Buried Seeds Research Articles

Soil seed banks of woodland, heathland, grassland, mire and montane communities, Cairngorm Mountains, Scotland

The size and species composition of soil seed banks were assessed at 111 altitudinally diverse sites in the Cairngorm Mountains. Mean densities of germinable seeds varied from 83 000 m−2 in Scots pine (Pinus sylvestris L.) woodland at 230–490 m to 200 m−2 in moss (Racomitrium lanuginosum (Hedw.) Brid.) heath at 1000–1120 m. Seed banks were dominated by Calluna vulgaris (L.) Hull, not only wherever it was prominent in the vegetation, but also at some sites with less than 5% cover of parent plants in the ground vegetation. Many species conspicuous in the vegetation were under-represented in or absent from the seed bank and surface vegetation generally was more species rich than was the underlying seed bank, especially in high montane communities. Multiple regression was used to examine the relationship between the density of buried Calluna seeds and the abundance of parent plants in the vegetation, site altitude and the organic matter content of the soil. The model fitted to woodland communities accounted for 95% of the variation in seed density. The heathland model was less predictive but still explained 52% of the variation in seed bank size. In mire communities there was no relationship, collective or individual, between buried seed density and the measured environmental variables, possibly due to variations in the duration and frequency of waterlogging at these sites. The potential role of seed banks for initiating the recolonisation of disturbed ground is discussed. Densities of buried seeds at most Calluna-dominant sites were probably sufficient to generate successful recolonisation but the prospects for recovery were poor at other sites, particularly in graminaceous communities at 800 m or higher.

Soil Texture Involvement in Germination and Emergence of Buried Weed Seeds

Laboratory trials were performed to test germination and emergence characteristics of jimsonweed (Datura stramonium L.) seeds buried in 10 different soil types (with or without the control of soil external gas environment) with pronounced sandy or clay texture. The aim of the experiments was to investigate if the physical characteristics of the soils were involved in both buried‐seed ecology and emergence dynamics. Germination inhibition due to burial depth was found to be directly proportional to clay content and inversely proportional to sand content. Measurement of soil air permeability showed a close relation between gas exchange potential and depth‐mediated germination inhibition. Comparative analysis of the germination response in nonsoil and soil hypoxia suggested that inhibition is caused not so much by hypoxia per se as by the presence of fermenting metabolites that could not easily be eliminated due to decreased respiratory activity. In situ inspection of buried seeds also revealed that the increased time required for emergence in clay soils is primarily due to increased mean germination time rather than greater difficulty in seedling penetration upwards through the soil before emergence. Partial removal of germination inhibition of buried seeds was facilitated by elevated air oxygen availability but only with sandy soils, showing that inhibition is closely linked to soil ability to induce gas exchange with external air. At excessive burial depth (12 cm), seeds exhibited induction of secondary dormancy independent of soil texture. In conclusion, these experiments demonstrated that soil physical properties have a strong effect on buried‐seed ecology and consequently on seedbank dynamics in the agroecosystem.

Soil Texture Involvement in Germination and Emergence of Buried Weed Seeds

Laboratory trials were performed to test germination and emergence characteristics of jimsonweed (Datura stramonium L.) seeds buried in 10 different soil types (with or without the control of soil external gas environment) with pronounced sandy or clay texture. The aim of the experiments was to investigate if the physical characteristics of the soils were involved in both buried-seed ecology and emergence dynamics. Germination inhibition due to burial depth was found to be directly proportional to clay content and inversely proportional to sand content. Measurement of soil air permeability showed a close relation between gas exchange potential and depth-mediated germination inhibition. Comparative analysis of the germination response in nonsoil and soil hypoxia suggested that inhibition is caused not so much by hypoxia per se as by the presence of fermenting metabolites that could not easily be eliminated due to decreased respiratory activity. In situ inspection of buried seeds also revealed that the increased time required for emergence in clay soils is primarily due to increased mean germination time rather than greater difficulty in seedling penetration upwards through the soil before emergence. Partial removal of germination inhibition of buried seeds was facilitated by elevated air oxygen availability but only with sandy soils, showing that inhibition is closely linked to soil ability to induce gas exchange with external air. At excessive burial depth (12 cm), seeds exhibited induction of secondary dormancy independent of soil texture. In conclusion, these experiments demonstrated that soil physical properties have a strong effect on buried-seed ecology and consequently on seedbank dynamics in the agroecosystem.

Seasonal variation of the soil seed bank of grasses in central Argentina as related to grazing and shrub cover

The objectives of this research were to (a) study seasonal variation of the seed bank of grasses in two areas with different grazing history, (b) analyse the effect of the presence of shrubs on the seed bank and (c) study seed viability and dormancy in buried seeds of Piptochaetium napostaense and Stipa tenuis. The seed density of grasses was in general low and showed seasonal variation. Most of the grasses showed maximum seed density in December when seed dispersal occurs. Shrub cover did not show a marked influence in seed accumulation. The relatively high number of damaged seeds suggests that predation may be an important factor in seed bank dynamics in the Caldenal. Seeds of dominant perennial forage grasses showed dormancy that could explain, at least in part, persistence of these species in spite of periodical disturbance.

Sexual reproduction in SE Asian seagrasses: the absence of a seed bank in Thalassia hemprichii

We report the absence of a persistent seed bank in Thalassia hemprichii in NW Philippine seagrass beds. The survival of buried seeds was assessed experimentally since such a capacity is a prerequisite for the formation of seed bank. We found a rapid germination of non-dormant seeds and development into seedlings. Such seedlings could not survive under buried conditions (5 and 10 cm) for longer than a week.

Effect of rodents on acorn dispersal and survival of the Liaodong oak ( Quercus liaotungensis Koidz.)

We used a new method of labeling seeds with small pieces of coded tin-tags to investigate the effect of rodent on the seed fate of Liaodong oak ( Quercus liaotungensis) in a mountainous area (40°00′N, 115°30′E) of Beijing, China. In the fall of 1999 and 2000, a total of 1994 and 660 acorns were released and then seed loss was checked. Both sides of the 50 m wide transect were extensively checked to locate the tagged seeds or their fragments. The results indicated that Apodemus speciosus, Rattus confucianus and A. agrarius were potential Liaodong oak acorn predators. Nearly all acorns were consumed by small rodents within 10 days after acorn placement, demonstrating that seed predation was very heavy and that rodent predation contributes to the poor seed regeneration of the oak. The dispersal distances of most seeds were within 20 m. The dispersal distance of the buried seeds was the longest and it was in favor of seed survival and seedling recruitment. Rodents preferred to eat tagged seeds under dense shrub. This is mostly related to predation risk in different micro-environments. Rodents tended to bury the tagged seeds under dense shrub. This burial place of rodent does not favor the seedling recruitment of the oak. The rodents preferred to move seeds to the horizontal and down directions of a slope and this tendency would save energy for rodents. The seeding regeneration rate of tagged acorns were very low in 2 years. Rodent predation is the causative factor of low regeneration of Liaodong oak in the study region.

Dung beetles in a Central Amazonian rainforest and their ecological role as secondary seed dispersers

Abstract1. The role of several factors that affect the composition of the dung beetle assemblages in an Amazonian rainforest was quantified, together with the effect of these factors on the role that dung beetles play as secondary seed dispersers.2. A total of 61 dung beetle species was captured during 3360 h of trapping. During nocturnal trapping periods, more dung beetles, of larger mean size, and more species were captured per trap than during diurnal trapping periods.3. During the rainy season, more dung beetle species were captured per trap than during the dry season, but the number of individuals and their mean size did not vary between seasons.4. Bait size had a significant effect on the mean number of beetles and mean number of species but not on mean beetle size. As bait size increased from 5, 10, 25, to 50 g, more beetles and more species were captured per trap.5. Between 6 and 73% of plastic beads, used as seed mimics, were buried by dung beetles at depths that ranged from 0.5 to 7 cm. Both the proportion of beads buried and burial depth decreased with increasing bead size, and increased with increasing amounts of dung surrounding each bead (5, 10, and 25 g).6. The proportion of buried seeds for three species varying in size between 5 and 27 mm, increased with increasing dung beetle size, using beetles of seven sizes, varying between 10 and 25 mm.7. Seeds surrounded by dung were buried more often and more deeply when placed on the forest floor during the late afternoon than when placed during the early morning. Seeds were also buried more often when placed on the forest floor during the rainy season than when placed during the dry season, but season had no effect on burial depth.8. Forests in Central Amazonia hold a rich dung beetle community that plays an active role in secondary seed dispersal, and consequently in plant regeneration. The interaction between seeds and beetles is complex because it is affected by many factors.

Germination characteristics and emergence time of annual Bromus species of differing weediness in Sweden

The germination ecology of four annual Bromus species, which differ in weediness on arable land in southern Sweden, was investigated. The most problematic species is Bromus sterilis, while Bromus hordeaceus frequently occurs on arable land. In contrast, Bromus arvensis is a rare weed, and Bromus tectorum is found infrequently in fields despite being a widespread ruderal species. Five experiments were conducted to identify germination characteristics that could explain differences in habitat and abundance: (i) intraspecific variation in dormancy level; (ii) germination response to different light conditions; (iii) light and temperature interactions at germination; (iv) timing of seedling emergence; and (v) seed persistence in soil. Bromus sterilis and B. tectorum behaved similarly in all tests. For both these species, there were large differences in dormancy level among populations and strong inhibition of germination by light. In addition, emergence from seeds sown on the soil surface was both delayed and reduced compared with buried seeds. In contrast, B. hordeaceus and B. arvensis showed generally weak dormancy, and germination was only slightly inhibited by light. It was concluded that germination characteristics alone do not explain the differences in weediness between these four species.

Altitudinal gradients in seed dynamics of Calluna vulgaris in eastern Scotland

Abstract. Relationships between seed deposition, size of soil seed banks and some of the environmental factors affecting them were assessed for Calluna vulgaris throughout its altitudinal range (150–960 m a.s.l.) in eastern Scotland. Seed rain was assessed using pitfall traps, collected every 5–10 wk for 3 yr; germinability was determined by laboratory incubation. Seed bank size was estimated, once only, by counting seedlings emerging from soil cores kept for 50 wk in a glasshouse.Seed deposition varied annually, was related to parent plant cover but always declined with altitude, falling sharply above 600 m a.s.l. Seed bank size was more closely correlated with the proportion of organic matter in the soil than with the amount of seed rain. Seed bank sizes declined gradually with altitude but did not differ significantly between four altitudinal zones. The mean density of buried seeds was less than half the mean annual seed rain at sites below 300 m a.s.l. but was over 200 × greater than annual seed rain above 800 m, suggesting that seeds buried at high altitudes remain viable for much longer than those at lower altitudes.

The comparative germination ecology of nine Rumex species

The germination requirements, dormancy cycle and longevity of nine Rumexspecies were studied in field conditions and laboratory experiments to show theadaptations of the related species to their specific habitat. Within one genus,rather striking differences were observed in germination ecology. However, theclosely related species, R. acetosa and R.scutatus, are very similar: they fruit in early summer; theirseeds can germinate immediately after dispersal, and they are nondormant andshort-lived. R. acetosella also has fruits insummer, but the seeds do not germinate the first season after dispersal. Theyare long-lived, but buried seeds do not show a dormancy cycle; they mightgerminate in different seasons after exposure to light. Seeds of four species (R. conglomeratus,R. maritimus, R. sanguineus andR. crispus) are long-lived and undergo aseasonal dormancy cycle, with a low level of dormancy in winter and early springand a deep dormancy in summer as was already known for R.obtusifolius. These seeds are shed in the autumn, and they germinatemainly in the spring in consecutive years. R. maritimusalso germinates in summer and autumn on drying muddy soils. The seeds of R. hydrolapathum only germinate onwaterlogged soils, which explains its growth at the edge of streams and ponds.Its seeds are rather short-lived. The seeds of the species on very wetplaces require a higher temperature for germination.

Germination, emergence, growth, ecotypes and control of Carex appressa R. Br. (tussock sedge)

Germination of seeds of Carex appressa R.Br. (tussock sedge) collected in 1989 and 1990 from Bigga, Boorowa and Kerrs Creek, New South Wales, Australia, stored in a laboratory and germinated annually in 45-day tests, declined from an initial 75–90% in year 1 to 0.5–14% in years 10 and 11. The germination of seeds collected from Bigga and Boorowa in 1991 declined from 90–91% in year 1 to 12–61% in year 9. This decline was best described by generalised logistic curves (Bigga) and exponential curves (Boorowa). Most seeds that failed to germinate were shown to be non-viable by the tetrazolium test. Rate of germination declined with seed age, so that days for 50% of final germination percentage increased from 8 days for 1 year-old seeds to >40 days for 11-year-old seeds. Of 8–11-year-old seeds that germinated between days 45 and 140, 62–70% had deformed seedlings. Germination of seeds buried in the soil for 0.5–2.7 years was lower than that of the same seed stored in the laboratory. Germination of seeds buried at 5 mm (19%) was lower than that of the same seeds buried at 40 mm (50%). Almost all the decline in germination occurred in the first 6 months of burial. Increased depth of sowing reduced emergence (%), height of the shoot and length of the primary root and increased the time taken for emergence and length of the mesocotyl. The maximum depth C. appressa seedlings could emerge from was 44 mm. Growth of C. appressa seedlings was slower than that of pasture species and responded to nitrogen and nitrogen + phosphorus and/or sulfur but not to phosphorus and/or sulfur. Differences were recorded in the morphology of plants grown from seeds collected from various locations and grown in the 1 environment at Orange, New South Wales. Control of C. appressa was achieved by draining, slashing and removing litter, applying glyphosate, surface-sowing pasture species and topdressing with superphosphate. Five years after sowing, the foliage cover of legumes and grasses on the best treatment was 71% and that of C. appressa 2%, a substantial decline from the original 81% infestation. The best technique for control of C. appressa on infested creek flats suitable for pasture production would be to drain, plough and bury seeds below 44 mm and then sow pastures with superphosphate. Where ploughing is not possible, drainage, burning to remove foliage, spraying with glyphosate and surface-sowing pastures with superphosphate would be successful. In both situations, long-term control can be achieved by heavy grazing for short periods only when the soil is firm and removing re-infesting plants by annual spot spraying.

Seed softening, imbibition time, and seedling establishmentin yellow serradella

The first (preconditioning) and final stages of seed softening were studied over a 4-year period in 4 lines of yellow serradella (Ornithopus compressus L.): cvv. Santorini and Charano, and accessions GEH72-1A and GRC5045-2-2. Pods grown in 1997 were collected in December (start of summer) and placed on the soil surface or buried at a depth of 1 cm. Measurements of seed softening between years were made from pod samples removed in June each year. The progress of preconditioning and seed softening within the first 3 years was determined from samples taken at the end of February. Numbers of soft and viable seeds were determined from each sampling. Preconditioned seeds were identified by subjecting seeds to 7 gradual diurnal temperature cycles of 48/15°C in darkness before testing for permeability. Seed softening was markedly accelerated by pod burial in all 4 lines, with most buried seeds of GEH72-1A and Santorini softening during the first year. Seed softening was slower in GRC5045-2-2 and Charano, approaching a constant annual rate over the 4 years of the experiment. Despite this marked effect of burial the differences between lines in rates of softening of buried seeds were sufficient to have important implications for persistence under some management systems. Most seeds of all lines softened between February and June, indicating that shallow pod burial could be delayed in these lines until at least the end of February to promote the final stage of seed softening. Although large numbers of seeds of GEH72-1A and GRC5045-2-2 had preconditioned at the soil surface by the end of February, few went on to complete the softening process by June, when most had lost their preconditioned state. Treatment at 48/15°C was less successful in identifying preconditioned seeds of Santorini and Charano. Rates of imbibition differed markedly between lines. Most soft seeds of GEH72-1A and GRC5045-2-2 imbibed within days, whereas they took weeks in Santorini and an intermediate time in Charano. Seedling age distributions in the 4 lines in June closely reflected the times their soft seeds took to imbibe in the laboratory. Imbibition time can be an important germination regulating mechanism having implications that may be either favourable or unfavourable depending on rainfall distribution around the break of season and the system of management.

Altitudinal gradients in seed dynamics of Calluna vulgaris in eastern Scotland

Abstract Relationships between seed deposition, size of soil seed banks and some of the environmental factors affecting them were assessed for Calluna vulgaris throughout its altitudinal range (150-960 m a.s.l.) in eastern Scotland. Seed rain was assessed using pitfall traps, collected every 5-10 wk for 3 yr; germinability was determined by laboratory incubation. Seed bank size was estimated, once only, by counting seedlings emerging from soil cores kept for 50 wk in a glasshouse. Seed deposition varied annually, was related to parent plant cover but always declined with altitude, falling sharply above 600 m a.s.l. Seed bank size was more closely correlated with the proportion of organic matter in the soil than with the amount of seed rain. Seed bank sizes declined gradually with altitude but did not differ significantly between four altitudinal zones. The mean density of buried seeds was less than half the mean annual seed rain at sites below 300 m a.s.l. but was over 200 × greater than annual seed rain ...

熱水散布が埋土種子の発芽に及ぼす影響

熱水散布が埋土種子の発芽に及ぼす影響

Multiple-landmark piloting in pigeons (Columba livia): landmark configuration as a discriminative cue.

Using the landmark-transformation technique, researchers have shown that pigeons (Columba livia) tend to encode a goal location relative to 1 landmark, even when multiple landmarks are in the vicinity of the goal. The current experiments examined pigeons' ability to use configural information from a set of landmarks by making the arrangement of 4 landmarks a discriminative cue to the location of buried seeds. Results showed that pigeons used information from the 3 consistently placed landmarks to search accurately when 1 landmark was displaced. Findings indicate that pigeons are able to search for a goal using information from multiple landmarks instead of just 1 and that landmark use by these birds may be more flexible than previously theorized.

Effects of fungal pathogens on seeds of native and exotic plants: a test using congeneric pairs

SummaryIt has previously been hypothesized that low rates of attack by natural enemies may contribute to the invasiveness of exotic plants.We tested this hypothesis by investigating the influence of pathogens on survival during a critical life‐history stage: the seed bank. We used fungicide treatments to estimate the impacts of soil fungi on buried seeds of a taxonomically broad suite of congeneric natives and exotics, in both upland and wetland meadows.Seeds of both natives and exotics were recovered at lower rates in wetlands than in uplands. Fungicide addition reduced this difference by improving recovery in wetlands, indicating that the lower recovery was largely attributable to a higher level of fungal mortality. This suggests that fungal pathogens may contribute to the exclusion of upland species from wetlands.The effects of fungicide on the recovery of buried seeds did not differ between natives and exotics. Seeds of exotics were recovered at a higher rate than seeds of natives in uplands, but this effect was not attributable to fungal pathogens.Fungal seed pathogens may offer poor prospects for the management of most exotic species. The lack of consistent differences in the responses of natives vs. exotics to fungicide suggests few aliens owe their success to low seed pathogen loads, while impacts of seed‐pathogenic biocontrol agents on non‐target species would be frequent.

Experiments on the mechanism of tree and shrub establishment in temperate grassy woodlands: Seedling emergence

AbstractField experiments were designed to examine tree and shrub seedling emergence in temperate grassy woodlands on the New England Tablelands. The effects of study sites, intensity of previous grazing, removal of ground cover by fire or clearing, burial of seeds and ant seed theft on seedling emergence were tested in two field experiments. Six tree and seven shrub species were used in the experiments and their cumulative emergence was compared with laboratory germination studies. All species used in field experiments had lower cumulative emergence than those in laboratory germination studies despite prolonged periods of above average rainfall before and after seeds were sown. Eucalypt species emerged faster in the field than the shrub species and generally attained higher cumulative emergence than the shrubs. Spatial effects of sites and patches within sites, and of previous grazing history did not strongly influence patterns of seedling emergence in most species. Ground and litter cover generally did not enhance or suppress the emergence of seedlings, although the removal of cover in recently grazed areas enhanced the emergence of some species. Burning enhanced the emergence of some tree and shrub species where plots had more fuel and intense fires, but this effect was not strong. Compared with other treatments, seedbed manipulations produced the strongest effects. In the absence of both invertebrate and vertebrate predators, seedling emergence was lower for surface‐sown seed, compared with seed sown on scarified soil surfaces. Higher seedling emergence of buried seeds in the presence of invertebrate predators probably resulted from the combined effects of predator escape and enhanced moisture status of the germination environment. Some promotion of emergence was achieved for all species in most sown treatments probably as a result of a prolonged above average rainfall. In contrast, the natural recruitment of trees and shrubs was negligible in experimental plots, highlighting the importance of seed supply and dispersal as ultimate determinants of recruitment.

EVOLUTIONARY SIGNIFICANCE OF AWN LENGTH VARIATION IN A CLONAL GRASS OF FIRE-PRONE SAVANNAS

We investigated the selective advantage of continuous variation of awn length in the clonal grass Hyparrhenia diplandra (Poaceae) in a West African tropical savanna (Ivory Coast) that burns every year. This species is apomictic, so all seeds produced by one mother plant have the same genotype. H. diplandra produces diaspores with a hygroscopic awn whose length varies within and among plants. In other grass species, awns play a significant role in secondary dispersal on the ground and in seed burial. Using an experimental approach, we quantified (1) the environmental and genetic components of awn length variation, (2) the influence of awn length variation on seed burial depth, (3) the effect of awn length on seed germination and seedling survival rates in burned and unburned plots, and (4) the potential role of fire intensity in selecting diaspores with different awn lengths. Awn length varied from 35 to 70 mm and was highly heritable (h2 = 0.63). Variation within individuals was not related to flowering phenology or flower position on the inflorescence. Awn length was significantly and positively correlated with seed burial depth. The range of depths from where buried seeds were recovered varied between 0 and 2.4 cm; this represents the layer where high soil temperature was recorded during fires in both field and experimental conditions. Thus, short-awned seeds were more likely to be affected by soil temperature elevation during a fire than were long-awned seeds. During two consecutive years, a significant relationship between mean seedling survival and mean awn length was only found in 3 ha of naturally burned plots. No such significant relationship existed in experimentally unburned plots in 1997 or 1998. In burned plots, the relationship between mean awn length and mean proportion of surviving seedlings was negative in 1997, while in 1998 the same relationship was positive. In natural conditions, fire intensity was significantly different between years, and variation in fire intensity could be related to between-year differences in climatic conditions and the amount of biomass that was available for burning. Furthermore, seed germination probability increased when seed burial depth increased and when elevation of the soil temperature was moderate (<100°C). We suggest that, depending on fire intensity, different awn lengths are selected because of different soil temperatures, with very intense fires selecting for long-awned diaspores. Since fire intensity is unpredictable from year to year, this maintains the continuous variation of awn length within populations. The spatial and temporal heterogeneity select for different clones that have contrasting awn morphologies.

The use of relative and absolute bearings by Clark’s nutcrackers,Nucifraga columbiana

Two groups of Clark’s nutcrackers were trained to find buried seeds whose location was defined by a constant angle from two landmarks whose interlandmark distance and position in the room varied across trials. The first group had a landmark array that was always placed in the same orientation with respect to the walls, allowing the animals to use both relative and absolute bearings. The second group had a landmark array that rotated across trials so that only relative bearings could be used to locate the seeds. The birds in each group learned the task and transferred to new interlandmark distances both within and beyond the range of training distances. Results from these experiments indicate that nutcrackers can learn a geometric relationship that relies exclusively on relative bearings even though the use of absolute bearing yields more efficient search.

Light, temperature and burial depth effects on Rumex obtusifolius seed germination and emergence

Trials were carried out to investigate the effects of light and temperature on germination of Rumex obtusifolius L. After several months of storage, seeds gradually lost dormancy and became photosensitive. Thermal optima for germination were between 20 °C and 25 °C in light or in darkness. At lower temperatures there was a greater demand for light, so that the greatest differences in germination percentage (between low and high temperatures) were found within the 10–15 °C temperature range. The calculated thermal minima (x‐intercept method) in light and darkness were 8.3 °C and 6.1 °C respectively. Daily temperature fluctuation increased germination even after seed irradiation with far‐red light, suggesting a lower demand for the far‐red‐absorbing form of phytochrome. Seed burial inhibited germination in proportion to depth; however, germination inhibition was independent of seed phytochrome photo‐equilibrium, which had been diversified by seed pretreatment with light. Seedlings did not emerge when seeds were buried &gt;8 cm deep. Recovery of ungerminated seeds showed that excessive burial did not impede seedling emergence but rather prevented seed germination. However, this induction of dormancy was lost once germination processes were activated (24–48 h at 20 °C) that made germination irreversible. Temperature was also involved in inhibition, and low temperature (&lt;15 °C) induced the least inhibition. This is discussed in terms of processes of respiration and fermentation in buried seeds.