Root Architecture and Plant Productivity

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 ac- quisition of soil resources by plant root systems is therefore a subject of considerable interest in agriculture and ecol- ogy, as well as a complex and challenging problem in basic plant biology. Symbioses between roots and otlier organ- isms (notably mycorrhizas and N-fixing bacteria), modifi- cation 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 ac- tively researched by plant biologists. Another aspect of this problem that has received less attention, despite its prob- able importance, is root architecture. Recent methodologi- cal innovations present opportunities for improved under- .standing of the functional importance of root architecture in the efficient acquisition of soil resources and plant ad- aptation to suboptimal soil conditions. The purpose of this Update is to briefly summarize conceptual issues and re- cent developments in the study of root architecture and to propose a framework for understanding its physiological basis.