Arbuscular mycorrhizae and water stress tolerance of Wyoming big sagebrush seedlings

Although Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle and Young) is widespread in the western USA, reestablishment of this native shrub on disturbed lands by direct seeding is problematic. A number of theories have been proposed to explain this difficulty. Included are the hypotheses that seedlings are unable to obtain adequate moisture and are handicapped by reduced levels of mycorrhizae in perturbed soils. We conducted a greenhouse study to examine the influence of vesicular arbuscular mycorrhizae (VAM) and seedling age on soil moisture stress tolerance of Wyoming big sagebrush seedlings. Results demonstrated greater survival of mycorrhizal seedlings than nonmycorrhizal seedlings as soil dried down past soil water potential values 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 resulting 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 mycorrhizae on moisture stress tolerance. Experimental data suggest that as sagebrush seedlings age, the beneficial influence of arbuscular mycorrhizae on soil mater stress tolerance increases.