Seedling Emergence Studies Research Articles

Seed banks of rare Physostegia correllii (Lamiaceae) in Lady Bird Lake, Austin, Texas, U.S.A.

Rare species threatened by climate and land-use change may harbor seeds in soil seed banks for periods of time even if adults have disappeared from the site. Soil samples were collected from sites with current Phyostegia correllii populations and from sites with former populations in Lady Bird Lake (a reservoir of the Colorado River, Austin, Texas. A seedling emergence study was conducted under greenhouse conditions, and the presence/absence of seedling emergence was recorded for two years. Seeds germinated from the seed banks of all current and former colonies tested. The presence of seed banks in a historical site (Blunn Creek) of Physostegia correllii suggests that management to encourage the germination of seeds might help to encourage the establishment of populations of this species. The re-establishment of disturbance fugitives might be facilitated by removing overhanging ground vegetation or imposing water management regimes that mimic natural floodplain dynamics.

Seed fate in ant‐mediated dispersal: Seed dispersal effectiveness in the Ectatomma ruidum (Formicidae)—Zanthoxylum ekmanii (Rutaceae) system

AbstractPlants are often dispersal limited relying on passive or active agents to find suitable microhabitats for germination. Seeds of pioneer tree species, for example, require light gaps for growth but have short median dispersal distances and often do not provide a food reward to encourage animal dispersal. Zanthoxylum ekmanii seeds are frequently moved by ants but evaluating the effectiveness of ant‐mediated seed removal requires knowledge of the species moving the seeds, how far they are moved, and the deposition site. To assess the effectiveness of ants as seed dispersers of Z. ekmanii, we utilized the seed dispersal effectiveness framework. We tracked the movement of seeds from caches on the forest floor, revealing that foragers of Ectatomma ruidum moved 32.8% of seeds an average first distance of 99.8 cm with 68.3% of those seeds taken into a colony. The quality of deposition location was assessed using a seedling emergence study where freshly germinated seeds were buried at different depths. Seedlings were primarily able to emerge from the shallowest depths. Wax castings of E. ruidum colonies demonstrated that seeds brought into the colony were deposited in chambers that had larvae present and experienced more damage than seeds unhandled by ants. Foragers, however, did not have a strong enough bite force to rupture Z. ekmanii seeds likely because their muscle morphology is not structured to maximize force generation. Overall, E. ruidum may help fine tune deposition location, incorporating seeds into the topsoil, though few seeds will likely emerge if soil bioturbation is low.Abstract in Spanish is available with online material

Perennial plant patches are sinks for seeds in semi‐arid woodlands in varying condition

AbstractQuestionsUnderstanding the processes that influence resilience in semi‐arid woodland communities is of critical importance in landscapes where livestock grazing is the dominant land use and an important driver of site condition. Seed banks are a critical component of site resilience as their persistence can be crucial for recovering from disturbances. We predicted that site condition and landscape structural elements (perennial plant patches) would strongly influence the richness and density of the soil seed bank.LocationNew South Wales, Australia.MethodsWe conducted a seedling emergence study to investigate the germinable seed bank in semi‐arid woodland. Soil samples were collected from three woodland communities (Cypress pine, Black box, Red gum) from sites in three levels of site condition (poor, average, good) and from four patch types (tree, shrub, grass, open). Seed bank species were assigned to three plant trait groups based on: (a) origin; (b) lifespan; and (c) palatability. We used linear models to assess the effects of community, site condition and patch type on the richness and seed density of the germinable seed bank.ResultsSite condition did not affect the seed bank density or richness, except for a lower density of highly palatable species at poor‐condition sites. Across all communities the importance of patch type on the soil seed bank density and richness varied with plant traits. The seed bank of perennial plant patches had a greater density of perennial species, a lower density of low palatability plants, and a greater richness of native and perennial species than interspaces.ConclusionsOur results demonstrate that the germinable soil seed bank in semi‐arid woodlands can be relatively resilient to degradation. This suggests that disturbed sites where perennial patches remain, may still have the ability to recover, because these patches act as important seed reservoirs.

Recovery of terrestrial plants in vegetative vigor and seedling emergence tests from exposure to atrazine.

Ten species of terrestrial plants, including 6 dicotyledonous and 4 monocotyledonous species, were exposed to a direct overspray of atrazine according to US Environmental Protection Agency seedling emergence and vegetative vigor study guidelines and subsequently evaluated for potential recovery. For each species, no-observed-effect rate (NOER), 10% effect rate, 25% effect rate, and 50% effect rate values were calculated (where possible) for a variety of guideline-required endpoints (but focusing on growth rate) for both the standard experimental phase and a recovery phase; and the rates subsequently were compared. For the seedling emergence study, the standard experimental (designated test 1) and recovery (designated test 2) phases encompassed days 0 to 14 and days 14 to 28, respectively. Similarly, for the vegetative vigor study, test 1 and test 2 encompassed days 0 to 21 and days 21 to 42, respectively. Plants were exposed to atrazine at nominal application rates ranging from 1.1 g active ingredient (a.i.)/ha (0.0010 lb a.i./A) to 28,000 g a.i./ha (25 lb a.i./A), depending on the species; the 28,000 g a.i./ha rate is greater than 12 times the maximum application rate of 2250 g a.i./ha (2 lb a.i./A) registered on corn. For seedling emergence, only 2 of 10 species tested, cabbage and tomato, provided clear rate responses in the initial 14 d of exposure (test 1). Based on a comparison of x% effect rate (ERx) and NOER values for growth rates of shoot length and shoot dry weight for days 0 to 14 relative to days 14 to 28, recovery was apparent for cabbage shoot length growth rate and tomato shoot length and shoot dry weight growth rates. Test application rates selected for the remaining 8 species showed either a weak response that did not allow a clear assessment of recovery or no response at all. For the vegetative vigor study, 9 of the 10 species tested provided clear rate responses in test 1 (days 0-21); corn did not demonstrate any herbicidal response up to the highest rate tested, 28,000 g a.i./ha. Based on comparison of day 0 to 21 (test 1) relative to day 21 to 42 (test 2) ERx and NOER values for shoot length, average growth rates indicated that 8 of 9 species clearly demonstrated an increase in 2 or more metrics (cabbage did not demonstrate a response based on shoot length). Clear recovery was also indicated by an increase in ERx and/or NOER values from test 1 to test 2 for shoot dry weight average growth rates for 7 of the 9 species (corn did not show a response, and oat and soybean showed variable responses). Thus, in most species, where initial herbicidal effects were observed, the effects are largely ameliorated over time.

Seed banks as a source of vegetation regeneration to support the recovery of degraded rivers: A comparison of river reaches of varying condition

Anthropogenic disturbance has contributed to widespread geomorphic adjustment and the degradation of many rivers. This research compares for river reaches of varying condition, the potential for seed banks to support geomorphic river recovery through vegetation regeneration. Seven river reaches in the lower Hunter catchment of south-eastern Australia were assessed as being in poor, moderate, or good condition, based on geomorphic and ecological indicators. Seed bank composition within the channel and floodplain (determined in a seedling emergence study) was compared to standing vegetation. Seed bank potential for supporting geomorphic recovery was assessed by measuring native species richness, and the abundance of different plant growth forms, with consideration of the roles played by different growth forms in geomorphic adjustment. The exotic seed bank was considered a limiting factor for achieving ecological restoration goals, and similarly analysed. Seed bank native species richness was comparable between the reaches, and regardless of condition, early successional and pioneer herbs, sedges, grasses and rushes dominated the seed bank. The capacity for these growth forms to colonise and stabilise non-cohesive sediments and initiate biogeomorphic succession, indicates high potential for the seed banks of even highly degraded reaches to contribute to geomorphic river recovery. However, exotic propagules increasingly dominated the seed banks of moderate and poor condition reaches and reflected increasing encroachment by terrestrial exotic vegetation associated with riparian degradation. As the degree of riparian degradation increases, the resources required to control the regeneration of exotic species will similarly increase, if seed bank-based regeneration is to contribute to both geomorphic and ecological restoration goals.

Digging deep for diversity: riparian seed bank abundance and species richness in relation to burial depth

Summary Soil and sediment seed banks contribute to the diversity of riparian plant communities. In degraded river systems, seed banks represent an important regeneration niche that may contribute to restoration efforts through the establishment of vegetation. The vertical dimension of seed banks has been neglected in river research, despite its importance for the regeneration of vegetation after disturbances such as erosive floods. We sampled sediment at various depths within three geomorphological features: bars, benches and the floodplain, across four river reaches in the Wollombi subcatchment of New South Wales, Australia. A seedling emergence study was conducted to characterise the abundance and species richness of the germinable seed bank within these sediments. We hypothesised that the vertical distribution of seeds in bars and benches would show no clear pattern, but that bars would have lower propagule counts overall, due to their non‐cohesive sediment and potential for frequent reworking by low‐level flows. The floodplain seed bank, in contrast, would resemble that of terrestrial systems, with propagule abundance decreasing markedly with depth due to infrequent inundation and sediment reworking. In total, 9456 seedlings emerged, representing 131 different species (83 native and 47 exotic) from 47 families. Propagule abundance and species richness in bar and bench seed banks were highly variable with depth, with the greatest average propagule numbers found at 25–30 cm and 20–25 cm, respectively. In contrast, and as hypothesised, propagule abundance and species richness in the floodplain decreased significantly with depth. Propagule abundance was surprisingly variable in bars, with some displaying extremely high values and others containing no detectable seeds, although overall species richness was significantly lower than in benches and the floodplain. The vertical distribution of seeds in bars, benches and floodplains may be determined by the proportional influence of hydrochory (seed transport and deposition by water) during deposition events and seed losses, resulting from sediment reworking and erosion, set within the timescales over which they are formed and reworked. Bar seed banks are continually flushed by frequent inundation and reworking, especially at the surface, reducing seed deposition and burial. Abundant seed fall may be provided by local vegetation, however. Diverse seed banks in benches may form through alternating periods of hydrochoric seed deposition along with sediment, augmented during periods of exposure when propagules from the extant vegetation accumulate. Decreases in germinable propagule abundance and species richness with depth in the floodplain may reflect much slower rates of vertical accretion and seed losses due to mortality over time. Finally, we present some implications for the management of riparian vegetation and applications for river restoration.

The potential for endozoochorous dispersal of temperate fen plant species by free‐roaming horses

AbstractQuestionsCan free‐roaming Konik horses digest and subsequently disperse seeds of plant species growing in a temperate fen environment? Which species have the potential to be dispersed internally (endozoochory), and do they share common plant and seed traits? How could potential dispersal via endozoochory impact upon grazing management and the natural recolonization of wetland vegetation at a landscape scale?LocationWicken Fen NNR, Cambridge, UK.MethodsTwelve dung samples were collected for one calendar year (Jun 2009–May 2010) from a free‐roaming herd of Konik horses grazing vegetation at Wicken Fen NNR. Germinable seed content of the dung was determined by means of a seedling emergence study. Species presence and estimated cover/abundance were recorded for the grazed (background) vegetation in spring and summer 2009.ResultsAlmost one‐third of all species present in the background vegetation were also identified in the dung samples. There was an equal split between graminoids and forbs, but substantially more graminoid germinable seeds. Species were dispersed year‐round, with the number of species peaking in Sep and again in Dec. Of the 13 traits measured, there were significant differences between dung and background vegetation for six traits. Mean values for seed release heights (minimum and maximum) and dispersule weight were significantly lower in species found in the dung, whilst dung species had significantly greater numbers of seeds per shoot, inferred Ellenberg nitrogen values and seed bank persistence.ConclusionYear‐round free‐roaming grazing has the potential to make a considerable contribution to the long‐range dispersal of species growing in temperate fen habitats, and is likely to complement alternative dispersal strategies. However, germination and establishment of species post‐dispersal fate will be governed by a wide range of environmental conditions.

Seasonal rhythms of seed rain and seedling emergence in two tropical rain forests in southern Brazil

Seasonal tropical forests show rhythms in reproductive activities due to water stress during dry seasons. If both seed dispersal and seed germination occur in the best environmental conditions, mortality will be minimised and forest regeneration will occur. To evaluate whether non-seasonal forests also show rhythms, for 2 years we studied the seed rain and seedling emergence in two sandy coastal forests (flooded and unflooded) in southern Brazil. In each forest, one 100 x 30-m grid was marked and inside it 30 stations comprising two seed traps (0.5 x 0.5 m each) and one plot (2 x 2 m) were established for monthly monitoring of seed rain and a seedling emergence study, respectively. Despite differences in soil moisture and incident light on the understorey, flooded and unflooded forests had similar dispersal and germination patterns. Seed rain was seasonal and bimodal (peaks at the end of the wetter season and in the less wet season) and seedling emergence was seasonal and unimodal (peaking in the wetter season). Approximately 57% of the total species number had seedling emergence 4 or more months after dispersal. Therefore, both seed dormancy and the timing of seed dispersal drive the rhythm of seedling emergence in these forests. The peak in germination occurs in the wetter season, when soil fertility is higher and other phenological events also occur. The strong seasonality in these plant communities, even in this weakly seasonal climate, suggests that factors such as daylength, plant sensitivity to small changes in the environment (e.g. water and nutrient availability) or phylogenetic constraints cause seasonal rhythms in the plants.

Toxicity bioassays for ecological risk assessment in arid and semiarid ecosystems.

Substantial tracts of land in the southwestern and western U.S. are undergoing or will require ERA. Toxicity bioassays employed in baseline ERAs are, for the most part. representative of mesic systems, and highly standardized test species (e.g., lettuce, earthworm) are generally not relevant to arid system toxicity testing. Conversely, relevant test species are often poorly characterized with regard to toxicant sensitivity and culture conditions. The applicability of toxicity bioassays to ecological risk assessment in arid and semiarid ecosystems was reviewed for bacteria and fungi, plants, terrestrial invertebrates, and terrestrial vertebrates. Bacteria and fungi are critical to soil processes, and understanding their ecology is important to understanding the ecological relevance of bioassays targeting either group. Terrestrial bacteria require a water film around soil particles to be active, while soil fungi can remain active in extremely dry soils. It is therefore expected that fungi will be of greater importance to arid and semiarid systems (Whitford 1989). If microbial processes are to be measured in soils of arid environments, it is recommended that bioassays target fungi. Regardless of the taxa studied, problems are associated with the standardization and interpretability of microbial tests, and regulatory acceptance may hinder widespread incorporation of microbial toxicity bioassays in arid system risk assessments. Plant toxicity bioassays are gaining recognition as sensitive indicators of soil conditions because they can provide a cost-effective and relatively rapid assessment of soil quality for both pre- and postremediation efforts. Phytotoxicity evaluations commonly target germination because environmental stressors have the greatest potential for exerting adverse effects in the early stages of growth. In arid systems, seeds respond rapidly to precipitation events, and it is typically after germination has occurred that plants must cope with water stress. Consequently, seedling emergence studies should be conducted under nonlimiting moisture conditions characteristic of mesic plant testing. Further ecological realism can be incorporated into advanced growth stages by creating moisture conditions representative of the arid system study site. Although the choices of suitable plant species for assessing mesic system soils are numerous, the choices for arid system soils are limited. Guidance is provided for evaluating plant species with regard to their suitability for serving as representative arid system flora. Terrestrial invertebrates can survive and flourish in extremely dry conditions. They play key roles in ecosystem functioning in arid environments. Perhaps the biggest drawback to using terrestrial invertebrates for toxicity bioassays involves uncertainties associated with choosing appropriate test species. Several examples of standard species exist for mesic soils (e.g., the earthworm Eisenia foetida and the collembolan Folsomia candida), whereas no analogous organisms are available for testing arid and semiarid soils. The aid of an expert taxonomist and some basic research are prerequisite to using ecologically relevant invertebrates. The use of birds for ecotoxicity testing in arid and semiarid environments is not recommended. On the other hand, mammals, especially rodents, are well represented in arid ecosystems. Much of the ecotoxicity testing performed on rodents is generally applicable to arid-adapted species; few demonstrations of rodent ecotoxicity testing for dry environments exist. Relative to other organisms discussed, such as soil invertebrates, the use of mammals in toxicity bioassays faces several obstacles. Terrestrial plants and soil invertebrates appear to be the most appropriate and feasible organisms for ecotoxicity testing in arid and semiarid environments. Potentially relevant test species for arid system testing are often poorly characterized with regard to toxicant sensitivity and culture conditions. Table 6 presents examples of standard and nonstandard species with these considerations in mind, and the best estimate of regulatory acceptance for each of the organisms is suggested. If currently accepted bioassays are not appropriate for evaluating risks in arid and semiarid ecosystems, their use in conducting ERAs in such environments may result in inadequate expenditure of time and money to develop data that accurately characterize risks. The inapplicability of this technical tool will thus hamper the risk management decision-making process and result in flawed decisions.

Solution pH and Papaya Seed Germination and Seedling Emergence

Two studies were conducted to determine the influence of pH on papaya seed germination and seedling emergence. The germination test was conducted with `Waimanalo' and `Tainung 1' seeds, using a double layer of filter paper disks in plastic petri dishes placed within a growth chamber. Each dish received 40 seeds, and germination was defined as when the radicle was visible. Disks were wetted daily with nutrient solution adjusted to pH of 3, 4, 5, 6, 7, 8, or 9. Germination began on day 5, and the study was terminated on day 23. Solution pH did not influence germination rate or ultimate germination percentage. `Waimanalo' exhibited 58% germination and `Tainung 1' exhibited 64% germination in this test. The seedling emergence study was conducted with `Waimanalo' seeds using sand culture within a growth chamber. Thirty seeds were planted in 10-cm containers, and the sand was irrigated daily with the solutions from the first study. Emergence was defined as when the hypocotyl hook was visible above the sand. Emergence began on day 10, and the study was terminated on day 30. Solution pH did not influence seedling emergence, and mean emergence was 69% in this study. The results indicate that the seed germination and seedling emergence stages of papaya seedling growth are adapted to a wide range of substrate pH.

Relationships between position on the parent plant and germination characteristics of seeds of parsley (Petroselinium crispum Nym.)

The percentage germination of seeds of parsley cv. Imperial Curled was higher in the light than in the dark, the high temperature limits for germination being 30 and 28°C for light and dark respectively. At the higher temperatures, the germination rate was slower in the dark. At 30°C, treatment with a gibberellin A4/7 mixture at 2 × 10−4 M partially alleviated the inhibiting effect of darkness on the germination percentage. Pre-incubation of parsley seeds at 35°C in the dark for 30 h increased the rate, but decreased the percentage, of germination of seeds incubated at 15°C in the light. Germination and seedling emergence studies were made on seed harvested from four different umbel positions. Although heavier seeds were produced from primary umbels than from other umbel orders, they were less viable as measured by seedling emergence in the glasshouse. The rate of emergence was decreased with increasing umbel order i.e. with later seed development: this was reflected in subsequent seedling weights, with seedlings from quarternary umbel seeds being about half the weight of those from primary umbel seeds. The upper temperature limit for dark germination was only slightly affected by umbel order, with quarternary umbel seeds being the most thermo-inhibited.

Phytotoxicity of a Chemical Weapon Simulant, Triethyl Phosphate

AbstractTriethyl phosphate (TEP) is proposed to be used as a chemical weapon simulant in missile testing at White Sands Missile Range in New Mexico. Studies were conducted to determine the phytotoxicity of TEP using sorghum‐sudangrass [Sorghum bicolor (L.) Moench], tomato (Lycopersicon lycopersicum Mill.), and glossy privet (Ligustrum lucidum Ait.) as test plants grown on Mimbres‐Glendale (MG) and Nickel‐Tencee (NT) soil associations obtained from White Sands Missile Range. Triethyl phosphate was applied to soil and foliar tissue at rates of 0, 4, 400, and 40 000 mg m−2 soil surface. Triethyl phosphate also was applied in a thickened formulation, as used in missile testing, at an application rate of 40 000 mg m−2 on both soil and foliar tissue. Toxicity was only observed at the highest application rate with pure and thickened TEP. The method of TEP application to soil or foliar tissue did not affect the dry matter weight of tomato or glossy privet growth. There were inconsistent effects of TEP application method on sorghum‐sudangrass dry matter weight, depending on soil type. Triethyl phosphate affected the test plants differently with resistance to TEP toxicity increasing in the order: tomato ≃ sorghum‐sudangrass on NT soil < sorghum‐sudangrass on MG soil < glossy privet. A seedling emergence study using sorghum‐sudangrass, tomato, and cucumber (Cucumis sativus L.) resulted in similar conclusions from the whole plant studies showing TEP toxicity only at the highest application rate of 40 000 mg m−2. There were indications from sorghum‐sudangrass growth and cucumber seedling emergence that TEP toxicity may be less on soil having a higher clay and organic matter content, which may have been due to TEP sorption in soil and decreased TEP bioavailability to plant roots. The absence of phytotoxicity symptoms indicated plants would not be harmed if application rates were at or below 400 mg TEP m−2.

Seed survival and patterns of seedling emergence studies of Rottboellia cochinchinensis (Lour.) W.D. Clayton in cultivated soils

Summary:The longevity of buried Rottboellia cochinchinensis (Lour.) W.D. Clayton seed represents a major survival mechanism for the weed, enabling the persistence of a continuing source of weed seeds in crop land. The pattern of seed persistence and depletion of R. cochinchinensis in cultivated maize soils was investigated by means of (1) studies on the effect of depth and duration of burial on the viability of the weed seeds, (2) quantitative estimation of the seed population and viability in cultivated fields, and (3) the periodicity of emergence and effects of cultivation on seed germination both in the field and in the greenhouse. The results indicated that the mode of persistence was innate (8.5%) and enforced (35%) dormancy after 1 year of burial, and that the persistency component of the seed population on cultivated soils ranged from 40.60%. The weed was able to remain viable at depths of 45 cm, indicating an excellent mechanism of escaping the effects of most soil‐applied herbicides, and it was shown that tillage increases the depletion rate of the weed seed reserve by 32% per year.

Seed dormancy and seedling emergence studies in Avena fatua L

Summary:Studies were made of seedling emergence of three phenotypes of Avena fatua L. with dif ferent coloured lemmas (fA, fB, fC) originally collected from one site. Each phenotype was grown under the same conditions in 1975 and the resulting seed buried 25 mm deep in soil im mediately after collection. The soil was either left uncultivated (all phenotypes) or cultivated monthly (phenotype fA only). Seedling emergence was assessed weekly and the number of remaining viable seeds was determined at the end of three years. Seeds of different lines of A. fatua (fA phenotypes) obtained from separate locations were grown under the same conditions in 1983, buried and seedling emergence moni tored for 85 months.Without cultivation, overall emergence (mean of three phenotypes) in successive autumns and springs was 9%, 18%, 9%, 33%, < 1%, 14% and <1%. A further 3% of viable seeds were recovered at the end of the experiment. Periodicity of emergence was the same for all phenotypes. Actual numbers of seedlings emerging in each of the periods varied between phenotypes. Total emergence of seed from the inner zone of panicles was significantly less than that from the outer zone, although there was little difference between the two zones in each of the natural emergence periods. Cultivation increased emergence, particularly from secondary seed in the first spring after burial, but did not changes its periodicity. By the second spring seed numbers had declined, and seedling counts were similar from cultivated and non‐cultivated soil. No viable seed remained in the cultivated soil after three years. Emergence from the two lines of fA was very different. Seedling emergence occurred after hot dry con ditions, or in warm periods immediately after periods of chilling, particularly those below 4°C.

The dynamics of a succulent karoo vegetation

Strong inference techniques were used in a preliminary study of the structure and dynamics of the vegetation the Prince Albert region of the Great Karoo, South Africa. Seedling emergence studies indicate that open areas in the interstices of the existent vegetation are colonized by mound-building species of the Mesembryanthemaceae. Later, these species serve as sites of establishment for seedlings of several species of woody shrubs. Eventually, the woody shrubs replace the mound-building mesems through interspecific competition. The woody shrubs persist in the community until they reach senescence and die or are removed through overgrazing. Superimposed on this dynamic pattern is a further temporal pattern involving a combination of disturbance and subsequent soil changes. Much of this effect is caused by fossorial animals, which are associated with large circular (10–20 m diameter) mounds. Burrowing by these animals changes the soil characteristics and establishes an additional sequence of vegetation succession in which the mounds serve as refuges from which non-palatable species, such as Pteronia pallens, can invade the rangeland. Later, as the mounds are abandoned and disturbance effects cease, more palatable species, such as P. empetrifolia, will replace P. pallens, overcoming finally the effects of the adjacent mounds on the surrounding vegetation.

SMP: Solid matrix priming of seeds

The purpose of these studies was to develop the technique of solid matrix priming (SMP) and then evaluate its ability to improve seedling establishment of small-seeded vegetable crops under either sub- or supra-optimal temperatures. SMP is a process in which seeds are mixed with a solid material and water in known proportions. This mixture allows the seeds to imbibe and attain a threshold moisture content, but prevents radicle emergence. The solid material used in these studies was a ground Leonardite Shale, “Agro-Lig”, which was a friable material and had a high water-holding capacity. The water potential of the Agro-Lig was determined after SMP and the osmotic potential accounted for >97% of the total water potential, which was attributed to solutes from the Agro-Lig and seed leachates. The matric potential contributed <1.5% of the total water potential. Seedling emergence studies were conducted on primed tomato ( Lycopersicon esculentum), carrot ( Daucus carota) and onion ( Allium cepa) seeds sown in an artificial soil media in flats maintained at 20 10° C with a 12-h photoperiod. The priming treatments consisted of polyethylene glycol 8000, inorganic salts and SMP. All priming treatments decreased the time for 50% seedling emergence and increased the plant dry weight compared with the non-treated controls for each crop. The seedling emergence characteristics of SMP-sown seeds were superior to, or equal to, conventional solution priming treatments. In addition, lettuce ( Lactuca sativa) seeds were primed with solutions or SMP and later germinated at 35°C in the dark. All priming treatments overcame thermodormancy.

Relationship between Position on the Parent Plant and Dormancy Characteristics of Seeds of Three Cultivars of Celery (Apium graveolens)

AbstractGermination and seedling emergence studies were made on seeds harvested from four different umbel positions of three cultivars of celery (Apium graveolens L.). Although heavier seeds were produced from primary umbels than from other umbels, these were less viable as measured by the germination percentage at I8°C in the light. However, germination of viable seeds from quaternary umbels was lower than that of seeds from primary umbels at 18°C in the dark when incubated with GA4, (2 × 10 −4M) and seed from secondary and tertiary umbels tended to be intermediate in response. All viable seeds germinated when N6‐benzyladenine (10−2M) was used in combination with GA4. Seeds from quaternary umbels of two of the cultivars had a lower high‐temperature limit for germination in the dark than did seeds from other umbels. In glasshouse experiments the emergence of viable ‘quaternary’ seeds of these cultivars was higher than that of ‘primary’ seeds. Under these conditions the time to 50% of the final emergence as determined after 42 days was similar for seeds from all umbel positions within each cultivar. In two varieties seedling weights were greater from seeds of primary as compared to quaternary umbels, and in general, the largest seedlings arose from the heaviest seeds and the smallest from the lightest seeds in all three cultivars.

Germination and Establishment of Salsola in Relation to Seedbed Environment. II. Seed Distribution, Germination, and Seedling Growth of Salsola and Microenvironmental Monitoring of the Seedbed1

AbstractThe purpose of this study was to ascertain when and under what conditions seed germination and seedling growth of Russian thistle (Salsola kali var. tenuifolia Tausch.) occurs in the field. Continuous monitoring of temperature and moisture parameters of the seedbed microenvironment was conducted during critical periods of germination and seedling growth. Seedling emergence was sampled weekly concurrent with seedbed monitoring. Seed dispersal investigations and seedling emergence studies in relation to burial depth were also carried on. Seed germination and seedling emergence of Russian thistle commenced in midwinter and early spring with below 0 C night temperatures alternating with 10‐ to 19‐C day temperatures. Optimum emergence occurred in March, with temperatures of 0 to 5 C alternating with those of 12 to 25 C. Afterripening requirements curtailed germination of 1970 seeds, compared with those of 1968, at early dates, but by March no depression occurred. Soil moisture potentials less than —15 bars reduced seedling emergence and increased mortality. Low relative humidity at the soil surface during the day curtailed establishment of plants from surface seeds. Seed burial, litter cover, and variable microtopography were all conducive to establishment of Russian thistle.