Response of blackbrush (Coleogyne ramosissima) seedlings to inoculation with arbuscular mycorrhizal fungi

Blackbrush, (Coleogyne ramosissima), occurs as a landscape dominant in the ecotonal region between hot and cold deserts of the western United States. Revegetation efforts using blackbrush have met with limited success, prompting speculation on possible interactions with soil microorganisms, including mycorrhizal fungi. From 1993 to 1997, we conducted a series of experiments designed to test the effect of inoculation with arbuscular mycorrhizal fungi on the growth of young blackbrush seedlings under a variety of soil nutrient conditions. In all cases, growth of blackbrush seedlings was enhanced in the presence of mycorrhizal fungi. Inoculation resulted in increased plant biomass, decreased allocation to root systems in general and to fine roots in particular, and increased tissue concentrations of both phosphorus and nitrogen. The addition of mycorrhizal fungi also significantly decreased the ability of cheatgrass to compete with blackbrush seedlings when grown at low soil nutrient levels. Revegetation of blackbrush areas would likely benefit from the use of mycorrhizal inoculum. Soil fertilization, however, is detrimental to the establishment of this species and is not recommended.