THE NINETY-YEAR PERIOD FOR DR. BEAL'S SEED VIABILITY EXPERIMENT

In 1879 Dr. W. J. Beal selected seeds of 23 different species of locally common plants, mixed 50 seeds of each species with moist sand in unstoppered one-pint bottles, and buried the bottles in a sandy knoll to be unearthed and the viability of the seeds tested periodically. The year 1970 marked the ninetieth year the seed had been buried, and the thirteenth bottle was recovered to test for seed viability. Of the three species which had germinated in the 1960 test (curly dock, Rumex crispus; evening primrose, Oenothera biennis; and moth mullein, Verbascum blattaria), only V. blattaria had viable seed with 20% germination. No other species germinated. All ten seedlings of V. blattaria were grown to maturity, and seeds were then harvested to study the possible deviations from normality and the requirements for seed germination. All seedlings emerging from the first progeny seed appeared normal. The most prominent requirement for germination was light, and this is a possible explanation of why the seeds had remained viable but dormant for so long a period. One-third of the freshly harvested seed germinated in darkness and, furthermore, redrying of dark-moistened seed in the absence of light induced additional germination. Germination of dark-moistened seed was not completely restored when the still moist seeds were subsequently exposed to light. However, when dark-moistened seeds were dried and then remoistened in the light, germination was about 95 %. About 5 % of the seed did not germinate under the conditions used. We find that 5 % of the population of V. blattaria seeds are dormant for unknown reasons, that 30 % will germinate if supplied only with moisture, and that 65 % are inhibited and require light and moisture simultaneously for germination. Supplying this 65 % of the population with moisture in darkness results in the development of a second type of inhibition which is no longer light reversible. It appears that the simultaneous requirement for light and moisture is an important factor in permitting V. blattaria seeds to remain dormant during prolonged burial.     

The 141-year period for Dr. Beal's seed viability experiment: A hybrid surprise

Premise

In 1879, Dr. William Beal buried 20 glass bottles filled with seeds and sand at a single site at Michigan State University. The goal of the experiment was to understand seed longevity in the soil, a topic of general importance in ecology, restoration, conservation, and agriculture, by periodically assaying germinability of these seeds over 100 years. The interval between germination assays has been extended and the experiment will now end after 221 years, in 2100.

Methods

We dug up the 16th bottle in April 2021 and attempted to germinate the 141-year-old seeds it contained. We grew germinants to maturity and identified these to species by vegetative and reproductive phenotypes. For the first time in the history of this experiment, genomic DNA was sequenced to confirm species identities.

Results

Twenty seeds germinated over the 244-day assay. Eight germinated in the first 11 days. All 20 belonged to the Verbascum genus: Nineteen were V. blattaria according to phenotype and ITS2 genotype; and one had a hybrid V. blattaria × V. thapsus phenotype and ITS2 genotype. In total, 20/50 (40%) of the original Verbascum seeds in the bottle germinated in year 141.

Conclusions

While most species in the Beal experiment lost all seed viability in the first 60 years, a high percentage of Verbascum seeds can still germinate after 141 years in the soil. Long-term experiments such as this one are rare and invaluable for studying seed viability in natural soil conditions.     

The viability of seeds of rainforest species after experimental soil burials under tropical wet lowland forest in north-eastern Australia

Seed samples of 50 rainforest species representative of all successional stages from tropical lowland forests in north-eastern Australia were buried in nylon material bags under rainforest for periods up to 2 years. The seed samples were exhumed after 6 weeks, 6 months, 1 year and 2 years, and their viabilities assessed. Substantial portions of the samples of 31 species of pioneer and early and late secondary species retained viability for 2 years in the buried samples, and germinated immediately they were exposed to greenhouse conditions. In approximately one-third of these species, the dormancy was completely enforced by the burial conditions since fresh, mature seed germinated immediately in the greenhouse. The remainder of the long-lived seeds showed some evidence of variable initial periods of innate dormancy produced by their hard, impermeable coats. There was no indication that the burial conditions enforced or induced any dormancy in the seeds of primary forest trees. The mean viability of the primary forest seeds examined was 10% after 6 months burial. The soft-coated seeds were obligate immediate germinators; they germinated or died. The remainder showed variably delayed germination, and this was interpreted as a mechanical dormancy produced by their leathery, fibrous, or stony endocarps. The group of late secondary species sampled contained both obligate immediate germinators and seeds with well developed dormancy mechanisms. Many of the buried 'seedlings’ of primary forest species remained alive for a year or more attached to seeds, demonstrating the ability of the larger primary seeds to sustain seedlings under conditions adverse to photosynthesis and growth. Some seedlings of Castanospermum australe were alive and were transplanted successfully after 2 years burial. This enables primary forest species to stock seedlings on the forest floor in contrast to the secondary species which store seed in the soil.     

Soil nutrient input effects on seed longevity: a burial experiment with fen-meadow species

1. Effects of high nutrient input on the longevity and viability of buried seed are examined. Seeds of 17 fen-meadow species were buried in nylon mesh bags at four sites in the Netherlands and one site in Great Britain in plots to which N, P, K fertilizers are applied. Prior to burial germination tests were conducted on the seeds of each species. This paper describes the results of the viability tests on the seeds that were exhumed after one and 2 years of burial.
2. The percentage of seeds that germinated after 1 year of burial was significantly lower than the pre-burial percentage for the majority of the species. After 2 years of burial the germination percentage further decreased. A few species, such as the Carex species, did, however, show an increase in germination percentage indicating that the burial conditions allowed dormancy controls to be broken.
3. Differences in the edaphic conditions between the sites appeared to affect germination percentages after 1 year of burial. A difference in germination response between sites was observed for Carex acutiformis, Filipendula ulmaria and Lychnis flos-cuculi .
4. A significantly higher germination percentage was found at the Great Britain site for F. ulmaria in the phosphate treatment compared with the potassium treatment and the control after 1 year of burial. In contrast to many literature assessments no significant effects of fertilizer application was found after 2 years.
5. For all sites, except one in the Netherlands, the total number of seeds that germinated was lower in 1996 than in 1995.     

Seed Longevity of Eucalyptus Victrix in Grassland in the Floodplain of the Fortescue River, Pilbara, Western Australia

Burial and removal techniques with seeds bags were used to examine the Eucalyptus victrix seed longevity. Seeds kept in room temperature (control) had 94% germination within 25 d, however, with increasing duration of burial the E. victrix seed viability decreased to zero before 142 d. Similarly, seed buried in shade and open had no significance difference in germination.     

DORMANCY AND GERMINATION IN SEEDS OF COMMON RAGWEED WITH REFERENCE TO BEAL'S BURIED SEED EXPERIMENT

Common ragweed (Ambrosia artemisiifolia L.) was one of 19 herbaceous weedy species used by Beal in his buried viable seed experiment started in 1879. No seeds germinated during the first 35 years of the experiment when germination tests were performed in late spring, summer or early autumn. Germination did occur in seeds buried for 40 years when seeds were exhumed and tested for germination in early spring. Data obtained in more recent research provide the probable explanation for these results. Seeds of common ragweed that do not germinate in spring enter secondary dormancy by mid to late spring and will not germinate until dormancy is broken the following late autumn and winter. Thus, during the first 35 years of the experiment seeds were dormant when tested for germination, whereas seeds buried for 40 years were nondormant. Seeds buried 50 years or longer did not germinate when tested in spring, probably because they had lost viability and/or seeds germinated during burial and seedlings died.     

Seed survival of the tropical tree Cryptocarya aschersoniana (Lauraceae): Consequences of habitat disturbance

Seed survival in soil could be strongly influenced by habitat characteristics, but little is known about the behaviour of seeds sensitive to desiccation in seed banks installed in natural or disturbed habitats. Cryptocarya aschersoniana seeds disperse at the end of the rainy season but do not germinate immediately; thus, they may form seed banks in soil. This study evaluated the behaviour of C. aschersoniana seed banks induced in the natural environment of the species and in a disturbed area. Recently harvested C. aschersoniana germination units were characterized according to their water content, germination and viability. In 2011 and 2012, seed banks were established by burying samples of seeds in the understory of a semi‐deciduous forest. In 2012, samples were also buried in a disturbed area. The seed banks were sampled at certain time intervals, and the samples were characterized as described above. Precipitation and air temperature data were collected. As a result, seeds in the seed bank established in the natural environment form a transient seed bank and showed the same behaviour in both years studied. A germination peak was observed starting 210 days after burial (coinciding with the onset of the rainy season) and reached germination percentages higher than 80% at the end of the experiment for both years. Seed mortality did not exceeded 28% in the natural environment. However, in the disturbed environment, the seeds lost their viability more rapidly, with 90% of the seeds becoming unviable 240 days after burial. Germinated seeds in the disturbed environment (maximum 21%) were not able to establish seedlings. These results underscore the importance of maintaining a natural, undisturbed forest for the conservation of this species.     

Common and distinct responses in phytohormone and vitamin E changes during seed burial and dormancy in Xyris bialata and X. peregrina

Temperature and humidity are the main factors influencing seed viability, dormancy and longevity of buried seeds. Unfortunately, very little is known about such processes in species of tropical regions, where temperature does not show major seasonal variations. The extent to which germination capacity, phytohormones and vitamin E levels were altered after burial of seeds of Xyris bialata and X. peregrina (Xyridaceae), two species endemic to rupestrian fields of Brazil, was examined. After 2 months of burial, seed germination capacity remained constant, which is associated with decreases in ABA and IAA content in both species. During this period, zeatin levels also decreased in X. bialata, but not in X. peregrina, the latter showing much lower levels of ABA. During the summer (rainy season), seeds of both species experienced a progressive, but severe, decrease in germination capacity, which reversed at the end of the winter (dry season), thus suggesting secondary dormancy. This dormancy appeared to be caused by drastic decreases in GAs, rather than increases in ABA. Levels of GA(4) decreased to non-detectable values during dormancy in both species. Furthermore, zeatin levels decreased in X. bialata but not in X.peregrina during this period. Both species accumulated γ-tocopherol as the major vitamin E form, and levels of this antioxidant remained constant or even increased during seed burial; however, X. bialata seeds showed a significant decrease in α-tocopherol during seed burial and dormancy. It is concluded that in X. peregrina and X. bialata, (i) burial causes significant changes in the phytohormone levels of seeds; (ii) secondary dormancy is induced in seeds; (iii) a GA(4) decrease, rather than an ABA increase, seems to be involved in the induction of secondary dormancy; and (iv) reductions in α-tocopherol in buried seeds are not necessarily indicative of reduced germination capacity.     

长白山哈泥泥炭地丘间生境泥炭藓孢子的寿命

长寿有性繁殖体对于植物种群的长存具有重要意义,迄今,泥炭地苔藓植物孢子长寿性研究还很少。在长白山哈泥泥炭地钻取丘间表层泥炭样品,测定泥炭腐殖化度和烧失量,逐层提取和培养泥炭藓孢子,研究埋藏时间对孢子萌发的影响。结果表明,丘间泥炭藓孢子埋藏环境中,随着埋深的增加即埋藏年限的增加,泥炭腐殖化度和烧失量总体上分别呈现增加和递减的趋势,而地层泥炭藓孢子萌发率呈现直线递减的规律,但在埋藏近150余年后孢子萌发率仍可达40%。研究进一步证明泥炭藓具有长期持久孢子库,根据推算,泥炭地丘间埋藏环境中,泥炭藓孢子最大寿命可超过400a。     

Postdispersal seed predation and seed viability in forest soils: implications for the regeneration of tree species in Ethiopian church forests

Almost all dry Afromontane forests of Northern Ethiopia have been converted to agricultural, grazing or scrub lands except for small fragments left around churches (‘Church forests’). Species regeneration in these forests is limited. We investigated (i) how intense postdispersal seed predation was in church forest, and if this seed predation varied with species and/or habitat, and (ii) for how long tree seeds maintained their viability while buried in forest soil. In the seed predation experiment, we monitored seeds of six tree species in four habitats for a period of 14 weeks (the peak seeding season). In the seed viability experiment, we assessed seed viability of five species in four habitats after being buried 6, 12, or 18 months. Ninety‐two percent of the tree seeds were predated within 3.5 months. Predation was mainly dependent on species whereas habitat had a weaker effect. Seed viability decreased sharply with burial time in soil for all species except for Juniperus. To minimize seed availability limitation for regeneration of such species in the forest, the standing vegetation needs to be persistently managed and conserved for a continuous seed rain supply. Additional seed sowing, and seed and seedling protection (by e.g. animal exclosures) may increase successful regeneration of important species in these forests.     

Patch Retention Time in an Omnivore, Dicyphus hesperus is Dependent on Both Host Plant and Prey Type

We examined patch residence times for an omnivorous predator, Dicyphus hesperus on a variety of plants and prey. Individual D. hesperus were placed in cages containing either mullein, tomato, pepper or chrysanthemum plants, and either no prey, Mediterranean flour moth eggs, greenhouse whitefly pupae or two-spotted spider mite adults. Patch residence times were typically greater than 24 h. The probability of remaining on the patch was greatest on mullein and tomato, followed by chrysanthemum and least on pepper, whereas probability of remaining on the patch was greatest when flour moth eggs were present, and least when no prey were available. Patch residence time in D. hesperus was determined by both the prey, and the species of plant, in an independent fashion. Our results reinforce the notion that for omnivores, the patch itself is as important as the prey that it harbors.     

Burial increases seed longevity of two Artemisia tridentata (Asteraceae) subspecies

? Premise of the study: Seed longevity and persistence in soil seed banks may be especially important for population persistence in ecosystems where opportunities for seedling establishment and disturbance are unpredictable. The fire regime, an important driver of population dynamics in sagebrush steppe ecosystems, has been altered by exotic annual grass invasion. Soil seed banks may play an active role in postfire recovery of the foundation shrub Artemisia tridentata, yet conditions under which seeds persist are largely unknown. ? Methods: We investigated seed longevity of two Artemisia tridentata subspecies in situ by retrieving seed bags that were placed at varying depths over a 2 yr period. We also sampled naturally dispersed seeds in litter and soil immediately after seed dispersal and before flowering in subsequent seasons to estimate seed persistence. ? Key results: After 24 mo, seeds buried at least 3 cm below the soil surface retained 30-40% viability whereas viability of seeds on the surface and under litter declined to 0 and < 11%, respectively. The density of naturally dispersed seeds in the seed bank was highly heterogeneous both spatially and temporally, and attrition varied significantly by region. ? Conclusions: Our study suggests that Artemisia tridentata has the potential to form a short-term soil seed bank that persists longer than has been commonly assumed, and that burial is necessary for seed longevity. Use of seeding techniques that promote burial of some seeds to aid in formation of a soil seed bank may increase restoration potential.     

Studies on the cultivation and uses of evening primrose (Oenothera spp.) in China

Evening primrose originated in North America and became naturalized in the north-east of China about one hundred years ago, where it has been used as famine food and animal feed. New uses for the seed oil, which contains γ-linolenic acid (GLA), that have been developed in China and overseas since 1980 have created a much larger commercial demand for the seed. There are eight species of Oenothera L. growing wild in China, of which Oenothera biennis L. is preferred. The maximum annual production of wild evening primrose seed is estimated to be about 3000 tons but, since 1986, evening primrose has also been cultivated for its seed and oil using O. biennis (primarily in the provinces of Jilin, Liaoning, Hebei, and Shandong) to meet the increasing demand. New production techniques have been developed and disseminated, and reported seed yields range from 750 to 3000 kg ha^-1. Commercial production follows a cyclical pattern, with the largest harvest to date, in 1999, estimated at 16 000-19 000 tons of seed. During 20 years of research on a wide range of wild oilseed plants, Chinese scientists found that evening primrose oil was antiatherosclerotic, lowered hyperlipidemia and was antithrombotic. The oil was developed and licensed as a drug (which required work on processing technology, physicochemical characteristics, pharmacology, formulation, and clinical studies) and it has since been widely used in clinical practice. Further research work has been done on other bioactive properties of evening primrose oil, alternative sources of GLA, the concentration of GLA, the synthesis of prostaglandin E1, and the development of health care drugs and cosmetics containing evening primrose oil. We believe that the prospects for the future development of evening primrose are good.     

Effects of burial and storage on germination and seed reserves of 18 tree species in a tropical deciduous forest in Mexico

The changes in germination and seed reserve composition that occur while seeds are stored in the laboratory or buried in the soil are important for understanding the potential and ecological longevity of seeds as well as seed-bank dynamics. Both germination and seed-bank dynamics depend on water availability. We studied 18 tree species, including those with permeable or impermeable seeds, from a tropical deciduous forest in Mexico. We measured seed germination in a growth chamber after (1) dispersal, (2) laboratory storage, (3) seed burial at two field sites and directly in the field, and (4) two rainy seasons. Lipids, nitrogen, and nonstructural carbohydrates were quantified after dispersal and after laboratory or field storage. Sixteen species were viable after three periods of laboratory storage (~3 years). Eleven species were viable after two burial periods in the field (~2 years). Nitrogen concentration decreased after storage and burial in 11 species. Species lipid concentration had a negative relationship with species water content at dispersal and after one burial period, whereas nonstructural carbohydrates showed the opposite trend. Potential and ecological longevities were similar in impermeable seeds. Most of the species studied can form persistent seed banks consisting mainly of species with impermeable seeds that can remain in the soil without degrading their viability. Germination in the field is staggered following natural precipitation pulses as a strategy to stagger seedling recruitment, which may insure against unfavorable conditions.     

Ignorant seed predators and factors affecting the seed survival of a tropical palm

In addition to acting as seed predators, some terrestrial mammals bury seeds via scatter hoarding. This study system used two permanent plots in examining the interaction between small rodents and the seeds of the palm Astrocaryum mexicanum. We tested how experimental burial, and fruiting status of the parent, distance to the parent, seed size, and microsite characteristics affect the survival of these seeds. Up to 34% of the buried seeds that were exposed only to ignorant rodent foragers (individuals not responsible for burial) survived. In comparison, less than 1% of seeds buried by scatter hoarding rodents survived in previous studies, a percentage that is comparable to the low survival of unburied seeds in this study (<2%). Although unburied seeds had very low survival, increasing distance and/or seed density positively affected survival of unburied seeds. Distance to parent had no effect on buried seed survival.
Buried seed survival was most strongly and significantly determined by the fruiting status of the trees under which they occurred. Seeds experienced significantly greater predation if buried under “parent” trees that fruited during the experiment. Buried seed survival was also negatively affected by germination, as germination may signal the presence of a seed to foraging rodents. There was some indication of a positive effect of tree density on seed survival between the two plots, whereas differences in rodent abundance appear to have no effect on seed survival. Seed size and microsite characteristics had no significant effect on buried seed survival, likely due to the greater proportional effects of other factors and the longevity of A. mexicanum seeds. The results of this study were used to generate a hypothetical causal network showing how comparatively low recovery of buried seeds by ignorant foragers – combined with processes determining the removal of scatter hoarding foragers from their scattered seed caches – may affect seedling recruitment in A. mexicanum.     

Seed characteristics and regeneration of some species in invaded coastal communities

The seed production, germination and regeneration characteristics of two native species (Acacia longifolia var. sophorae and Banksia integrifolia) and two invasive subspecies (Chrysanthemoides monilifera ssp. monilifera and ssp. rotundata) were compared. C. monilifera ssp. rotundata was similar in seed characteristics and regeneration to B. integrifolia in that: (1) seed production was over an extended period each year; (2) seed longevity was low (0–2% viable after burial for 3 years), but increased with depth of burial; and (3) regeneration from 26 to 28% of mature plants occurred after fire. By contrast, C. monilifera ssp. monilifera was similar to A. Iongifolia var. sophorae in that; (1) seed production was over a short period each year; (2) of the total buried, 6–13% of seeds were viable after 3 years, and again numbers increased with depth of burial (percentages of missing seeds of A. longifolia were high but all remaining seeds were viable after 3 years); and (3) regeneration after fire occurred only from seed, hence their seed longevity is an important factor for long-term survival. However, growth habit and niche occupation by ssp. rotundata is similar to that of A. longifolia and the above differences may contribute to the observed displacement of the native by the invasive species. The distribution of the two invasive subspecies is at present largely in separate areas in Australia and it is predicted this situation will continue because of their differing climatic preferences, morphology and regeneration from fire.     

Seed Dynamics of Early and Late Successional Tree Species in Tropical Abandoned Pastures: Seed Burial as a Way of Evading Predation

We explored different treatments to enhance the probability of sowed seeds of two early successional (ES, Cecropia obtusifolia and Ochroma pyramidale) and two late successional (LS, Brosimum costaricanum and Dialium guianense) species to escape predation and germinate in abandoned cattle‐raising pasture fields in Southeastern Mexico. ES species were sown in groups of 50 seeds under three treatments: invertebrate exclusion, burial, and exposition to seedeaters. LS species were sown in groups of 10 seeds under three treatments: vertebrate exclusion, burial, and exposition to seedeaters. We registered seed predation and germination 2, 4, 8, 16, 32, and 64 days after the initial sowing. Overall, ES showed higher predation rates (mean ± SE = 0.45 ± 0.07 seed seed^?1 day^?1; n = 3) than LS species (0.09 ± 0.02 seed seed^?1 day^?1). Cecropia obtusifolia was completely predated in all treatments after 8 days. Burial and exclusion treatments reduced final predation in circa 6% for O. pyramidale, relative to that of exposed seeds (85% after 8 days); most germination occurred in buried seeds (3.7%). In B. costaricanum, burial enabled germination by 10%; exposed and excluded seeds were removed 100%. Dialium guianense showed 12% germination in buried seeds and circa 20% of the seeds were not removed after 64 days. Direct sowing would be a recommended rainforest restoration practice for species with relatively large seeds if deposited in groups and buried. Studies which address variation across numerous sites are necessary in order to generate more consistent seed predation patterns and rainforest restoration principles in tropical pastures.     

Seed Dispersal by Monkeys and the Fate of Dispersed Seeds in a Peruvian Rain Forest1

Primary seed dispersal by two species of monkeys and the effects of rodents and dung beetles on the fate of dispersed seeds are described for a rain forest in southeastern Perú. During the six-month study period (June–November 1992) spider monkeys (Ateles paniscus) dispersed the seeds of 71 plant species, whereas howler monkeys (Alouatta seniculus) dispersed seeds of 14 species. Spider and howler monkeys also differed greatly in their ranging behavior and defecation patterns, and as a consequence, produced different seed rain patterns. Monkey defecations were visited by 27 species of dung beetles (Scarabaeidae). Dung beetles buried 41 percent of the seeds in the dung, but the number of seeds buried varied greatly, according to seed size. Removal rates of unburied seeds by rodents varied between 63–97 percent after 30 d for 8 plant species. The presence of fecal material increased the percentage of seeds removed by seed predators, but this effect became insignificant with time. Although seed predators found some seeds buried in dung balls (mimicking burial by dung beetles), depth of burial significantly affected the fate of these seeds. Less than 35 percent of Brosimum lactescens seeds buried inside dung balls at a depth of 1 cm remained undiscovered by rodents, whereas at least 75 percent of the seeds escaped rodent detection at a depth of 3 cm and 96 percent escaped at 5 cm. Both dung beetles and rodents greatly affected the fate of seeds dispersed by monkeys. It is thus important to consider postdispersal factors affecting the fate of seeds when assessing the effectiveness of frugivores as seed dispersers.     

Propagation of Rare Plants from Historic Seed Collections: Implications for Species Restoration and Herbarium Management

Herbaria are potentially important repositories of living seeds that could be useful for recovery of rare plant species. To examine this capacity, we tested seed germination of rare milkweed (Asclepias) and milkvetch (Astragalus) species representing different collection dates and different herbaria. These groups have contrasting seed characteristics, with greater potential for longevity in the nonpermeable hard-coated milkvetch seeds. Twelve-year-old Asclepias lanuginosa seeds failed to germinate. However, we achieved 45% germination from three-year-old Asclepias meadii seeds, but germination dropped to 0% after ages of four to five years. Astragalus neglectus seeds germinated from 97-, 48-, and 28-year-old herbarium specimens, and Astragalus tennesseensis seeds germinated from a four-year-old collection. Seedlings produced from these experiments were incorporated into ex situ garden populations for recovery or restoration of rare species populations. Different herbarium pest control techniques may have significant bearing on the viability of seeds stored on herbarium specimens. Microwaving can cause precipitous loss of seed viability, while deep-freezing appears to allow some seeds to remain viable. Potentially live seeds of rare species should be stored under conditions that enhance their long-term viability.