Evidence for Osmotic Adjustment in Phalaris tuberosa L. cvv. Australian and Sirosa

The temperate pasture grass Phalaris tuberosa L. (cvv. Australian and Sirosa) was grown in soil under glasshouse conditions. When water was withheld, leaf xylem potential (�) decreased at the rate of 0.02 and 0.05 MPa per day in cvv. Australian and Sirosa, respectively, between 7 and 17 days, and reached a dawn value -0.25 (� 0.02) MPa and -0.56 (�0.08) MPa in the respective cultivars. These plants were moderately stressed. Between 17 and 23 days, when the experiment was terminated, stress developed more rapidly and � at dawn reached final values of -2.1 (�0.09) and -2.2 (�0.08) MPa in Australian and Sirosa phalaris, respectively. These plants were severely stressed. The leaf osmotic potential (��) decreased at similar rates as � in the stressed plants, thus maintaining the turgor potential (�*p) relatively constant with increasing water stress. Osmotic adjustment (��100/�) was judged by comparing �� at full turgor (�100/�) in stressed plants which had been rewetted, with �100/� of control unstressed plants. ��100/� of moderately stressed plants was 0.46 and 0.48 MPa in Australian and Sirosa phalaris, respectively. In severely stressed plants, the respective ��100/� values were 0.67 and 0.85 MPa.