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.