Psychotria hoffmansegiana (Willd ex Roem. & Schult.) Mull. Arg. and Palicourea marcagravii st. Hil. (Rubiaceae): potential for forming soil seed banks in a brazilian Cerrado.

The germinability of artificially buried Psychotria hoffmansegiana and Palicourea marcagravii seeds in Cerrado soil was tested, with the aim of evaluating whether dispersed seeds may be able to form a soil seed bank. The assays were carried out at a Cerrado Reserve in S?o Paulo State, Brazil. Seed samples were placed in nylon bags and buried at two different depths and in two different sites. Samples were periodically exhumed and germination tests were performed with both exhumed and dry stored seeds. In general, soil storage favoured seed survival and germination when compared to dry stored seeds. The seed germination was little affected by soil depth and by burial environment. Seeds of both species remained viable for at least 13 months, considering the time lapse between the collection and the end of the germination tests. It was suggested that both species can potentially form a persistent soil seed bank in Cerrado.     

Seed germination and seedling growth of two Pseudobombax species (Malvaceae) with contrasting habitats from Brazilian Cerrado

Pseudobombax tomentosum and P. longiflorum are common trees in the Cerrado region, but the former species is more common in forest edges while the later is present in open cerrado areas. This work aimed to investigate differences in seed germination and seedling growth in these species, from seed collected from Cerrado areas in Central Brazil. For this, a seed germination experiment was designed and included four replicates with 25 seeds per species; seeds were randomly distributed in the germination chamber. To evaluate initial seedling growth, seedlings height was measured up to 67 days after seedling emergence; besides, some of these seedlings were grown for biomass evaluation during nine months. Results showed that seeds of the two species had the same germinability (near 100%) and mean germination time (ca. 12 days). However, P. longiflorum showed a more spread seed germination through time, with higher values of coefficient of variation in germination time and uncertainty index; and lower values of synchronization than P. tomentosum. The two species showed basically the same growth pattern, but lower values for height of apical meristem, diameter of underground structures (mostly roots), dry mass of shoots, underground structure and total mass of seedlings in P. tomentosum were obtained, compared to P. longiflorum. Both species allocated more dry mass to underground structures in detriment of shoot. This probably allows resprouting behavior which prevents hydric stress and detrimental fire action typical of the open Cerrado areas.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

Germination performance of congeneric Styrax species from the Cerrado sensu lato areas and their distribution pattern in different physiognomies

When studying congeneric species, it is of reasonable importance to understand different ecophysiological performances which might determine the distribution of species in habitats with different natural resources. Styrax ferrugineus is exclusive and well adapted to the Brazilian Cerrado sensu stricto (s. str.); S. camporum is widely distributed in the Cerrado sensu lato (s. l.) areas, with young trees being observed at the edge of cerradão and other vegetation fragments; and S. pohlii occurs in permanently waterlogged soils of the Cerrado region, such as those of riparian forests. We tested the hypothesis that the higher the soil water content in the physiognomic gradient of the vegetation, the higher is the germination success of S. pohlii, but the lower is the germination success of S. ferrugineus. We also discuss whether gap conditions inside a cerradão fragment imply a high germination rates of seeds of S. camporum. Seeds from each of the three species were buried within nylon bags containing soil from the respective sites. Burial occurred in a Cerrado s. str., in understory and gap conditions of a cerradão, and in the understory of a riparian forest fragment, and lasted for 60, 120, 180 and 240 days, respectively, after the fruit dispersal time of each of the three species. After 60 days, a relationship was found showing that the percentage of germinated seeds diminished, and the percentage of damaged seeds increased as soil water content increased (Cerrado s. str. < cerradão gap < cerradão understory ? riparian forest). S. camporum still showed viable seeds 60 days after burial (DAB), and germinated seeds 120 DAB, indicating that it needed a longer time to germinate, which might be associated to its thicker seed coat, in relation to the other two species. The germination performance of each of the three species was the same in the gap and understory conditions of the cerradão. The higher concentration of adult S. camporum plants at the edge of vegetation fragments is not related to a particular high germination performance and seedling establishment.     

Burning and Grazing Management in a California Grassland: Effect on Bunchgrass Seed Viability

Prescribed fire is an important management tool for reducing the dominance of non‐native species in annual grasslands; both annual and perennial native species show strong vegetative responses in the subsequent growing season. However, although the post‐fire contribution of native species to the seed bank is assumed to be larger than in pretreatment years, the effects on seed quality, particularly viability and longevity, are not well understood. In this study, I germinated Nassella pulchra (purple needlegrass) seed that had been stored for 10 years after collection from target plants receiving treatment combinations of summer burning and grazing by sheep. Seeds from burned plants were larger and had higher germinability than seed from unburned plants. Seeds from plants that were both burned and grazed had the highest germination. The strong relationship between long‐term viability and seed size suggests greater maternal provisioning and increased seed quality subsequent to burning and grazing. I conclude that managing for seed quality may be a useful approach for conservation of native species in California's critically endangered grassland habitats.     

After-Ripening in Festuca idahoensis Seeds: Adaptive Dormancy and Implications for Restoration

Festuca idahoensis (Idaho fescue) was a common native perennial bunchgrass in the sagebrush steppe of the western United States until the introductions of domestic livestock and alien plants. Restoration of Idaho fescue to degraded sites will likely involve reseeding, and one of the factors affecting reseeding success is germinability of the seeds employed. We investigated effects of after-ripening and storage temperature on germinability of Idaho fescue seeds collected from a central Oregon site. Six months of after-ripening were required before maximum germination was obtained. Storage of dry seeds at either room temperature (20°C) or at cooler, alternating temperatures (5/15°C) did not alter the rate at which dormancy was lost. Storage at the warmer temperature promoted rapid germination in seeds that had broken dormancy. Seed longevity varied greatly from year to year. Seeds produced in a very dry year had poorer germination and shorter longevity than seeds produced during a year with near normal precipitation. Because seed dispersal occurs in late July and early August for Idaho fescue in central Oregon, a six-month after-ripening requirement ensures that the greatest potential germination coincides with the spring period most likely to provide sufficient moisture for seedling establishment.     

Fire as a stimulant of shrub recruitment in northwestern Patagonian (Argentina) grasslands

One strategy of plant survival during post-fire succession is to persist and regenerate by recruiting new individuals from a fire-resistant seed bank. The heat, smoke, and charcoal released during plant combustion may act (individually or in combination) as a cue for post-fire seed germination. Fabiana imbricata is a shrub that forms persistent seed banks in the northwestern Patagonian grasslands and shows a high recruitment from seeds during post-fire succession. Mathematical models showed that this species is advancing over the grasslands in response to fires. To corroborate these findings, we studied the role of fire on F. imbricata seed germination. In order to achieve this, a factorial experiment was designed in laboratory conditions to study the effect of heat, charcoal, smoke, scarification, and their interactions on F. imbricata seed germination. Seeds treated with the higher temperatures required a longer period of time to germinate, thus, significantly affecting the mean germination time. Total germination percentages in F. imbricata were significantly enhanced by smoke and scarification, but the interaction of heat, smoke, and scarification was more important than the effect of each fire factor alone. The positive response to fire cues exhibited by F. imbricata indicates that this species would have an adaptive advantage to colonize these grasslands if fire frequency increased, as predicted for this environment. Hence, fire will contribute to the grassland encroachment by this species and, therefore, to the loss of biodiversity and productivity of northwestern Patagonian grasslands.     

Diaspore structure and germination ecophysiology of the babassu palm (Attalea vitrivir)

Both germination and seedling establishment in palm trees are strongly influenced by the morphoanatomy of the fruits, although the interactions of these processes with ecophysiological aspects are not yet well understood. The present work evaluated structural and physiological aspects of seed germination in Attalea vitrivir, a species living under the seasonal climate of the Cerrado (Brazilian savanna) biome. We studied morphology, anatomy and histochemistry of the fruits and seedlings, the effects on germination of the pericarp, of diaspore storage conditions, germination temperature, removal of the operculum, and of gibberellic acid (GA3) application, and characterized the imbibition process of the seeds. Germination depends on a series of complex interactions between structures and physiological processes. The pericarp protects the seed and also causes physical dormancy that, when interacting with the temperature regime, can delay germination until subsequent rainy periods. Some seeds demonstrated non-profound physiological dormancy associated with restricted germination imposed by the operculum. Germination and initial development result from the elongation of the cotyledon cells and are affected by the activities of two distinct meristems in the proximal region of the embryo. The haustorium develops an invaginated secretory epithelium and aerenchyma, and actively participates in seed reserve mobilization. The adaptation of A. vitrivir to the Cerrado environment, with a strongly seasonal climate, is favored by its diaspore structure, by the abundance of endosperm reserves that allow the seedlings to survive for a long period above soil level, and by a seedling development pattern that protects the vegetative axis by deep burial.     

Germinative behaviour of ten tree species in white-water floodplain forests in central Amazonia

Amazonian floodplain forests (known as várzea) are classified into high or low várzea depending on the spatial position on the plains. This topographic feature exposes the terrain over different time periods of inundation, causing a major limiting factor for tree seedling establishment. We hypothesize that, strategically, most of the seeds produced by trees in low várzea forests germinate faster and in synchrony (temporally concentrated germination), and that their seedlings tend to have cotyledons without reserve or foliaceous cotyledons (PEF). By contrast, seeds produced by high-várzea specialist trees exhibit slower and temporally scattered germination, and their seedlings tend to have reserve storage cotyledons (CHR). Generalist species may show no clear pattern or may be related to high-várzea species. To test this hypothesis, diaspores of 10 tree species were collected: five of low-várzea specialist trees, three of high-várzea specialist trees and two of generalist species. Seedling emergence and morphology were monitored daily in a nursery for a period of 150 days of being subjected to non-flooded (sown directly in várzea soil) and flooded conditions (15 days in water before sowing in the same soil). The seedling emergence of low-várzea species showed an increase of 37% in germinability whereas high-várzea and generalist species exhibited a decrease of 38% and 35% of germinability, respectively. Foliaceous cotyledons were preferentially found in seedlings of low-várzea species, and storage cotyledons were more common in those of high-várzea species, indicating how cotyledon morphology may determine the amount and use of resources available to a seedling during the first stages of establishment and growth. Conservation plans aiming for the maintenance of ecosystem services must consider these strategies.     

Underdeveloped embryos and germination in Aristolochia galeata seeds

Aristolochiaceae have been described as having seeds with underdeveloped embryos and morphological or morphophysiological dormancy. Aristolochia galeata is a native climber found in the Cerrado biome, associated with road and gallery forest edges. The aims of this study were to investigate: embryo growth rate, morphology and seed germination parameters under different treatments. Embryos were excised to obtain embryo length at four stages: initial, seeds after coat rupture, radicle tip protrusion and cotyledon emergence from the seed coat. Germination tests were conducted at 30 °C under three nitrate concentrations (1, 10 and 20 mM), fluctuating temperature (27/20 °C) and light and dark conditions. We found that seeds have underdeveloped embryos, which take about 301 ± 178 h (±SD) to achieve seed coat rupture, another 205 ± 126 h to reach radicle protrusion and 176 ± 76 h more to the final stage of cotyledon emergence. Germinability was above 52% in all treatments, except in the dark (15%). For all treatments, average germination time was above 290 ± 123 h. Potassium nitrate increased germinability to >87%. No particular treatment was required for embryo development, but seeds in the population that continued to germinate after 1 month were probably in various states of non-deep, simple morphophysiological dormancy. Increased germinability in nitrate treatments and light requirement for germination could prevent germination under unsuitable environmental conditions and be a strategy to increase seedling establishment in the cerrado.     

Maternal warming affects early life stages of an invasive thistle

Maternal environment can influence plant offspring performance. Understanding maternal environmental effects will help to bridge a key gap in the knowledge of plant life cycles, and provide important insights for species’ responses under climate change. Here we show that maternal warming significantly affected the early life stages of an invasive thistle, Carduus nutans. Seeds produced by plants grown in warmed conditions had higher germination percentages and shorter mean germination times than those produced by plants under ambient conditions; this difference was most evident at suboptimal germination temperatures. Subsequent seedling emergence was also faster with maternal warming, with no cost to seedling emergence percentage and seedling growth. Our results suggest that maternal warming may accelerate the life cycle of this species via enhanced early life‐history stages. These maternal effects on offspring performance, together with the positive responses of the maternal generation, may exacerbate invasions of this species under climate change.     

A molecular framework for the embryo growth in germinating seeds of Solanum lycocarpum A. St.‐Hil., a nurse plant species

We are clarifying how the functional embryo growth occurs in germinating seeds of Solanum lycocarpum A. St.‐Hil., a nurse plant with a central role in forest dynamics in the Cerrado (a biodiversity hotspot). For that, we used classical seed germination measurements (germinability, mean germination time, mean germination rate, coefficient of variation of the germination time, synchronisation index and germination time range) and gene expression of mRNA codifying key proteins/enzymes for the success in the seed–seedling transition (Cyclin, Actin, Small Heat Shock Protein, Glutathione S‐transferase, Malate Dehydrogenase, Alcohol Dehydrogenase). Our findings demonstrate: (a) Although germination kinetics in S. lycocarpum seeds is slower than that in tomato seeds, the fold change of genes codifying key enzymes for the embryo development is similar in germinating seeds of both species. (b) The genes used here are useful, from a technical point of view, for classifying commercial seed samples of the species in relation to physiological quality. More notably, cyclin and malate dehydrogenase genes have a greater expression, both in germination sensu stricto and in immediate post‐germination. (c) A molecular framework for the embryo growth in germinating seeds of S. lycocarpum can be a functional explication for the species to be a nurse plant. Thus, the overlapping of classical and contemporary measurements is especially interesting to those species playing a central role in the environment, such as nurse plants, and may represent a new conservationist paradigm.     

Nurse‐plant effects on the seed biology and germination of desert annuals

Nurse‐plants generally have positive effects on understorey species by creating more suitable conditions for stress‐intolerant plants relative to open micro‐habitats. However, long‐term effects of this plant–plant facilitation system have been rarely examined. Seeds of five desert annual species from Atiquipa coastal desert in Southern Peru were used to examine whether different microenvironmental conditions under the nurse‐plants Caesalpinia spinosa Molina (Kuntze) lead to differences in seed biology and germinability of annual plants relative to open, canopy‐free conditions. Seeds collected from plants associated with nurse‐plants were predicted to be (i) larger due to more favourable growing conditions, (ii) more viable and with greater germination rates, (iii) less variable in size and viability due to reduced environmental heterogeneity, and (iv) to germinate faster to avoid apparent competition with other annuals. Seed attribute measurements and germination trials in growth chambers were used to test these predictions. Although the plant abundance of only 2 of 5 species was strongly facilitated by the nurse‐plant, no significant differences were found in seed mass, viability or relative variability between understorey and open micro‐habitats for any of the species. Contrary to our predictions, final seed germination rates of seeds from open micro‐habitats were higher, and the open micro‐habitat treatment was more favourable for germination of seeds from both open and understorey environments. Taken together, these results suggest that plant–plant facilitation does not necessarily affect seed biology traits. Further studies addressing larger distribution ranges and/or density gradients of understorey species will illuminate the potential evolutionary effects of nurse‐plants.     

Why some species cannot colonise restored habitats? The effects of seed and microsite availability

Restoration of calcareous grasslands was promoted as a conservation strategy to reduce the risks imposed by habitat loss and fragmentation. Restoration already provided promising results for several taxa, however some specialist species still fail at colonising restored habitats. We aimed at explaining this lack of colonisation success for three calcareous grasslands specialist species in southern Belgium: Pulsatilla vulgaris; Trifolium montanum; and, Veronica prostrata. We studied: (i) germination in control and outdoor conditions (cold, heat, smoke and litter effects); (ii) in situ seedling emergence patterns (effects of seed addition and germination microsites availability). The three species were able to germinate in Petri dishes in the absence of treatment. Cold enhanced the germination of V. prostrata. Fire-related treatments (heat shock and smoke exposure) did not enhance germination and were deleterious to V. prostrata. Litter cover improved P. vulgaris emergence in outdoor containers, but had a negative effect on V. prostrata. In the field, V. prostrata did not emerge. T. montanum seedlings were observed in the reference grasslands when seeds were added, but not in the restored grasslands. P. vulgaris emerged in the reference grasslands, and to a lower degree in the restored grasslands. The combination of seed addition and microsites availability for seed germination resulted in enhanced seedling emergence for P. vulgaris. Our results suggest that seed and microsite availability can be limiting factors for site colonisation, but the combination of both is likely much more limiting. Lower seedling emergence in restored than in reference grasslands suggests a lower habitat quality in restored grasslands.     

Seed germination patterns in green dragon (Arisaema dracontium,Araceae)

Arisaema dracontium (green dragon) is a perennial herb that is widely distributed in eastern North America. However, in Canada, at the northern edge of its distribution, the species is designated as “vulnerable” with respect to conservation status. In natural populations, seedlings are uncommon; the present study was undertaken in order to characterize seed and seedling properties in green dragon. Seeds were sampled from five sites, ranging from Ontario at the northern limit of the distribution range, to Louisiana in the south. Seed germinability ranged from 25 to 55%, depending upon source. Experiments indicated that neither the hard seed coat nor a water-soluble exudate from the seed was responsible for inducing or maintaining dormancy. Patterns of seed germination appear to reflect general climatic conditions at the sites where seeds had originated. Cold stratification at 3°C produced significantly greater relative germinability in all seed collections except the most southerly one, from Baton Rouge. These seeds also had a slower overall speed of germination. In contrast, germination of seeds from the most northerly site was promoted by cold stratification and occurred over a relatively brief period. Germination in alternating light and dark conditions decreased the speed of germination compared to germination in the dark, however exposure to light changed the phenology of germination by promoting development of adventitious roots and primary leaves in these seedlings.     

Germination,survival, and growth of grass and forb seedlings: Effects of soil moisture variability

Seed germination and seedling growth, survivorship, and final biomass and their responses to watering interval were studied in two grass and six forb species to assess germination and seedling growth responses to increased soil moisture variability as might occur with future increases in precipitation variability. Seeds were planted in prairie soil and watered at 1, 2, 4, or 7 d intervals (I). Seed germination peaked at I = 4 d whereas leaf growth in grasses and forbs, and final biomass in grasses peaked at I = 7 d, suggesting that growth and biomass were favored at greater soil moisture variability than seed germination. Biomass responses to I were stronger than the germination responses, suggesting that soil moisture variability more strongly influenced post germination growth. Individual species responses to I fell into three groups; those with responses to I for: (1) seed germination and seedling survival, (2) biomass, or (3) both germination and biomass production. These species groups may be more useful than life form (i.e., grass/forb) for understanding seed germination and seedling dynamics in grasslands during periods of soil moisture variability. Seed germination and early growth may assume more importance in grassland plant community dynamics under more variable precipitation patterns.     

Linking seed dispersal,germination and seedling recruitment in the invasive species <Emphasis Type="Italic">Berberis darwinii</Emphasis> (Darwin’s barberry)

Seedling recruitment is a multi-phased process involving seed production, dispersal, germination, seedling establishment and subsequent survival. Understanding the factors that determine success at each stage of this process is of particular interest to scientists and managers seeking to understand how invasive species spread and persist, and identify critical stages for management. To understand the factors and processes influencing recruitment of the invasive species Berberis darwinii Hook. (Darwin’s barberry), temporal and spatial patterns of seed dispersal, germination and seedling establishment were examined. Seed dispersal from a large source population was measured over two fruiting seasons, and subsequent patterns of seedling emergence and survival within each cohort were measured. Seed longevity was tested under both natural and artificial conditions. Seeds were widely dispersed by birds, up to 450 m from the source population. Dispersal was essential to seedling establishment, as few seedlings survived beneath the parent canopy. Seeds were relatively short-lived in the soil under both field and glasshouse conditions, with few surviving for more than 1 year. Patterns of newly emerged seedlings largely reflected patterns of seed rain, but seedling survival was significantly affected by distance from source population, seedling density and light environment. These results suggest that recruitment of B. darwinii is dependent on dispersal of seeds to favourable microsites. Management priorities should include the removal of fruiting plants, and seedling control in highlight areas.     

Seed Germination in Amaranthus retroflexus L. as Affected by the Photoperiod and Age During Flower Induction of the Parent Plants

Seed germination in Amaranthtis retroflexus, a facultative shortday plant, was affected by the parental photoperiodic conditions.Seeds from parents grown continuously in short days (SD, 8 h)had a higher dark germination and a greater response (at 30°C) to a short irradiation or low temperature pretreatmentthan seeds from plants grown continuously in long days (LD,16 h). Daily night breaks of 1 h in the middle of the long-nightinhibited the SD induction of flowering as well as the SD promotionof germinability. Germinability of seeds produced by plantsinduced to flower in LD by 1, 2, or 3 SD was lower than thatof seeds produced by plants grown continuously in SD, and decreasedwith the age of the parent plants at the time of flower induction.     

Ample germination ability under wide‐ranging environmental conditions in a common understory tropical palm

Although palms play an important ecological role in tropical forests, characteristics related to their germinative niche remain largely unknown. We evaluated the seed germination characteristics of Geonoma schottiana, an abundant palm in the understory of different ecosystems of the Atlantic Rain Forest biome and the gallery forests of the Cerrado biome. We conducted experiments under light and dark conditions at Ψ = 0 MPa, and under two low‐water‐potential conditions and a flooded condition. Seed germination was highest at Ψ = 0 MPa under light (72%) and dark (67%) conditions. We observed moderate (51%) and low (18%) seed germination at Ψ = ?0.4 and ?0.8 MPa. About 20% of ungerminated seeds subjected to low water potentials for 300 days remained viable. No seeds germinated under flooded conditions; however, 23% of them maintained germinability. A delay in seed germination time was observed at low water potentials and an increase in synchrony occurred at Ψ = ?0.8 MPa. G. schottiana seeds did not require specific light conditions to germinate, and the species possesses germinative characteristics to cope with deficit and excess of water. Probably, this wide germination niche allows for its seeds to germinate over a wide range of habitats in different types of ecosystems.     

Rapid adaptation of seed germination requirements of the threatened Mediterranean species Malcolmia littorea (Brassicaceae) and implications for its reintroduction

Malcolmia littorea (Brassicaceae) is a threatened species growing in the coastal sandy dunes of the west-Mediterranean basin. In this study, the seed germination and seedling emergence requirements of this species were investigated in the only remaining native population in Italy. The highest germination percentage was achieved in darkness with scoring under safe green light at 5–10 °C. Seedling emergence was highest when seeds were buried between 1 and 10 mm in depth. The results suggest that germination and seedling emergence are adapted to Mediterranean coastal habitats by employing a common mechanism of light-inhibited germination and by germinating at cooler temperatures before the onset of the summer drought. Seeds were also collected from plants cultivated at a botanical garden and from plants reintroduced by sowing or by transplanting. For those populations, germination was maximal between 10–25 °C, suggesting that the thermal germination behaviour may be affected by the maternal environment of seed production within one generation. It is suggested to use seeds produced in the same environment to which they will be used for the reintroduction of this species.