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Dodonaea viscosa (Sapindaceae) is widespread in the mountainous highlands of the southwestern part of Kingdom of Saudi Arabia, where it is a medicinally important species for the people in Saudi Arabia. Seeds of this species were collected from Mount Atharb in Al-Baha region, at an altitude of 2100 m. The aims of this study were to determine if the seeds of D. viscosa have physical dormancy (i.e. a water-impermeable seed coat) and, if so, what treatments would break dormancy, and what conditions promote germination after dormancy has been broken. The dormancy-breaking treatments included: soaking of seeds in concentrated sulfuric acid (H 2 SO 4) for 10 min, immersion in boiling water for 10 min and exposure to 50 °C for 1 min. After seeds had been pre-treated with H 2 SO 4 , to break dormancy, they were incubated at constant temperatures from 5 to 35 °C, under 12-h photoperiods or in continuous darkness, and germination recorded. Salinity tolerance was investigated by incubating acid-scarified seeds in different concentrations of mM NaCl in the light at 25 °C. Untreated seeds had low final germination 30%. Seeds that had been acid-scarified, immersed in boiling water or exposed to 50 °C all achieved 91% subsequently when incubated at 25 °C. Thus, seeds of this species in Saudi Arabia have physical dormancy, which can be broken by all three treatments designed to increase the permeability of the testa. After pre-treatment, there was a broad optimum constant temperature for germination that ranged between 5 and 25 °C but germination was inhibited by higher temperatures (30 and 35 °C). Light had little effect on this germination response. Scarified seeds were also sensitive to salinity, with the highest germination in distilled water and complete inhibition in 400 mM NaCl. Seeds that failed to germinate in saline treatments were mostly able to germinate on transfer to distilled water, suggesting osmotic inhibition. [ABSTRACT FROM AUTHOR]

Plant-derived smoke promotes germination in Mediterranean-like environments, but its effect is unclear in the Mediterranean Cistaceae. This article investigates the role of smoke in the comparative germination ecology of five Helianthemum taxa. Laboratory germination experiments were conducted using seeds collected in the field and stored in a seed bank. All seeds were mechanically scarified prior to testing. Various pre-treatments with smoke solutions and gibberellins were applied, and seeds were incubated in three germination temperature regimes (30/20 °C, 22/12 °C, 14/4 °C). In H. cantabricum , H . nummularium , H. oelandicum and H. urrielense germination was very high at the three temperatures, and no effect of smoke was detected. In H. tinetense germination was generally poor and a significant effect of smoke was found, but the effect size was small. The thermal niche of Helianthemum appears to follow an opportunistic strategy, being limited only by physical dormancy at the time of dispersal. H. tinetense follows a more conservative strategy, with physiological dormancy retarding germination. In the Mediterranean basin and surrounding areas, smoke appears to be one of a multitude of environmental signals controlling germination. The smoke effect might be more relevant in certain species such as H. tinetense . [ABSTRACT FROM AUTHOR]

Physical dormancy is the water impermeability of the seed coat caused by one or more palisade cell layer(s) called macrosclereids. The specialised structure for water entry sites is the water gap, which serves as a detector of environmental cues for germination. In Fabaceae, the water gap is the lens, although another seed structure for water entry could exist. In this study, we identified the initial site of water entry, observed the hydration of a cushion-like structure near the radicle, described the anatomy of the water gap, and analysed the association of anatomical seed traits with the initial site of water entry and the imbibition velocity of six species of Lupinus from the state of Jalisco, Mexico. Dye tracking with a toluidine blue solution was used to identify the initial site of water entry. The anatomical description was performed using conventional microtechnique and a light microscope. The entry of the toluidine solution into seeds of L. montanus was observed after 6 h, followed by L. exaltatus and L. mexicanus after 18 h and L. elegans , L. reflexus and L. rotundiflorus after 48 h. The site of water entry was the lens in L. elegans , L. exaltatus , L. reflexus and L. rotundiflorus and the micropyle in L. mexicanus and L. montanus . The cushion-like structure was responsible for water accumulation in embryo imbibition. Significant differences among anatomical seed traits such as thickness in the hilar region, the counter-palisade layer, cushion-like structure, epidermis, hypodermis, and innermost parenchyma layer were found among the species. [ABSTRACT FROM AUTHOR]

Reproductive output and seed traits can be altered by water availability during seed formation and maturation, which could affect the population recovery after fire of seeders (i.e., species regenerating from seeds). This is important for species in fire-prone, dry areas that are projected to encounter reduced total precipitation and longer annual drought with climate change. Here we determine the sensitivity of several reproductive processes to drought in Cistus ladanifer , a plant widely distributed in the shrublands of the western part of the Mediterranean Basin. Three levels of annual drought were simulated in a shrubland by means of a rainout shelter and an irrigation system in 6 × 6 m plots. Fruits and seeds from drought-exposed mother plants were collected, and reproductive output, seed size and anatomy studied. Seeds non-exposed/exposed to fire cues (heat plus smoke) were germinated at five levels of water stress (Ψ s = 0.0 to −0.50 MPa). Hydrotime modeling was applied to germination under water stress. Plant growth was sensitive to drought, but reproductive output, seed size, dormancy and viability were not. Drought significantly affected seed anatomy, increasing the palisade layer at the micropyle. Drought in the maternal plants, in interaction with seed exposure to fire cues, significantly reduced final germination. Water stress during germination decreased final germination, independent of maternal plant drought, and interacted with fire cues to decrease germination when exposed. Hydrotime modeling confirmed that fire cues made seeds highly sensitive to water stress (Ψ b (50) = −0.25 MPa). Post-germination viability was reduced in seeds from drought-treated maternal plants that were exposed to fire cues and germinated under water stress. Reproductive output showed low plasticity in response to drought. However, the effects of drought in the mother plant affected seed anatomy and germination in interaction with fire cues. The conclusion is that exposing C . ladanifer maternal plants to drought arguably increases seed sensitivity to water limitations during germination after fire. [ABSTRACT FROM AUTHOR]

Soil seed banks play a major role in the post-fire regeneration of semi-arid mountain grasslands. Plant species present before fire can determine the soil seed bank (SSB) characteristics in fire-prone ecosystems. However, it remains unclear how the density and species composition of the SSB under the canopy cover of specific shrub species may be affected by fire. Therefore, we designed a study to test the effects of prescribed burning on the viable SSBs under the canopies of two shrub species: Berberis integerrima (with open canopies) and Onobrychis cornuta (with dense canopies). We selected 20 study sites that included separate patches of the two shrub species and nearby herbaceous patches as control. Soil sampling was carried out pre- and post-burning of shrub canopies and the control patch. Soil samples were collected at two depths: 0–5 cm and 5–10 cm, and transported to the greenhouse for germination experiments. The results showed that canopy fire of shrubs decreased SSB density and species richness. However, the effects of shrub burning on SSB were species-specific and these reductions were more pronounced for canopy burning of O. cornuta than for B. integerrima. Total SSB densities decreased by 61% for B. integerrima and 71% for O. cornuta after canopy fire at soil depth of 0–5 cm. At soil depth of 5–10 cm, total SSB density decreased by 45% under O. cornuta after canopy fire, while canopy fire of B. integerrima did not affect SSB density. Herbaceous patch burning had no statistically significant effects on SSB density at soil depths of 0–5 cm and 5–10 cm. The comparison of quantitative and qualitative similarity indices between pre- and post-fire species composition of shrub canopy showed that the statistically significant effect of B. integerrima burning on SSB composition was less pronounced compared with O. cornuta. This study indicated that seeds stored within the soil under certain shrub species are at a high risk of mortality during fire. Thus, successful post-fire recovery does not rely on the seed bank reservoir under these shrubs. [Display omitted] [ABSTRACT FROM AUTHOR]

Nolana (Solanaceae) is a genus composed of 88 species that inhabit arid and semi-arid environments throughout the Atacama Desert of Chile and Peru, and one from Galapagos Islands. Its greatest diversity is found in coastal localities, termed lomas formations, which are small isolated patches of vegetation sustained by the presence of low cloud layers. Alto Patache corresponds to one of these ecosystems, and Nolana jaffuelii I.M. Johnst., a summer annual herb, is the most abundant species in its persistent seed bank. Little is known about the seed germination requirements of this and other species present in Chilean lomas formations, despite the importance of that knowledge for taking appropriate conservation actions. The main objective of this study was to identify the germination requirements and possible dormancy mechanisms of N. jaffuelii ’s dispersal units, which are mericarps. Mature mericarps of N. jaffuelii were collected at Alto Patache. Histological analyses of cross and longitudinal sections of the mericarps suggested the presence of physical dormancy imposed by an impermeable pericarp. Different germination treatments were also evaluated: (T1) control, i.e., intact mericarps imbibed in water; (T2) intact mericarps washed under running water; (T3) scarified mericarps (cut at the funicular scar) imbibed in water; (T4) scarified mericarps imbibed in gibberellic acid (500 mg l −1 GA 3 ); (T5) scarified mericarps imbibed in water with 2 weeks of stratification at 4 °C; and (T6) intact mericarps imbibed in GA 3 . Only mericarps cut at the funicular scar were able to germinate, and the highest germination percentage was observed when the mericarps were imbibed in GA 3 (T4). The results of this investigation reveal the existence of physical and physiological dormancy in N. jaffuelii propagules, an adaptation that would allow this species to spend long periods waiting for favorable conditions for seedling establishment, which is characteristic of the coastal lomas formations of the Atacama Desert. [ABSTRACT FROM AUTHOR]

Abstract: Although Astragalus is the largest genus of seed plants, it contains only a relatively few annual species, about which little is known with regard to seed dormancy and germination. Thus, seed dormancy-break and germination were investigated in the cold-desert annual Astragalus arpilobus Kar. et Kir. Most of the seeds had a water-impermeable seed coat that became permeable after mechanical or acid scarification, i.e. physical dormancy. Both wet heat and alternate wet heat and cold (ice water) made only a small portion of the seeds permeable, and neither exposure to high nor to low temperatures was effective in breaking dormancy. Scarified seeds germinated at temperatures ranging from 5/2 to 30/15°C, with 20/10°C and 25/15°C being optimal. Non-dormant seeds germinated to high percentages in light and in darkness across the range of temperatures. Germination percentages did not increase with duration of dry storage at room temperature. Scarified seeds germinated to nearly 100% at water potentials between 0 and −0.30MPa but to 0% at −0.77MPa. Seedling emergence was higher for seeds buried at soil depths of 1 and 2cm than at 0 or >2cm. Forty-three percent of the scarified seeds sown in July in an experimental garden under natural conditions germinated in autumn, and an additional 5% germinated in spring. In contrast, no non-scarified seeds germinated in autumn, and only 5.3% of them germinated in spring. Most of the non-scarified seeds that did not germinate became part of the persistent seed bank. Our results indicate that the high intensity of hard-seed dormancy in the annual A. arpilobus is similar to that reported for the perennial species of Astragalus. [Copyright &y& Elsevier]

Abstract: Medicago marina (L.) is a Mediterranean species whose seeds show strong dormancy that prevents germination. We used an integrated approach of physiological analyses and proteomics to investigate the mechanisms that control M. marina dormancy/germination and that underlie stress tolerance. First, we evaluated the effects on dormancy breaking of the following treatments: mechanical scarification, freezing at −20°C, storage for 4 months and heating at 100°C for 1h. Mechanical scarification and freezing were the most effective treatments in overcoming dormancy. The role of abscisic acid (ABA) in M. marina dormancy was studied by ELISA immuno-enzymatic assay. The ABA content of germinated and non-germinated mature (control) and treated seeds was determined. The level of ABA was higher in treated seeds than in control seeds; the most significant increase occurred in the heated seeds. A comparison of the ABA level in the germinated, control and treated seeds suggests that different mechanisms modulate ABA content in response to different stresses, and that a specific ABA-signalling pathway regulates germination. Proteomic analysis revealed 46 proteins differentially expressed between treated and untreated seeds; 14 of these proteins were subsequently identified by mass spectrometry. Several of the proteins identified are important factors in the stress response, and are involved in such diverse functions as lipid metabolism, protein folding and chromatin protection. Lastly, an analysis of the phosphoproteome maps showed that the function of many proteins in seeds subjected to temperature treatment is modulated through post-translational modifications. [Copyright &y& Elsevier]

• Heat shocks reduce seed water content and seed germination of Sesbania virgata and Guazuma ulmifolia. • Direct exposure to fire kills nearly all seeds placed upon the soil surface. • Inside the corky fruits, seeds often remain hard or decrease viability. • Seeds may survive the experimental burns when buried 2 cm belowground. • Fire has little to no effect on the enhancement of germination in a tropical wetland. Contrasting responses of seed germination to fire have been reported in different vegetation worldwide. In Brazil, the Pantanal harbors one of the world's most extensive floodplains, marked by flooding periods alternating with a dry fire-prone season. The present study aimed to understand the role of fire on regeneration from seed in the Pantanal wetland, using two pioneer species displaying physically dormant seeds as study models: Sesbania virgata (Cav.) Pers. and Guazuma ulmifolia Lam. Seeds were subjected to (1) heat shocks and (2) experimental burns, besides the controls. In Experiment 1, heat shocks of 65, 85, 105, 125, and 145°C (all treatments ± 5°C), were applied for 5 minutes of exposure. In Experiment 2, seeds and corky fruits were placed upon the soil surface, and seeds were buried at 2 cm belowground, then subjected to experimental burns. Germination trials were conducted under optimal conditions and recorded the proportions of germinated, hard, and dead seeds. Increasing temperature of heat shocks had an increasingly negative effect on seed water content and germination of both species as well as increasing the proportion of dead seeds. A slight enhancement in germination of buried seeds (18%) was found in the experimental burns for S. virgata seeds. Moreover, buried seeds remained hard (dormant) up to 80 and 40% for S. virgata and G. ulmifolia , respectively. Inside the corky fruits, seed germination was not promoted, and there was a decrease in the proportion of hard seeds after burning, while direct exposure to fire killed nearly all seeds placed upon the soil surface. Fire has little to no effect on the enhancement of seed germination, but seeds mainly survive when buried belowground. Our study provides crucial information to understand seed tolerance to increased fire occurrence in disturbed tropical wetlands. [ABSTRACT FROM AUTHOR]

• Heat tolerance drives regeneration from seed in Cerrado legume shrubs. • No effect on physical dormancy break mediated by post-fire temperature fluctuation. • Seed structures take part on water uptake in nondormant seeds within the seed lots. Multiple environmental cues may break seed physical dormancy (PY) in fire-prone ecosystems, but disentangling the roles of such cues remains challenging. Current research has mostly focused on the role of high temperatures (heat shocks) in PY alleviation, while post-fire environmental conditions are less understood. Here, we examined the role of post-fire temperature fluctuation on seed germination and viability of Cerrado legume shrubs. Specifically, we investigated (1) whether PY is broken by temperature fluctuation; (2) whether seed viability is affected by temperature fluctuations; and (3) micromorphological changes in the seed coat following exposure to temperature fluctuation. Seeds of nine legume species were collected in frequently burned Cerrado savannas. We simulated post-fire temperature fluctuation in germination chambers, with daily temperature fluctuation ranging from 18 to 55 °C for 90 days; controls consisted of untreated seeds (room temperature). We conducted germination trials with unblocked and blocked hilar region of seeds. In addition, seed samples were fixed and subjected to micromorphological analysis. Instead of dormancy break, three species showed decreased seed germination for both unblocked and blocked hilar regions, while other two species showed decreased germination in blocked seeds only. Nevertheless, random cracks formed across the seed coat were found in control and treated seeds, which displayed a proportion of nondormant seeds. Within nondormant seeds, both hilar and extra-hilar regions (such as the pleurogram) may take part on water uptake. Despite the lack of dormancy break, most Cerrado legume seeds persisted viable after post-fire temperature fluctuation, thus avoiding establishment under hazardous conditions. Seed tolerance to heat shocks and post-fire temperature fluctuation likely drives regeneration from seed in burned Cerrado areas. [ABSTRACT FROM AUTHOR]

• Seeds of Melilotus albus exhibited physical dormancy. • Scarification or alternated wet heat / ice water cycles broke dormancy effectively. • Wet heat or dry heat alone were ineffective for dormancy break. • More than 60% of the seedlings emerged in spring. • Persistence of the seed bank might spread risks over years. Information on seed germination and the soil seed bank of a species is important because it contributes to a better understanding of plant reproductive strategies. Melilotus albus (Fabaceae) is considered valuable for honey production and is frequently cultivated as livestock forage. However, it is difficult to germinate M. albus seeds. The primary goal of the present study was to determine the environmental requirements for breaking seed dormancy and the dynamics of soil seed bank. The results indicate that seeds of M. albus have a water impermeable seed coat which can be penetrated by scarification or alternating wet heat and ice water cycles; however, wet heat or dry heat alone were ineffective. After receiving 30 cycles of alternating wet heat and ice water treatments, cracks formed in the lens of seeds. Under natural precipitation and temperature, > 60% of the seedlings emerged in spring. A persistent soil seed bank formed and most seeds were found in the 0–2 cm soil layer. Our findings indicate that seeds of M. albus have physical dormancy; persistence of the seed bank might spread risks associated with a specific seed cohort over multiple years. [ABSTRACT FROM AUTHOR]