Survival of Subnivean vs. Supranivean Plants

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Transcript Survival of Subnivean vs. Supranivean Plants

Survival of Subnivean
vs. Supranivean Plants
*The Snow Buttercup and
Engelmann Spruce*
Arden Piland
Winter Ecology – Spring 2005
Mountain Research Station – University of Colorado, Boulder
Two Environments
• Subnivean: The environment below the
snow (Snow buttercup)
• Supranivean: The environment above the
snow (Engelmann Spruce)
• Living through the winter:
-most plants well adapted to these
• Reproduction and success of offspring:
-directly related to winter conditions
leading into growing season
• What factors affect the reproductive
success and the survival of seedlings
of the two species?
• How do the species help to ensure the
survival of progeny?
Effects of Snowdepth
• Growing season length
-outer regions of snowpack= earlier melt=longer
growing season
-30% decrease in growing season from shallow
to deep parts
• Soil fertility
-shallower depths more fertile (more nutrients)
*overtime, more vegetation and microbial
activity (Galen and Stanton, 1999)
• Water availability
-more snow in winter = more available moisture
Snow Buttercup (Ranunculus
• Hemicryptophytes
• Store starch in roots to
• Start to grow under snowpack
• Emerge with established
flowers and photosynthesizing
(Stanton et al, 1997)
Effects of growing season length
• Seeds
-fewer seeds produced in late
melt sites (G&S,1991)
-33% decrease in seed mass
in late melt sites
*Larger seeds 6 times more
likely to germinate (G&S,
Effects cont…
• Seedlings
*30% increase in production of true
leaves in early melt sites
*22% decrease in winter survival if
didn’t produce true leaves in first
Effects of soil fertility
• Higher nutrient content= more conducive
to infection by mycorrhizae
• Higher starch content in roots
• More resistant to yearly differences in
growing season length (Scherff et al, 1994)
Some things they do….
• Habitat affinity: more
abundant in early
melting sites (G&S, 1999)
• Symbioses with
-Vesicular arbuscular
mycorrhizae (VAM)
(Mullen & Schmidt, 1993)
endophytic (DSE) fungi
(Mullen et al, 1998)
• Photosynthetic seeds
(G&S, 1997)
• Main stresses:
-growing season length
*affects time for production-less
seeds, less viable seeds, weaker
-soil fertility
*less nutrient gain, less starch
storage, slower growth from snow
(problems of growing season), less
Engelmann Spruce (Picea Engelmanni)
• Not limited by snowpack determined
growing season..
-water? Yes, but can still set seeds..
• Greatest mortality occurs during
seedling life stage
• Survival of seedling critical
Stress factors for seedlings
• Water availability
-in unusually dry year (not much winter
snowfall) no seedlings emerged-1st time in 16
years (Johnson et al, 2004)
-multiyear study-most seedlings emerged in
wettest year (Germino et al, 2001)
-measure of seedling water potentials
*lowest levels of photosynthesis when
lowest water potentials (Johnson et al,
Stress cont…
The problem of low temperature photoinhibition
• Photoinhibition= low levels of photosynthesis
Low night temperatures + high light exposure
• High sky exposure= lots of heat lost to night sky=low leaf
temperature=frost formation=stomate damage.
• Next day high light=rapid warming, can’t adjust=respiration
>>photosynthesis (Germino & Smith 1999)
• Coupling of effects means reduced photosynthesis.
-restricted carbohydrate and energy gain, don’t form good
roots=more water stress=chance of survival decreases
(Johnson et al, 2004)
Seedling survival tactics
• Tree islands
-seedling density decreases farther from
tree islands
*reduces sky exposure (insulation/less
light), convective heat gain = less
photoinhibition (Germino et al, 2001)
• Grass cover
-90% survival rate
*same protection as from trees
(Germino et al, 2001)
Survival cont..
• Crown architecture
-needles inclined from horizontal
*decreases sky exposure
* heat dissipation between needlesgradual warming in day, slower cooling at night
(Germino & Smith, 1999)
• Habitats with water retention
-high % new seedlings found on moss layers
and fallen logs (Johnson et al, 2004)
Yep, still goin’…..
• Ribbon forests
-Seedlings establish selves on leeward side
*more water available
*protection from high light and low
temps. (Marchand, 1996)
Conclusions of ES seedlings
• Stresses-#1 water availablity (if low, extremely low levels of
photosynthesis, dessication, death)
-High sky exposure=low night temps & high day light
levels=photoinhibition= plant growth decreased (bad
• Cope methods
- “choose” sheltered habitat (Tree islands/ribbon forests,
grass cover)
-alter crown structure to reduce photoinhibition
- “choose” site with more water (mosses, logs,
leeward side of ribbon forest)
• Snow buttercup
-survival restricted by growing
season length and soil fertility
-Survive by:
*habitat selection (longer
growing season, more fertile soilmore/better seeds)
*mycorrhizae symbioses
(more nutrient acquistion, more
explosive growth, longer grow
season, more resilient)
*photosynthetic seeds (more
carbohydrate production, better
reserves, better survival )
Engelmann Spruce (seedlings)
• Survival restricted by:
-low temps/high light
(photoinhibition, bad roots)
-water (less photosynthesis,
dessication, death)
• Ensure survival by:
-Increasing cover (tree islands,
grass, alter crown structure)
-moister habitat selection
(leeward of ribbons, mosses,
• Subnivean (snow buttercup) and
Supranivean (Engelmann Spruce) both
affected by winter conditions but in different
-Subnivean: snowpack restricts length of
growing season and alters nutrient
-Supranivean: snowpack restricts amount of
water available but also restricted by poor
plant health (reduced roots) from
*Plants from both environments developed
behavioral and morphological adaptations to
ensure their survival.
Galen, C, Stanton M.L. 1991. Consequences of emergence phenology for reproductive
success in Ranunculus adoneus. American Journal of Botany. 78(7):978-988.
Galen, C, Stanton M.L. 1993. Short term responses of alpine buttercups to experimental
manipulations of growing season length. Ecology 74(4):1052-1058.
Galen, C., Stanton, M.L. 1999. Seedling establishment in alpine buttercups under experimental
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Germino, M.J., Smith, W.K. 1999. Sky exposure, crown architecture, and low-temperature
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survival in alpine-treeline ecotone. Plant Ecology. 162:157-168.
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buttercup, Ranunculus adoneus. Evolution. 51(1):79-94.
Survival Strategies
• Habitat affinity, mycorrhizae and
photosynthetic seeds =
-more carbohydrate production
-more reserves
-faster growth from snow (longer grow
-more seeds/ better seeds