Seedbank, seed-bank, or seed bank (≈ buried seeds)

1. A store of viable seed (種子) buried and dormant (休眠) in the soil or underwater sediments.
2. The place where seeds of rare plants or obsolete varieties are sotred in carefully controlled conditions to preserve their genetic material for research and possible future use.

Seedbank dynamics

s = (p + i) - (c + c' + o), where

s: number of seeds present in a given soil
p: number of seeds prodcued in a unit time, e.g., year
i: number of immigrated seeds from the outside
c: number of germinated seeds
c': number of dead seeds

c' = d + h (d: dead (s.s.), h: fed by herbivores)

o: number of seeds escaped from the soil

Seeder vs sprouter

1. Germination: sowing soil on pot
   easy way
   waste long time (occasionally more than 6 months), low accuracy (all seeds do not always germinate)
   low seed recovery rate in general
2. Hand sorting: power play under a binocular stereomicroscope
   easy way
   restricted sample volume, Boring job
   high seed recovery rate
3. Sieving: seiving with various mesh sizes
   easy way, quick treatment
   difficult to extract all sedds, in particular, small seeds
   seed recovery rate depending on the soil sample
4. Flotation: seeds floated by a high-concentration solution
   quick treatment, high seed recovery
   complicated manipulation, seeds damaged by flotation solution
   very-high seed recovery rate

(Feast & Robert 1973)

Germination test

for the estimation of the density of buried seeds

(Ter Heerdt et al. 1996)

Improved germination test

Coarse = 4.00 mm mesh width
Fine = 0.212 mm

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1. Seedling emerged more than by unconcentrate samples
2. Hand-sorting afterwards shows that the germination rates vary between 81 and 100% of the viable seeds present
3. 95% seedlings emerge within 6 weeks

(Traba, et al. 1998)

Concentrating samples can lead to seed losses in soil bank estimations

Traba et al. (1998) = 0.100 mm-diameter sterile nylon mesh

[ter Heerdt et al. (1996) = 0.212 mm in mesh width]

vs

Seedling emergence (/432 cm³)

NC > C (Wilcoxon range test, P < 0.05)
Those species produce small seeds.

Discriminant criteria on seed survival (種子生死判別)

TTC staining on seed embryo for viability check

Preparation of artificial buried-seed populations

Small plastic capsules, each of which contains 50 seeds and sea sand, are buried into soil. Four pin holes were drilled through each capsule so that the contents of air and humidity might equilibrate with those outside.

Seed extraction from soils by a flotation method (Tsuyuzaki 1994)

Principle

Flotation method with centrifugation

↓ - add 50% K₂CO₃ (specific gravity = 1.54)
↓ - agitation by a high-power mechanical stirrer for a few min.²
↓ - centrifugation at > 3000 g for 3-5 min

↓ - filtration using an aspirator ³
Seeds and organic debris are collected on 2-3 layered miracloth
↓ - inspection uder a binocular stereomicroscope

1. The volume of soil sample is dependent on the volume and number of centrifugation tubes. I usually use four 200-ml centrifugation tubes at a time. Do not use glass tube.
2. The power os Mini-stir is not enough to agitate soil sample.
3. Wash the organic debris well using distilled water to reduce seed damage by salt solution. The side-wall of centrifugation tubes should also be washed wall to remove organic depris on the wall.

[protocol (プロトコル)]

Preparation

For flotation

Flotation solution

For sorting

(Yamasaki et al. 2020)

Genebank ジーンバンク (農研機構)

Dr. Beal's experiments

Year                             50   80 100
Brassica nigra                 +   -     -
Polygonum hydropiper    +   -     -
Malva rotundifolia            -    -    2
Verbascum thapsus         -    -    2
Oenothera biennis        38  10    -
Rumex crispus              52   2     -
Verbascum blattaria     62  70   42