ROOT HYDRAULIC CONDUCTIVITY AND ITS COMPONENTS, WITH EMPHASIS ON DESERT SUCCULENTS

Plant growth and development are often limited by the ability of roots to extract water and nutrients from the soil and to transport them to the shoots. The water absorption and transport ability of roots can be quantified by the hydraulic conductivity, L(p). This quantity can be considered in terms of two components, the radial conductivity (L(R)) for water movement into the root and the axial conductance per unit pressure gradient (K(h)) for water movement along the root xylem. The pathways for water movement through roots are discussed, and the hydraulic conductivities are expressed mathematically. The technique currently used for determining L(P), L(R), and K(h) are presented and conductivities for various plant species are compared. Recent experimental results on structural factors controlling L(R) and K(h) together with the influences of two major environmental factors, temperature and soil water availability, are analyzed for roots of desert succulents. Interpreting the anatomical and physiological controls for L(P), L(R), and K(h) and the variations caused by environmental factors is essential to understand the functioning of root systems for water uptake.