Mycorrhizal contribution to nutrient acquisition from spatially heterogeneous soil was investigated using two-way comparisons of non-mycorrhizal and arbuscular mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in soil with either a patchy or a uniform nutrient distribution. Double-labelling allowed a comparison between acquisition of an ion of lower abundance and mobility, phosphate (P), and an ion of higher abundance and mobility, nitrate. As expected, root density increased in enriched-nutrient patches relative to either unenriched soil or to soil where the same quantity of nutrients was applied to the entire soil volume (uniform-nutrient treatment). However, the increase of local root density in patches was less for mycorrhizal plants than for non-mycorrhizal plants. Mycorrhizal infection enhanced plant acquisition of labelled P relatively more in the enriched patches (patchy-nutrient treatment) than in soil with uniform nutrient distribution, both when expressed on a shoot mass and on a root-length basis. As expected, plant nitrate acquisition and shoot nitrogen concentration were not significantly affected by either mycorrhizal infection or patterns of soil nutrient distribution. Hence, arbuscular mycorrhizas can enhance root P acquisition and, thus, contribute to plant exploitation of soil P heterogeneity.