Soil seed bank

The soil seed bank is the natural storage of seeds, often dormant, within the soil of most ecosystems.[1] 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.[2] 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.

This article is about natural seed repositories. For other uses, see Seed bank (disambiguation).

Background

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.[3] 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.

Seed longevity
Dried lotus seeds.

Longevity of seeds is very variable and depends on many factors; few species exceed 100 years.[4] 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.[5]

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).[6]

Environmental significance

Soil seed banks play an important role in the natural environment of many ecosystems. For example, the rapid re-vegetation of sites disturbed by wildfire, catastrophic weather, agricultural operations,[7] and timber harvesting is largely due to the soil seed bank. Forest ecosystems and wetlands[7] contain a number of specialized plant species forming persistent soil seed banks.

Before the advent of herbicides a good example of a persistent seed bank species, Papaver rhoeas sometimes was so abundant in agricultural fields in Europe that it could be mistaken for a crop.

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.

Population densities and diversity

The mortality of seeds in the soil is one of the key factors for the persistence and density fluctuations of plant populations, especially for annual plants. 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.

There are indications that mutations are more important for species forming a persistent seed bank compared to those with only transient seeds. The increase of species richness in a plant community due to a species-rich and abundant soil seed bank is known as the storage effect.

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.[8] Each plant has the capability to produce between 90,000 and 450,000 seeds, although a majority of these seeds are not viable.[9] It has been estimated that only two witchweeds would produce enough seeds required to refill a seed bank after seasonal losses.[10]

Associated ecosystem processes

The term soil diaspore bank can be used to include non-flowering plants such as ferns and bryophytes.

In addition to seeds, perennial plants have vegetative propagules to facilitate forming new plants, migration into new ground, or reestablishment after being top-killed. These propagules are collectively called the 'soil bud bank', and include dormant and adventitious buds on stolons, rhizomes, and bulbs.[1]

The relationship between soil seed bank and aboveground vegetation

Soil seed bank is significant breeding source for vegetation restoration[11] and species-rich vegetation restoration,[12] as they provide memories of past vegetation and represent the structure of future population.[13] Soil seed bank did not very differ in overall seed density or species diversity,[14] and there was little relative between the species composition of the seed bank and the composition of the aboveground vegetation.[7][15] These two facts could lead to the conclusion that the species composition of the aboveground vegetation and the soil bank can differ.[16] Additionally, it is a key point that the relationship between soil seed bank and original potential to measure the revegetation potential.[17][18] In endangered habitats, such as mudflats, rare and critically endangered species may be present in high densities within the soil seed bank and survive between 50 years or a century.[19]

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References
  1. Jack Dekker (1997). "The Soil Seed Bank". Agronomy Department, Iowa State University. Retrieved 10 December 2015.
  2. P.J. Christoffoleti; R.S.X. Caetano 1998. Soil seed banks Scientia Agricola: 55: 74-78.
  3. Iowa State University: College of Agriculture and Life Science: Lambsquarters
  4. 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. 276 p.
  5. J. Derek Bewley, Michael Black and Peter Halmer (2006). The Encyclopedia of Seeds: Science, Technology and Uses. CABI. pp. 14–15. ISBN 978-0851997230.CS1 maint: uses authors parameter (link)
  6. Frank W. Telewski. "Research & Teaching". Department of Plant Biology, Michigan State University. Retrieved 10 December 2015.
  7. Poschlod, Peter; Fennel, Sabine; Hartig, Florian; Valdez, Jose W. (2019). "The Recruitment Niche Predicts Plant Community Assembly Across a Hydrological Gradient Along Plowed and Undisturbed Transects in a Former Agricultural Wetland". Frontiers in Plant Science. 10: 88. doi:10.3389/fpls.2019.00088. ISSN 1664-462X. PMC 6372561. PMID 30787938.
  8. Ross, Merrill A.; Lembi, Carole A. (2008). Applied Weed Science: Including the Ecology and Management of Invasive Plants. Prentice Hall. p. 22. ISBN 978-0135028148.
  9. Faiz F. Bebawi, Robert E. Eplee and Rebecca S. Norris (March 1984). "Effects of Seed Size and Weight on Witchweed (Striga asiatica) Seed Germination, Emergence, and Host-Parasitization". Weed Science. 32 (2): 202–205. doi:10.1017/S0043174500058811. JSTOR 4043831.CS1 maint: uses authors parameter (link)
  10. Daniel M. Joel, Jonathan Gressel, Lytton J. Musselman (2013). Parasitic Orobanchaceae: Parasitic Mechanisms and Control Strategies. Springer Science & Business Media. p. 394. ISBN 9783642381461.CS1 maint: uses authors parameter (link)
  11. 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.
  12. Fisher, J., Loneragan, W., Dixon, K., and Veneklaas, E.,Soil seed bank compositional change constrains biodiversity in an invaded speciesrich woodland, Biol. Conserv., 2009, vol. 142, no. 2, pp. 256–269
  13. Fisher, J., Loneragan, W., Dixon, K., and Veneklaas, E.,Soil seed bank compositional change constrains biodiversity in an invaded speciesrich woodland, Biol. Conserv., 2009, vol. 142, no. 2, pp. 256–269
  14. Wang, Y., Jiang, D., Toshio, O., & Zhou, Q. (2013). Recent advances in soil seed bank research. Contemporary Problems of Ecology, 6(5), 520-524.
  15. 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.
  16. Hopfensperger, K.N., A review of similarity between seed bank and standing vegetation across ecosystems,Oikos, 2007, vol. 116, pp. 1438–1448.
  17. 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
  18. Wang, Y., Jiang, D., Toshio, O., & Zhou, Q. (2013). Recent advances in soil seed bank research. Contemporary Problems of Ecology, 6(5), 520-524.
  19. Poschlod, Peter; Rosbakh, Sergey (2018). "Mudflat species: Threatened or hidden? An extensive seed bank survey of 108 fish ponds in Southern Germany". Biological Conservation. 225: 154–163. doi:10.1016/j.biocon.2018.06.024.
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