Ecolog:
As Kent has pointed out, the quote apparently is from David Attenborough's
book; I found it on a website concerning "biomimicry."
http://www.asknature.org/strategy/2386af151126ef7579cf5c506b6dc7de
I have also received some off-list comments that lead me to be more direct,
although I did not want to add my own opinions initially, trying to keep it
simple and short, without bias. So here's my take on the paragraph, and I
would like to stand corrected where I am wrong or off-base. Thanks to all
who have responded thus far.
First, Attenborough has done a lot to foster appreciation of Nature via film
and print, and I do not want this to appear disrespectful. On the other
hand, if people are being mislead about how plants function, perhaps there
are Ecolog subscribers who have both the competence and the status, not to
mention the courage, to set us all straight, including, if necessary,
Attenborough.
1. It is my understanding that plants do not "find" water, nor do they
"seek" it; they develop where conditions conducive to root development
exist--where such conditions do not exist, they do not develop. For example,
if my understanding is correct, the most basic requirements for plant root
development are the presence of available water in sufficient quantity and
pore spaces at least equal to the diameter of the root tip. I don't remember
(if I ever knew) how much energy a root tip can exert when growing forward,
but have a dim memory that it was relatively slight. Of course roots seem to
be able to exert very high pressures laterally, but I don't have recent
research on either. I am acutely sensitive to the fact that some of the
"facts" I "learned" in years past, or those which are simply wrong, may
constitute a flawed personal paradigm, so I hope y'all will fill me in on
the latest references.
2. It is also my understanding that plants do not "position" their leaves
"for" optimal absorption of light, but that photochemical reactions,
gravity, and other forces are involved in complex processes that result in
what an observer, unaware of those conditions, might attribute to perhaps an
interesting bit of "cleverness" on the part of the plant.
3. I am not aware of any mechanism possessed by any plant that can cause it
to "drive a tap root" deep into the ground "to reach" THE water[-]table. I
have investigated profiles where roots (of phreatophytes) were confined to
the upper soil profile even though a water-table existed at a greater depth
and had not developed through an intervening part of the profile of
relatively dry soil after many years of light rainfall seasons which were
not sufficient to produce a wetted profile to the depth of the capillary
fringe of the water table. Of course, observations are not controlled
experiments. The third sentence seems to comport with the theory I have
learned, with the exception of the implication that they "had" to develop
root systems "far deeper than they are tall." Though this seems quite true,
the implication that there might or should be some relationship between
height or spread of the above-ground part of the plant seems odd, since I
know of no reason why there should be a connection--both above-ground and
below-ground parts of plants develop according to the conditions of their
environment, hence both above-ground and below-ground environments that are
quite different. Similarly, the areal extent of root systems and their depth
beneath the surface are a function of the presence of conditions favorable
to root growth, not an expression of some "competitive strategy" on the part
of the plant.
This is not to pick on Attenborough, but it does serve as an example of
science writing that may go a bit too far with conclusions, when a
discussion of the actual facts of how plants work would not have only been
more informative but more interesting. There is no need to write down to
"the general public," and science writers have a responsibility to make sure
that their writing does not "lead them down the garden path," as it were,
especially as the general population contains a fraction who may go beyond
entertainment and with whom the opportunity exists to lay a firm and factual
foundation for their growth into scientists.
So there, as briefly as possible, is my own take on this particular
paragraph. It has caused me to pay closer attention to science writing in
general and to Attenborough in particular, because he is so widely respected
in the field. I recently watched one of his nature films in which he
advanced the idea that species "advanced" through evolution. That left me
wondering how many people think that evolution is a process by which a
species "improves" or "progresses" over time rather than adapts to changing
environments--a concept which seems to be common amongst non-evolutionary
biologists. It seems to me that getting it right is not the responsibility
of the public, but the responsibility of scientists and science writers. At
least such writing should not be misleading. And, it seems of vital
importance in interpreting ecology to the world at large.
I look forward to your corrections.
WT
----- Original Message -----
From: "Wayne Tyson" <landr...@cox.net>
To: <ECOLOG-L@LISTSERV.UMD.EDU>
Sent: Thursday, November 18, 2010 12:15 PM
Subject: [ECOLOG-L] Roots find water
Ecolog:
Please advise whether or not the following quote is completely valid; if
not, what specifically is invalid and why :
"To find water, a plant has to position its roots with just as much
precision as it arranges its leaves. If moisture is in very short supply,
then a plant may have to drive a tap root deep into the ground to reach the
water table. Some desert plants have had to develop root systems that are
far deeper than they are tall and extend laterally a very long way beyond
the furthest extent of their foliage. Even if the environment is
well-watered, a plant may still need to compete with others for this
essential commodity, so it positions a network of roots within a few inches
of the soil surface, where it can gather the rain water before others can."
WT
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