In Utah, Busso and Richards studied the effects of water stress and clipping on leaf extension rate, using field-grown plants of Agropyron desertorum and Pseudoroegneria spicata during three growing seasons. This study demonstrated that long-term water stress substantially reduced leaf extension rates in A. desertorum and P. spicata, despite mean tugor of leaf maintenance under field conditions. Leaf extension rates and regrowth yields were lowest under the combination of water stress and clipping after both species were clipped in 1986. These results indicate that the regrowth of these species, after repeated periods of grazing under water stress, could be limited by reduced leaf extension rates. The grazing tolerant species, A. desertorum, did not appear to have any significant advantage in more rapid leaf extension under water stress in comparison to the grazing intolerant species, P. spicata. For both species, leaf extension rates, water potential, and mean tugor were greatest during the night, compared to day time observations. Leaf extension rate correlated with air temperature, modified by other factors that also appear to be involved in control of leaf extension.
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