Influence of an Environmental Gradient on Physiology of Singleleaf Pinyon

Abstract

The acquisition of water and regulation of its loss are important to plant 'success' in arid environments. Species existing over a range of environmental conditions should respond physiologically to varying conditions to maximize water use efficiency and avoid low tissue water potentials. Seasonal and diurnal ecophysiological responses of singleleaf pinyon (Pinus monophylla Torr. and Frem.) were investigated along an environmental gradient involving elevation, moisture and temperature in Nevada. The gradient was represented by study sites in black sagebrush (Artemisia nova A. Nels), mountain big sagebrush (Artemisia tridentata ssp. vaseyana Nutt.), and mountain mahogany (Cercocarpus ledifolius Nutt.) communities. Xylem pressure potential, conductance, and transpiration were measured over 2 growing seasons. Xylem pressure potential and leaf conductance ranged from -3.0 to -0.7 MPa and 0.01 to 0.43 cm s-l, respectively, during the study. Carbon isotope discrimination (delta) of needles was determined in August 1990. Differences in delta values were not significant between sites at the lowest and highest elevations but were significant between the driest site (black sage) and the relatively wetter site (mountain mahogany). Leaf conductance was influenced by but not strongly correlated with predawn xylem pressure potentials, relative humidity, and temperature. Generally, there was little difference in water use characteristics of singleleaf pinyon along the environmental gradient in this study. Thus, it appears that singleleaf pinyon's ability to exist over a range of environmental conditions is not a function of variable ecophysiological responses but an opportunistic response to the availability of resources and conditions suitabie for erowth to occur.