Abstract Similar-sized and -aged plants of the semiarid C₄ species, Bouteloua scorpioides, were exposed either to a single drying cycle or to three successive drying cycles during the early vegetative growth or early flowering states. Leaf water potentials of all plants exposed to drought stress decreased to -4.0 MPa at the end of each drying cycle and for each phenological stage, whereas that of non-water-stressed plants remained above -0.5 MPa. At this level of leaf water potential, leaf rolling and chlorosis were evident. Photosynthesis for the water-stressed plants was significantly reduced by 80% relative to non-water-stressed plants. These low leaf water potentials and depressed photosynthesis rates returned to prestressed levels after rewatering at the end of each drying cycle. With the return of prestress photosynthetic rates and leaf water potentials, leaf rolling and chlorosis were no longer evident. Return to pre-water-stressed levels, however, was delayed by up to 4 d in plants exposed to repeated cycles of water stress. Plants exposed to repeated cycles of water stress exhibited the greatest biomass reduction. The level of water stress or the phenological stage at which this stress occurred had no effect on the partitioning of biomass or reproductive capacity, although a high water stress level generally reduced the number of flowering tillers produced. Although there was no statistically significant interaction between level of water stress and the phenological stage at which water stress occurred, the late growth stage consistently appeared to be the most sensitive to water stress.

Contribution no. 450 of the Idaho Forest, Wildlife and Range Experiment Station.