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We conducted an experiment to determine the reproductive biology of Erigeron speciosus (Asteraceae), a perennial montane herb that is widespread throughout Western North America. Pollination of E. speciosus was manipulated to understand the following questions: (1) What is the mating system for E. speciosus (outcrossing vs. selfing)? (2) Is E. speciosus self-incompatible? (3) Does pollen donor distance affect reproductive success? (4) Is reproductive success limited by pollen receipt (i.e., pollen limitation)? We compared seed set and seed viability among five pollination treatments: ambient pollination (control), pollinator exclusion (bagged capitula), self-pollination only, and two outcrossing treatments (near and far pollen donors). We found that E. speciosus is largely self-incompatible and depends on outcrossing for its reproduction. Despite this, reproduction was not pollen-limited at our study site. We also found some evidence that E. speciosus reproduction is susceptible to outbreeding depression. Realizamos un experimento para determinar la biología reproductiva de Erigeron speciosus (Asteraceae), una hierba montano perenne que se extiende por el Oeste de Norteamérica. Polinización de E. speciosus fue manipulado para entender: (1) >cuál es el sistema de apareamiento para E. speciosus (cruzamiento vs. autofecundación)? (2) >Es E. speciosus autoincompatible? (3) >La distancia del donador de polen afecta el éxito de la reproducción? (4) >El éxito de la reproducción será limitada por la recepción de polen (i.e., limitación polínica)? Comparamos la producción de semillas y la viabilidad de semillas por cinco tratamientos de polinización: polinización ambiente (control), exclusión de polinización (flores embolsadas), autopolinización solamente, y dos tratamientos de cruzamiento (donadores de polen cercanos y lejanos). Encontramos que E. speciosus es por gran parte autoincompatible y depende en cruzamiento para su reproducción. Aun así, la reproducción no fue limitada por polen en el sitio de nuestra investigación. También encontramos evidencia que la reproducción de E. speciosus es susceptible a depresión por exogamia. [ABSTRACT FROM AUTHOR]

The international plant trade results in the accidental movement of invasive pests and pathogens, and has contributed significantly to recent range expansion of pathogens including Dothistroma septosporum. Seeds are usually thought to present a lower biosecurity risk than plants, but the importation of Pinus contorta seeds from North America to Britain in the mid-1900s, and similarities between British and Canadian D. septosporum populations suggests seeds could be a pathway. Dothistroma septosporum has not been isolated from seeds, but inadequately cleaned seed material could contain infected needle fragments. This case study investigated whether cone kilning, and wet and dry heat treatments could reduce D. septosporum transmission without damaging seed viability. Pinus needles infected with D. septosporum were incubated alongside cones undergoing three commercial seed extraction processes. Additional needles were exposed to temperatures ranging from 10 to 67 °C dry heat for up to 48 h, or incubated in water heated to between 20 and 60 °C for up to one hour. Pinus sylvestris seeds were exposed to 60 and 65 dry heat °C for 48 h, and further seed samples incubated in water heated to between 20 and 60 °C for up to one hour. Dothistroma septosporum survived the three kilning processes and while seeds were not damaged by dry heat exceeding 63.5 °C, at this temperature no D. septosporum survived. Wet heat treatments resulted in less than 10% pathogen survival following incubation at 40 °C, while at this temperature the seeds suffered no significant impacts, even when submerged for one hour. Thus, commercial seed kilning could allow D. septosporum transmission, but elevated wet and dry heat treatments could be applied to seed stock to minimise pathogen risk without significantly damaging seed viability. [ABSTRACT FROM AUTHOR]

Key message: Black spruce (Picea mariana (Mill.) B.S.P.) has historically self-replaced following wildfire, but recent evidence suggests that this is changing. One factor could be negative impacts of intensifying fire activity on black spruce seed rain. We investigated this by measuring black spruce seed rain and seedling establishment. Our results suggest that increases in fire activity could reduce seed rain meaning reductions in black spruce establishment. Context: Black spruce is an important conifer in boreal North America that develops a semi-serotinous, aerial seedbank and releases a pulse of seeds after fire. Variation in postfire seed rain has important consequences for black spruce regeneration and stand composition. Aims: We explore the possible effects of changes in fire regime on the abundance and viability of black spruce seeds following a very large wildfire season in the Northwest Territories, Canada (NWT). Methods: We measured postfire seed rain over 2 years at 25 black spruce-dominated sites and evaluated drivers of stand characteristics and environmental conditions on total black spruce seed rain and viability. Results: We found a positive relationship between black spruce basal area and total seed rain. However, at high basal areas, this increasing rate of seed rain was not maintained. Viable seed rain was greater in stands that were older, closer to unburned edges, and where canopy combustion was less severe. Finally, we demonstrated positive relationships between seed rain and seedling establishment, confirming our measures of seed rain were key drivers of postfire forest regeneration. Conclusion: These results indicate that projected increases in fire activity will reduce levels of black spruce recruitment following fire. [ABSTRACT FROM AUTHOR]

On‐plant storage of seeds (serotiny) is a feature of many fire‐prone dominant trees and shrubs in North America, Mediterranean Basin, South Africa and Australia. Understanding how it has responded to the prevailing fire regime and recruitment/growing conditions, and its genetic basis and adaptive significance, depends on the use of an accurate index of the level of serotiny.Seven indices, three measuring 'apparent' serotiny and four measuring 'inherent' serotiny, were evaluated for their ability to reflect the extent to which seeds are stored in the crown for later release. The most widely used indices ignore the temporal aspects of seed attrition and are vulnerable to plant size, age, fecundity and local growing‐condition effects, while age of the oldest crop year with closed cones/fruits depends on the accuracy of a single observation. Presence/absence of serotiny at the individual tree level ignores the effect of plant age on the expression of serotiny.The slope of the line through the percentage of cones/fruits that still retain their seeds in progressively older crop years, the 'degree of serotiny' (100/slope), is shown to be unbiased by annual fluctuations in crop size, differences in plant age or variations in local growing conditions. It also corresponds to a probability, and thus more accurate, estimate of age of the oldest unopened structures. Since seeds have a lower % viability than the % of supporting cones/fruits closed at any age, there is a case for applying the slope method to the fraction of viable seeds retained to arrive at an estimate of the age of the oldest viable seeds on the plant, as the ultimate index of serotiny.If the level of serotiny is to be related to the fire regime, then care needs to be taken to use records over a sufficiently long time to have had an evolutionary impact, unless this is being used against controls to examine a genetic response to the new fire regime.Synthesis. Among seven currently available indices of serotiny, the slope measure is shown to be the most accurate for studies that relate the level of serotiny to the fire regime and habitat conditions under which the species evolved, as well as for examining its heritability. Attention needs to shift from just recording cones/fruits closed to include the viability of seeds that remain as a better basis for understanding the role of serotiny in post‐fire recruitment. [ABSTRACT FROM AUTHOR]

Bromus tectorum is expanding across western North America. This spread is due to its own competitive abilities, land management practices, and unintended transport by the public as the plant's spikelets often lodge in clothing. Many assume that washing in a laundry machine makes the seeds nonviable: we decided to test this assumption. We hypothesized that seeds would exhibit lower rates of germination and emergence after being laundered, and the effect would be stronger if bleach was used. We found that washing with detergent, followed by drying, had no effect on germination when seeds were allowed to sprout 20 days later. We also found that a 6.0% solution of sodium hypochlorite bleach reduced germination and growth if planting occurred 180 days after laundering. [ABSTRACT FROM AUTHOR]

•To understand prerequisites of biological invasions, it is imperative to know whether species have traits that pre-adapt them to become invasive elsewhere. However, few experimental studies have explicitly tested this by comparing traits between invasive and noninvasive species in their native range instead of in the nonnative range. •We used native plant material of 14 European congeneric pairs of herbaceous species that were all introduced to North America, and of which one species per pair is invasive. •In our germination and common garden experiment with and without fertilizer addition, the invasive species germinated faster, produced more biomass and had a higher proportion of flowering plants than the noninvasive congeners. •Our results indicate that species traits, which lead to a high plant performance in the native range, can confer pre-adaptation to become invasive. We suggest that such traits may be especially relevant for use in risk-assessment protocols before introduction elsewhere. [ABSTRACT FROM AUTHOR]

Abstract: Dandelion Taraxacum agg. (formerly Taraxacum officinale G.H. Weber ex Wiggers) is a common weed species associated with pastures, grasslands and no-tillage cropping systems throughout its native range in Europe, and more recently introduced into North America, Australasia and elsewhere. Following wind-dispersal from the parent plant, its seeds are subject to predation from a host of invertebrate predators. Similarly, seedling predation may also significantly limit dandelion recruitment. Although such post-dispersal mortality is central to our understanding of dandelion population dynamics and therefore weed control, the precise spatio-temporal role played by different putative seed and seedling predators is poorly understood. Here we studied how seed viability, and seed and seedling predation influenced dandelion recruitment at two contrasting sites in central Europe. The abundance in the field and seed and seedling consumption in the laboratory were determined for the main groups of predators—ground beetles (Coleoptera: Carabiade), terrestrial isopods (Isopoda: Oniscidea) and molluscs (Gastopoda: Pulmonata). At particular sites, seed viability and seedling predation were negatively correlated while the percentage of seeds that succumbed to seed predation was similar. Combined factors accounted for the death of 98% and 87% of exposed seeds. Ground beetles (particularly Amara spp.) and terrestrial isopods (Armadillidium vulgare) were efficient and dominant seed predators, while slugs (Arion lusitanicus) and isopods were important predators of seedlings. While there was no seasonal trend in the intensity of seed predation it decreased towards autumn in parallel with the feeding activity of the declining population of A. lusitanicus. The mortality factors thus varied in their importance, largely between sites and less with the course of the season. Although seed inviability, seed and seedling predation did not stop the recruitment of dandelion seedlings they are crucial factors limiting dandelion populations. Methods of increasing the efficiency of predation of seed as a means of managing weeds are worthy of further study, particularly in areas where dandelion is an invasive species. [Copyright &y& Elsevier]

Populations at the edge of their range are known to have decreased fitness. However, the factors that cause this and the specific plant characters involved are not well understood. To determine whether symbiotic interactions play a role in altering fitness, I examined population age, seed viability, and nodulation in relation to population size of Ceanothus herbaceous Raf. at the northern limit of its range. Tap roots from three populations were grown in each of the three population’s soils to examine the specificity between C. herbaceous and Frankia. Population size ranged from 14 to 7300 individuals. There was a positive exponential relationship between population size, seed germination, and the proportion of plants forming nodules in the field. Populations varied in age by 26 years and age was not related to size. Recruitment into these populations was episodic and was positively correlated to growing season temperatures. Nodulation rates in the growth experiment were similar to those in the field, and plants showed much greater growth when nodulated. Plants from the largest population showed the greatest growth when infected with Frankia from their own soil. These plants also had significantly higher nitrogen-fixing activity per total plant mass than all other plant–soil combinations, suggesting that the plants from this population show some degree of specificity to the Frankia they are normally found with. Plants from the largest population grown in soil from other populations showed lower nitrogen-fixing activity per nodule mass than any other plant–soil combination. There was a positive relationship between nodule mass allocation and plant growth, a trend not seen in other nitrogen-fixing symbioses where nodule allocation is much higher. These results illustrate the importance of considering both the regeneration and growth phases when evaluating the effects of small population size on plant performance [ABSTRACT FROM AUTHOR]

To increase our knowledge of the seed dormancy breaking and germination requirements of native and non-native winter annual Apiaceae in temperate eastern North America, a study was conducted on seeds of Cyclospermum (Apium) leptophyllum, which is native to South America, but naturalized in North America and elsewhere. A high percentage of fresh seeds germinated over a narrow range of temperatures, but the range increased when seeds were incubated continuously in light or buried in soil at high summer temperatures, indicating the presence of conditional physiological dormancy (PD). Embryos grew from approximately 0.3 to 1.25 mm (316% increase in length) inside the seeds before the radicle emerged; thus, seeds had morphological dormancy (MD) as well as PD, that is, morphophysiological dormancy (MPD). Embryo growth did not occur during summer in seeds exposed to natural temperatures, but embryos did grow in autumn. For seeds sown in the field in June, both embryo growth and germination occurred in autumn. Thus, seeds have non-deep simple MPD, with PD being broken in summer and MD in autumn. A comparison of C. leptophyllum with native and non-native winter annual Apiaceae in the region reveals that all species have MD, but the proportion of fresh seeds that also has PD (thus, MPD) varies between species. A combination of factors, including PD, an inability to germinate at high summer temperatures, a relatively low temperature requirement for embryo growth and a lack of dispersal until autumn (in two non-natives), delays germination of both natives and non-natives until autumn, when conditions are favorable for both germination and seedling establishment. [ABSTRACT FROM AUTHOR]

A survey of seed production and germination potential in five populations of Antennaria howellii from eastern North America indicates that the species exhibits characteristics that would confer a high colonizing potential. Though water availability in previous germination trials of Antennaria species affected both seed production and germination, water availability did not directly affect the likelihood of a seed germinating or of a seedling surviving the current study. The likelihood of a seed germinating was more affected by embryo weight than either overall seed weight or seed coat weight. Although overall seed weight could be attributed to local environmental conditions during seed development, differences in allocation between seed coat weight and embryo weight during the developmental process would be attributed to genetic differences among the populations. Seedling survival is also believed to be genetically based though further studies are required to clarify this relationship. [ABSTRACT FROM AUTHOR]

In monocarpic plants, reproduction is closely associated with senescence, which is itself often correlated to specific environmental signals. Floerkea proserpinacoides (Limnanthaceae) is a spring ephemeral annual of the deciduous forests of eastern North America. The phenology of its growth and reproduction is considered to be a specific adaptation to the short period during which there is a high availability of resources (mostly light). Indeed, flowering starts 2–3 wk following seedling emergence soon after snowmelt and continues until tree canopy closure. However, fruit maturation is postponed for several weeks and is followed by the plant's death. The objective of this study is to determine if senescence in F. proserpinacoides is primarily cued by fruit maturation or deteriorating light conditions associated with tree canopy closure. Plants for which reproductive investment was manipulated by removing their carpets were grown either in full light or in the shade. Carpel-removal plants reached a higher biomass than control plants (46.0–57.5% higher), especially in full light. However, longevity was greater in carpel-removal plants, particularly in the shade (25.3–37.8% greater). These results thus suggest that fruit maturation, not deteriorating light conditions associated with canopy closure, is the primary cue of plant senescence in F. proserpinacoides. [ABSTRACT FROM AUTHOR]

Premise of the Study: Because seeds have essential functions in the life cycle of plants, even subtle changes in their characteristics may have important demographic consequences. In this study, we examined whether potential changes in seed characteristics as a result of polyploidy or postintroduction evolution may have contributed to the invasion of Centaurea stoebe (Asteraceae). This plant occurs as diploid and tetraploid cytotypes in its native range in Europe, whereas only tetraploids have been found and become invasive in North America. Specific comparisons among these three "geo-cytotypes" allow us to explore hypotheses of preadaptation resulting from polyploidy (European diploids vs. European tetraploids) and postintroduction evolution (European tetraploids vs. North American tetraploids)., Methods: Using seeds collected from plants of each geo-cytotype grown in a common maternal environment, we compared seed mass, morphology (achene and pappus size), dispersal potential (falling velocity, seed roughness), survival, germination, and seedling emergence in a combination of laboratory, greenhouse and field experiments., Key Results: We found increased seed mass in North American tetraploids compared with European tetraploids. Seed morphology and dispersal potential were largely similar in all geo-cytotypes. Seed survival under field conditions was higher in native and invasive tetraploids compared with diploids. Germination in the laboratory was similar among all geo-cytotypes, but seedling emergence under field conditions was higher in invasive tetraploids than in the other geo-cytotypes., Conclusions: Our findings suggest that a combination of preadaptation due to polyploidy (increased seed survival) and further postintroduction evolution in North American tetraploids (increased seed mass and seedling emergence) may have contributed to their invasion.