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.

Associations between arbuscular mycorrhizal fungi and Sporobolus wrightii in riparian habitats in arid South-western North America

“…AM colonization of S. wrightii continued at a higher level in the summer ( July) at two sampling sites ( UP and UI), but then declined to the lowest levels in fall (September) when big sacaton shifted from vegetative growth to reproduction, and in December when hosts were dormant, or approaching dormancy. This pattern of change in fungal colonization is similar to that reported by Ebbers et al (1987) in their study of S. heterolepsis. Bentivenga & Hetrick (1992) found total colonization of other warm-season tallgrasses to be greatest in late summer or fall and suggested the fungal symbiont might be parasitic at this time.…”

Growth dynamics and associated mycorrhizal fungi of little bluestem grass [Schizachyrium scoparium (Michx.) Nash] on burned and unburned sand prairies

“…Dickman et al (1984) reported a decrease in little bluestem colonization from May to September. However, in a study of prairie dropseed {Sporobolus heterolepis) on two sites there was no change in colonization during the growing season on one site, while colonization on the other increased from spring to fall (Ebbers et aL, 1987). In contrast, in this study, percent colonization did not vary significantly on the burned sites, although colonization levels always increased toward the end of the growing season.…”

“…Similar peaks in VAM fungi spore counts were found within the root zone of crop plants in autumn (October) (Sulton & Baron, 1972) and in native sunfiower plants in fall (September) (Anderson & Liberta, 1987). However, Dickman et al (1984) reported, for several sites, peak spore counts in spring (May) which declined in the summer (July) and then increased slightly in autumn (September).…”

“…The same trend was observed for a burned and unburned sand prairie (Dhillion et aL, 1988). In contrast, in England, spore counts in soil associated with wheat roots increased in midsummer and declined in fall (Hayman, 1970) and, in an Illinois taligrass prairie, spore counts declined from spring to summer and remained the same in autumn (Ebbers, Anderson & Liberta, 1987). The decline of spore counts on all sites may be due to loss of viability and predation as well as germination (Mosse, 1973).…”

“…This seasonal pattern of variation in MIP may be species specific. For example on another Illinois sand prairie, Anderson & Liberta (1987) reported MIP levels of the root zone soil of sunflower {Helianthus occidentalis) and sand lovegrass {Eragrostis triehodes) were highest in early spring. These levels then declined to late spring and did not change significantly for rest of the growing season.…”