Daily fluctuations in water potential and associated ionic changes in Atriplex canescens.

Water potential (Ψ) measurements of Atriplex canescens at the base of the Red Desert near Tipton in Wyoming, revealed a range between-15.5 to-45.1 bars. Minimum values coincided with the lowest air and soil temperatures, maximum with the greatest atmospheric evaporative demand. Change in Ψ exceeded 12 bars h-1 during periods of rapidly moving storm systems. Changes in Ψ appeared to be independent of plant size, age, sex, and the spatial location of plants. Chemical analyses revealed that xylem sap was up to three times more concentrated at high than at low Ψ. It was observed that the flow rate of sap was greater at lower than at higher Ψ and that the increase in water movement accounted for the dilution of the baseline concentration of sap solutes. Together, Ca, Mg, K and Na contributed 58% of the mean osmolality of the xylem sap; the dominant ions, however, were K and Cl. We suggest that the ability of the species to respond rapidly to changing atmospheric conditions affords it a distinct advantage in a harsh environment.