Sensitivity to Desiccation of Leaf Extension in Prairie Grass

The short-term response of leaf extension rates and leaf water potential (Ψ1) to controlled diurnal changes in the environment of a pasture species, prairie grass (Bromus catharticus) was followed over a soil drying cycle. Consistent relationships between rates of leaf extension and leaf water status were found only when measurements had been made under a common environment or when the effects of the environmental differences were allowed for by comparing the response of desiccated plants to that of well watered control plants under the same conditions. In the early stages of desiccation, leaf extension rates were extremely sensitive to reduction in Ψ1. Water potentials of only 2-3 bars below that of well watered control plants were sufficient to depress leaf extension rates by 50%. However, as desiccation became more severe, leaf extension rates became much less responsive to further reductions in Ψ1. We infer that it will be possible to resolve some of the apparent discrepancies among various reports on the sensitivity of leaf extension rates to desiccation when allowance can be made for the actions of other important influences, such as temperature in this experiment, and when Ψ1 at the site of measurement can be related unequivocally to Ψ1 at the region of elongation.