MYCORRHIZAL FUNGI ASSOCIATED WITH 3 SPECIES OF TURFGRASS

Small plots of highly maintained turfs of creeping bentgrass (Agrostis palustris cv. Penncross) and velvet bentgrass (Agrostis canina cv. Ki ngstown) and a marginally maintained stand of annual bluegrass (Pea an nua) were sampled intensively over a 15-month period to measure the po pulations of spores of arbuscular mycorrhizal fungi (AMF) associated w ith their root systems. Direct isolation of spores and trap cultures w ere used to assess the AMF communities. Spores of more than 18 species of AMF were isolated. The six dominant species (as measured by the ab undance and frequency of occurrence of spores) were Acaulospora mellea , an undescribed species of Acaulospora, Scutellospora calospora, Glom us occultum, Glomus etunicatum, and Entrophospora infrequens. Spares o f 17 species of AMF were recovered from the root zones of velvet bentg rass, 15 species from creeping bentgrass, and 14 from annual bluegrass . Soil fertility differed among the three sites, and it was not possib le to ascribe differences in the AMF communities in each plot to any p articular variable (e.g., host, pH, soil P). Average spore abundance w as greatest in the creeping bentgrass plot (191.0 spores/100 mt), next in the velvet bentgrass plot (82.4 spores/100 mt), and least in the b luegrass plot (28.4 spores/100 mt). Spores were recovered from a signi ficantly greater percentage of the samples from the bentgrass plots (8 8.5-96.8%) than from the bluegrass plot (76.6%). Spores of an average of 4.5 species of AMF were isolated monthly from creeping bentgrass, 3 .3 from velvet bentgrass and 2.0 from bluegrass. Average species richn ess and spore abundance were positively correlated in the creeping ben tgrass and bluegrass plots (r = 0.77, p = 0.001, and r = 0.68, p = 0.0 06), but not in the velvet bentgrass plot. Spore abundance showed stro ng seasonal trends in all three plots (p = 0.03-0.001), with numbers i ncreasing from spring until November. Richness and abundance declined from December until the following spring. In the bluegrass area, which experienced summer drought, spore populations and richness also showe d a precipitous decline in July and August in the Ist year of the stud y (1990), but not in the 2nd year (1991). No such summer decline occur red in the bentgrass plots that received irrigation. The AMF community that was circumscribed by direct spore counts from the field usually was highly dissimilar to the community that was estimated by trap cult ures initiated using soil from the turf areas.