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In degraded forest ecosystems, reintroduction of keystone-woody species is an important step for restoration because it provides regeneration niches. However, lack of information on how to propagate species restricts the use of native species; specially in tropical dry forests where seed germination is seasonal and is synchronized with the onset of the wet season. We evaluated the dormancy-breaking and germination requirements of nine keystone-woody species from Dry Chaco Forest. Most fresh viable seeds of the keystone species are nondormant, but viability decreases during dry-cold storage restricting the use of some species. Seeds of three keystone species germinated to higher percentages in light than darkness and those of five species germinated equally well in light and darkness; seeds of Castela coccinea germinated to higher percentages in darkness than in light. Alternating vs. constant temperatures had no effect on germination in seven species. Seeds of Anisocapparis speciosa and Cynophalla retusa were nondormant and remained viable for only 1 month during cold-dry storage; and 62–95% of the seeds of the other seven species were nondormant. Dormancy-break was studied in five of the seven species; seeds of four species had physiological dormancy and one had physical dormancy. Dormancy-breaking was promoted by environmental conditions in the habitat, i.e. warm stratification, after seed dispersal. Castela coccinea, Achatocarpus praecox, Mimosa detinens, and Capparicordis tweedieana are the most suitable keystone species for the restoration of overgrazed areas in the Dry Chaco Forest because their seeds germinate to a high percentage and retain viability during dry storage at low temperatures. Seeds of Mimosa detinens and Capparicordis tweedieana required mechanical scarification and 6-weeks of warm stratification, respectively, for dormancy-break. [ABSTRACT FROM AUTHOR]

Main conclusion: Differences in dispersal and dormancy of heteromorphic diaspores of Aegilos tauschii may increase its flexibility to invade/occupy weedy unpredictable habitats by spreading risk in space and time. In plant species that produce dimorphic seeds, there often is a negative relationship between dispersal and dormancy, with high dispersal–low dormancy in one morph and low dispersal–high dormancy in the other, which may function as a bet-hedging strategy that spreads the risk of survival and ensures reproductive success. However, the relationship between dispersal and dormancy and its ecological consequences in invasive annual grasses that produce heteromorphic diaspores is not well studied. We compared dispersal and dormancy responses of diaspores from the basal (proximal) to the distal position on compound spikes of Aegilops tauschii, an invasive grass with heteromorphic diaspores. Dispersal ability increased and degree of dormancy decreased as diaspore position on a spike increased from basal to distal. There was a significant positive correlation between length of awns and dispersal ability, and awn removal significantly promoted seed germination. Germination was positively correlated with GA concentration and negatively correlated with ABA concentration, and the ABA: GA ratio was high in seeds with low germination/high dormancy. Thus, there was a continuous inverse–linear relationship between diaspore dispersal ability and degree of dormancy. This negative relationship between diaspore dispersal and degree of dormancy at different positions on a spike of Aegilops tauschii may facilitate seedling survival in space and time. [ABSTRACT FROM AUTHOR]

Purpose: All secondary dispersal by wind, important for predicting, modeling and regulating diaspore dispersal processes, and for biodiversity conservation and vegetation restoration, is influenced by underlying surface matrix. But little is known about how matrix determines diaspore secondary dispersal. Here we focus on how lift-off velocity, good proxy for secondary dispersal of seeds by wind, is linked to the underlying surface matrix. Methods: We investigated the effect of the underlying surface matrix on diaspore lift-off velocity in a wind tunnel. Our study used 11 matrix types with different particle size, including four pure substrates (loam, aeolian sand, river sand, gravel) and seven mixtures thereof and diaspores of 28 species differing in length, width, height, mass, projected area, shape index, wing loading, and terminal velocity. Results: Diaspores were more easily dispersed from loam, aeolian sand and river sand than from the gravel substrates. For mixed matrices, lift-off velocity was closer to that of the small-sized than of the large-sized component of the substrate. Underlying surface matrix contributed more to diaspore dispersal by wind than diaspore attributes. In addition to wing loading, terminal velocity, and projected area also were important diaspore attributes determining lift-off velocity of the diaspores. Conclusion: Lift-off velocity of diaspores is influenced by particle size of underlying surface matrix during secondary wind dispersal: lift-off velocity is the largest on large-sized particles for pure matrices, and determined by the small-sized component for mixed matrices. [ABSTRACT FROM AUTHOR]

Purpose: Burial of diaspores has significant influence on diaspore fate, seedling recruitment and population dynamics. Some studies indicated that wind speed determines burial, neglecting the effect of matrix. Burial during wind dispersal basically occurs at the matrix surface. However, little is known about how substrate, wind speed and diaspore attributes interact to determine burial. Methods: Four pure substrates with a wide span of particle sizes (from 89.10 μm to 25000 μm) were selected to investigate how the particle size affects burial. Since the real substrates in nature are mainly mixtures of these substrates in different proportions, seven mixtures were also designed to represent some real filed matrices (farmland, riparian, desert and Gobi). Diaspores from 28 species with various length, width, height, mass, shape index, projected area, terminal velocity and wing loading were selected for the burial experiments simulating by a wind tunnel. Results: Substrate but not diaspore attributes or wind speed, contributed the most to burial during wind dispersal. Burial was poorest when placed on a matrix of intermediate-sized particles (200-600 μm) at a high wind speed. With increased matrix particle size, increased wind speed changed from promoting to inhibiting burial. Effects of diaspore attributes on burial were only significant on a substrate with large particle size at all wind speeds or a substrate with small particle size at high wind speeds. Conclusion: Our most important finding is that diaspores are most difficult to be buried by wind if they are dispersal onto a substrate with intermediate-sized particles. [ABSTRACT FROM AUTHOR]

"Dust seeds" with an undifferentiated embryo and unipolar germination are produced by holoparasitic species in 10 families of angiosperms. However, aside from a few Orobanchaceae species important in agriculture (crop weeds) and in Chinese traditional medicine we know little about seed germination in these achlorophyllous plants. Our primary purpose was to review the literature on seed germination in nine families of the mostly economically-nonimportant taxa of holoparasites and (briefly) of Cynomoriaceae, an economically important medicinal family for which several publications on its germination are in Chinese. A second purpose was to pull together information on sizes of dust seeds and their undifferentiated embryos and endosperm in both economically- and noneconomically-important holoparasitic plants. We found that not much progress has been made in understanding dormancy-break/germination in these holoparasites since 1969, when the author of a book on parasitic flowering plants pointed out how little we know about their germination. Lack of progress on germination of dust seeds of these holoparasites is not necessarily due to lack of research but at least in part to their nonresponsiveness to well-known treatments used to break dormancy in seeds of autotrophic and hemiparasitic flowering plants. For most species, seed length is <1.0 mm (in many <0.50 mm) and embryo length < 0.40 mm (in many <0.10 mm); endosperm is scant to copious. We suggest that seed conditioning, an essential step in germinating seeds of weedy Orobanchaceae holoparasites, be added to the protocol for germinating the dust seeds of noneconomically-important holoparasites with an undifferentiated embryo. [ABSTRACT FROM AUTHOR]

Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s−1), while that of diaspores with low wing loading (0.5 mg mm−2) and terminal velocity (2.5 m s−1) was promoted by relatively high (6 m s−1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community. [ABSTRACT FROM AUTHOR]

Soil seed banks represent a critical but hidden stock for potential future plant diversity on Earth. Here we compiled and analyzed a global dataset consisting of 15,698 records of species diversity and density for soil seed banks in natural plant communities worldwide to quantify their environmental determinants and global patterns. Random forest models showed that absolute latitude was an important predictor for diversity of soil seed banks. Further, climate and soil were the major determinants of seed bank diversity, while net primary productivity and soil characteristics were the main predictors of seed bank density. Moreover, global mapping revealed clear spatial patterns for soil seed banks worldwide; for instance, low densities may render currently species-rich low latitude biomes (such as tropical rain-forests) less resilient to major disturbances. Our assessment provides quantitative evidence of how environmental conditions shape the distribution of soil seed banks, which enables a more accurate prediction of the resilience and vulnerabilities of plant communities and biomes under global changes. Soil seed banks are reservoirs of plant biodiversity. Here the authors compile a global dataset of soil seed banks in natural plant communities and report a spatially explicit analysis of environmental controls of seed bank density and diversity. [ABSTRACT FROM AUTHOR]

Aims: We determined effects of soil from three habitats differing in physiochemical properties on transgenerational plasticity in diaspore production of the diaspore-polymorphic annual Ceratocarpus arenarius. Methods: Production of three disapore morphs and size of F0 plants in a sand desert (S) were evaluated. F1 plants from morphs at soil surface (a) and middle (c) and upper (f) parts of canopy of F0 plants were grown in soil from S, salt desert (SD) and desert steppe (DS) and evaluated for diaspore production and plant size. Results: Number of dispersal unit morphs for F0 plants in S was (f > c)> > a. Plants from all three morphs varied in size, mass and mass allocation. For F1 plants (compared to F0), a:(c + f) was the same or increased in S (poor soil) and decreased in DS (good soil); c:(a + f) increased in S and DS; and f:(a + c) decreased in S and DS. In SD, ratios for F1 plants from a and c were the same as those in S, but ratios for F1 plants from f were the same as those in S and DS. Conclusions: Differences in soil physiochemistry caused flexibility in plant size, mass and mass allocation and proportion of diaspore morphs across generations. [ABSTRACT FROM AUTHOR]

Astragalus is the largest genus of seed plants; however, information on its reproductive biology and life history is widely scattered in the literature. About 96% of the species are perennials and 4% annuals; many are rare endemics. Astragalus species are obligate or facultative outcrossers, and inbreeding depression is higher in self-compatible (SC) than in self-incompatible (SI) species. The most frequent pollinators are Bombus, Osmia and Anthophora. On average, 48% of ovules produce seeds, and 40% of flowers produce fruits. Seed/ovule and fruit/flower ratios are lower in SC than in SI species. Predispersal insect seed predation ranges from 0 to 93%, and major predators are Acanthoscelides, Bruchophagus and Tychius. Seeds have physical dormancy and typically form a seed bank. C3 is the only photosynthetic pathway in the genus. Population growth may be cyclic or noncyclic, and genetic diversity of a taxon may or may not be related to size of geographic range. [ABSTRACT FROM AUTHOR]

Background: With increased grazing disturbance of wetlands, soil moisture decreases, which could have an effect on the seed bank. The seed bank is a crucial resource for vegetation restoration; however, the effects of grazing disturbance on density and richness of seed banks and consequences on restoration of degraded wetlands are unclear. Methods: We selected six alpine wetlands along a degradation gradient on the Tibetan Plateau for study. The structural equation model was used to explore the direct and indirect effects of soil moisture on transient and persistent seed banks through soil physicochemical factors and vegetation. Non-metric multidimensional scaling was used to explore the role of seed banks in alpine wetland vegetation regeneration. Results: A decrease in soil moisture directly increased richness and density of the transient seed bank. However, decreased soil moisture indirectly decreased density of transient and increased richness and density of the persistent seed bank though soil pH and richness and abundance of vegetation. The similarity between the seed bank and vegetation increased with wetland degradation. Slope of the Bray-Curtis dissimilarity between transient seed bank and vegetation was higher than that for the persistent seed bank and vegetation. Conclusions: Transient seed banks remained almost constant under grazing disturbance, which favours persistent seed bank formation. Transient and persistent seed banks were determined by aboveground vegetation and soil environment, respectively. Seed banks provide strong resistance and resilience to degradation of wetland ecosystems, while persistent seed banks play a more important role than transient seed banks in restoration of degraded alpine wetlands. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity has been studied in diaspore-dimorphic species, but no such study has been done on a diaspore-polymorphic species. Our aim was to determine the effects of abiotic and biotic factors on phenotypic plasticity of the diaspore-polymorphic cold desert annual Ceratocarpus arenarius. Plants produced from dispersal units near the soil surface (a, basicarps) and at the middle (c) and upper (f) parts of the plant canopy were subjected to different levels of soil moisture, nutrient supply and intramorph and intermorph densities. Different levels of these biotic and abiotic factors resulted in significant variation in total plant mass, diaspore mass, mass allocation to stem and reproductive organs and total number and proportion of morphs a, c and f on an individual. The effect of stress on number and mass of a dispersal unit morph varied by treatment, with dispersal unit f having the highest CV and dispersal unit a the lowest. The success of this diaspore polymorphic species in its rainfall-unpredictable environment likely is enhanced by plasticity in production of the different types of diaspores. [ABSTRACT FROM AUTHOR]

Main conclusion: Individuals of the annual halophyte Atriplex centralasiatica produce three kinds of diaspores that differ in dispersal, dormancy/germination response and type of seed bank formed, which likely is a bet-hedging strategy in the rainfall-unpredictable environment on the semi-arid, saline Ordos Plateau in Inner Mongolia, China. Seasonal fluctuations in environmental conditions provide germination cues for the establishment of seedlings at the right time and place to ensure plant survival and population regeneration. Diaspore heteromorphism is a phenomenon in which diaspores with stark qualitative differences in morphology and ecology are produced by the same maternal plant. Germination responses and dispersal times of the annual halophyte Atriplex centralasiatica were examined to determine the role of diaspore heteromorphism in its adaptation to salt desert conditions. A. centralasiatica is a tumbleweed that produces three types of diaspores that differ in morphology and ecophysiology. The relative potential dispersal ability and intensity of dormancy of the three diaspore types was type A (fan-shaped diaspores with yellow fruits) < type B (fan-shaped diaspores with black fruits) < type C (globular diaspores with black fruits). In the field, type A retained high germinability, but all of them were depleted from the (transient) soil seedbank in the first growing season. Types B and C cycled between dormancy and nondormancy, and 0 and > 90.0% remained in the soil seedbank 2 years after dispersal, respectively. The dormancy, dispersal and salt tolerance of type B diaspores were intermediate between those of A and C. Type A exhibited low dispersal–nondormancy, type B exhibited intermediate dispersal–intermediate dormancy and type C exhibited high dispersal ability–high dormancy. In the unpredictable salt desert habitat, the functional differences in germination and dispersal of the three diaspores act as a bet-hedging mechanism and ensure population establishment in different years by spreading germination over time and space. [ABSTRACT FROM AUTHOR]

In annually flooded and dewatered mudflats, does the big flush of germination following dewatering exhaust the seed bank, and if not, how long can seeds remain viable and nongerminated under annual flooding cycles? Soil samples from mudflats in Land Between the Lakes in western Kentucky and northwestern central Tennessee (USA) were collected in 1990, 1991, and 1992 and annually flooded in winter and kept moist during summer for 15, 14, and 13 years, respectively. Beginning in 1996, all samples were stirred when dewatered in June. Seedlings were counted and removed, thus preventing any input of new seeds. During the study, seeds of 37 species germinated, and there were 2 to 8588 seedlings m−2, depending on the species. Ten of the species germinated in only one set of samples (2–4 seedlings m−2) in 1 year, but the number of years before germination ranged from 1 to 9; one species germinated in two sets of samples (2–4 seedlings m−2) after 6 and 9 years. Eighteen species germinated in 2–12 of the years but not necessarily in consecutive years. Eight species germinated in 14 and/or 15 years. Regardless of seed bank size, seeds of many species lived in the samples for extended periods of time with 31 (83.8%) germinating after ≥ 5 years and 19 (48.6%) after ≥ 10 years. New species appeared in the 1990, 1991, and 1992 samples after 8, 9, and 11 years, respectively. Thus, if the seedling emergence method is used to study mudflat soil seed banks and monitoring is terminated after only a relative short period of time, the size and species richness of the seed bank may be greatly underestimated. [ABSTRACT FROM AUTHOR]

Background and aims: If and how eutrophication influences the persistent soil seed bank is poorly understood. Here, we hypothesized that eutrophication alters the composition of the persistent seed bank indirectly through changes in the soil characteristics and aboveground plant community and productivity. We also hypothesized that changes in the persistent seed bank will consequently impact the aboveground vegetative composition. Methods: We tested these hypotheses using data from a 9-year nitrogen and phosphorus fertilization experiment in an alpine meadow ecosystem on the eastern Qinghai-Tibet plateau. Results: We found that long-term nitrogen and phosphorus fertilization indirectly impacted the composition of the persistent seed bank through changes in soil pH, aboveground vegetation composition and annual net primary productivity (ANPP). Changes in the composition of the persistent seed bank, however, were relatively minor in comparison to changes in aboveground vegetation composition. Finally, changes in the persistent seed bank did not feedback on aboveground vegetation composition. Conclusion: Our findings demonstrate the importance of soil pH, ANPP and vegetation composition in regulating the persistent seed bank under eutrophication. Our results also highlight the relative stability of the persistent seed bank to long-term eutrophication and their important contribution to the sustainability of grassland ecosystems. [ABSTRACT FROM AUTHOR]

Main conclusion: Most Paeonia species have epicotyl dormancy. Germination of peony seeds requires warm stratification for embryo growth and radicle protrusion followed by cold stratification for epicotyl growth.The genus Paeonia (Paeoniaceae) includes many popular ornamentals, has colorful flowers and contains several Chinese medicinal species. The germination protocol for seeds of Paeonia species is complex and impedes the breeding of new cultivars and contributes to the rarity and high cost of the plants. Although numerous reports on seed dormancy/germination in peonies are scattered throughout the literature, most of them are in Chinese. The primary aims of this paper are to provide a general overview of the available information on seed dormancy/germination in peonies and to make some suggestions regarding propagation for the peony industry and breeders. Most Paeonia species have epicotyl dormancy. The embryo is differentiated into organs, but it is underdeveloped (small) and must grow inside the seed before the radicle can emerge. Germination of peony seeds requires warm stratification for embryo growth and radicle protrusion followed by cold stratification for epicotyl growth. In addition, the epicotyl is sensitive to cold stratification only after the root has grown to a certain length. GA3 treatment enhances embryo growth and subsequent germination percentages. Further investigations on the physiology, genetics and proteomics would contribute to a better understanding of seed dormancy in Paeonia. [ABSTRACT FROM AUTHOR]

Heretofore, no study has determined how germination of ingested seeds is affected by the kind (class) of dormancy nor by seed dormancy x seed size interaction. Thus, we aimed to determine the effects of seed size, kind of dormancy and their interaction on germination of defecated seeds using a meta-analysis. We collected data for 366 plant species in 97 plant families from 76 publications. In general, gut passage significantly increased germination percentage of defecated seeds by 5% compared with that of control seeds. Germination percentages of non-dormant, physiologically dormant, and morphologically/morphophysiologically dormant seeds (all water-permeable) significantly decreased after gut passage by 40, 18, and 14%, respectively, compared with control seeds (non-gut-passed). Changes in germination percentage of seeds with physical dormancy (water-impermeable) were positive, and gut passage increased germination by 69% compared with control seeds. Germination of small seeds decreased 8% after gut passage, whereas germination of both medium and large seeds increased by 18%. However, changes in germination percentage differed between categories of seed size in each class of dormancy. In physically dormant seeds, germination of all seed sizes improved after gut passage, and the magnitude of increase was higher for large than for medium and small seeds. Thus, gut passage increased germination of medium-size water-permeable seeds (physiologically dormant and morphologically/morphophysiologically dormant) more than it did for large and small seeds. However, gut-passage decreased or did not change the germination percentage of non-dormant seeds. Seed size and kind of dormancy should be included in studies on the effect of gut passage on germination. [ABSTRACT FROM AUTHOR]

Background and aims: Results of studies on plant responses to salt stress often are difficult to compare because different salt parameters were used. Our aim was to compare the effects of different combinations of sodium salts on germination/seedling growth of two forage species and determine which salt solution parameter(s) was(were) most closely related to these responses.Methods: Seeds of the legume Medicago sativa and the grass Elymus dahuricus were germinated in different concentrations of saline and sodic salts. Various parameters of the salt solutions were determined, and seed germination and seedling growth metrics were measured.Results: Seeds of both species were more tolerant to saline than to sodic salts, and seedlings of E. dahuricus were more salt tolerant than those of M. sativa. Na2SO4 and Na2CO3 were more inhibitory to germination/growth of the two study species than the same concentration of NaCl and NaHCO3 for saline and sodic salts, respectively. For both species, electrical conductivity, salt content (%) and Na+ concentration best correlated with germination/growth for saline salts and Na+ concentration for sodic salts.Conclusions: In evaluating the effects of salt on seed germination and seedling growth, both saline and sodic salts need to be considered, and Na+ concentration is the best salt solution parameter to use in comparing and communicating the results. [ABSTRACT FROM AUTHOR]

Post-dispersal seed removal by animals can lead to extensive seed loss and thus is an important factor in structuring plant communities. However, we know much less about post-dispersal seed predation than about other forms of herbivory. Mucilage plays many ecological roles in adaptation of plants to diverse environments; nevertheless, until now the role of mucilage in ant-mediated seed movement remains largely hypothetical. We studied the role of mucilage in seed removal of Artemisia sphaerocephala by ants in Mu Us Sandland in Inner Mongolia, China. Messoraciculatus was the most active seed predator of Artemisia sphaerocephala. Time to first ant collecting ( T1st) of wet intact seeds was longest and significantly different from that for dry intact seeds, wet demucilaged seeds, and dry demucilaged seeds; number of seeds removed to ant nests was lowest for wet intact seeds. After they were collected by ants, 5 % of wet intact seeds were dropped during transport. Our results indicate that seed mucilage of Artemisia sphaerocephala may play a significant role in post-dispersal seed removal by (1) making seeds less attractive to ants, thus resulting in a delay of collection time; (2) forming a strong bond to soil particles, making it difficult for ants to remove seeds; and (3) making seeds more likely to be dropped during transport, thereby allowing them to escape from predation even after collection by ants. This study demonstrates the importance of mucilage in reducing seed removal by ants and thus in anchoring seeds of desert plants in the vicinity of mother plants. [ABSTRACT FROM AUTHOR]

Buttress trees are prominent in tropical rainforests, providing mechanical support for canopy trees. Other ecological functions of these structures remain unclear. Here we demonstrate that buttresses are physical structures that regulate soil moisture, soil nutrient status and seedling diversity near tree trunks. We monitored soil moisture over a year in plots on the uphill, downhill and lateral sides of buttresses on a tropical seasonal rainforest slope in Xishuangbanna, Southwest China. Soil nutrient status was examined in dry and rainy season and seedlings were identified and counted in the plots. Leaf litter accumulation was sampled at the end of the study. Higher levels of soil moisture were maintained uphill of the buttresses throughout the year and leaf litter accumulation was also much higher. Total soil carbon, total N, and hydrolysable N were much higher on the uphill side but other nutrient concentrations did not differ significantly. Seedling species composition varied significantly among different locations with the densest and most diverse seedling assemblages on the uphill side. This study illustrates an important function of buttress trees in providing soil heterogeneity and promoting seedling diversity in rainforests. [ABSTRACT FROM AUTHOR]

We tested the effects of phylogeny, life history and habitat conditions for seedling establishment on seed germination of 69 arid/semi-arid zone species from northwest China. Final germination percentages had a bimodal distribution, whereas, days to first germination were skewed toward short periods. Stepwise multi-way ANOVAs showed that the amount of variance in final germination percentage among species for seeds incubated in light was explained by phylogeny (13.6%), dispersal mode (11.9%), seed mass (3.6%), and habitat (0.2%); in darkness by dispersal mode (17.5%), phylogeny (12.7%), seed mass (5.7%), and habitat (0%). A series of ANOVAs revealed that the variance in final germination percentages among species is largely dependent upon phylogeny and dispersal mode but that it is also influenced by seed mass and habitat. The effects of dispersal mode and seed mass on final germination percentage among species were phylogenetic group- and habitat-specific. Wind-dispersed seeds had higher germination percentages than unassisted and vertebrate-dispersed seeds. Compared to xerophytes, mesophytes tended to have smaller seed mass, higher mean germination percentages and a greater effect of seed mass on final germination fractions. Our results suggest that phylogeny and life history should be taken into account in studies on the role of natural selection in regulation of seed germination. [ABSTRACT FROM AUTHOR]

The term ‘cedar glades’ has been applied to several different types of plant communities that occur on rocky calcareous soils in eastern North America. A previous paper by the first two authors reviewed in considerable detail the use of this term with regard to type of vegetation on rocky limestone soils in the Nashville (Central) Basin of Tennessee. The present paper reviews use of ‘cedar glades’ as a descriptive term for vegetation in other physiographic regions of eastern North America. In the Nashville Basin, and in some other physiographic regions, the term has been applied to true open cedar glades (‘glades’) plus the surrounding redcedar/redcedar-hardwood forest, or (more recently) to the natural rocky treeless openings only. However, outside the Nashville Basin, it has also been used to describe several other disparate vegetation types, such as xeric limestone prairies (limestone glades, prairie barrens), redcedar-little bluestem savanna, dense redcedar forest, redcedar-hardwood forest, and even an open stand of redcedar-pine-sweetgum with warm-season perennial prairie grasses in the understory. In the Great Lakes region of North America and in the Baltic region of Europe, some atvars are similar to cedar glades sensu stricto of southeastern United States. Since many of the rocky calcareous openings in eastern North America can be classified as either cedar glades or xeric limestone prairies, a suite of abiotic, biotic, and anthropogenic-related factors is presented for use in distinguishing between these two vegetation types. [ABSTRACT FROM AUTHOR]

Agriophyllum squarrosum Moq. is a dominant annual on sand dunes in the arid regions of central Asia. A high percentage of seeds is retained on dead plants which become covered by moving sand, but little is known about the ecological significance of burial of canopy-stored seeds. We investigated the size and dynamics of the buried canopy-stored seed bank and effects of burial on seed germination. In March (during the windy season), May (beginning of the germination season), and July (middle of the growing season), the number of seeds per square meter in sample plots in the dunes was 623, 223 and 22, respectively, with 54.6, 30.6 and 12.9% of the total seeds retained on buried plant canopies. In a controlled experiment, more seedlings emerged from released (dispersed) than from canopy-stored seeds when burial depth was the same. No viable ungerminated released seeds were found, but 45–80% of the ungerminated canopy-stored seeds were viable. In general, with an increase in applied water germination of released seeds buried at a depth of 1 or 2 cm and of canopy-stored seeds buried at 1 cm increased, but regardless of watering regime few or no released seeds at 4 cm or canopy-stored seeds at 2 or 4 cm germinated. Significantly more seedlings emerged from plants buried in a horizontal than in a vertical position. Seedlings originating from buried canopy-stored seeds on an active dune accounted for only 5.4% of the total seedlings emerging, and most of them emerged later than those from released seeds. Thus, seed release is more effectively postponed in buried than in exposed canopies, and burial of canopy-stored seeds is a mechanism that helps regulate seed germination and seedling emergence of A. squarrosum on active dunes. [ABSTRACT FROM AUTHOR]

Xeric limestone prairies (XLPs) are open, nonforested areas in which herbaceous plant communities occur on shallow. rocky soils derived from calcareous substrates. These grasslands are characterized by dominance of C4 perennial grasses (particularly Schizachyrium scoparium) and are distributed in eastern United States from Missouri and Pennsylvania south to Arkansas and Georgia. XLPs occur in the Ozark Plateaus. Central Lowland. Interior Low Plateaus. Appalachian Plateaus. Ridge and Valley, and Coastal Plain physiographic provinces, and they are developed on Alfisols. Ultisols. Mollisols. Inceptisols, and Vertisols derived from Paleozoic limestones (also Eocene), dolomites, and calcareous shales. The C4 perennial prairie grass S. scoparium is the characteristic dominant taxon in XLPs of eastern United States. However, C, perennial forbs are dominant in some sites, and C, annual grasses (Sporobolus spp.) may be locally dominant in shallow-soil-zone microsites. Thirteen taxa apparently are endemic, or nearly so, to this vegetation type, including eight in the Ridge and Valley in Alabama (Cahaba River valley), four in the Ozark Plateaus in Missouri and Arkansas, and one in the Ridge and valley of West Virginia and Virginia. Various types of information are used to construct a conceptual model of the origin, maintenance, and successional dynamics of XLPs. Affinities of XLPs in eastern United States to other herbaceous vegetation types in eastern and western North America are discussed, and directions for future research are suggested. [ABSTRACT FROM AUTHOR]

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Use of "cedar glades" and other terms by geologists, botanists, soil scientists, and zoologists to describe vegetation on rocky limestone soils in the Central (Nashville) Basin of Tennessee from 1851 to 2003 is reviewed. Historically, in the Central Basin "cedar glades" has been applied to the rocky openings / redcedar / redcedar-hardwood / hardwood forest complex primarily on the (thin-bedded) Lebanon limestone but also on other (thick-bedded) Ordovician limestones. However, "cedar glades," "limestone glades," and "limestone cedar glades" increasingly are being used by botanists and plant ecologists for the rocky openings only, which have C4 native annual grass--C3 annual/perennial forb-cryptogam-dominated vegetation. Some erroneous statements in the literature that have resulted from misinterpretation or misunderstanding of "cedar glades" and other terms are discussed. Finally, a graphical model of the (apparent) pathways of development of cedar glade vegetation from bare rock to forest in the Central Basin is presented. [ABSTRACT FROM AUTHOR]

The seed germination of Polymnia canadensis was studied in relation to its wide variation in life history and its ecology as a mostly facultative biennial, a life cycle type that is rare in stable forest habitats in eastern North America. The seed dormancy and germination characteristics of P. canadensis were like some other herbaceous woodland species of diverse life cycle types. That is, its seeds have physiological dormancy, and they (1) germinated to higher percentages after cold stratification, (2) germinated better in light than in darkness and (3) formed a persistent soil seed bank. Since its seed dormancy and germination characteristics are not uncommon and are not particularly associated with any one life cycle type in woodlands, those properties do not contribute to the rarity of its life cycle type in deciduous forests. These properties are also found in many facultative biennials of open, disturbed habitats and in other Asteraceae of various life cycle types. In addition, the germination phenology of P. canadensis differed between mesic and dry field sites in central Kentucky. At the dry sites, most of the yearly germination occurred in fall, while at the mesic sites most germination occurred in the spring due to being inhibited during fall. A reciprocal seed transplant experiment conducted in two different years demonstrated that the cause of this difference was environmental and that there was no source x site interaction; i.e., no difference between sources in phenotypic plasticity for germination phenology. Absence of genetic effects was also shown by no consistent pattern in the few differences between seed sources in seed incubation laboratory experiments and in a germination phenology experiment in glasshouse flats. Exposure of seeds to a high ratio of far-red/red light prior to or during incubation did not inhibit germination. Neither did changes in leaf litter thickness qualitatively alter germination phenology in field quadrats or in glasshouse flats. Thus, germination in fall at mesic sites was inhibited by other unknown factor(s), perhaps interacting with the effects of closed tree canopy and/or thick leaf litter. [ABSTRACT FROM AUTHOR]

Investigates seed dormancy and germination of Xyris tennesseensis in the U.S. Description of Xyris; Objectives of a recovery plan for Xyris; Effects of substrates on seed germination.

Main conclusion: Better seed germination of females than of hermaphrodites is not a major contributor to the greater geometric lifetime fitness that females require to be maintained in a gynodioecious population. Gynodioecy is a sexually dimorphic breeding system in which females (F, male sterile) and hermaphrodites (H) coexist in the same population. For plants with nuclear (biparental) inheritance of male sterility, theory predicts that except when the product of selfing rate (s) and inbreeding depression (δ) in H is high (sδ > 0.50), F must compensate (female advantage) for the loss of gene transmission via pollen production by producing more or higher-quality offspring than H to be maintained in the population. For species with cytoplasmic (maternal) inheritance of male sterility, the female requires only a small compensation in seed production or some other offspring fitness trait to persist. Reallocation to seeds of resources saved by loss of pollen production is expected to increase the quantity (number) and/or quality (mass, germinability) of seeds produced by F, thus compensating for the lack of pollen production. The primary aim of our study was to compare seed germination of F and H via a literature review. Based on theoretical considerations, we hypothesized that seeds of F should germinate better or equally as well as those of H. We found that of 235 case studies for 47 species Fgerm > Hgerm in 48.1%, Fgerm = Hgerm in 38.3% and Fgerm < Hgerm in 13.6%. Our results are very similar to those of a previously published meta-analysis that included germination of F and H for 12 species. For 162 cases on seed size, F > H in 29.0%, F = H in 63.6% and F < H in 7.4%. Since [(Fgerm > Hgerm) < (Fgerm ≤ Hgerm)] and [(Fseedsize > Hseedsize) < (Fseedsize ≤ Hseedsize)], these results suggest that seed quality is not a major fitness component of female advantage. [ABSTRACT FROM AUTHOR]

Amphicarpic plants produce aerial and subterranean fruits on an individual plant, and these heteromorphic diaspores give rise to plants that differ in growth and ecology. Amphicarpaea edgeworthii is a summer annual amphicarpic species that grows over a range of light levels. We aimed to compare the response to shading intensity of plants of A. edgeworthii grown throughout their life cycle from aerial seeds (ASP) and from subterranean seeds (SSP). We hypothesized that vegetative and reproductive growth of plants from ASP and SSP respond differently to light. Plants were grown from ASP and SSP under 0, 46, 71 and 90% shading intensities. With plant height as a covariate, vegetative biomass of ASP and SSP did not differ. Leaf area and seed production of SSP were greater and internode length less than they were for ASP in all shading intensities. Aerial and subterranean seed yield, seed mass and number for both ASP and SSP were highest in full light. Aerial seed yield was affected more than subterranean seed yield by shading intensity. The growth and reproductive responses of ASP and SSP of A. edgeworthii may be adaptive to the range of low to high light environments in which this species grows. [ABSTRACT FROM AUTHOR]

Studies the seeds of the summer annual mudflat species Ammannia coccinea and Rotala ramosior to determine the effects of flooding during late autumn to late spring on dormancy break, and optimum temperature for dormancy break. Impact of dormancy break on seeds of R. ramosior and A. coccinea; Results of nonheated greenhouse tests; Data suggesting that seeds are nondormant when mudflats become dewatered in summer.

Seeds (mericarps) of Ptilimnium nuttallii have linear, underdeveloped embryos that must grow from about 0.2 to 1.3 mm in length before the radicle emerges from the seed (fruit); thus, seeds have morphological dormancy (MD). In addition to MD, about 70% of the seeds also havephysiological dormancy (PD) at maturity in mid-July; thus, seeds have morphophysiological dormancy (MPD). Whereas fresh seeds with only MD (26-29%) germinated in light during 2 weeks of incubation at 15/6, 20/10, or 25/15 deg. C, those with MPD required exposure to high temperatures (25/15, 30/15 deg. C), which broke PD, before they would germinate. The high temperature requirement for loss of PD means that seeds have nondeep simple MPD. Seeds buried in soil in July 1991 and exposed to natural seasonal temperature changes came out of PD duringthe summers of 1991-1996, and those failing to germinate in autumn of each year re-entered PD during winter. Thus, seeds have an annual dormancy/nondormancy cycle with respect to PD, and MD can be broken only while seeds are not physiologically dormant. Light was required for embryo growth in 55-98% of the seeds, but the light requirement varied with year. Consequently, embryo growth and germination are restricted to autumn, and seeds on the soil surface are more likely to germinate than those buried in soil. Results of this study indicate that P. nuttallii is a strict winter annual with a long-term soil seed bank. The annual dormancy/nondormancy cycle would prevent germination inspring when high water levels in the habitat might be inhibitory forsuccessful seedling establishment. [ABSTRACT FROM AUTHOR]