VESICULAR ARBUSCULAR MYCORRHIZAS RESPOND TO CORN AND SOYBEAN CROPPING HISTORY

Communities of vesicular-arbuscular (VA) mycorrhizal fungi were studied in a long-term crop rotation experiment at two locations (Waseca and Lamberton, Minnesota, USA). Spores of mycorrhizal fungi were counted and identified in experimental plots with a cropping history of either corn (Zea mays L.) or soybean [Glycine max (L.) Merrill]. Mycorrhizal fungal communities were affected by both location and cropping history. At Waseca, Glomus aggregatum Schenck & Smith, G. leptotichum Schenck & Smith and G. occultum Walker spores were more abundant in soil with a corn history than a soybean history, while spores of G. microcarpum Tul. & Tul. exhibited the reciprocal pattern. Approximately 90% of the spores recovered at Lamberton were G. aggregatum and did not vary with crop history. However, the spores of three other species: G. albidum Walker & Rhodes, G. mosseae Gerdemann & Trappe, and G. occultum, were more abundant in plots with a corn history than a soybean history. Densities of G. aggretatum spores were negatively correlated with soil pH at Waseca, but were unrelated to pH at Lamberton were the mean soil pH was lower. Our results indicate that mycorrhizal fungal species are individualistic in their responses to cropping history and edaphic factors.