Facilitation of plant phosphate acquisition by arbuscular mycorrhizas from enriched soil patches

summary 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.