GROWTH AND NUTRITION OF COMBINATIONS OF NATIVE AND INTRODUCED PLANTS AND MYCORRHIZAL FUNGI IN A SEMIARID RANGE

The symbiotic responses of native and introduced plant-fungus combinat ions were determined. Indian ricegrass (Oryzopsis hymenoides (R.&S.) R icker) and crested wheatgrass (Agropyron desertorum (Fisch.) Schult.) were pre-inoculated with an introduced fungus, three native fungi, or a mixed native inoculum (VAM plants), and transplanted to fumigated fi eld plots on a semiarid range in western Nevada. Non-fumigated and fum igated plots with non-VAM plants were used as controls. No treatment p roduced significant plant growth responses relative to controls. Crest ed wheatgrass generally had the lowest levels of VAM fungal colonizati on, yet the highest levels of nutrient uptake when compared with India n ricegrass. Differences in nutrient concentrations, but not contents, were significant among fungal inoculum treatments. Glomus pallidum in creased N shoot concentrations above the fumigated control levels for both Indian ricegrass and crested wheatgrass, and the native Glomus mo sseae increased N concentration for Indian ricegrass only. For Indian ricegrass, G. pallidum increased P shoot concentrations above controls . G. mosseae and G. pallidum enhanced the uptake of P when compared wi th the introduced isolate. The introduced G. mosseae and the native Gl omus etunicatum enhanced Mn uptake for Indian ricegrass only. The upta ke of N and P were reduced in plants colonized by a mixture of three n ative isolates when compared with uptake by single native isolates for Indian ricegrass. The lack of a shoot growth effect for Indian ricegr ass and crested wheatgrass in the presence of introduced or native VAM fungi suggests that these plants are facultative mycotrophs. Mycorrhi zae appear to facilitate luxury consumption of nutrients by these gras ses, which may be an important adaptation in nutrient-poor desert envi ronments. Further knowledge of effects by native and introduced VAM fu ngi, and of host effects on the symbiotic association will contribute to more effective establishment of plants in new areas.