January-February 2022 • Nebraskaland 45
Seed Dormancy
Seeds are plants' life blood: its
agent of dispersal to new habitats,
as well as the foundation of its
next generation. Seed dormancy
is an adaptation to increase seed
efficiency by delaying and staggering
germination over time, allowing at
least some seeds to sprout under
conditions favorable for seedling
survival and growth.
Dormancy provides plants many
advantages. Key in our climate, the
dormancy of most prairie wildflower
and grass seeds are broken by
exposure to the cold and dampness
of winter. The seed coat softens
or chemical changes occur within
the seed, allowing the embryo to
sprout in spring. Without dormancy,
a potential worst-case scenario is
that a plant's entire summer bounty
of seed sprouts during a warm,
wet spell in autumn, and winter's
chill kills an entire generation of
seedlings.
A far better strategy is for the
precious seed to lay dormant in
the soil through winter and sprout
the following spring, allowing the
seedlings to mature under the warm
summer sun. Prairie restorationists
typically plant seed in fall so it can
naturally break dormancy over
winter.
Exposure to sunlight breaks the
dormancy of some buried seed,
brought to the surface by erosion,
tunneling animals or trampling by
large ungulates. The hard seeds of
starry false Solomon's seal and other
plants are stimulated to germinate
by passing through an animal's gut,
where stomach acids or a gizzard's
grinding action weaken the seed
coat, allowing water uptake and the
seed to sprout.
The seed of some plants lay
dormant in the soil until stimulated
to sprout by favorable events.
Researchers, for example, have
recently discovered that the heat
and smoke of prairie fires chemically
weaken the seed coat of some prairie
wildflowers, such as buffalo bean and silver-leaf
nightshade, allowing their seedlings to take root
in fire-bared, sun-soaked soils temporarily free of
competition from other vegetation.
The length of time a seed can remain dormant
varies by species. Hard-coated seeds, such as
those of the Illinois bundleflower (shown above), a
widespread species in eastern Nebraska prairies,
can remain dormant and viable in the soil for
decades. The longest documented seed dormancy:
Researchers sprouted seeds of the narrow-
leafed campion that had been buried in Siberian
permafrost for an estimated 31,800 years.
Illinois bundlefl ower, a common species in eastern Nebraska prairies,
produces hard-coated seeds that can remain dormant and viable in soil
for decades.
