Root Systems of Arboreal Plants

Plant growth depends on water and nutrient supply from the soil and upon limitations for uptake imposed by the root system. Plant roots continuously exploit new soil regions where water and nutrients are available. The root systems of trees differ from those of annual plants by their woody framework of longlived structural roots supporting a mass of shortlived, nonwoody fine roots associated with mycorrhizal fungi. Investigations of tree root systems have been hampered since visual examination of the roots requires laborious methods whereby surrounding soil must be removed to expose the roots (Vogt and Persson, 1991). Additional impediments to the investigation of the distribution and function of root systems are their variable form and extensive branching that complicate their excavation. For example, exploration of the root system of one tree, which occupies an area of 10m2, requires the removal of up to 30 tons of soil. Once a root system is exposed, description of its threedimensional structure remains a major problem. A detailed morphological description of the root system of even a young tree is a formidable task. The excavation of complete tree root systems gives a good presentation of their morphology. Still it does not answer questions about the functional importance of each constituent with regards to water and nutrient uptake. Study of the differences between tree species and competition for soil resources between individual trees require functional analysis. Important factors that determine the competitive strength of plants are those expressed by the relative size of the absorbing root surface and by the disposition of root tips of competing root systems in relation to the soil available nutrients. Basically, roots within a single plant compete with each other for carbohydrates, and those occupying favorable soil regions tend to grow at the expense of the other roots.