Frosts, supercooling, and other fun stuff

chuck schwartz puppincuff@cox.net
Wed, 14 Nov 2007 16:41:14 PST
My experience with palms which burned at temperatures 10 degrees above 
freezing when the sun hit them first thing tn the morning led to surmise 
that the free electrons generated by the chloroplasts are not utilized since 
the enzymes responsile for their being passed along are not 'up to speed' 
due to the depressed temperature.
chuck Schwartz
San Clemente CA
----- Original Message ----- 
From: "Joe" <jshaw@opuntiads.com>
To: <pbs@lists.ibiblio.org>
Sent: Tuesday, November 13, 2007 8:42 PM
Subject: Re: [pbs] Frosts, supercooling, and other fun stuff


> Hi Gang,
> 1. I'm still confused about the sunshine vs. warm water notion of reducing
> damage to plants that have gotten too cold. Wives' tale or note, the 
> notion
> persists and some folks seem to have good luck by pouring water over their
> plants before the sun shines on them. I can't figure it out.
>
>
>
>
> 2. I like the term I first encountered in email from a South African email
> friend. It was immediately obvious what she meant when she referred to a
> "black frost."
>
>
>
>
> 3. In the absence of ice forming nuclei (e.g., tiny particles), water can
> supercool to about -38 C, the homogeneous nucleation point. Dissolved 
> salts
> or sugars can depress this temperature a few degrees more. Thus, with or
> without "antifreeze" type solutions, trees (not sure about bulbs) can
> prevent ice crystals from forming in their cells if they can achieve
> supercooling of their cellular liquids (apoplast and symplast).
>
> There is some correlation between the northern limit of certain trees, and
> the homogeneous nucleation point. It is proposed (but I don't know if it's
> true) that some species are limited in their northward ranges because -40 
> C
> is about the limit for this effect.
>
> Oddly, some evidence indicates that water can supercool to -70 C under
> laboratory conditions. Pehraps some plant out there can perform such a
> trick, but I've not hear of it.
>
>
>
>
> 4. To survive temperatures lower than -40 C, plants may resort to
> dehydration, pulling water out of their living cells. This my be the
> antifreeze-like effect that has been mentioned because water outside the
> cells freezes and serves to pull even more water out of living cells,
> leaving their cytoplasm ever more saturated with proteins, lipids, sugars,
> etc.
>
> The reason ice can "pull" water out of cells is that frozen water has a
> concentration of zero, in terms of liquid water, and water moves from 
> higher
> concentrations (i.e. inside cells) to areas of lower concentration. Just
> think of the water pulled out from foods in some freezers-eventually foods
> can become nearly freeze dried.
>
> I think dehydration mechanisms are responsible for the survival of some
> plants (not all plants) in areas where they are routinely exposed to
> temperatures below -40 C (or so).
>
>
>
>
> 5. The heat of fusion refers to the extra energy that must be released by
> water if it is to freeze. As was mentioned, sprinklers over citrus can 
> often
> be useful because the ground water keeps hitting the leaves and even
> freezing. However, the whole process keeps all the ice at about 32 F (0 C)
> even when air temperatures might be in the mid- to low-20s.
>
> As long as you can keep new water freezing on plants you can generally 
> keep
> the plants at about 32 F. If no new water arrives the ice on the plants, 
> and
> the plants too, will continue to cool to ambient temperatures. Ground 
> water
> offers two benefits: 1) it brings some warmth with it (perhaps it is 40-50
> F) and it has energy to release (heat of fusion) before it will freeze.
>
>
>
>
>
>
> LINK: Enthalpy of fusion, Wikipedia
> http://en.wikipedia.org/wiki/Enthalpy_of_fusion/
>
>
>
>
> LINK: Supercooling Water to -70 C
> http://geog.ubc.ca/crpoints/papers/…
>
>
>
>
>
>
> Cordially,
>
>
>
> Joe
>
> Conroe TX, where a bit of cool weather would be appreciated.
>
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