Effects of arbuscular mycorrhizas (AM) on plant exploitation of soil nutrient heterogeneity were studied with non-mycorrhizal and mycorrhizal Agropyron desertorum (Fisch. ex Link) Schult. in two-compartment containers. A central cylindrical plant compartment was separated from an outer hyphal compartment by two layers of stainless-steel screen with a 2 mm air gap between the screen layers. Patchy or uniform nitrate (NO2−) and phosphate (P) distribution patterns were created in the outer compartment. Only AM hyphae could cross the double-screen barrier to access those nutrients. Mycorrhizal plants acquired significantly more labelled P in both the patchy- and the uniform-nutrient treatments than did non-mycorrhizal plants. Mycelia in root-free soil delivered similar amounts of P from the more distant rich patches to mycorrhizal plants as from the uniform and more proximate labelling. The uptake of a more mobile and abundant element, nitrate, was not affected significantly by either mycorrhizal infection or by nutrient distribution patterns in the root-free soil. Despite a lower root:shoot mass ratio, mycorrhizal plants had significantly greater shoot phosphorus concentration than did nonmycorrhizal plants. There was no significant difference in P uptake or phosphorus concentration between the two nutrient distribution patterns for mycorrhizal plants, indicating that AM hyphae can explore the root-free soil for available P and transport it to host plants equally well when P was distributed in either patchy or uniform patterns in the root-free soil.
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