Soil seed bank
{{About|natural seed repositories|other uses|Seed bank (disambiguation)}}
The soil seed bank is the natural storage of seeds, often dormant, within the soil of most ecosystems.{{cite web |author=Jack Dekker |year=1997 |title=The Soil Seed Bank |url=http://agron-www.agron.iastate.edu/~weeds/Ag317/bioeco/lifecycle/seedbank.html |access-date=10 December 2015 |publisher=Agronomy Department, Iowa State University}} The study of soil seed banks started in 1859 when Charles Darwin observed the emergence of seedlings using soil samples from the bottom of a lake. The first scientific paper on the subject was published in 1882 and reported on the occurrence of seeds at different soil depths.{{Cite journal|title=Soil seed banks|first1=P. J.|last1=Christoffoleti|first2=R. S. X.|last2=Caetano|date=July 17, 1998|journal=Scientia Agricola|volume=55|pages=74–78|doi=10.1590/S0103-90161998000500013|doi-access=free}} Weed seed banks have been studied intensely in agricultural science because of their important economic impacts; other fields interested in soil seed banks include forest regeneration and restoration ecology.
Henry David Thoreau wrote that the contemporary popular belief explaining the succession of a logged forest, specifically to trees of a dissimilar species to the trees cut down, was that seeds either spontaneously generated in the soil, or sprouted after lying dormant for centuries. However, he dismissed this idea, noting that heavy nuts unsuited for distribution by wind were distributed instead by animals.{{cite journal |last1=Mcartney |first1=Eugene S. |title=Forest Succession and Folklore |journal=The Classical Weekly |date=1931 |volume=25 |issue=6 |pages=47–48|doi=10.2307/4389644 |jstor=4389644 }}
The ecological importance of seed bank
The seed bank is one of the key factors for the persistence and density fluctuations of plant populations, especially for annual plants.{{Cite journal |last1=DeMalach |first1=Niv |last2=Kigel |first2=Jaime |last3=Sternberg |first3=Marcelo |date=2023-03-01 |title=Contrasting dynamics of seed banks and standing vegetation of annuals and perennials along a rainfall gradient |url=https://www.sciencedirect.com/science/article/pii/S1433831923000021 |journal=Perspectives in Plant Ecology, Evolution and Systematics |volume=58 |pages=125718 |doi=10.1016/j.ppees.2023.125718 |issn=1433-8319|arxiv=2301.12696 }} Perennial plants have vegetative propagules to facilitate forming new plants, migration into new ground, or reestablishment after being top-killed, which are analogous to seed bank in their persistence ability under disturbance. These propagules are collectively called the 'soil bud bank', and include dormant and adventitious buds on stolons, rhizomes, and bulbs. Moreover, the term soil diaspore bank can be used to include non-flowering plants such as ferns and bryophytes.{{citation needed|date=December 2023}}
Soil seed bank is significant breeding source for vegetation restorationLu, Z.J., Li, L.F., Jiang, M.X., Huang, H.D., and Bao, D.C., Can the soil seed bank contribute to revegetation of the drawdown zone in the Three Gorges reservoir region? Plant Ecol., 2010, vol. 209, no. 1, pp. 153–165. and species-rich vegetation restoration,{{Cite journal |last1=Fisher |first1=Judith L. |last2=Loneragan |first2=William A. |last3=Dixon |first3=Kingsley |last4=Veneklaas |first4=Erik J. |date=2009-02-01 |title=Soil seed bank compositional change constrains biodiversity in an invaded species-rich woodland |url=https://www.sciencedirect.com/science/article/pii/S0006320708004011 |journal=Biological Conservation |language=en |volume=142 |issue=2 |pages=256–269 |doi=10.1016/j.biocon.2008.10.019 |issn=0006-3207}} as they provide memories of past vegetation and represent the structure of future population. Moreover the composition of seed bank is often more stable than the vegetation to environmental changes,{{Cite journal |last1=DeMalach |first1=Niv |last2=Kigel |first2=Jaime |last3=Sternberg |first3=Marcelo |date=March 2021 |editor-last=Dalling |editor-first=James |title=The soil seed bank can buffer long-term compositional changes in annual plant communities |url=https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13555 |journal=Journal of Ecology |language=en |volume=109 |issue=3 |pages=1275–1283 |doi=10.1111/1365-2745.13555 |issn=0022-0477|arxiv=2010.15693 }} although a chronic N deposition can deplete it.{{Cite journal |last1=Eskelinen |first1=Anu |last2=Elwood |first2=Elise |last3=Harrison |first3=Susan |last4=Beyen |first4=Eva |last5=Gremer |first5=Jennifer R. |date=December 2021 |title=Vulnerability of grassland seed banks to resource-enhancing global changes |journal=Ecology |language=en |volume=102 |issue=12 |pages=e03512 |doi=10.1002/ecy.3512 |issn=0012-9658|doi-access=free |pmid=34358331 }}{{Cite journal |last1=Basto |first1=Sofía |last2=Thompson |first2=Ken |last3=Phoenix |first3=Gareth |last4=Sloan |first4=Victoria |last5=Leake |first5=Jonathan |last6=Rees |first6=Mark |date=2015-02-04 |title=Long-term nitrogen deposition depletes grassland seed banks |journal=Nature Communications |language=en |volume=6 |issue=1 |pages=6185 |doi=10.1038/ncomms7185 |issn=2041-1723|doi-access=free }} In many systems, the density of the soil seed bank is often lower than the vegetation, and there are a large differences in species composition of the seed bank and the composition of the aboveground vegetation.Sanderson, M.A., Goslee, S.C., Klement, K.D., and Soder, K.J., Soil seed bank composition in pastures of diverse mixtures of temperate forages, Agron. J., 2007, vol. 99, no. 6, p. 1514.{{Cite journal |last1=White |first1=S. |last2=Bork |first2=E. |last3=Karst |first3=J. |last4=Cahill |first4=J. |date=2012-11-21 |title=Similarity between grassland vegetation and seed bank shifts with altered precipitation and clipping, but not warming |url=https://akjournals.com/view/journals/168/13/2/article-p129.xml |journal=Community Ecology |language=en |volume=13 |issue=2 |pages=129–136 |doi=10.1556/comec.13.2012.2.1 |issn=1588-2756}}Hopfensperger, K.N., A review of similarity between seed bank and standing vegetation across ecosystems, Oikos, 2007, vol. 116, pp. 1438–1448. Additionally, it is a key point that the relationship between soil seed bank and original potential to measure the revegetation potential.Lu, Z.J., Li, L.F., Jiang, M.X., Huang, H.D., and Bao, D.C., Can the soil seed bank contribute to revegetation of the drawdown zone in the Three Gorges reservoir region? Plant Ecol., 2010, vol. 209, no. 1, pp. 153–165{{Cite journal |last1=Wang |first1=Yongcui |last2=Jiang |first2=Deming |last3=Toshio |first3=Oshida |last4=Zhou |first4=Quanlai |date=2013-09-01 |title=Recent advances in soil seed bank research |url=https://www.researchgate.net/publication/271904467 |journal=Contemporary Problems of Ecology |language=en |volume=6 |issue=5 |pages=520–524 |doi=10.1134/S1995425513050181 |issn=1995-4263 |s2cid=255553677}} In endangered habitats, such as mudflats, rare and critically endangered species may be present in high densities, the composition of the seed bank is often more stable than the vegetation to environmental changes[7][7],{{Cite journal|last1=Poschlod|first1=Peter|last2=Rosbakh|first2=Sergey|date=2018|title=Mudflat species: Threatened or hidden? An extensive seed bank survey of 108 fish ponds in Southern Germany|journal=Biological Conservation|language=en|volume=225|pages=154–163|doi=10.1016/j.biocon.2018.06.024|s2cid=91872044}}
Soil seed banks are a crucial part of the rapid re-vegetation of sites disturbed by wildfire, catastrophic weather, agricultural operations, and timber harvesting, a natural process known as secondary succession. Soil seed banks are often dominated by pioneer species, those species that are specially adapted to return to an environment first after a disturbance.{{cite journal |last1=Tang |first1=Yong |last2=Cao |first2=Min |last3=Fu |first3=Xianhui |date=2006 |title=Soil Seedbank in a Dipterocarp Rain Forest in Xishuangbanna, Southwest China |journal=Biotropica |volume=38 |issue=3 |pages=328–333 |doi=10.1111/j.1744-7429.2006.00149.x |s2cid=53974012}} Forest ecosystems and wetlands contain a number of specialized plant species forming persistent soil seed banks.{{citation needed|date=December 2023}}
The absence of a soil seed bank impedes the establishment of vegetation during primary succession, while presence of a well-stocked soil seed bank permits rapid development of species-rich ecosystems during secondary succession.{{citation needed|date=December 2023}}
Seed longevity
Many taxa have been classified according to the longevity of their seeds in the soil seed bank. Seeds of transient species remain viable in the soil seed bank only to the next opportunity to germinate, while seeds of persistent species can survive longer than the next opportunity—often much longer than one year. Species with seeds that remain viable in the soil longer than five years form the long-term persistent seed bank, while species whose seeds generally germinate or die within one to five years are called short-term persistent. A typical long-term persistent species is Chenopodium album (Lambsquarters); its seeds commonly remain viable in the soil for up to 40 years and in rare situations perhaps as long as 1,600 years.{{Cite web |title=Iowa State University: College of Agriculture and Life Science: Lambsquarters |url=http://www.agron.iastate.edu/~weeds/weedbiollibrary/u4lq1.html}} A species forming no soil seed bank at all (except the dry season between ripening and the first autumnal rains) is Agrostemma githago (Corncockle), which was formerly a widespread cereal weed.{{citation needed|date=December 2023}}
Longevity of seeds is very variable and depends on many factors. Seeds buried more deeply tend to be capable of lasting longer.{{cite journal |last1=Burnside |first1=Orvin C. |last2=Wilson |first2=Robert G. |last3=Weisberg |first3=Sanford |last4=Hubbard |first4=Kenneth G. |date=1996 |title=Seed Longevity of 41 Weed Species Buried 17 Years in Eastern and Western Nebraska |journal=Weed Science |volume=44 |issue=1 |pages=74–86 |doi=10.1017/S0043174500093589 |s2cid=82721189}} However, few species exceed 100 years.Ken Thompson, Jan P. Bakker, and Renée M. Bekker. 1997. The soil seed banks of north west Europe : methodology, density and longevity. New York : Cambridge University Press. p. 276 In typical soils the longevity of seeds can range from nearly zero (germinating immediately when reaching the soil or even before) to several hundred years. Some of the oldest still-viable seeds were those of Lotus (Nelumbo nucifera) found buried in the soil of a pond; these seeds were estimated by carbon dating to be around 1,200 years old.{{cite book |author1=J. Derek Bewley |url=https://books.google.com/books?id=aE414KuXu4gC&pg=PA15 |title=The Encyclopedia of Seeds: Science, Technology and Uses |author2=Michael Black |author3=Peter Halmer |publisher=CABI |year=2006 |isbn=978-0-85199-723-0 |pages=14–15}} One cultivar of date palm, the Judean date palm, successfully sprouted in 2008 after accidental storage for 2,000 years.{{Cite news |last=Fountain |first=Henry |date=2008-06-17 |title=Date Seed of Masada is Oldest Ever to Sprout |newspaper=New York Times |url=https://www.nytimes.com/2008/06/17/science/17obseed.html |access-date=December 9, 2021}}
The famous seed longevity experiments
One of the longest-running soil seed viability trials was started in Michigan in 1879 by James Beal. The experiment involved the burying of 20 bottles holding 50 seeds from 21 species. Every five years, a bottle from every species was retrieved and germinated on a tray of sterilized soil which was kept in a growth chamber. Later, after responsibility for managing the experiment was delegated to caretakers, the period between retrievals became longer. In 1980, more than 100 years after the trial was started, seeds of only three species were observed to germinate: moth mullein (Verbascum blattaria), common mullein (Verbascum thapsus) and common mallow (Malva neglecta).{{cite web |author=Frank W. Telewski |title=Research & Teaching |url=http://www.cpa.msu.edu/beal/research/research_frames.htm |access-date=10 December 2015 |publisher=Department of Plant Biology, Michigan State University}} Several other experiments have been conducted to determine the long-term longevity of seeds in soil seed banks.
| class="wikitable"
|+ Soil seed bank longevity of seeds in experimental conditions ! Species ! Time ! Comments |
| Verbascum blattaria
| |
| Verbascum thapsus
| |
| Malva neglecta
| At least 100 years | |
| Oenothera biennis
| 10% of seeds sprouted after the 80-year mark |
| Rumex crispus
| 80 years |
| Datura stramonium
| At least 39 years | Over 90 percent germination rate was reported{{cite journal |last1=Brown |first1=E. |last2=Toole |first2=E.H. |date=1946 |title=Final Results of the Duvel Buried Seed Experiment |url=https://naldc.nal.usda.gov/download/IND43970084/pdf |journal=Journal of Agricultural Research |volume=72 |issue=6}} |
| Phytolacca americana
| At least 39 years |
| Solanum nigrum
| At least 39 years | Over 80 percent germination rate was reported | |
| Robinia pseudoacacia
| At least 39 years | |
| Ambrosia artemisiifolia
| At least 39 years | |
| Potentilla norvegica
|At least 39 years | |
| Onopordum acanthium
|At least 39 years | |
| Rudbeckia hirta
|At least 39 years | |
| Cuscuta polygonorum
|At least 39 years | |
| Lespedeza frutescens
| At least 39 years | |
| Convolvulus sepium
|At least 39 years | |
| Ipomoea lacunosa
|At least 39 years | |
| Verbena hastata
|At least 39 years | |
| Verbena urticifolia
|At least 39 years | |
| Nicotiana tabacum
|At least 39 years | |
| Arctium lappa
|At least 39 years | Only 1 percent germination was reported. |
| Boehmeria nivea
|At least 39 years | |
| Setaria verticillata
|At least 39 years | |
| Trifolium pratense
|At least 39 years | |
| Rumex obtusifolius
|At least 39 years | |
| Rumex salicifolius
|At least 39 years | |
| Chenopodium album
|At least 39 years | |
| Chenopodium hybridum
|At least 39 years | |
| Abutilon theophrasti
|At least 39 years | |
| Leucanthemum vulgare
|At least 39 years | |
| Hibiscus militaris
|At least 39 years | |
| Hypericum hypericoides
|At least 39 years | |
| Sporobolus cryptandrus
|At least 39 years | |
| Polygonum scandens
|At least 39 years |Germination rate was very low throughout the experiment. |
| Poa pratensis
|At least 39 years | |
| Setaria viridis
|At least 39 years | |
| Phalaris arundinacea
|30 years |Only 1 percent of seed survived. |
| Portulaca oleracea
|30 years |38 percent of the most deeply buried seeds were viable at 21 years, 1 percent of more shallowly buried seeds are reported sprouting after the 30 year mark. |
| Polygonum pensylvanicum
|30 years | |
| Polygonum persicaria
|30 years | |
| Cassia marilandica
|30 years | |
| Thlaspi arvense
|30 years | |
| Trifolium hybridum
|30 years | |
| Ambrosia trifida
|21 years | |
| Brassica nigra
|21 years | |
| Dracocephalum parviflorum
| |
| Rorippa islandica
|24.7 years | |
| Matricaria discoidea
|24.7 years | |
| Polygonum aviculare
|24.7 years | |
| Helianthus annuus
| |
| Setaria parviflora
|17 years | |
| Cirsium arvense
|17 years | |
| Cirsium flodmanii
|17 years | |
| Ipomoea hederacea
|17 years | |
| Persicaria amphibia
|17 years | |
| Amaranthus tuberculatus
|17 years | |
| Solanum sarrachoides
|17 years | |
| Ambrosia grayii
|17 years |Only 1% of seed germinated. |
| Bassia scoparia
|17 years |Only 1% of seed germinated. |
| Echinochloa crus-galli
|17 years |Only 1% of seed germinated. |
| Amaranthus retroflexus
| |
| Pyrus calleryana
| |
Other studies
Species of Striga (witchweed) are known to leave some of the highest seed densities in the soil compared to other plant genera; this is a major factor that aids their invasive potential.{{cite book |last1=Ross |first1=Merrill A. |title=Applied Weed Science: Including the Ecology and Management of Invasive Plants |last2=Lembi |first2=Carole A. |publisher=Prentice Hall |year=2008 |isbn=978-0-13-502814-8 |page=22}} Each plant has the capability to produce between 90,000 and 450,000 seeds, although a majority of these seeds are not viable.{{cite journal |author1=Faiz F. Bebawi |author2=Robert E. Eplee |author3=Rebecca S. Norris |date=March 1984 |title=Effects of Seed Size and Weight on Witchweed (Striga asiatica) Seed Germination, Emergence, and Host-Parasitization |journal=Weed Science |volume=32 |issue=2 |pages=202–205 |doi=10.1017/S0043174500058811 |jstor=4043831 |s2cid=89078686}} It has been estimated that only two witchweeds would produce enough seeds required to refill a seed bank after seasonal losses.{{cite book |author=Daniel M. Joel |url=https://books.google.com/books?id=JW9EAAAAQBAJ&pg=PA394 |title=Parasitic Orobanchaceae: Parasitic Mechanisms and Control Strategies |author2=Jonathan Gressel |author3=Lytton J. Musselman |publisher=Springer Science & Business Media |year=2013 |isbn=978-3-642-38146-1 |page=394}}
Before the advent of herbicides, a good example of a persistent seed bank species was Papaver rhoeas, sometimes so abundant in agricultural fields in Europe that it could be mistaken for a crop.{{citation needed|date=December 2023}}
Studies on the genetic structure of Androsace septentrionalis populations in the seed bank compared to those of established plants showed that diversity within populations is higher below ground than above ground.{{citation needed|date=December 2023}}