Leaf water potential, component potentials and relative water content in a xeric grass, Agropyron dasystachyum (Hook.) Scribn.

Leaf water potential (ψ l ), osmotic potential (ψ s ), pressure potential (ψ p , turgor pressure), relative water content (R) and their interrelationships were determined for a xeric grass (Agropyron dasystachyum) found in the grasslands of Canada. Thermocouple psychrometers were used to measure ψ l and ψ s ; ψ p was obtained by subtraction. ψ l dropped from near 0 bars to about-28 bars as R went from 90% to 75%. R greater than 90% was not observed, perhaps because of a systematic error in determination of turgid water content. R remained relatively high in A. dasystachyum, even at low ψ l . The slope of the ψ l -R relationship was similar to other species which are generally considered to be drought tolerant. ψ p as high as 14 bars was observed. Most of the decrease in ψ l was accounted for by a decline in ψ p . The ability of A. dasystachyum to adjust to fluctuating water stress over the growing season is probably as much related to changes in tissue structure and turgor relationships as to simple changes in osmotic potential.