When you consider the timing of observations of root position relative to
available water, the situation can be even more confusing. When conditions
in the soil are favorable to do so (say, during a rainy season) roots may
grow deep, passing through soil that will later not support the growth of
tip meristems. Putting it another way, the growing root tips may follow the
capillary fringe downward as it lowers with the advancing dry season. If
one excavated said roots in the high dry season, they would indeed be found
to cross soil that was too dry at the present to support root elongation,
(though they may thicken, since they have access to the water brought up
from below). Unless the observer took into account previous conditions,
he/she might indeed think the roots had set out to "cross the desert" of dry
soil to reach the wetter soil below. Even someone fairly sophisticated
might get taken in.
Martin
2011/5/31 Jason Hernandez <[email protected]>
> The problem is that "people" (meaning laypersons from the point of view of
> the particular scientific discipline) do not actually read *scientific*
> literature on it. How often have we seen -- in books about horticulture,
> landscape architecture, and so on -- that willows should not be planted near
> underground pipes because their roots will enter and thus destroy said
> pipes? To someone unfamiliar with the science behind it, it would *appear*
> to be saying that the willows somehow detect the presence of water in the
> pipes and grow into them seeking said water. Such literature does not make
> explicit what we know: that this phenomenon presupposes that the pipes are
> already leaking, the willow roots are already in contact with the resulting
> gradient, and grow along the gradient into the existing leaks in the pipes.
> Add to this the phobia of most non-scientists toward reading scientific
> literature -- because they already assume they will not understand
> it -- and there is little to counter such misconceptions arising from
> oversimplification.
>
>
>
> Date: Thu, 26 May 2011 22:56:18 -0700
> From: Wayne Tyson <[email protected]>
> Subject: Re: Plant roots matter Re: [ECOLOG-L] Communication Science to
> Public Plant Roots
>
> Dave, I don't know what "people" would say about the sealed container =
> exactly; I only know what many people, some who seem quite certain about =
> it, who apparently not only believe that roots search for water, but =
> think that water rises from the depths (all the way to the surface, far =
> above the capillary fringe, and who also apparently believe that water =
> from a single precipitation event, no matter how small, will eventually =
> reach the water table (capillary fringe, but I won't argue that). Most =
> people don't have any idea what a moisture gradient is, but are they =
> well- or ill-informed by science writing that implies or states outright =
> that roots can detect water and seek it out; that is, that roots can =
> grow through almost anything, no matter how dry, to "find" water?=20
>
> WT
>
> Here's a story: Several years (decades) ago I heard a paper by a =
> "restoration ecologist" who was quite proud of spending well over =
> $200,000 ($218,000 as I recall) per acre to "create" riparian habitat =
> adjacent to a river in the southwestern USA. Many years later I was =
> asked by the responsible federal agency to assess why that "created" =
> riparian habitat was not working; why the trees (mature riparian trees =
> salvaged via "tree-spade") were not growing and were dying. The apparent =
> theory behind the "creation" project was that by cutting an adjacent =
> hill down to a level area adjacent to the river, tree-spading the trees =
> in, and watering them with a single drip emitter each, that the roots =
> would reach the water table and the trees would thrive. I had several =
> trenches dug to about 18 feet, sectioning a sampling of the trees in =
> question; the tree roots had not grown down through the intervening =
> formation to the water table because that formation did not contain =
> available water and there was no water table (except for one site, where =
> water was found, near the river, at about fifteen feet). The few roots =
> that could survive on the very little water from the drip emitter that =
> did not evaporate or was not transpired by weedy vegetation managed to =
> support about half of the leaf area of the tree-spaded trees. Adequate =
> irrigation would have provided a moisture gradient and adequate water =
> for growth or at least kept the trees alive, but they would have been =
> almost entirely dependent upon artificial irrigation forever. The =
> restoration ecologist had done no coring to confirm her theory that =
> there would be a water table adjacent to the river just like the =
> textbook says, but in many areas in the Southwest, rivers, especially =
> those with hillsides adjacent to their banks, are not textbook cases. =
> This fundamental error has been committed, I have been told, in other =
> places. There is no substitute for facts (determining feasibility), =
> especially when six- or seven-figure project costs are at stake. Any =
> such project should be based on what is actually feasible, not what is =
> desired, and an understand of plant-soil water relations is essential. =
> Yes, this is an anecdote. I have others, and they all answer to the same =
> fundamental principles.=20
>
