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Soil microorganisms affect survival and growth of shrubs grown in competition with cheatgrass.
Pendleton, Rosemary1, Pendleton, Burton*,1, Johansen, Jeffrey2, St. Clair, Larry3, 1 Rocky Mountain Research Station, Albuquerque, New Mexico, USA2 Department of Biology, University Heights, Ohio, USA3 Department of Integrative Biology, Provo, Utah, USA
ABSTRACT- Invasive annual grasses such as cheatgrass (Bromus tectorum) create changes in soil microorganism communities and severely limit shrub establishment. We examined the effects of biological crust-forming algae and arbuscular mycorrhizal fungi on growth and survival of five western shrub species with and without competition from cheatgrass. Germlings of Ephedra viridis (EPVI), Coleogyne ramosissima (CORA), Artemisia filifolia (ARFI), Chrysothamnus nauseosus(CHNA), and Artemisia nova (ARNO) were planted into pots with and without fertilizer additions. We used four inoculation treatments; algal crust inoculum of the genus Schizothrix, arbuscular mycorrhizal inoculum of spores extracted from soil collected from a mixed shrub location, dual inoculation, and a non-inoculated control. Half of the low fertility pots were planted with one seed of cheatgrass. Shrub survival declined as soil fertility increased. Few shrubs were able to survive in competition with cheatgrass in fertilized growth medium. Algal inoculation increased shrub survival. Soil fertility level and competition with cheatgrass significantly affected growth of all five shrub species. At high fertility, the faster-growing shrubs grew best with no microorganism additions. The slower-growing CORA grew best in the presence of mycorrhizae and EPVI in the presence of the algae. Under low nutrient conditions, all shrub species responded positively to the addition of mycorrhizal inoculum. CHNA and EPVI responded positively to the algal inoculum. The addition of mycorrhizal inoculum intensified competition with cheatgrass, reducing shrub shoot biomass over that of the control treatment in all species except ARFI. However, shoot growth in cheatgrass was reduced to an even greater extent in all shrubs except ARNO. Algal inoculation appeared to beneficially affect the growth of ARFI and EPVI at the expense of cheatgrass. Fire or other disturbance that results in a nutrient flush can put native species at a competitive disadvantage with cheatgrass. Our findings suggest that soil microorganisms can, to some extent, mitigate this disadvantage.
Key words: biological soil crust, arbuscular mycorrhizal fungi, shrub establishment, Bromus tectorum