SEASONAL DYNAMICS OF DOMINANT SPECIES OF ARBUSCULAR MYCORRHIZAE IN BURNED AND UNBURNED SAND PRAIRIES

Seasonal variation in abundance of spores of arbuscular mycorrhizal fu ngi was examined for four growing seasons on burned and unburned sand prairies in Illinois. The three leading mycorrhizal species were an un described species of Glomus, Scutellospora heterogama, and Sclerocysti s rubiformis, in order of decreasing abundance. Mycorrhizal spore abun dance for all species generally showed similar seasonal patterns on bu rned and unburned sites during the sampling period, i.e., minimal in t he middle of the growing season and maximal near the end of the season . Individual species, however, exhibited different seasonal patterns o f sporulation or sporulation strategies. Burning caused a 2-year depre ssion in spore abundance for Glomus species and Scutellospora heteroga ma, and a 3-year long depression in spore abundance for Sclerocystis r ubiformis. The seasonal patterns observed were more discernible in roo t zone than in randomly collected soil. Spore abundances were always s ignificantly lower on burned sites than on unburned sites early in the growing season. The results of this study, and studies conducted para llel to this one, suggest that the greater decline in spore abundance in burned sites than in unburned sites early in the growing season may be indirectly due to greater root growth, and (or) related changes in host physiology, in response to fire.