Báo cáo khoa học: Factors affecting the direction of growth of tree roots

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Báo cáo khoa học: "Factors affecting the direction of growth of tree roots" affecting the direction of growth of tree rootsFactorsM.P. Coutts EH25 9SY, Scotland, U.K.Forestry Commission, Northern Research Station, Roslin, Midlothian, originally growing in many directions.Introduction were In practice, both the direction of growth and differential development contribute toThe direction of growth of the main roots the final form.of a tree is an important determinant of the There is scant information about theform of the root system. It affects the way principal controls over the orientation ofthe system exploits the soil (Karizumi, tree roots. Most studies deal with herba-1957) and has practical significance for ceous species, and even for them experi-the design of containers and for cultivation mental work and reviews have generallysystems which can influence tree growth been confined to geotropism of the seed-and anchorage. This review discusses the ling radicle. The direction sensing appara-way in which root orientation is esta- tus lies in the root cap (Wilkins, 1975).blished and how it is modified by the envi- The structure of the root cap is variable,ronment. but there is no essential difference be- The form of tree root systems can be tween those of herbaceous species andclassified in many ways but the common- trees. Work on herbaceous species there-est type in boreal forests is dominated by fore has a strong relevance for trees, buthorizontally spreading lateral roots within certain differences must be noted. Forabout 20 cm of the ground surface (Fayle, example, any correlative effects between1975; Strong and La Roi, 1983). A vertical the taproot and laterals may be modifiedtaproot may persist or may disappear in trees by the size, age and complexity ofduring development. Sinker roots are their root systems. Furthermore, the rootsmore or less vertical roots which grow of herbs, and especially of annuals, maydown from the horizontal laterals. They have evolved optimal responses to sea-are believed to be important for anchorage sonal conditions, whereas the young treeand for supplying water during dry peri- must build a root system to support it phy-ods. Roots which descend obliquely from sically and physiologically for many years.the tap or lateral roots are also present An example of response to temporaryand the distinction between these and influences is given by soybean, in whichsinkers is a matter of definition. Dif- the lateral roots grow out 45 cm horizon-ferences in root form could arise from dif- tally from the taproot, then turn down verti- cally during the summer (Raper and Bar-ferences in root direction or from differen- ber, 1970), possibly in response totial growth and survival of roots which inclined at an angle (plagiogeotropic). or high temperature (Mitchell anddrought areRussell, 1971). A forest tree could not sur- The angle bei:ween the lateral root and thevive on a root system so restricted lateral- plumb line is called the liminal angle, and is known to vary with species (Sachs,ly. 1874). Billan et al. (1978) even found dif- ferences in the liminal angles between twoOrthogeotropic roots provenances of Pinus taeda L.: the pro- venance from the driest site had the small-In both herbs and trees the seedling est angle (i.e., the most downwardly di-taproot (or radicle) is usually positively ...