasingly dormant through exposure to temperatures and water potentials in this range, confirming laboratory results. They were released from dormancy through secondary after-ripening the following summer. Different genotypes showed contrasting responses to dormancy induction cues in both laboratory and field. To examine secondary dormancy induction and release in the field in terms of hydrothermal time parameters, we first created a model that allowed mean base water potential (Ψb(50)) to vary while holding other hydrothermal time parameters constant, as in models for primary dormancy loss under dry conditions. The second model allowed all three model parameters to vary through time, to account for changes (e.g. hydrothermal time accumulation) that could occur simultaneously with dormancy induction in imbibed seeds. Shifts in Ψb(50) could explain most changes in dormancy status for seeds retrieved from the field, except during the short period prior to dormancy induction, when hydrothermal time was accumulating. This study illustrates that hydrothermal modelling, and specifically changes in Ψb(50), can be used to characterize secondary dormancy induction and loss in B. tectorum.

In Mediterranean fire-prone ecosystems, annual species specific to post-fire habitats should have a soil seed bank and should be able to germinate after a fire. Therefore, various fire-related cues can be expected to stimulate germination in post-fire annuals. Germination patterns of the rare annual Chaenorhinum rubrifolium (Plantaginaceae) were examined in response to mechanical scarification, heat shock, aqueous smoke, nitrogenous compounds, gibberellic acid, karrikinolide (KAR1), and mandelonitrile (a cyanohydrin analogue, MAN) under dark and photoperiod conditions in the laboratory. Combinations of these treatments were also included in the experiment. Strong physiological dormancy in the seeds of C. rubrifolium was partially broken by several fire-related germination cues, including smoke and nitrate, under light conditions. KAR1 and MAN also stimulated germination, and the highest improvement in germination was achieved in the KAR1 treatment in the presence of light. Heat shock + smoke and KAR1 + MAN combinations had positive synergetic and additive effects on germination under light conditions, respectively. The light played a crucial role in the promotion of germination. The results suggest that multiple fire-related cues operate to stimulate germination in C. rubrifolium, an annual species from the Mediterranean Basin. However, the species may have a broader germination niche than a fire-restricted one.

Hypseocharis is a genus endemic to the high Andes and sister to all other Geraniaceae genera. Regarding its basal position in Geraniaceae evolution, its germination ecology can provide important insights into the early evolution of physical dormancy. Imbibition tests performed on seeds of two Hypseocharis populations from Bolivia indicate that their seeds indeed have physical dormancy like all other Geraniaceae. These results indicate that physical dormancy in Geraniaceae evolved during the Eocene before the uplift of the Andes mountains and before the events that led to the cross-Atlantic disjunct distribution of Geraniacae.

Endozoochorous dispersal of seeds by livestock has long attracted the attention of grassland scientists. However, little is known about seed dispersal after ingestion by Kazakh sheep on dry grasslands in the Tianshan Mountains. The objective of this experiment was to learn more about the recovery and germinability of seeds from 17 plant species after either actual or simulated ingestion (i.e. insertion through a rumen fistula) by Kazakh sheep. The passage time of seeds through the sheep gut ranged from 12 to 96 h. More than 80% of all recovered seeds were defecated 24–48 h after ingestion. The mean retention time of seeds in the gut ranged from 27.3 to 42.2 h. Seed recovery percentage ranged between 12.6 and 17.6% for leguminous species and between 0.8 and 3.2% for gramineous species. Seed recovery percentage was positively correlated with seed mass, but negatively correlated with seed shape. The germination percentages of the gramineous species were greater in the non-ingested treatment (66–98%) than in the simulated ingestion treatment (3–10%). In contrast, for leguminous species, seed germination percentages were greater in the simulated ingestion treatment (23–70%) than in the non-ingested one (5–12%). Seed germination percentage after simulated ingestion was positively correlated with seed mass, but negatively correlated with seed shape. In conclusion, leguminous seeds were more likely than gramineous ones to pass through the gut of Kazakh sheep and then germinate. Free-ranging Kazakh sheep can contribute to the spread of plant species, especially leguminous species, in the Tianshan Mountains.

The broad aim of this work was to study intraspecific variation of seed germination in Phillyrea angustifolia L. (Oleaceae), a species with a hard (water-permeable) endocarp. Germination of seeds from six different wild populations was correlated with traits related either to seed morphology or to environmental parameters. Germination of naked seeds (seeds without endocarp) at the optimum germination conditions was similar among populations and individuals, but great differences could be detected regarding the germination of seeds with endocarp both at inter- and intra-populational levels. Differences among populations could be related to climatic parameters and to morphometric variables of seeds with endocarp. A higher germination was associated with populations growing in habitats with more severe summer (higher temperature, lower precipitation and a longer drought period) and producing elongated seeds (lower Feret ratio and roundness). Moreover, seeds from eight different individuals within a population were tested independently, and great differences regarding the germination of seeds with endocarp could be detected among individuals. Our results suggest that the morphological variation found in P. angustifolia endocarp is both under strong maternal genetic control as well as influenced by environmental factors, as indicated by the high variability among individuals within one population and the significant correlation between climate variables and seed germination among populations. Finally, it is emphasized that standardization of plant propagation protocols should take into account the degree of intraspecific variation of Mediterranean species.