Soil Seed Bank
Encyclopedia
The soil seed bank refers to the natural storage of seed
s, often dormant, within the soil
of most ecosystem
s. 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. 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
.
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.. 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 is a formerly widespread cereal weed.
(Nelumbo nucifera) found buried in the soil of a pond; these seeds were estimated by carbon dating to be 1,040 years old.
of many ecosystems. For example, the rapid re-vegetation of sites disturbed by wildfire, catastrophic weather, agricultural operations, and timber harvesting is largely due to the soil seed bank. Forest ecosystems and wetland
s contain a number of specialized plant species forming persistent soil seed banks.
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
.
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.
bank can be used to include non-flowering plants such as ferns
and bryophyte
s.
In addition to seeds, many 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, which includes dormant and adventitious buds on stolons, rhizomes, and root
s.
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s, often dormant, within the soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
of most ecosystem
Ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
s. The study of soil seed banks started in 1859 when Charles Darwin
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
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. Weed seed banks have been studied intensely in agricultural science
Agricultural science
Agricultural science is a broad multidisciplinary field that encompasses the parts of exact, natural, economic and social sciences that are used in the practice and understanding of agriculture. -Agriculture and agricultural science:The two terms are often confused...
because of their important economic impacts; other fields interested in soil seed banks include forest regeneration
Silviculture
Silviculture is the practice of controlling the establishment, growth, composition, health, and quality of forests to meet diverse needs and values. The name comes from the Latin silvi- + culture...
and restoration ecology
Restoration ecology
-Definition:Restoration ecology is the scientific study and practice of renewing and restoring degraded, damaged, or destroyed ecosystems and habitats in the environment by active human intervention and action, within a short time frame...
.
Background
Many taxaTaxon
|thumb|270px|[[African elephants]] form a widely-accepted taxon, the [[genus]] LoxodontaA taxon is a group of organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement...
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
Chenopodium album
Chenopodium album is a fast-growing weedy annual plant in the genus Chenopodium.Though cultivated in some regions, the plant is elsewhere considered a weed...
(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.. 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 is a formerly widespread cereal weed.
Seed longevity
Longevity of seeds is very variable and depends on many factors; few species exceed 100 years. 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 and still viable seeds were those of LotusLotus (genus)
Lotus is a genus that includes bird's-foot trefoils and deervetches and contains many dozens of species distributed world-wide. Depending on the taxonomic authority, roughly between 70 and 150 are accepted. Lotus is a genus of legume and its members are adapted to a wide range of habitats, from...
(Nelumbo nucifera) found buried in the soil of a pond; these seeds were estimated by carbon dating to be 1,040 years old.
Environmental significance
Soil seed banks play an important role in the natural environmentNatural environment
The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....
of many ecosystems. For example, the rapid re-vegetation of sites disturbed by wildfire, catastrophic weather, agricultural operations, and timber harvesting is largely due to the soil seed bank. Forest ecosystems and wetland
Wetland
A wetland is an area of land whose soil is saturated with water either permanently or seasonally. Wetlands are categorised by their characteristic vegetation, which is adapted to these unique soil conditions....
s contain a number of specialized plant species forming persistent soil seed banks.
The absence of a soil seed bank impedes the establishment of vegetation during primary succession
Primary succession
Primary succession is one of two types of biological and ecological succession of plant life, occurring in an environment in which new substrate devoid of vegetation and usually lacking soil, such as a lava flow or area left from retreated glacier, is deposited...
, while presence of a well-stocked soil seed bank permits rapid development of species-rich ecosystems during secondary succession
Secondary succession
Secondary succession is one of the two types of ecological succession of plant life. As opposed to the first, primary succession, secondary succession is a process started by an event that reduces an already established ecosystem Secondary succession is one of the two types of ecological...
.
Population dynamics 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 the 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.
Associated ecosystem processes
The term soil diasporeDiaspore (botany)
In botany, a diaspore is a plant dispersal unit consisting of a seed or spore plus any additional tissues that assist dispersal. In some seed plants, the diaspore is a seed and fruit together, or a seed and elaiosome. In a few seed plants, the diaspore is most or all of the plant, known as a...
bank can be used to include non-flowering plants such as ferns
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
and bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s.
In addition to seeds, many 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, which includes dormant and adventitious buds on stolons, rhizomes, and root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s.