Studies of the Root Development of Plants in The Field Using Radioactive Tracers

Abstract

The direct investigation of the extent of root systems in plant communities is a very tedious and difficult task. One of the best methods has been found to be that used by Weaver & Darland (1949) whereby a monolith of soil is taken from the field back to the laboratory and the roots then washed free of the soil by means of a jet of water. In some cases, especially under a close grass sward, it is virtually impossible to separate single plants and trace their roots down the profile. Alternative methods that have been employed have been to grow plants in containers easily taken apart, or in nutrient solutions. However, these methods do not provide much useful information when plant communities in their natural habitats are being studied. The absorption by plants of dyes and of elements which are not normally present in the soil, such as lithium and rubidium, has been used to indicate the regions of root activity (Sayre & Morris 1940). The use of radioactive isotopes as tracers of absorbed nutrients offers advantages since great sensitivity in detecting the absorbed elements is possible by electronic apparatus. Hall et al. (1953) have studied the root systems of four species of crops-cotton, corn, peanut and tobacco, by growing plants in soil in which the native phosphate was labelled by injecting small quantities of p32, as potassium dihydrogen phosphate (KH 2P320 4). The activity of the root system in different parts of the soil could be calculated by measuring the specific activity (i.e. the ratio of radioactive phosphorus to total phosphorus) of the plant. * Now at the Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen. This method was used in work done by R. B. for the degree of Doctor of Philosophy which was accepted by the University of Aberdeen.