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

Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Factors affecting the direction of growth of tree roots. | 277s Ann. Sci. For. 1989 46 suppl. 277s-287s Forest Tree Physiology E. Dreyer et al. eds. Elsevier INRA Factors affecting the direction of growth of tree roots . Coutts Forestry Commission Northern Research station Roslin Midlothian EH25 9SY Scotland . Introduction The direction of growth of the main roots of a tree is an important determinant of the form of the root system. It affects the way the system exploits the soil Karizumi 1957 and has practical significance for the design of containers and for cultivation systems which can influence tree growth and anchorage. This review discusses the way in which root orientation is established and how it is modified by the environment. The form of tree root systems can be classified in many ways but the commonest type in boreal forests is dominated by horizontally spreading lateral roots within about 20 cm of the ground surface Fayle 1975 Strong and La Roi 1983 . A vertical taproot may persist or may disappear during development. Sinker roots are more or less vertical roots which grow down from the horizontal laterals. They are believed to be important for anchorage and for supplying water during dry periods. Roots which descend obliquely from the tap or lateral roots are also present and the distinction between these and sinkers is a matter of definition. Differences in root form could arise from differences in root direction or from differential growth and survival of roots which were originally growing in many directions. In practice both the direction of growth and differential development contribute to the final form. There is scant information about the principal controls over the orientation of tree roots. Most studies deal with herbaceous species and even for them experimental work and reviews have generally been confined to geotropism of the seedling radicle. The direction sensing apparatus lies in the root cap Wilkins 1975 . The structure of the root cap is variable but there is no essential difference .