LEAF EXTENSION RATE IN 2 TUSSOCK GRASSES - EFFECTS OF WATER-STRESS AND CLIPPING

The effects of water stress and clipping on leaf extension rate were s tudied using field-grown plants of Agropyron desertorum and Pseudoroeg neria spicata during three growing seasons. Leaf extension rate was me asured over 0,5 h intervals during 12 to 65 h periods using precision resistors connected to a data logger. Integrated daily leaf extension in both species was at least 70% lower under water stress than under h igher moisture levels. Following clipping in 1986, leaf extension rate s and regrowth yields were lowest under the combined effects of water stress and clipping for both species, despite maintenance of turgor (m ean psi(p) = 0.7 MPa) in the extending laminae. Hourly leaf extension rates in both species were on average 27% higher during die day than a t night with maxima near sunset and minima at sunrise. This extension pattern was opposite to the diurnal trends in lamina water potential o r turgor. Leaf extension rate correlated with air temperature, modifie d by other factors that also appear to be involved in control of leaf extension.