Determination of root diffusivity during water flow in root-soil systems
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We are concerned with determining plant (cotton) root hydraulic diffusivity by measurement of the water flow from the region between two horizontal cross sections into the soil from root xylem through root epidermis over a period of time. The results of the experiment conducted by Yamauchi et al.  to measure the potential gradient in the root xylem of an intact, transpiring cotton plant are utilized to estimate the hydraulic difFusivity of the combined root tissues between root xylem and root epidermis. Figure 1.1 shows the cross-section of a root. Figure 1.2 is a schematic illustration of the laboratory setup used by Yamauchi et al. to collect water and measure the gradient in xylem water potential and water flow rate. The measurements were made in rigidly controlled environments. Temperature, soil moisture level, and lighting condition were all under control. The water potential of the xylem at a particular point along a root was measured while the plant was actively transpiring; the plant was still alive. There was no destruction of the root. This technique also allowed the xylem water potential at a particular point to be monitored dynamically. The water was collected by enclosing a small length of root in specially constructed Teflon psychrometer chambers. For a more detailed experimental description, refer to .