Browsing Journal of Range Management, Volume 48, Number 3 (May 1995) by Subjects
Now showing items 1-2 of 2
Influence of an environmental gradient on physiology of singleleaf pinyonThe 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.
Influence of temperature on germination of Japanese brome seedJapanese brome (Bromus japonicus Thunb.), an introduced annual grass, is now common in some northern mixed-prairie communities. This species has the potential to alter both the seasonality of standing crop and forage quality. We sought to gain a greater understanding of Japanese brome seed germination by subjecting seed to a series of 55 constant or alternating temperature regimes following 3 to 9 months of dry laboratory storage. Cold and moderate temperature regimes provided optimum germination conditions (defined as not lower than the maximum observed minus one-half its confidence interval at the 0.05 level of probability). Extremely cold or warm temperatures suppressed germination. Germination of afterripened seed over a wide range of temperature combinations, many of which occur during fall in the Northern Great Plains, should enhance establishment and perpetuation of Japanese brome on rangelands.