Management Influences on Arbuscular Mycorrhizal Fungal Species Composition in a Corn-Soybean Rotation

Crop and edaphic factors influence arbuscular mycorrhizal (AM) fungal species composition and populations. This study was conducted to determine the effect of management history, crop, and input system on species composition of AM fungal spore populations. Corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] sequences receiving no inputs (NI), organic inputs (OI), minimum inputs (MI), and conventional inputs (CI) were established in two adjacent areas with differing management histories: one area, the Koch Farm, had received no fertilizer or herbicide inputs for the past 25 yr; the other area, the experiment station, received recommended herbicide and fertilizer inputs. Fifteen AM fungal species were found in a survey of mycorrhizal fungal spore populations. Glomus aggregatum populations were positively correlated with Setaria spp. populations (r = 0.56), pH (r = 0.47), and K (r = 0.25) and negatively correlated with soil P (r = −0.57). Populations of Gl. geosporum, Gl. leptotichum, Gl. macrocarpum, and Gl. occultum were also positively correlated with soil pH and negatively correlated with soil P. Gigaspora margarita spore populations were positively correlated with soil P. level (r = 0.272). Although species richness was greater (13 species vs. 10), species diversity (Hw) was lower at the Koch Farm than the experiment station (0.57 vs. 0.64) because of large Gl. aggregatum spore populations. The correlation of AM fungal spore populations with Setaria spp. and P, K, and pH indicates that management practices influence AM fungal species composition through both biotic and abiotic factors. Published as Paper no. 21,733 of the contribution series of the Minn. Agric. Exp. Stn. based on research conducted under Project 22-94H and support from competitive grant USDA 92-37101-7395.