Aspects of the Mycorrhizal Ecology of Prairie Dropseed, Sporobolus heterolepis (Poaceae)

Abstract

Vesicular-arbuscular mycorrhizal (VAM) fungal colonization of prairie dropseed and rhizosphere spore abundance were sampled seasonally at two sites in Illinois. At Goose Lake Prairie (GLP), Gaussian ordination of 49 vegetation stands, using plant cover data for 40 species, assigned stands x-vector values and ordered them along a soil moisture-nutrient gradient. Prairie dropseed cover data plotted over ordered stands yielded a significant Gaussian curve across a relatively narrow gradient segment. In contrast, colonization and spore abundance had significant negative linear correlations with stand x-vector values that decreased from the drier, low-nutrient portion of the gradient to the wetter, high-nutrient sector. Variation in spore abundance suggested that no VAM fungal species responded to environmental gradient conditions in a manner similar to that of prairie dropseed. The differential responses of host and VAM mycobionts across the gradient suggest that their respective success may be partially independently determined or limited by different parameters. Also, the generally ubiquitous VAM fungal distributions suggest that the host may be more sensitive to gradient conditions than its mycobiont associates. Colonization and spore abundance at GLP were significantly negatively correlated with available Ca and Mg, and pH. Spore abundance was significantly positively correlated with available K. Neither colonization nor spore abundance were significantly correlated with available P, total N, or organic matter. Seasonally, patterns of VAM colonization and rhizosphere spore abundance varied, having significant positive correlations at GLP and Weston Cemetery Prairie (WCP) in some seasons but not others. In general, colonization levels were highest in fall 1983 for GLP and fall 1984 for WCP. For 1984, increasing colonization was observed from spring (WCP) or summer (GLP) to fall.