The effect of water stress on phenological and ecophysiological characteristics of cheatgrass and Sandberg's bluegrass

Abstract

Comparative field studies of cheatgrass (Bromus tectorum L.) with Sandberg’s bluegrass (Poa sandbergii Vasey) were conducted to further our understanding of the plant characteristics that contribute to success in habitats where water is a limiting factor. To evaluate the effect of soil water on phenological development, stomata1 conductance, and xylem pressure potential of these grasses, observations were made in the field for 2 growing seasons (1986 and 1987). Stomata1 conductance, transpiration, and xylem pressure potential data, gathered as soils dried during 1986, indicated that water stress developed earlier and to a greater degree in Sandberg’s bluegrass than in cheatgrass. Xylem pressure potential was lower in Sandberg’s bluegrass than in cheatgrass, and the difference increased throughout the growing season. Stomata1 conductance and transpiration were greater for cheatgrass than for Sandberg’s bluegrass. Maintenance of high soil water potentials by irrigating through the 1987 growing season retarded phenological development and delayed senescence by about 10 days for both species. Predawn xylem pressure potential for irrigated plants remained higher than for nonirrigated plants; however, as the plants senesced, xylem pressure potential also decreased in the nonstressed plants.