Paul J. Kramer's "Plant and Soil Water Relationships" was a great text, and Paul S. Boyer did a good job putting out a revised edition as "Water Relations of Plants and Soils," but both of these, while excellent works on the fundamental phenomena, were primarily oriented toward agriculture. Being a dry-farmer's son for starters (and one who grew up around sandy soils and relatively high water-tables, most of it made sense to me. But then, as I was cast into the crucible of arid and semi-arid ecosystems, I started running into problems.
I had to literally and figuratively do a lot of digging to plumb the depths of wildland soils, and the holey grail of agricultural and horticultural theory led me down the garden path more than once. I had the good fortune to be present at some major excavations where deep profiles could be observed, if not studied as well as a well-funded research project might have might have been. (At one time I had a beautiful collection of photographs of profile and roots, but I gave them to a young graduate ecologist who took over when I retired, but he left for greener academic pastures after five years, and my pleas for their return have repeatedly been ignored.)
I am sure that Martin knows that gravitational and capillary movement each have their limits and that vertical movement stops from a given precipitation event. This is well-demonstrated in good textbooks as well as the abovementioned ones. But the behavior of water movement in wildland soils varies a lot more than the textbook illustrations. For example, the textbooks typically show a cross-section of a homogeneous soil showing a penetration profile of a deeper wetted zone below the irrigation ditches that on the crop rows, complete with capillary movement. In wildland soils, the same principles operate, but the penetration profile is a lot more complex and variable. Root casts, rodent and other animal burrows, rock fractures and interfaces, shrinking and swelling, ground movement, and other discontinuities create a mind-blowing complexity of routes for roots and water crucially different from agricultural soils. These are some of the ways that roots can appear to traverse otherwise "dry" soil. The rhizosphere, of course, must maintain a state of available moisture sufficient to maintain turgidity; and certainly growth. I still do not fully understand the mysteries of the soil atmosphere and root dormancy, much less the influence of cell and soil solutions and their different states under different conditions, but hope to learn more.
I "know" only what I have observed; I have not put together the physics of the process or published on the phenomena responsible, or advanced a complex, well-worded hypothesis--this requires a level of skill that I have not yet achieved. In the absence of "good science," I have, however, applied the "theories" I have developed over the years and they seem to have held up under the pressure of performance. That is, the interpretation of the principles put forward by a large assemblage of relevant research, my observations and provisional conclusions, and some rough guesses, have produced results more or less consistent with the predictions--the recolonization of disturbed sites with species assemblages that strongly resembled those which existed before treatment, and which were fully self-sufficient and self-reproducing, even resistant to continued invasion by initial colonists, both indigenous and alien. Although some of these "projects" have been destroyed by development over the years, some of them still exist for as much as 11 to 39 years. None have been studied by independent ecologists, despite my urging for them to do so. The methods which have been developed in this rough way, though variable under different conditions, all answer to the same principles--and a certain amount of "dumb" but consistent luck.
Of course, the course of water is only one aspect, but a key one. WT----- Original Message ----- From: "Martin Meiss" <[email protected]>
To: <[email protected]> Sent: Tuesday, May 31, 2011 1:28 PMSubject: Re: [ECOLOG-L] Plant roots matter Re: [ECOLOG-L] Communication Science to Public Plant
When you consider the timing of observations of root position relative toavailable water, the situation can be even more confusing. When conditionsin 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 oftip meristems. Putting it another way, the growing root tips may follow thecapillary fringe downward as it lowers with the advancing dry season. Ifone excavated said roots in the high dry season, they would indeed be foundto 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 drysoil 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 ofthe 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 nearunderground pipes because their roots will enter and thus destroy saidpipes? To someone unfamiliar with the science behind it, it would *appear*to be saying that the willows somehow detect the presence of water in thepipes 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----- No virus found in this message. 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