Decision Making within Plant Root Systems

Abstract

Architecture of a root system is the expression of the potential of various root types to branch, to grow and to coordinate with other plant organs, under the specific limitations of the environmental conditions. The present investigation has proven the following points. 1) Genotypes with different types of root systems were identified. The growth patterns of their roots and the distribution of laterals along their main axes were recorded. 2) The patterns of development of the root systems of four cotton genotypes, throughout the entire life cycle of the plants, were described, even at such a late stage of development when the total length of the roots exceeded two kilometers. To the best of our knowledge, this is the first time that an analysis of this type is accomplished. 3) The development of root systems under restrictive soil conditions were compared with those that have developed under the non-restrictive conditions of aeroponics. Results indicate that in the absence of the mechanical impedance of the soil, cotton plants develop single roots that reach the length of 6 m, and have a total root length of 2000 m. Thus, root growth is strongly inhibited by the soil, with some root types being inhibited more than others. 4) One of the important decisions, in constructing an operational root system architecture of mature plants, is the shift of the balance between various root fractions in favor of the very fine roots. 5) Root system architecture is determined, in part, by the sites of initiation of the lateral roots. This is determined genetically by the number of xylem archs and by the totuosity of the stele. Selection for such traits should be sought.