Water and nutrient availability limit plant growth in a11
but a very few natural ecosystems. They limit yield in most
agricultural ecosystems, and in the United States and other
industrialized nations, intensive irrigation and fertilization
have generated serious environmental problems. The acquisition
of soil resources by plant root systems is therefore
a subject of considerable interest in agriculture and ecology,
as well as a complex and challenging problem in basic
plant biology. Symbioses between roots and otlier organisms
(notably mycorrhizas and N-fixing bacteria), modification
of the rhizosphere through root exudates, and the
uptake and transport characteristics of root axes are a11
important dimensions of this problem that are being actively
researched by plant biologists. Another aspect of this
problem that has received less attention, despite its probable
importance, is root architecture. Recent methodological
innovations present opportunities for improved under-
.standing of the functional importance of root architecture
in the efficient acquisition of soil resources and plant adaptation
to suboptimal soil conditions. The purpose of this
Update is to briefly summarize conceptual issues and recent
developments in the study of root architecture and to
propose a framework for understanding its physiological
basis.