ARBUSCULAR MYCORRHIZAE AND WATER-STRESS TOLERANCE OF WYOMING BIG SAGEBRUSH SEEDLINGS

Although Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomin gensis Beetle and Young) is widespread in the western USA, reestablish ment of this native shrub on disturbed lands by direct seeding is prob lematic. A number of theories have been proposed to explain this diffi culty. Included are the hypotheses that seedlings are unable to obtain adequate moisture and are handicapped by reduced levels of mycorrhiza e in perturbed soils. We conducted a greenhouse study to examine the i nfluence of vesicular arbuscular mycorrhizae (VAM) and seedling age on soil moisture stress tolerance of Wyoming big sagebrush seedlings. Re sults demonstrated greater survival of mycorrhizal seedlings than nonm ycorrhizal seedlings as soil dried down past soil water potential valu es of -2.5 MPa to as dry as -3.8 MPa. For all different aged seedlings tested (30, 45, 60, 90, 120, 150 d), the degree of soil dryness resul ting in death of mycorrhizal seedlings was significantly greater (P < 0.01) than that causing death of nonmycorrhizal seedlings. Analysis of variance indicated a significant interaction of seedling age and myco rrhizae on moisture stress tolerance. Experimental data suggest that a s sagebrush seedlings age, the beneficial influence of arbuscular myco rrhizae on soil mater stress tolerance increases.