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The plant species Sesbania tomentosa ('ōhai; Fabaceae) is endemic to the Hawaiian Islands, federally listed as endangered in the USA and has been proposed for categorization as Vulnerable on the IUCN Red List. In 2021, c. 12,000 seeds from 12 seed lots collected during 1990–1992 from across the Hawaiian Islands were discovered in ambient herbarium conditions (55% relative humidity (RH) at 20 °C). International gene bank standards suggest drying seeds in equilibrium with 15% RH and stored at −18 °C. To investigate seed viability, we mechanically scarified then sowed 15 seeds from each accession at daily alternating regimes of 12 h light and 12 h dark at temperatures of 25/15 °C, respectively. Germination was observed after 7 days and ended after 34 days. Mean final germination was 88.9 ± SD 0.1% (range 73–100%). Each seed lot was accessioned into the National Tropical Botanical Garden's Seed Bank and Laboratory. In seeds with a water-impermeable seed coat (i.e. physical dormancy), such as S. tomentosa , seeds can desorb but not absorb water. Therefore, if the seeds were initially dried, although exposed to high RH for up to 32 years, seed equilibrium RH may have remained low, which may in part explain the observed high germinability. This study holds significance for managers who are working to conserve this endangered Hawaiian species and suggests that even suboptimal conditions may still yield highly viable seeds several decades into the future. [ABSTRACT FROM AUTHOR]

Argyreia is the most recently evolved genus in the Convolvulaceae, and available information suggests that most species in this family produce seeds with physical dormancy (PY). Our aim was to understand the evolution of seed dormancy in this family via an investigation of dormancy, storage behaviour, morphology and anatomy of seeds of five Argyreia species from Sri Lanka. Imbibition, germination and dye tracking of fresh intact and manually scarified seeds were studied. Scanning electron micrographs and hand sections of the hilar area and the seed coat away from the hilar area were compared. Scarified and intact seeds of A. kleiniana , A. hirsuta and A. zeylanica imbibed water and germinated to a high percentage, but only scarified seeds of A. nervosa and A. osyrensis did so. Thus, seeds of the three former species are non-dormant (ND), while those of the latter two have physical dormancy (PY); this result was confirmed by dye-tracking experiments. Since >90% of A. kleiniana, A. hirsuta and A. zeylanica seeds survived desiccation to 10% moisture content (MC) and >90% of A. nervosa and A. osyrensis seeds with a dispersal MC of ~12% were viable, seeds of the five species were desiccation-tolerant. A. nervosa and A. osyrensis have a wide geographical distribution and PY, while A. kleiniana , A. hirsuta and A. zeylanica have a restricted distribution and ND. Although seeds of A. kleiniana are ND, their seed coat anatomy is similar to that of A. osyrensis with PY. These observations suggest that the ND of A. kleiniana , A. hirsuta and A. zeylanica seeds is the result of an evolutionary reversal from PY and that ND may be an adaptation of these species to the environmental conditions of their wet aseasonal habitats. [ABSTRACT FROM AUTHOR]

Many Astragalus species exhibit seeds with physical dormancy (PY), but little is known about the ecological context of this dormancy. We focused on A. maritimus and A. verrucosus, two threatened Sardinian endemic species inside the subgenus Trimeniaeus Bunge. Fresh seeds collected from the only two respective known populations were used to investigate the effect of mechanical scarification, heat shock, and water imbibition processes on PY release and germination. PY can be overcome through mechanical scarification of the water-impermeable seed coats, while no dormancy break was detected, nor a subsequent increase in seed germination due to fire-induced heat. This suggests that fire does not trigger dormancy release and seed germination in these species. The seeds tolerate relatively high heat shock temperatures (up to 120 and 100 °C for A. verrucosus and A. maritimus, respectively), but after 120 °C for 10 min, the number of dead seeds increases in both species. These facts suggest the capacity to develop a soil seed bank that can persist after fires and delay germination until the occurrence of optimal conditions. As regards water imbibition, both Astragalus species did not show the typical triphasic pattern, as germination started without further water uptake. This study emphasizes the significance of understanding germination processes and dormancy in threatened species. In fire-prone ecosystems, PY dormancy plays a crucial role in soil seed bank persistence, and it may be selectively influenced by post-fire conditions. Understanding such adaptations provides useful insights into conservation strategies. [ABSTRACT FROM AUTHOR]

Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The current method to break oil palm seed dormancy is the dry heat method which requires approximately 90 days for seeds to germinate with an average germination percentage. Therefore, hastening the process with a higher ratio of germinated seeds becomes necessary. This experiment aims to hasten and increase germination percentage by applying fine bubble water during the dormancy-breaking process. A seed lot derived from one bunch as replication is divided into two sets where fiber plugs from one of the sets are removed while the other set remains intact. Each set was re-divided into six experimental units soaked with tap water or fine bubble water for 1 to 3 days. The result showed that applying fine bubble water provided a better germination rate than tap water treatments. However, the total germination percentage between all treatments does not differ significantly. The germination peak of oil palm seed in the fine bubble water treatments occurred on the 26th day, 8 days faster than in the tap water treatments. The occurrence showed the potential use of fine bubble water application during dormancy breaking using the dry heat method.

The persistence of subtropical seasonally dry forests urgently requires the implementation of ex situ conservation and restoration programs. We studied variation in seed traits and dormancy of six native species growing in seasonally dry Chaco forests of Argentina. We documented high intra- and interspecific variability in seed traits and dormancy. Fresh seeds of Geoffroea decorticans and Parasenegalia visco (Fabaceae) were water-permeable and nondormant (ND), while those of Parkinsonia praecox and Vachellia aroma (Fabaceae) were water-impermeable and had physical dormancy (PY). Seeds of Schnopsis lorentzii (Anacardiaceae) and Sarcomphalus mistol (Rhamnaceae) were water-permeable and had physiological dormancy (PD). Mechanical and chemical scarification were the most effective methods to break PY, and dry storage for 3 months was effective in breaking PD. Seeds of large-seeded species were ND or had PD, and those of small-seeded species had PY. Species inhabiting moist habitats had ND seeds, whereas those from seasonally dry habitats had seeds with PY or PD. These results suggest that seed traits and dormancy are species-specific and that intraspecific variation in seed traits is likely associated with high phenotypic plasticity of species in response to local environmental heterogeneity. These findings should be considered at the time of implementation of conservation techniques and for seed sourcing decisions for restoration. [ABSTRACT FROM AUTHOR]

This article deals with the breaking down of seed dormancy in black locust (Robinia pseudoacacia L.) seeds. These seeds have a hard testa that is impermeable to water and air. In this investigation, seeds of black locust were treated with non-thermal plasma (NTP) for 0, 5, 10, and 20 min. The testa of the treated seeds had an eroded surface (SEM analysis) and showed an increased oxygen content (EDS) and increased hydrophilicity (contact-angle measurement). The exposed seeds also had a higher water absorption (seed water uptake) than the untreated ones. In seeds treated for 20 min, a significant difference (p < 0.05) was recorded in seed germination (eight times greater than the control set) and in other parameters of initial seedling development, such as the fresh weight of both seedling root and shoot and all three indexes of seedling vitality. The detected changes in the seed surface and changes in germination proved that NTP can partly break dormancy in black-locust seeds. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of Botanical Research is the property of Bulletin of Botanical Research Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Most tree species native to arid and semiarid ecosystems produce seeds with physical dormancy, which have impermeable coats that protect them from desiccation and prevent germination when the environmental conditions are unfavorable for seedling establishment. This dormancy mechanism may confer some degree of tolerance to seeds facing warmer and drier conditions, as those expected in several regions of the world because of climate change. Scarification of these seeds (removal of protective coats) is required for stimulating germination and seedling development. However, as scarification exposes seeds to the external environmental conditions, it can promote desiccation and viability loss in the future. To test these hypotheses, we performed field experiments and sowed scarified and unscarified seeds of a pioneer tree native to semiarid ecosystems of Mesoamerica (Vachellia pennatula) under the current climate and simulated climate change conditions. The experiments were conducted at abandoned fields using open-top chambers to increase temperature and rainout shelters to reduce rainfall. We measured microenvironmental conditions within the experimental plots and monitored seedling emergence and survival during a year. Air temperature and rainfall in climate change simulations approached the values expected for the period 2041–2080. Seedling emergence rates under these climatic conditions were lower than under the current climate. Nevertheless, emergence rates in climate change simulations were even lower for scarified than for unscarified seeds, while the converse occurred under the current climate. On the other hand, although survival rates in climate change simulations were lower than under the current climate, no effects of the scarification treatment were found. In this way, our study suggests that climate change will impair the recruitment of pioneer trees in semiarid environments, even if they produce seeds with physical dormancy, but also indicates that these negative effects will be stronger if seeds are scarified. [ABSTRACT FROM AUTHOR]

Alstroemeria pelegrina (A. pelegrina), a Chilean endemic, is considered vulnerable as its natural habitat is currently threatened. The decline in the reproductive capacity of the species due to anthropogenic impacts and climate change has made it imperative to address the problem by developing large-scale propagation methods. The objective of this study was to establish protocols for breaking the dormancy and in vitro germination of A. pelegrina seeds to speed up the germination and seedling production processes. The research began with morphological observations of the reproductive process, followed by in vitro sowing. The results showed that the seeds reached full maturity in 51 days, and physiological maturity in 41 days, at which point the seeds could be harvested for in vitro germination. The mechanical scarification pretreatment improves the in vitro germination rate to 96% and the germination time to 7 days, showing that the species is characterized by physical seed dormancy. On the other hand, if the seed coat incisions are deeper than 0.5 mm, 30% of the potential plants are lost due to embryo damage. The study provides scientific evidence for the feasibility of large-scale in vitro propagation of the species and establishes an efficient method of seedling production. [ABSTRACT FROM AUTHOR]

This review provides a revised and expanded word-formula system of whole-seed primary dormancy classification that integrates the scheme of Nikolaeva with that of Baskin and Baskin. Notable changes include the following. (1) The number of named tiers (layers) in the classification hierarchy is increased from three to seven. (2) Formulae are provided for the known kinds of dormancy. (3) Seven subclasses of class morphological dormancy are designated: 'dust seeds' of mycoheterotrophs, holoparasites and autotrophs; diaspores of palms; and seeds with cryptogeal germination are new to the system. (4) Level non-deep physiological dormancy (PD) has been divided into two sublevels, each containing three types, and Type 6 is new to the system. (5) Subclass epicotyl PD with two levels, each with three types, has been added to class PD. (6) Level deep (regular) PD is divided into two types. (7) The simple and complex levels of class morphophysiological dormancy (MPD) have been expanded to 12 subclasses, 24 levels and 16 types. (8) Level non-deep simple epicotyl MPD with four types is added to the system. (9) Level deep simple regular epicotyl MPD is divided into four types. (10) Level deep simple double MPD is divided into two types. (11) Seeds with a water-impermeable seed coat in which the embryo-haustorium grows after germination (Canna) has been added to the class combinational dormancy. The hierarchical division of primary seed dormancy into many distinct categories highlights its great diversity and complexity at the whole-seed level, which can be expressed most accurately by dormancy formulae. [ABSTRACT FROM AUTHOR]

This study investigated seed germination of Cardiospermum halicacabum, a medicinally important invasive species.We compared mass, moisture content (MC), dormancy and dormancy‐breaking treatments and imbibition and germination of scarified and non‐scarified seeds of C. halicacabum from a low‐elevation dry zone (DZ), low‐elevation wet zone (WZ1) and mid‐elevation wet zone (WZ2) in Sri Lanka to test the hypothesis that the percentage of seeds with water‐impermeable seed coats (physical dormancy, PY) decreases with increased precipitation.Seed mass was higher in WZ2 than in DZ and WZ1, while seed MC did not vary among the zones. All scarified DZ, WZ1 and WZ2 and non‐scarified DZ and WZ1 seeds imbibed water, but only a few non‐scarified WZ2 seeds did so. When DZ and WZ1 seeds were desiccated, MC and percentage imbibition decreased, showing that these seeds have the ability to develop PY. GA3 promoted germination of embryos excised from fresh DZ and WZ1 seeds and of scarified WZ2 seeds.At maturity, seeds from DZ and WZ1 had only physiological dormancy (PD), while those from WZ2 had combinational dormancy (PY+PD). Thus, our hypothesis was not supported. Since a high percentage of excised embryos developed into normal seedlings; this is a low‐cost method to produce C. halicacabum plants for medicinal and ornamental purposes. [ABSTRACT FROM AUTHOR]

Caragana shrublands are the main type of vegetation in some cold desert ecosystems in Xinjiang in northwest China, and information on seed dormancy and germination of Caragana species is needed to help restore disturbed areas. Freshly matured seeds of Caragana aurantiaca, C. dasyphylla C. polourensis, C. roborovskyi, C. soongorica, C. spinosa and C. tekesiensis, collected from three natural ecosystems were tested for germination in light at 15/5, 20/10, 25/15 and 30/15 °C after dry storage at room temperature for 1 week and 9 months. Depending on the species, 1–84% of the seeds had physical dormancy (i.e., water-impermeable seeds). At 15/5, 20/10, 25/15 and 30/15 °C, fresh seeds of C. aurantiaca, C. spinosa and C. dasyphylla germinated from 74% to 100%, those of C. soongorica 15% to 52% and those of C. roborovskyi and C. polourensis 13–73%. After 9 months of storage, germination percentages increased significantly over wide range of temperatures for seeds of C. soongorica, C. tekesinsis C. roborovskyi and C. polourensis but decreased significantly for C. spinosa and C. dasyphylla. Most fresh seeds of the floodplain species and desert species are water-permeable and can germinate over a wide range of temperatures; consequently, they could be planted in the field at any time during the growing season. Dry storage of seeds of C. roborovski and C. tekesiensis increased the percentage of water-permeable seeds. Seeds of these species germinate best at high temperatures and should be planted in summer. If C. polourensis is used for restoration, the seeds need to be scarified before planting. [ABSTRACT FROM AUTHOR]

???Ceanothus velutinus Douglas ex Hook. (snowbrush ceanothus [Rhamnaceae]) and Cercocarpus montanus Raf. (alderleaf mountain mahogany [Rosaceae]) are native species with urban landscape value and potential to create unique aesthetics as well as to conserve water. Propagation protocols for these native species are not well established. Because of dormancy, seed propagation requires scarification and (or) stratification. We designed a study to further define protocols necessary to consistently produce high rates of germination for these 2 species. Ceanothus velutinus seeds were scarified in hot water at 50, 70, or 90 °C (122, 158, or 194 °F) and soaked with gibberellic acid (GA3) at 0, 50, 250, or 500 mg/l (0, 50, 250, or 500 ppm) for 24 h before stratification for 1, 2, or 3 mo. Seeds of C. velutinus stratified for 2 mo after being scarified at 90 °C and treated with 500 mg/l (500 ppm) GA3 had the greatest germination percentage (74.2 ± 2.0%). Percent germination was the lowest when seeds were scarified at 50 °C (122 °F) and treated without GA3 but with 2 mo stratification. Cercocarpus montanus seeds were treated with GA3 at 0, 50, 250, or 500 mg/l (0, 50, 250, or 500 ppm) and stratified for 1, 2, or 3 mo. Seed germination of C. montanus increased as stratification time increased. Seeds dipped in 50 mg/l (50 ppm) GA3 and stratified for 2 mo had the greatest germination percentage (64.2 ± 3.6%). [ABSTRACT FROM AUTHOR]

Astragalus is the largest genus of seed plants with 3000 or more species that occurs naturally on several continents. The genus has some use as a forage and medicine and in industry, and many of the species are rare endemics threatened with extinction. The seeds are reported to be dormant at maturity, and various treatments have been used in an attempt to germinate them. Our primary aim was to determine via a meta-analysis the most effective way(s) to break dormancy in seeds of this species-rich genus. Mechanical and chemical (conc. sulphuric acid) scarification were by far the best of 12 treatments for breaking seed dormancy of the 40 species included in our meta-analysis, whereas prechilling, gibberellin and smoke were ineffective. These results along with those of imbibition tests confirm that seeds of the examined Astragalus species have physical dormancy (PY). Further, PY in these 40 species and (its documented occurrence) in 118 species that could not be included in our meta-analysis transcends climatic and geographic boundaries, edaphic conditions, life cycle/life form types and infrageneric phylogeny. Thus, it seems likely that most species of Astragalus have PY. However, in addition to PY, physiological dormancy (PD), that is, combinational dormancy (PY + PD), has been reported in a few species of Astragalus. This study should be useful to both basic and applied scientists who want to germinate seeds of Astragalus. [ABSTRACT FROM AUTHOR]

The genus Lupinus has potential use in ecological restoration, agroforestry systems, and commercial forest plantations, due to its ability to fix nitrogen to the soil. The physical dormancy of its seeds allows their storage for long periods. Its longevity is partially known. The objective of this study was to analyze the weight, moisture content, germinative capacity, germinative energy, and viability of seeds of L. bilineatus Benth., after they had been stored for 15 years in a glass jar at room temperature (fresh, approximately 10-15 °C), and without light. A randomized complete block design was used for the experiment and the ANOVA was performed with a mixed procedure. The treatments were: control, mechanical scarification (sanding with sandpaper), and chemical (5, 10, 30, and 40-min immersion in sulfuric acid), with a day/night regime of 25/20 °C, and a 12-h photoperiod (fluorescent light). The results were compared with those obtained 15 years before. The following results were obtained: 66 766.2 seeds per kg, with a 6.60% humidity (fresh basis), 45% viability (tetrazolium salts test), and a 3.2 d germinative energy. There were significant differences among the treatments (p ≤0.0001). Scarification with sandpaper favored a greater germination (48.9%). The annual decline rate of the germinative capacity was 2.24%. Scarification can eliminate the physical dormancy of the seeds. Scanning microscopy showed that the seed coat has cuticle, macrosclereids, osteoesclereids, and parenchyma. The seed of L. bilineatus without coat contains 52.15, 9.21, and 2.83% raw protein, raw fat, and raw fiber, respectively. [ABSTRACT FROM AUTHOR]

Background and aims: The occurrence of seeds with physical dormancy is an obstacle for the use and management of many plant species. Here, we studied the presence of physical dormancy in mericarps (seed-dispersal units) and seeds, the morphoanatomical structures responsible for physical dormancy, and the effects of possible methods for breaking dormancy in seeds of Malvastrum coromandelianum (Malvaceae). M&M: Imbibition essays were used to confirm the presence of physical dormancy in mericarps and seeds, and the morpho-anatomical seed structure was described by using a scanning electron microscopy. The effects of mechanical, chemical and thermal scarifications on seed germination and seed structure were also evaluated. Results: Mericarps and scarified seeds increased > 160% of their initial weight, whereas intact seeds increased < 40% of their initial weight. The presence of a palisade cell layer in seed coat and a water-gaps complex in the chalazal region were observed. Higher germination percentages and lower t50 were registered after mechanical scarification, followed by chemical and thermal scarifications (dry heat). Chemical and thermal scarifications caused the chalazal cap elimination and the contiguous cracks to form around the chalazal region; whereas the formation of a chalazal blister and its elimination were only observed after chemical scarification. Conclusions: Seeds of M. coromandelianum have physical dormancy. Water enters the seeds through a water-gap complex (Type III compound) located in the chalazal region. Mechanical, chemical and thermal scarifications are effective methods for breaking physical dormancy and increase germination. [ABSTRACT FROM AUTHOR]

Weeds associated with rice fields cause severe yield reduction and many other problems. Effective weed management strategy depends on knowledge of weed seed biology. This study aimed to determine basic seed biology information of seven rice field weeds in Sri Lanka. Seeds were collected from at least five individuals from each species. Dormancy classes of seeds were determined using germination and imbibition experiments. Effect of light, dry storage, temperature and salinity on dormancy and germination was studied. Experiments were conducted with three replicates of 25 seeds. Among the tested species, seeds of Eclipta prostrata and Ludwigia peruviana were non-dormant where the non-treated fresh seeds germinated > 60 %. Seeds of Aeschynomene indica and Melochia corchorifolia are physically dormant as only scarified seeds imbibed and germinated. Fimbristylis miliacea, Cyperus pilosus and L. decurrens seeds germinated only on GA3. Thus, they have physiological dormancy. E. prostrata and L. peruviana seeds required light for germination. Five month- dry storage reduced the viability of E. prostrata seeds. In contrast, dry storage increased the sensitivity to the dormancy breaking treatment of A. indica, M. corchorifolia, C. pilosus and L. decurrens seeds and decreased the sensitivity of F. miliacea seeds. Germination of E. prostrata and L. peruviana seeds decreased with decreasing osmotic potential. Although, dormancy and dormancy breaking requirements vary among study species, keeping the rice field dry during the intercropping period could induce the seed germination of most of the above species and could be used as a mechanism to reduce the soil seed bank. [ABSTRACT FROM AUTHOR]

The genus Larrea includes five species of desert shrubs distributed along the American Continent. These species produce dormant mature seeds, but the type of dormancy and the factors that produce it have been poorly assessed. The objective of this work was to determine the optimum germination temperatures of L. cuneifolia and L. nitida, to analyze the response to pre-germination treatments, and to evaluate the type of seed dormancy these species have. Seeds were incubated at five constant temperatures and were subjected to mechanical scarification and rinsed with running water to break dormancy. Seed coat permeability and the presence of water-soluble germination inhibitors were also assessed. The optimum germination temperature range was between 15-40°C for both species. A positive response to all pre-germination treatments was observed in L. cuneifolia (37-47%), while L. nitida showed higher germination percentage only with mechanical scarification (73%). Both species presented water-permeable seed coats, ruling out the occurrence of a physical dormancy. The inhibitory test of seed-coat extracts was positive for L. cuneifolia, suggesting the possible presence of a chemical dormancy. These results are valuable for conservation purposes and directly contribute to improving production of seedlings required for restoration projects. [ABSTRACT FROM AUTHOR]

Bixa orellana L. (annatto) is economically and ecologically important specie. However, the seeds of this species have some mechanisms of dormancy that prevent their germination even on favorable conditions. The aim of this work was to evaluate methodologies to promote the dormancy overcoming of annatto seeds, including the use of gibberellic acid. It was used seeds of two annatto accesses, which were submitted to the germination test and germination speed index after submission to mechanical scarification, incision, sulfuric acid for 3, 5, 10, 15 and 20 minutes and hot water for 30, 60, 90 and 120 seconds. In addition, whole or incised seeds were soaked in gibberellic acid at concentrations of 0, 400, 800 and 1200 mg L-1. The experimental design was completely randomized, with 11 treatments for each access in the evaluation of dormancy overcoming methods and 4 treatments for each access in GA3 application, with and without spike. In annatto seeds, it is not evident the dormancy seed overcoming by the use of incision, mechanical scarification, sulfuric acid, hot water and gibberellic acid; however, mechanical scarification, sulfuric acid and gibberellic acid can increase the speed of germination. The results of each method to overcoming seed dormancy depend of many factors, including the origin of access. [ABSTRACT FROM AUTHOR]

Development of embryo envelopes in Leucospermum cordifolium (Salisb. ex Knight) Fourcade is presented in a detailed anatomical study, and their structure interpreted ecologically. To support interpretation results for at least six other species of Leucospermum are reviewed, confirming that L. cordifolium is representative of this shrubby group occurring in fynbos, a fire-prone Mediterranean-type vegetation subject to summer drought. The fate of the water-permeable seed coverings subsequent to dispersal is followed in seeds stored experimentally underground. The testa at maturity effectively excludes oxygen in intact soil-stored seeds, thus creating a less common type of physical dormancy which we term 'anoxia PY' (oxygen-impermeable physical dormancy). We postulate 'fire-mediated desiccation-scarification' testa breakage on a large scale in freshly dispersed (by ants) soil-stored young-seeds, dynamically regulated by drying of different testa layers through fire heat shock (but also by post-fire ambient climate heat), thus alleviating anoxia PY in, and causing undelayed germination of, a major part of the young-seed bank within the ensuing winter germination season. Concurrently a patchy disturbance pattern within a lesser portion of the young-seed cohort causes uneven underground desiccation-scarification by fire, resulting in variable degrees of oxygenation and thus temporally extended (erratic) germination of young-seeds. Both of these strategies are primary long term fitness traits in Leucospermum. By contrast the persistent older-seed cohort, stored underground during the inter-fire period, may become weathered by soil and climate factors ('soil-mediated abrasion'), which alleviates anoxia PY in old seeds. Thermodormancy of these embryos (physiological dormancy, PD) is enforced in unburnt vegetation by two narrow habitat-dependent daily temperature requirements (~10°C × 20°C), and these have specific ecological functions. The complex Leucospermum system includes balanced adaptive responses to multiple selective pressures. We propose a coherent mechanistic profile for this fynbos genus, synthesising data partly from the literature of other fire-prone ecosystems. Anatomical changes in the testa of Leucospermum during its growth and subsequent degradation in the soil after burial by ants are linked with environmental cues for dormancy and germination control in fynbos. Roles for oxygen impermeability of the testa and embryo thermodormancy are explained. Results from the substantial Leucospermum literature are reviewed and a seed biological profile developed. Parallels are drawn with other fire-prone Mediterranean-type vegetations. [ABSTRACT FROM AUTHOR]

Background A water-impermeable testa acts as a barrier to a seed's imbibition, thereby imposing dormancy. The physical and functional properties of the macrosclereids are thought to be critical determinants of dormancy; however, the mechanisms underlying the maintenance of and release from dormancy in pea are not well understood. Methods Seeds of six pea accessions of contrasting dormancy type were tested for their ability to imbibe and the permeability of their testa was evaluated. Release from dormancy was monitored following temperature oscillation, lipid removal and drying. Histochemical and microscopic approaches were used to characterize the structure of the testa. Key results The strophiole was identified as representing the major site for the entry of water into non-dormant seeds, while water entry into dormant seeds was distributed rather than localized. The major barrier for water uptake in dormant seeds was the upper section of the macrosclereids, referred to as the 'light line'. Dormancy could be released by thermocycling, dehydration or chloroform treatment. Assays based on either periodic acid or ruthenium red were used to visualize penetration through the testa. Lipids were detected within a subcuticular waxy layer in both dormant and non-dormant seeds. The waxy layer and the light line both formed at the same time as the establishment of secondary cell walls at the tip of the macrosclereids. Conclusions The light line was identified as the major barrier to water penetration in dormant seeds. Its outer border abuts a waxy subcuticular layer, which is consistent with the suggestion that the light line represents the interface between two distinct environments – the waxy subcuticular layer and the cellulose-rich secondary cell wall. The mechanistic basis of dormancy break includes changes in the testa's lipid layer, along with the mechanical disruption induced by oscillation in temperature and by a decreased moisture content of the embryo. [ABSTRACT FROM AUTHOR]

Background and Aims Different structures have been shown to act as a water gap in seeds with physical dormancy (PY), and in Fabaceae they are commonly located in the hilar region. However, the function of the pleurogram, a structure in the extra-hilar region that is common in legume seeds, remains unknown. Our aims were to review the literature for occurrence of the pleurogram in Fabaceae, determine if the pleurogram can open, and compare the functional morpho-anatomy of water gaps in seeds of 11 Senna species. Methods Imbibition tests showed that all 11 species had PY. Structural features of the hilar and extra-hilar regions of the seeds were investigated using light and scanning electron microscopy, and dye-tracking was performed to trace the pathways of water through the seed coat. Key Results A pleurogram has been reported for 37 legume genera. Water gaps differed among Senna species, with lens, hilum, micropyle and pleurogram taking up water after PY was broken. In Senna alata seeds, only the pleurogram acted as a water gap, whereas in S. reniformis and S. silvestris water entered the seed through both the pleurogram and the hilar region. In the pleurogram of S. alata and S. reniformis, the palisade layer moved outward, exposing the hourglass cells, whereas in S. silvestris the palisade layer was broken. Conclusions The pleurogram acts as a water gap in some of the 11 Senna species examined, but it is non-functional in others. Opening the pleurogram occurs due to the formation of a linear slit in the palisade layer. The pleurogram is of functional significance by creating a wide opening, whereby water can reach the embryo and start germination. This is the first report of the pleurogram functioning as a water gap. Because this structure is shared by at least 37 genera, it also may be a water gap in many other legume species. [ABSTRACT FROM AUTHOR]

Desmanthus virgatus (L.) Willd. has significant fodder potential, but its seeds have high and persistent levels of physical dormancy which interfere with its field establishment. The purpose of this study was to analyse the variability of physical dormancy in three populations of seeds from humid and arid regions of Argentina, grown and collected in different years and locations. The hardseededness and the percentage of seeds with intact lenses after a softening treatment and the seed coat thicknesses were compared. The variability observed in the obtained percentages of hardseededness, intact lenses and seed coat thicknesses was related to the origin and the environment in which these seeds had developed. Although further work is needed, arid environments seem to favour the development of thicker seminal layers, being an important factor that determines the impermeable nature of the seeds in this species. This information is required for future genetic improvement programs and for understanding the evolutionary process of the populations of this species in different environments. [ABSTRACT FROM AUTHOR]

Physical dormancy (PY) occurs in at least 18 angiosperm plant families and is caused by water-impermeable palisade cells in seed (or fruit) coats. Breaking of PY involves disruption or dislodgement of water-gap structures causing the seeds/fruits to become water permeable (non-dormant). The water-gap region is a morphologically distinct area of the seed or fruit coat that forms a water-gap complex. The location, anatomy, morphology and origin of water-gaps can differ between and even within families and genera. Water-gap structures sense environmental conditions that allow seeds with PY to become permeable just prior to the commencement of conditions favourable for germination and plant establishment. There are three basic water-gap morpho-anatomies characterized by the way the water-gap opens: Type-I, Type-II and Type-III. In Type-I water-gaps, specific kinds of cells pull apart to form a surface opening, while in Type-II a portion of the surface structure is pulled away from adjacent cells, opening the water-gap. Type-III is the least common type and has a circular, plug-like structure that is dislodged, whereby water entry occurs. In addition, water-gap complexes are either simple or compound, depending on whether only a single primary water-gap structure is involved in dormancy release or an additional secondary water-gap structure opens, permitting water entry. [ABSTRACT FROM AUTHOR]

Aims Seed dormancy and the soil seed bank are crucial to plant regeneration strategy, especially in semiarid ecosystems with unpredictable precipitation. The aim of this study was to investigate how seed dormancy is controlled by environmental factors and how it is correlated with the soil seed bank and regeneration of the perennial legume Oxytropis racemosa, a dominant perennial herb in Mu Us Sandland of semiarid China. Methods Germination and imbibition experiments on fresh intact and scarified seeds of O. racemosa were used to identify physical dormancy (PY) in seeds of this species. Soil seed bank dynamics, timing of seedling emergence and the fate of buried seeds in the natural habitat were investigated. Important Findings PY was broken by mechanical scarification or wet heat/ice water cycles but not solely by dry heat or wet heat treatment. The soil seed bank exhibited seasonal changes in the number of seeds, which was highest in September and lowest in July. Seeds buried at different sand depths gradually lost dormancy; 20-42% of the seeds remained dormant after 20 months of burial. Dormancy break occurs gradually throughout the year. Our results indicate that O. racemosa exhibits hardcoatedness heterogeneity that spreads germination of a seed cohort between seasons and years in the semiarid environment, where the amount of precipitation during the growing season is highly variable. [ABSTRACT FROM AUTHOR]

Differences in fruit morphology among or within species might indicate differences in other regenerative traits, such as seed dormancy and germination. In species with physical dormancy (PY), environmental conditions are suggested to be responsible for dormancy break in field. Seeds of Vachellia caven have PY. This species exhibits two fruit morphs highly represented in Córdoba forests, Argentina: one is dehiscent and the other is indehiscent. In this study we performed a burial experiment with the aim to determine if the differences in V. caven fruit morphology were related to different patterns of PY break of their seeds in field conditions. We related these patterns to (1) environmental conditions that could influence the loss of PY, and (2) histological features of the lens zone. Seeds of both morphs exhibited dormancy break within 14 months of the start of the experiment, but with different patterns. The dehiscent morph showed an abrupt percentage of seeds that broke dormancy 14 months after the beginning of the experiment, probably after undergoing environmental changes similar to those suggested by the two-stage softening model. The indehiscent morph showed a gradual increase in seeds that broke dormancy, not clearly related to any of the environmental variables studied. No differences in seed coat structure of the lens zone were observed between morphs. The existence of both morphs could confer the species with higher possibilities of establishing and coping with environmental heterogeneity. Those characteristics contribute to the understanding of the success of this species in open and disturbed environments. [ABSTRACT FROM AUTHOR]

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Seed dormancy is expected to provide ecological advantages by adjusting germination to the favorable growth period. However, many species produce nondormant seeds, particularly in wet tropical forests, a biogeographic pattern that is not well accounted for in current models., We hypothesized that the global distribution of dormant seeds derives from their adaptive value in predictably fluctuating (i.e. seasonal) environments. However, the advantage conferred by dormancy might ultimately depend on other seed attributes, particularly size. This general model was tested within a phylogenetically informed framework using a data set comprising > 216 000 world-wide observations of Fabaceae, spanning three orders of magnitude in seed size and including both dormant and nondormant seeds., Our results confirmed our hypothesis: nondormant seeds can only evolve in climates with long growing seasons and/or in lineages that produce larger seeds. Conversely, dormancy should be evolutionarily stable in temperate lineages with small seeds. When the favorable season is fleeting, seed dormancy is the only adaptive strategy., Based on these results, we predict that, within a given lineage, taxa producing larger, nondormant seeds will necessarily predominate in aseasonal environments, while plants bearing small, dormant seeds will be dominant under short growing seasons. [ABSTRACT FROM AUTHOR]

Seed of Townsville stylo (Stylosanthes humilis H.B.K.) is known to exhibit a hard seed coat and when freshly harvested also show a physiological dormancy, however, the nature of the co-actions between seed coat and embryo growth that determine dormancy is poorly understood. In this study, physical dormancy of Townsville stylo seeds was not reduced during natural ageing at room temperature, in contrast to the physiological dormancy, which is gradually overcome during after-ripening. Furthermore, the permeability of seed coat was affected by scarification treatments as well as by low-pH solutions. Together, these data indicate that physical dormancy overcome of seed is prerequisite for radicle protrusion and physiological dormancy of Townsville stylo seeds contribute to its timing. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Species differ in their temperature germination niche. Populations of a species may similarly differ across the distribution range of the species. Anticipating the impacts of climate variability and change requires understanding the differential sensitivity to germination temperature among and within species. Here we studied the germination responses of four hard-seeded Cistaceae seeders to a range of current and future temperatures. M ETHODS: Seeds were collected at sites across the Iberian Peninsula and exposed or not exposed to a heat shock to break dormancy, then set to germinate under four temperature regimes. Temperatures were varied daily and seasonally, simulating the temperature range across the gradient, plus an increased temperature simulating future climate. Time to germination onset and cumulative germination at the end of each season were analyzed for the effects of temperature treatments, seasons, and local climate (temperature of the germination period, T gp ) at each site. KEY RESULTS: T gp was a significant covariate of germination in all species but Cistus populifolius. Temperature treatments significantly affected Cistus ladanifer, C. salviifolius, and Halimium ocymoides. Germination occurred in simulated autumn conditions, with little germination occurring at later seasons, except in unheated seeds of H. ocymoides. Exposure to a heat shock changed the sensitivity to temperature treatments and the relationships with T gp. CONCLUSIONS: Germination responses to temperature differ not only among species but also within species across their latitudinal range. The responses were idiosyncratic and related to the local climate of the population. This germination variability complicates generalizing the impacts of climate variability and climate change. [ABSTRACT FROM AUTHOR]

Physical dormancy (PY) plays a crucial role in the control of the reseeding process of Vicia villosa Roth, a winter annual species cultivated for pasture and hay, naturalized in several semi-arid temperate agroecosystems. As PY is considered a seed trait modulated by natural selection, populations from different origins are expected to show different responses to environmental regulatory factors. The present study aimed to determine the effect of: (1) water availability on PY-break dynamics of a naturalized population from Argentina (ASC) under both laboratory and field conditions; (2) the seed source on initial PY and dormancy release rate (wet storage at 20°C) of ASC compared to 45 other populations of V. villosa, including wild, naturalized, landraces and cultivars. Water availability increased PY loss rate under both storage and field conditions. ASC PY-break dynamics was adequately described by a Gompertz model with a lower thermal-time requirement estimated for dormancy break under fluctuating soil water conditions compared to seeds buried inside impermeable bags. During the field burial experiment, a considerable proportion of seeds (~70%) became water permeable during the summer season after dispersal, and retained low levels of residual PY for soil seed bank replenishment. Improved populations (i.e. breeding cultivars) showed the lowest percentages of initial PY compared to landraces, naturalized and wild populations. Naturalized populations of Argentina showed similar initial PY compared to landraces, although PY release rate was lower in the former and might be attributed to local environmental selection. Wild types showed the lowest PY release rates. [ABSTRACT FROM AUTHOR]

Seeds of most Great Basin lupine (Lupinus spp. [Fabaceae]) species are physically dormant and thus, difficult to establish in uniform stands in seed production fields. We designed this study to examine 5 seed scarification techniques, each with 11 levels of application (including a non-scarified control), to reduce the physical seed dormancy of longspur lupine (L. arbustus Douglas ex Lindl.), silvery lupine (L. argenteus Pursh), hairy bigleaf lupine (L. prunophilus M.E. Jones), and silky lupine (L. sericeus Pursh). These 4 perennial Great Basin lupine species are of interest for both rehabilitation and restoration of degraded rangelands. We evaluated 10 treatments of each of 5 scarification methods, one mechanical, 2 thermal, and 2 chemical (sulfuric acid and sodium hypochlorite) techniques on the above-mentioned species. The sulfuric acid and the mechanical scarification treatments significantly improved germination for both silvery and silky lupine. Additionally, one thermal scarification method (60 s at 95 °C [203 °F]) was effective for silvery lupine. Both sulfuric acid and sodium hypochlorite scarification methods had treatment levels that significantly improved germination of hairy bigleaf lupine. For longspur lupine, all treatments within the 5 scarification methods either decreased or were not a significant improvement of germination as compared with the control, except for the treatment of soaking the seeds for 35 s at 95 °C (203 °F). We found scarification to be an effective tool for reducing physical dormancy in silvery lupine, hairy bigleaf lupine, and silky lupine, thus allowing for a more efficient use of limited seeds. [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]

Determining the phylogenetic and biogeographic distribution of physical dormancy remains a major challenge in germination ecology. Here, our goal was to describe a novel water-impermeable seed coat mechanism causing physical dormancy (PY) in the seeds of Chaetostoma armatum (Melastomataceae). Although seed coat permeability tests indicated a significant increase in seed weight after soaking in distilled water, anatomical and dye-tracking analyses showed that both water and dyes penetrated the seed coat but not the embryo, which remained in a dry state. The water and dye penetrated the lumen of the exotestal cells, which have a thin outer periclinal face and thickened secondary walls with U-shaped phenolic compounds. Because of this structure, water and dye do not penetrate the inner periclinal face of the exotestal cells, indicating PY. Puncturing the seeds increased germination more than tenfold compared to that of the control, but GA3 did not increase germination further. A significant fraction of the seeds did not germinate after puncturing, indicating that embryos are also physiologically dormant (PD). This paper constitutes the first report of the water-impermeable seed coat in the Myrtales and the first report of physiophysical (PD+PY) dormancy in a shrub from a tropical montane area. [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]

Seed dormancy is a phenomenon that affects the distribution of plant species in time. However, it may slow germination and consequently hinder seedling production in nurseries. Many seeds of forest species of the Fabaceae family, such as Libidibia ferrea (Brazilian ironwood), have physical dormancy caused by impermeability of the seed coat to water. Therefore, the aim of this study was to evaluate the physiological, physical, and morpho-anatomical characteristics of L. ferrea seeds before and after application of different treatments for overcoming dormancy. We evaluated the imbibition curves, germination percentage, germination speed index (GSI), the force required to puncture the micropylar region, and morphoanatomical changes through images obtained from a scanning electron microscope (SEM) before and after application of treatments for overcoming dormancy. L. ferrea seeds immersed in sulfuric acid show a triphasic pattern of imbibition. The required force to puncture the micropylar region of L. ferrea seeds is less for both the treatment with boiling water and for treatments with sulfuric acid. In addition, the required force to puncture the micropylar region decreases during imbibition of the seeds after application of sulfuric acid. The time of application of sulfuric acid influences the thickness of the material removed from the macrosclereid layer of the seed coat. [ABSTRACT FROM AUTHOR]

The physical dormancy of seeds has been poorly studied in species from tropical forests, such as the Atlantic Forest. This study aimed to examine the effect of moderate alternating temperatures on breaking the physical dormancy of seeds, the morphoanatomy and histochemistry of seed coats, and to locate the structure/ region responsible for water entrance into the seed, after breaking the physical dormancy of seeds of two woody Fabaceae (subfamily Faboideae) species that occur in the Brazilian Atlantic Forest: Sophora tomentosa and Erythrina speciosa. To assess temperature effect, seeds were incubated in several temperature values that occur in the Atlantic Forest. For morphological and histochemical studies, sections of fixed seeds were subjected to different reagents, and were observed using light or epifluorescence microscopy, to analyze the anatomy and histochemistry of the seed coat. Treated and non-treated seeds were also analyzed using a scanning electron microscope (SEM) to observe the morphology of the seed coat. To localize the specific site of water entrance, the seeds were blocked with glue in different regions and also immersed in ink. In the present work a maximum temperature fluctuation of 15℃ was applied during a period of 20 days and these conditions did not increase the germination of S. tomentosa or E. speciosa. These results may indicate that these seeds require larger fluctuation of temperature than the applied or/and longer period of exposition to the temperature fluctuation. Blocking experiments water inlet combined with SEM analysis of the structures of seed coat for both species showed that besides the lens, the hilum and micropyle are involved in water absorption in seeds scarified with hot water. In seeds of E. speciosa the immersion of scarified seeds into an aniline aqueous solution showed that the solution first entered the seed through the hilum. Both species showed seed morphological and anatomical features for seed coats of the subfamily Faboideae. Lignin and callose were found around all palisade layers and the water impermeability and ecological role of these substances are discussed in the work. [ABSTRACT FROM AUTHOR]

Germination from the soil seed bank (SSB) is an important determinant of species composition in tropical forest gaps, with seed persistence in the SSB allowing trees to recruit even decades after dispersal. The capacity to form a persistent SSB is often associated with physical dormancy, where seed coats are impermeable at the time of dispersal. Germination literature often speculates, without empirical evidence, that dormancy-break in physically dormant seeds is the result of microbial action and/or abrasion by soil particles. We tested the microbial/soil abrasion hypothesis in four widely distributed neotropical pioneer tree species (Apeiba membranacea, Luehea seemannii, Ochroma pyramidale, and Cochlospermum vitifolium). Seeds were buried in five common gardens in a lowland tropical forest in Panama, and recovered at 1, 3, 6, and 12 months after burial. Seed permeability, microbial infection, seed coat thickness, and germination were measured. Parallel experiments compared the germination fraction of fresh and aged seeds without soil contact, and in seeds as a function of seed permeability. Contrary to the microbial/soil abrasion hypothesis the proportion of permeable seeds, and of seeds infected by cultivable microbes, decreased as a function of burial duration. Furthermore, seeds stored in dark and dry conditions for 2 years showed a higher proportion of seed germination than fresh seeds in identical germination conditions. We determined that permeable seeds of A. membranacea and O. pyramidale had cracks in the chalazal area or lacked the chalazal plug, whereas all surfaces of impermeable seeds were intact. Our results are inconsistent with the microbial/soil abrasion hypothesis of dormancy loss and instead suggest the existence of multiple dormancy phenotypes, where a fraction of each seed cohort is dispersed in a permeable state and germinates immediately, while the impermeable seed fraction accounts for the persistent SSB. Thus, we conclude that fluctuations in the soil temperature in the absence of soil abrasion and microbial infection are sufficient to break physical dormancy on seeds of tropical pioneer trees. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM PUBLISHER]

Background and aims Seed dormancy enhances fitness by preventing seeds from germinating when the probability of seedling survival and recruitment is low. The onset of physical dormancy is sensitive to humidity during ripening; however, the implications of this mechanism for seed bank dynamics have not been quantified. This study proposes a model that describes how humidity-regulated dormancy onset may control the accumulation of a dormant seed bank, and seed experiments are conducted to calibrate the model for an Australian Fabaceae, Acacia saligna. The model is used to investigate the impact of climate on seed dormancy and to forecast the ecological implications of human-induced climate change. Methods The relationship between relative humidity and dormancy onset was quantified under laboratory conditions by exposing freshly matured non-dormant seeds to constant humidity levels for fixed durations. The model was field-calibrated by measuring the response of seeds exposed to naturally fluctuating humidity. The model was applied to 3-hourly records of humidity spanning the period 1972–2007 in order to estimate both temporal variability in dormancy and spatial variability attributable to climatic differences among populations. Climate change models were used to project future changes in dormancy onset. Key Results A sigmoidal relationship exists between dormancy and humidity under both laboratory and field conditions. Seeds ripened under field conditions became dormant following very short exposure to low humidity (<20 %). Prolonged exposure at higher humidity did not increase dormancy significantly. It is predicted that populations growing in a temperate climate produce 33–55 % fewer dormant seeds than those in a Mediterranean climate; however, dormancy in temperate populations is predicted to increase as a result of climate change. Conclusions Humidity-regulated dormancy onset may explain observed variation in physical dormancy. The model offers a systematic approach to modelling this variation in population studies. Forecast changes in climate have the potential to alter the seed bank dynamics of species with physical dormancy regulated by this mechanism, with implications for their capacity to delay germination and exploit windows for recruitment. [ABSTRACT FROM AUTHOR]

Seeds of legumes are generally considered to have physical dormancy and to be orthodox, but most seed biologists are unaware of the various kinds and combinations of dormancy and storage behaviour in seeds of this family. The aim of our study was to document the dormancy and storage behaviour of seeds of 100 native and introduced tropical Fabaceae species in Sri Lanka and classify them into germination/storage behaviour categories. Moisture content (MC) was < 16% for fresh seeds of 94 species and >29% for those of six. Seeds of these six species had low tolerance for desiccation and for low temperatures. Thus, seeds of six species are non-orthodox and 94 species orthodox. Nine of the 100 species were non-dormant, and 2, 3 and 86 had physiological, physiological epicotyl and physical dormancy, respectively. Six germination/storage behaviour categories were identified among the 100 species. However, as in extratropical regions of the world, orthodox storage behaviour and physical dormancy are characteristic of seeds of the majority of species of Fabaceae in tropical Sri Lanka. [ABSTRACT FROM PUBLISHER]