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The Root of Plant Science: Rhizobotany
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17429 |
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NATURAL SCIENCE
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1 / 1990 |
2,890 Words |
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Richard W. Zobel
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A plant is a paradox. Part of it reaches up to the light of the sun while part of it dwells in perpetual darkness. Plants are as much a part of the invisible world beneath the surface of the soil as they are a part of the visible world above the soil. Yet if we imagine a plant, we are most likely to visualize only the portion protruding above the ground - the shoot.
Unlike animals whose boundaries are clearly recognizable to our vision, plants disappear into the ground right at their thickest part, leaving us to imagine their underground shape. If we do try to observe a whole plant by digging up its roots, we discover a rather formless, tangled mass that is surely quite different from the form assumed by the roots corrupted by our act of washing them to gain a clearer definition of the roots' boundaries. In fact, the search for sharp edges of the roots may well be in vain. The roots coexist so intimately with other life forms and elements of the soil that the boundary of root and nonroot is intrinsically fuzzy.
Although plant roots are one of the most important parts of the food chain, the study of plant roots, rhizobotany, is only in recent years gaining support and recognition commensurate with this importance. National and international pressures today are demanding changes in agriculture for which rhizobotany must be considered a primary field of research and application. Increasingly we hear news that underscores the need for more rhizobotany research: Forests are being destroyed to provide more land for food crops; residential water supplies are being contaminated by agricultural runoff; soils are eroding with a resultant loss in crop land; agricultural production is being increased by the farming of marginal lands such as deserts, yet doing this causes buildup of salt which reduces crop productivity; and so on.
Rhizobotany deals with plant root growth and development, and the interactions of roots with the surrounding rhizosphere. [See "Terra Obscura; The Earth's Rhizosphere," December 1989, p.304.] In the late 1800s, scientists attempted to describe root anatomy and root system structure very thoroughly. However, because of the opacity of the rhizosphere and the difficulty in excavating undamaged roots, early researchers inevitably settled for generalizing their findings based on small numbers of samples. As a result, many disagreements about the characterizations of roots developed, which in many instances are only slowly being resolved even now. Thus the foundations of modern rhizobotany are delicate at best, and attempts to breed or select agricultural plants for specific rhizosphere characteristics are hindered as a result.
What is the Role of Roots?
Most basic biology texts for elementary and secondary schools do an excellent job of describing the most obvious roles of plant roots: Roots are the primary channel by which water and minerals are brought into the plant; they also provide anchorage in the soil so that plants can resist strong winds. Besides these most obvious roles, however, roots perform many other important functions. Through the production of plant growth regulators and the selective transport of minerals and other nutrients, roots control the growth and developmental rates of the above-ground portion of the plant. Reduction of water to the leaves of plants in a drought situation, for example, is achieved by abscisic acid, a plant-growth regulator produced by roots. The transfer of
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