FACILITATION OF SUCCESSION BY THE NONMYCOTROPHIC COLONIZER SALSOLA KALI (CHENOPODIACEAE) ON A HARSH SITE: EFFECTS OF MYCORRHIZAL FUNGI

The effects of inoculation with vesicular-arbuscular mycorrhizal fungi on nonmycotrophic (plants which do not form a mycorrhizal association) colonizing annuals and on mycotrophic perennials were investigated in southwestern Wyoming. A subsoil containing no initial mycorrhizal inoculum was used, and seeds of the later successional perennials were planted. The annuals were removed from one-half of the sampling quadrats to test for the interaction of competition and mycorrhizae on the perennials. During the third and fourth years of succession, the density and percent cover of Salsola kali, the most abundant nonmycotrophic annual, decreased by one-half to one-third with inoculation. Mycorrhizal hyphae and spores were found in the rhizosphere of S. kali, with only occasional (1–2% of the root length) penetration of hyphae into the cortex. There were no differences in tissue phosphorus and nitrogen concentrations or water relations of inoculated vs. uninoculated S. kali. The planted grasses, all Agropyron species, had no significant increase in density or percent cover with inoculation. The percent root infection of A. smithii was 5–30%. Grass density and percent cover was greatest where S. kali was present, suggesting facilitation of grass establishment by annuals on this harsh, windy site. However, grass density was lower where 5. kali density was lower following inoculation. Mycorrhizal fungi were hypothesized to hasten the rate of succession on other sites. On this site where facilitation is an important process, inoculation of early seral plants and their subsequent decline may slow primary succession in the early years.