Seeds of many Amazonian floodplain forest trees are dispersed during high-water periods and spend weeks or months underwater until the flooding retreats. To assess whether prolonged seed submersion affects germination and early seedling development, an experiment was carried out in a greenhouse with seeds of Campsiandra laurifolia, Cassia leiandra, Crataeva tapia, Ilex inundata, Macrolobium acaciifolium, Nectandra amazonum, Pouteria glomerata, Psidium acutangulum, Sorocea duckei, and Vitex cymosa. They are common in this type of forest, differ in fruit type, number of seeds per fruit, fruit dimensions, and fresh mass and have fruits or seeds that can float. Seeds were collected in a Central Amazonian floodplain forest (flooded approximately 6 months year−1; water column of 5 m) and germinated in (1) irrigated soil or (2) underwater (water column of 5–7 cm) for 6 months. Seeds that germinated underwater were transferred to drained soil. Seeds of all species germinated underwater and developed seedlings when transferred to soil. However, submersion reduced the germination percentage of Psidium acutangulum, N. amazonum, P. glomerata and V. cymosa. Six species delayed germination in water. Ca. leiandra, I. inundata and P. glomerata did not differ in mean germination time in drained soil and underwater, whereas S. duckei seeds germinated faster underwater. Seed submersion negatively affected seedling growth (shoot length) of three species but did not affect seedling biomass. Timing of fruit dispersal, fruit buoyancy and high number of seeds per fruit can be critical for species with seeds that are not as able to cope with long-term submersion.

Desiccation tolerance (DT) of seeds, one of the plant's environmental adaptation mechanisms, allows them to survive as seeds in a quiescent state under extremely water-deficient conditions during the plant's life cycle, followed by seed germination and seedling establishment under favourable water conditions. The seed-DT is lost after radicle emergence; however, there is a developmental period called the ‘DT window’ during which the germinating seeds can re-induce DT following a cue from their ambient low water potential (i.e. mild osmotic stress). The DT re-inducibility within the DT window has been used as a model biosystem for understanding molecular mechanisms that activate/supress DT in a number of plant species. However, the characteristics of the DT window for species particularly important to the agroindustry are still largely fragmented. Here, physiological analyses were performed, aiming to elucidate the properties of the DT window in tomato, a model species for Solanaceae, holding a key strategic position for the seed industry and commercial use around the world. We revealed that (i) the DT window of tomato seeds is closed when the developing radicle reaches about 4 mm after germination, (ii) the most effective ambient water potential to re-induce DT into seeds is about −1.5 MPa and (iii) there is organ specificity of DT re-induction with hypocotyls, showing a longer DT window than cotyledons and roots in post-germination seeds.

The intraspecific variations of phenotypic traits in the early life stages, such as seed germination and seedling establishment, are important components affecting species adaptation and differentiation. As one of the most common ways in which seeds are maintained, dry storage usually affects these traits, by either increasing or decreasing variation among populations. However, little is known about how the interaction between dry storage and population variation of a species affects the performance and adaptability of early life-cycle traits. In this study, we conducted experiments with seeds from ten populations of Elymus nutans along an altitudinal gradient on the eastern Qinghai-Tibet Plateau. Fresh seeds and seeds stored dry for 6 months were used to quantify the temperature thresholds for germination, determine seedling emergence and survival in two common gardens and examine the correlation between these traits and environmental conditions of population provenance. Dry storage increased germination percentage, germination speed and seedling emergence, and decreased intraspecific variation in germination traits of seeds (reduced by 33.36, 52.05 and 20.45% for Tb, θT(50) and σθT, respectively). Dry storage had little effect on the intraspecific variation of seedling emergence and survival. In addition, the temperature threshold for germination cannot be used to predict seedling emergence and survival in either common garden, regardless of whether seeds were stored or not. These results indicated that it is feasible to use dry-stored seeds to evaluate and select suitable provenances in ecological restoration, and using dry-stored seeds in ecological restoration projects is expected to achieve better vegetation restoration results than fresh seeds. On the other hand, the status of seeds (fresh vs. dry stored) should be considered in an evaluation of the adaptive value of plant functional traits, especially in the early life stages, otherwise, inconsistent conclusions may be drawn.

One of the many ecosystem services provided by dung beetles is that of secondary seed dispersal. This paper experimentally evaluates the effectiveness of this service using the chimpanzee–dung beetle seed dispersal system in Taï National Park, Côte d’Ivoire. The study focussed on the germination rate and success of four species of seeds contained in the faeces of Pan troglodytes verus: Dacryodes klaineana (Pierre) H.J. Lam, Diospyros mannii Hiern, Pycnanthus angolensis (Welw.) Warb., and Uapaca guineensis Muell. Arg. For each species, 600 seeds, half from chimpanzee faeces and half from mother trees, were sown in nurseries at depths of 0, 2, 5, 10, and 15 cm (i.e. 120 seeds per depth; 60 from chimp and 60 from mother trees). After germination, only the seeds of Uapaca guineensis and Diospyros mannii sown at 2 and 5 cm had a >14% rate (between 14.2 and 30.8%) of germination and seedling establishment, regardless of seed origin. An increase in the depth of seed burial appears to negatively affect the probability of seedling emergence and establishment. This study shows that dung beetles have positive impacts on seed fate. However, for these plant species, the chimpanzee’s role is limited to that of primary seed dispersal.

Seed germination is regulated by temperature and can thus be quantified by thermal models, which can predict germination occurrence in biomes and plant survival under possible climate change scenarios. The objective of this study was to quantify germination based on thermal time and survival risk of 14 species in the Brazilian Cerrado in scenarios of future climate change. Seeds were collected in the warmer regions of the Cerrado, central Brazil, placed in incubators to germinate at constant temperatures of 10–50°C and evaluated every hour or day. Germination rate (R50), time for germination of 50% of the seeds (T50) and dent-like function were used to determine cardinal temperatures. Thermal time parameters were estimated using the Weibull model. Seed germination forecasts were made based on the International Panel on Climatic Change (IPCC) scenarios of global temperature increase. Base temperatures (Tb) ranged from 3.5 to 16.5°C, maximum temperatures (Tmax) from 35 to 50°C and optimum temperatures (To) from 30 to 35°C. Estimated thermal time varied from 484°C h to 400°C d at sub-optimal temperatures and 108°C h at 126°C d at supra-optimal temperatures. Species more distributed showed a higher thermal range of germination and are less susceptible to extinction in temperature increase scenarios. The results of this study suggest that seeds that are non-dormant after dispersal may be the most vulnerable in the future. In this context, our predictions contribute to understand how the survival of trees and shrubs will be affected in the Cerrado in the future.

A low-cost technique named ‘on-farm’ seed priming is increasingly being recognized as an effective approach to maximize crop establishment. It consists of anaerobically soaking seeds in water before sowing resulting in rapid and uniform germination, and enhanced seedling vigour. The extent of these benefits depends on the soaking time. The current determination of optimal soaking time by germination assays and mini-plot trials is resource-intensive, as it is species/genotype-specific. This study aimed to determine the potential of the seed respiration rate (an indicator of metabolic activity) and seed morphological changes during barley priming as predictors of the priming benefits and, thus, facilitate the determination of optimal soaking times. A series of germination tests revealed that the germination rate is mostly attributable to the rapid hydration of embryo tissues, as the highest gains in the germination rate occurred before the resumption of respiration. Germination uniformity, however, was not significantly improved until seeds were primed for at least 8 h, that is, after a first respiration burst was initiated. The maximum seedling vigour was attained when the priming was stopped just before the beginning of the differentiation of embryonic axes (20 h) after which vigour began to decrease (‘over-priming’). The onset of embryonic axis elongation was preceded by a second respiration burst, which can be used as a marker for priming optimization. Thus, monitoring of seed respiration provides a rapid and inexpensive alternative to the current practice. The method could be carried out by agricultural institutions to provide recommended optimal soaking times for the common barley varieties within a specific region.

The tropical dry deciduous forest (TDF) of the semi-arid region of Bajio in Mexico is dominated by successional communities, in which Lysiloma microphyllum is irregularly distributed, however the environmental factors influencing its establishment have been poorly studied. We conducted field experiments to isolate the impact of three factors on the early life-history stages of this tree. Over a 2-y period, we monitored the effects of (1) predation, (2) understorey light and (3) aspect on germination, seed-to-seedling transition (establishment) and seedling survival, and we found that open space negatively affected germination (14.9 ± 1.5% vs 96 ± 1.5% in shade; mean ± SE), while shade increased seedling establishment and survival (36.9 ± 8.2% vs 4.7 ± 3.8% in open sites). Predation decreased survival and was strongest in open conditions (0 vs 62.7 ± 9.4% in shaded exclosures). In contrast, aspect had little influence on germination and survival. The results suggest that shaded microsites positively affect the early life stages of L. microphyllum, a key process in TDF recovery.

Laboratory and field experiments were conducted to determine whether manipulation of radiation environment during the period of winter wheat establishment can be used to improve wheat yields in Italian ryegrass-infested fields. Percentage of total irradiation and ratio of red (R) light (around 660 ηm) to far-red (FR) light (around 730 ηm) reaching the soil surface were important factors in regulating Italian ryegrass germination, growth, and competitive interactions with wheat. Reducing total irradiation to about 10% of full sunlight while maintaining the normal R/FR ratio of about 1.0 reduced wheat grain production in the presence of Italian ryegrass by about 40% compared with weed-free wheat in full sunlight. Further, reducing total irradiation to 3% of full sunlight plus reducing the R/FR ratio to about 0.2 reduced wheat grain production competing with Italian ryegrass by about 35% compared with production in the control conditions. Wheat production of dry matter, spikes, and seeds in the presence of Italian ryegrass increased more than threefold under both shading treatments compared with production in full sunlight.

Cogongrass is a highly invasive perennial grass that threatens agriculture, forestry, and native plant assemblages in many regions of the world. Cogongrass is a prolific seed producer, but the ecological importance of seeds as a vector of invasion has not been adequately addressed. Propagule pressure plays a key role in many successful invasions and the relative importance of propagule pressure across environmental gradients is an area of research that is quickly becoming important in understanding invasion success. The present study was conducted to test the effects of varying propagule density upon the ability of cogongrass seedlings to grow and establish across experimentally manipulated light and soil gradients. Seedlings growing in high-nutrient soil performed the best regardless of the amount of available light, but overall biomass was always greatest in high-light environments. Cogongrass showed a very strong trend in biomass allocation, with seedlings in reduced light environments partitioning more biomass to aboveground tissue. The data provided no evidence that initial propagule density affected the growth and establishment of cogongrass seedlings, but growth and biomass production were positively correlated with final seedling density.

Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.

Tamarisk, a shrub or small tree native to Eurasia, was introduced to North America in the early 1800s and is now naturalized throughout many riparian areas of the southwestern United States, where extensive research has been conducted. It is a more recent invader to the northern Great Plains, and fewer studies have been conducted on tamarisk ecology and management in this area. The objectives of this research were to investigate the overwintering potential of tamarisk seeds in Montana and the relationship between hydrologic conditions and historic tamarisk establishment. Emergence of seedlings from seeds stored for different time periods at a range of temperatures was evaluated in a greenhouse study. Emergence rates declined after a 7-d storage period, but storage time had no effect on subsequent emergence rates, and seeds stored at −14 C and 5 C had greater emergence rates than those stored at 20 C and 35 C. Patterns in tamarisk establishment were assessed through age and hydrologic data collected from a reservoir (Fort Peck), a regulated river (Bighorn), and an unregulated river (Yellowstone) in Montana. These data indicated that tamarisk establishment at the reservoir was closely related to historic water levels, whereas establishment on rivers was not related to flow. However, data from the rivers indicated that recruitment differed between regulated and unregulated rivers, with the regulated river having less recruitment after the period of initial colonization than the unregulated river. Our results show that tamarisk seeds have the ability to overwinter in Montana and can establish under a range of flow conditions, indicating potential recolonization of sites after tamarisk removal.

Vigorous stands of perennial grasses can effectively provide long-term control of many invasive plants on rangelands. However, in degraded conditions, successful reestablishment of perennial grasses can be compromised by invasive annual grasses, such as downy brome. Propoxycarbazone-sodium is a selective herbicide currently labeled for downy brome control in small grains, but its potential use on rangelands is unknown. Studies were conducted from 2004 through 2008 at three rangeland sites in Colorado and Nebraska to evaluate downy brome control and perennial grass injury with propoxycarbazone-sodium and imazapic. Propoxycarbazone-sodium provided satisfactory downy brome control with grass injury equal to or less than imazapic when rainfall followed the fall application. A second set of studies was conducted from 2007 to 2008 at Lingle, WY, and Scottsbluff, NE, to determine the plant-back interval and postemergence application response of seven perennial grass species to propoxycarbazone-sodium and imazapic. Grass tolerance to both herbicides was good when applied 90 and 120 d before planting (DBP). However, grass injury increased as plant-back interval decreased. The greatest impact on plant biomass was observed from herbicide applied at planting or after planting. Crested and intermediate wheatgrass (Agropyron cristatum and Thinopyrum intermedium) biomass production was not affected when herbicides were applied 90 or 120 DBP. Western wheatgrass (Pascopyrum smithii) and Russian wildrye (Psathyrostachys juncea) showed tolerance to imazapic applied before planting. Smooth brome (Bromus inermis), sheep fescue (Festuca ovina), and orchardgrass (Dactylis glomerata) showed the least amount of tolerance to propoxycarbazone-sodium and imazapic.

Downy brome inhibits revegetation efforts following ecosystem disturbance. Imazapic is a commonly used herbicide for downy brome management, but more information is needed regarding effective application timing for restoration efforts. We wished to determine (1) if native species establishment exhibited a tradeoff between downy brome competition and injury from herbicide and (2) if this differed between pre- and postemergent applications of imazapic. We used a standard replacement series design and overlaid herbicide treatments. Nine weeks after planting, aboveground biomass was harvested and relative yield (RY) indices calculated. Both imazapic applications reduced downy brome biomass by 91% or more (P < 0.05). Imazapic caused drastic reductions in native biomass but less than what was caused by downy brome competition (P < 0.05). Natives were less injured by a pre- than postemergent application (P < 0.05). In situations where downy brome may impact restoration efforts, pre-emergent applications of imazapic at 70 g ai ha−1 (0.06 lb ai ac−1) may reduce downy brome with less negative impacts on newly-seeded native grasses than post-emergent applications. Ensuring sufficient proportions of native species seeds on restoration sites may reduce downy brome.

The herbicide imazapic is registered for use on rangelands and provides effective short-term control of certain invasive annual grasses. However, details about optimal application rates for downy brome and susceptibility of simultaneously seeded species are lacking. Thus, we investigated downy brome and seeded species responses to variable rates of imazapic (0, 35, 70, 105, and 140 g ai/ha) in two plant communities (salt desert shrub and Wyoming big sagebrush). In autumn 2003, plots were treated with imazapic and seeded with one of five perennial plant materials (Siberian wheatgrass [‘Vavilov’ and the experimental source Kazak]; prostrate kochia [‘Immigrant’ and the experimental source 6X], and Russian wildrye [‘Bozoisky II’]). Downy brome cover and seeded species establishment were evaluated in spring 2004 and 2006. Downy brome cover in 2004 decreased with increasing imazapic rate at both sites, although more so at the Wyoming big sagebrush site. In 2006, no difference in downy brome cover existed among herbicide rates at the Wyoming big sagebrush site. At the salt desert shrub site, the high rate of imazapic reduced downy brome cover by about 25% compared to untreated plots. ‘Vavilov’ Siberian wheatgrass was the only seeded species with lower downy brome cover in 2006 than 2004. Seeded species establishment increased with imazapic rate in the salt desert shrub community, but in the Wyoming big sagebrush community it peaked at intermediate rates and declined at higher rates. Variation in downy brome control and seeded species establishment might have been associated with differences in precipitation, soil organic matter, and disturbance history between sites. Overall, imazapic was useful for helping establish desirable perennial species, but unless downy brome is reduced below a critical threshold, favorable precipitation can return sites to pretreatment levels within two years.

Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 53,000 seeds/m2 when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.

We investigated the intraspecific variation in propagule mass within red mangrove (Rhizophora mangle) and its effect on carbon assimilation and seedling growth. Propagule sizes of red mangrove varied considerably at all three study sites along the south-eastern coast of Florida, with propagule fresh mass from 3.9 to 20.7 g for the scrub form and from 5.3 to 35.8 g for the tall form. Highly significant correlations were observed between propagule length and fresh weight at all three study sites and for two growth forms. The scrub form had significantly smaller propagules than the tall form. A greenhouse study showed that CO2 assimilation rates were not correlated with propagule mass, but total leaf area per plant increased significantly with increasing initial propagule mass in all three family lines of both the scrub and tall forms. Consequently, total carbon fixation rate by each seedling increased significantly with increasing propagule fresh weight in all cases, and the biomass increment significantly increased with increasing mass. Relative growth rate, however, was not correlated with propagule mass. The differences in leaf areas and biomass accumulation among seedlings from different sizes of propagules seem to have resulted from the differences in maternal reserve of hypocotyls. The considerable intraspecific variation in propagule size observed for red mangrove may have a significant effect on seedling growth and competitive ability.

Introduced either accidentally or purposefully for the creation of cultivated pastures, African grasses are becoming major invaders of ecological reserves and national parks of the Brazilian savannas, the cerrado. African grasses are particularly good colonizers of disturbed sites. Germination in the field and laboratory, and seedling establishment in the field were studied for the African species Andropogon gayanus Kunth var. bisquamulatus (Hochst.) Hack., and for the native species Echinolaena infltxa (Poiret) Chase and Schizachyrium tenerum Nees. The African species had a higher and faster germination rate than the two native species, but its seedling mortality was higher. The main cause of seedling mortality in the field was herbivory by ants. It is suggested that the invasion of cerrado by African grasses depends on the kind of management being practised.

Seeds of Dryobalanops aromatica and D. lanceolata (Dipterocarpaceae) were sown in gaps and understorey on a ridge and a valley in a Bornean rainforest. Germination rates were 92–100% regardless of site and species. On the ridge, the proportion of seedlings that opened primary leaves was larger in D. aromatica (19–30%) than in D. lanceolata (7–19%) due to higher root predation on D. lanceolata. In the valley, on the other hand, the proportion was larger in D. lanceolata (71–74%) than in D. aromatica (56%). After primary leaf production, seedlings of both species had higher survivorship in the gaps than in the understorey. Interactions between predators, soil conditions and light environment and their effects on seedling establishment are discussed.

Plant establishment was studied in a swamp forest in the lowland Atlantic rainforest in southeastern Brazil. A topographic gradient allowed a clear distinction between a periodically flooded and a permanently flooded site in the study area. Both sites were mosaics of patches: the former showed soil patches of varying sizes subject to distinct flooding durations (from 0 to 300 d per year) and in the latter, the tank bromeliads which densely occupied the understorey, trap litter and provided ‘suspended soil’ patches. In the periodically flooded site, the occurrence of regenerants (< 1.0 m tall) of the actively regenerating tree populations of Calophyllum brasiliense, Symphonia globulifera and Tovomitopsis paniculata (all Clusiaceae), originating from seed or vegetative organs, was recorded for 1 m2 quadrats placed in flooded (n = 82) and unflooded (n = 103) patches. In the permanently flooded site, dominated by Tabebuia cassinoides (Bignoniaceae), the presence of germinated seedlings was counted for 400 rosettes of the terrestrial tank bromeliad Nidularium procerum. The results showed that unflooded patches, including tank bromeliads, favoured seedling establishment. However, T. paniculata and T. cassinoides colonize patches where flooding lasts longer or is permanent mostly by reproducing vegetatively, while the seeds of C. brasiliense, which showed no form of vegetative reproduction, and S. globulifera are successful in colonizing flooded patches. Germination tests and field observations indicated that, for C. brasiliense, pre- and post-dispersal seed dormancy, a two-phase seed dispersal (water and bats) and seedling tolerance to flooding accounted for this pattern.