COLONIZATION OF WESTERN WHEATGRASS (AGROPYRON SMITHII RYDB.) BY VESICULAR-ARBUSCULAR MYCORRHIZAL FUNGI DURING THE...

Development of vesicular-arbuscular mycorrhizas and proliferation of roots of western wheat-grass (Agropyron smithii Rydb.) were investigated in a revegetated mine soil in southeastern Wyoming, USA. Total rooting density (root length per volume of soil) and spore frequency increased as a function of age of the reclamation (time elapsed since reseeding). Topsoil replaced during reclamation was apparently the primary source of mycorrhizal inoculum in the most recently reclaimed site. Seedlings growing on spoil material without topsoil were generally non-mycorrhizal, but mycorrhizal rooting density was not significantly correlated with the residual content of soil organic matter (an indicator of the proportion of topsoil in the growth media). Mycorrhizal colonization in sites up to three years old was minimal in spite of rapid increases in overall rooting density. Mean rooting density, mean degree of infection, and mean spore frequencies in older sites (five to seven years) were comparable to those of an adjacent undisturbed rangeland, but were highly variable. Mature, non-mycorrhizal specimens were observed, suggesting that A. smithii is not highly dependent on mycorrhizal infection for survival on this disturbed site.