h a l f b a k e r yQuis custodiet the custard?
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Possibly MFD bad science... trying to avoid magic here. I
wonder if it would be possible to genetically modify a tree
with a long taproot, such as the mango tree, to use the root
to draw up geothermal heat (as in, more heat than they
currently get from the water and nutrients down there),
possibly
by
growing roots that grow very deep down, deeper
than is necessary for nutrients, in search solely of heat.
The goal I had in mind was to plant forests of these trees in
places that are home to migratory birds so they don't have
to migrate south for the winter to forests that are declining
due to logging operations. A forest of heat-emanating trees
would develop its own ecosystem in which the birds would
thrive so they don't have to go south for the winter. This
would reduce, in part, the damage caused by deforestation
in the warmer climates that they migrate to.
If it's MFD, it's MFD. I get it. What do you guys think?
Geothermal Energy
http://www.mpoweruk...othermal_energy.htm
Pretty deep [csea, Nov 19 2011]
Not that deep...
http://en.wikipedia...eothermal_heat_pump
//Depending on latitude, the temperature beneath the upper 6 metres (20 ft) of Earth's surface maintains a nearly constant temperature between 10 and 16 °C (50 and 60 °F)// [21 Quest, Nov 19 2011]
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Annotation:
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I think it could be done, using GM maple trees that not
only have the suggested heat-seeking taproot, but also an
internal plumbing system to circulate the heated maple
syrup. If the leaves could somehow be metallic, they may
serve as better fins. |
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This idea was played with in one of SF writer David Brin's
books. I think it was "Startide Rising". These trees were
found on an abandoned alien world and puzzled the
biologists mightily as it was an 'all or nothing' strategy by
the trees which couldn't have evolved naturally and
incrementally. |
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Hmm... I wonder if it could be done by 'tweaking' the
phototropism exhibited by many plants. The roots, of
course, aren't phototropic, but perhaps they could be made
so. And If they could be made phototropic, perhaps they
could be made thermotropic, causing them to grow deeper
and deeper. |
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I'm pretty sure the depths required to reach suitable temperatures exceed any reasonable guess as to possible taproot depth. [link]
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Hmm, I see you're just suggesting to keep the tree above freezing temperature. |
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I think a lot depends on what you mean by
"geothermal energy".
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Surface temperatures fluctuate seasonally, and
the top few inches of soil follow them, so there's
nothing there.
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A few feet further down, soil temperatures are a
pretty stable average of the year-round
temperature, so there's some excess energy
available in winter (but also an energy drain in
summer). I guess all deep-rooted plants in areas
with harsh winters benefit from this to an extent.
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Further still, the ground temperature is averaged
out over longer periods (over the last few years,
the last few decades, centuries, millennia...) as
you go deeper, so there might be some residual
heat from a previous warmer climate.
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All this heat is just stored atmospheric heat.
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Deeper yet, and the temperature rises (regardless
of local climate history) because of true
geogenic energy coming from radioactive stuff
decaying. So this is the only depth at which you
can really get "new" energy as opposed to stored
climate heat.
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The problem is, though, that very little biology is
able to harvest heat energy. Biology is very good
at adapting to the local temperature (to facilitate
reactions), but I don't see how it generally
harvests heat energy.
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For one thing, you need a thermal gradient to
benefit from heat energy. You also need an
efficient heat-pipe to let that gradient cause a
rapid heat flow. I don't see how a tree, even if its
roots are hotter than its crown, can transport
enough thermal energy to be useful. Sap moves
so slowly that hot sap from the roots is going to
simply equilibrate little by little with its
surroundings as it rises; there's never going to be a
big and sudden exchange of heat that will be
useful.
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So, I don't see how you're going to do anything
useful this way. Yes, trees can (and perhaps could
more so) benefit from having their roots in warm
soil (or even, in theory, in rock which was hot
from
geothermal energy), but their crowns still have to
grow in the local climate.
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So, a mango tree isn't going to thrive if its roots
are warm and its crown is cold; it can't pump up
enough heat (in sap or whatever) to keep the
leaves warm (they have a huge surface area). In
fact, it's going to be harder for a plant like this,
because it has to have one set of enzymes in its
roots (where they're warm) and a different set
optimised for the local climate in its leaves.
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And the birds themselves - they are adapted
largely to the relevant climate, and simply
extending the range of mango trees isn't
necessarily going to solve the problem - there's
insects and water availability and all that stuff to
think about.
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So, if you want to use geothermal energy to
create forests of tropical trees further from the
equator, I think your only hope would be to dig
down and harvest the energy with huge heatpipes
(steam geysers or whatever) and use that heat to
warm the local climate. But there may be some
complications with that idea too. |
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The roots should only need to go down 20-30 feet to absorb
enough heat to keep the tree's temperature above
freezing. Given the typical length ratio of taproot to plant,
a 30-40 tree should generate a taproot at least that long.
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Edit: after reading Maxwell's annotation, I realize that my
own assumptions may be a little... off. |
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I guess our annotations overlapped. But do you
know how much energy has to be pumped up from
a groundsource to keep the leaves above ambient
temperature? It'll be a huge amount, because
leaves are flat. I don't see any way to pump heat
that quickly from the ground to the leaves, unless
you're talking about a fraction of a degree of
temperature increase.
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Even then, heat energy will dissipate from the
warmed leaves way faster than it can be
transported through rocks to the roots. You're
trying to balance the heat flux at the surface of a
thousand big, flat leaves in air which can convect,
against the heat flux through a smaller area of
rock surrounding the roots.
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Even then, even if this heat flux could keep the
leaves a degree warmer (and I'd guess 0.1°C would
be the real limit), what happens when it rains or
snows, and the thermal energy being carried away
from the leaves increases by a factor of 10 or 100?
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The problem is not one of heat availability, it's
one of heat transport. If you really want to stop
the leaves freezing, you need to evolve frost-
tolerant leaves (doable), or figure out a way to
temporarily raise metabolic rates in the leaves to
generate heat locally in times of cold.
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[OK, we've got overalapping annos, so I'll go away
for a bit until we get back in synch.] |
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(Way out of my depth on the subject!)
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Even if a suitable temperature gradient were available, wouldn't the relative heat transfer ratios (earth/root) vs. (leaves/air) cause this to be extremely inefficient?
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{I see [MB] beat me to the same conclusion by a few minutes...} |
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Yes, if you're talking about a tree with flat leaves. I used
the mango tree as an example of a tree with a long
taproot, bit of a red herring. Sorry. What about conifers
with much more narrow leaves, such a juniper? |
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I dunno - I think that even then the heat loss
would far outrun the heat transfer.
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For conifer needles, imagine all the needles
joined end-to-end. Now imagine the roots joined
end-to-end. One is going to be much longer, and
have a larger surface area, than the other.
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You'd be best off with some sort of succulent
(large volume to surface area). Even then,
though, I don't think you could do it with any non-
spherical plant of a reasonable size - better to
raise the metabolic rate in the leaves and
generate the heat locally.
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If you *really* wanted to do this, you would have
to use chemical harvesting and then release of
the energy. So, you have a reaction in which A+B
is in equilibrium with AB, and where increasing
temperature shifts the reaction more towards AB.
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You pump A+B down to the roots, and then (and
only then) expose them to an enzyme which will
allow them to quickly reach equilibrium with AB.
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Then you pump the AB (plus residual A+B) up to
the leaves, where the temperature favours the
A+B side of the reaction. Then (and only then) do
you expose them to the enzyme again, allowing
AB to break down quickly into mostly A+B,
releasing the heat. Then you repeat.
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In other words, you could transport the energy
with less loss if you use a shifting chemical
equilibrium facilitated by local enzymes, than if
you transport it directly as
heat. It also means you could store AB in the
leaves (without enzyme) for some time, against
frost. What you're doing, really, is restricting the
heat
exchange to the two relevant areas (roots,
leaves).
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But I still don't think it'll work. |
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Inducing drastic climate change to allow unfettered
continuation of mass deforestation. Smart. |
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The deforestation is already happening, and will continue to
happen regardless of the plight of the wildlife being displaced.
This is Plan B. |
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It's always good to have a Plan B, even if it's a horrible
plan. |
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I keep reading this as "geothermal teapot", which is
probably another idea. |
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