Interaction of mycorrhizal infection, phosphorus level, and moisture stress in growth of field corn

Field corn from four locations sampled through the growing season was colonized by mycorrhizal fungi despite fairly high (56 μg/g) soil phosphorus fertilities. The mycorrhizal fungi indigenous to these sites were also assessed and Glomus spp. were found to predominate in all but one soil wherein Cigaspora spp. were most common. Adequately watered greenhouse corn exposed to a range of phosphorus fertilities and inoculated with Glomus mosseae showed increased growth in sand amended with 15.0 or 22.5 ppm KH 2 PO 4 over noninoculated controls. Growth of plants amended with 30.0 ppm KH 2 PO 4 , however, was smaller suggesting high fertility parasitism by the endophyte. In contrast, no mycorrhizal response was observed on plants exposed to cyclic drought stress, even though root colonization in draughted plants was greater than that observed in adequately watered plants at the lower phosphorus levels. Thus it appears that G. mosseae was unable to measurably improve the drought tolerance of corn and, in addition, any nutritional benefit from the fungus appears to be lost under drought stress.