Phosphorus acquisition from compacted soil by hyphae of a mycorrhizal fungus associated with red clover (Trifolium pratense)

The influence of an arbuscular mycorrhizal fungus, Glomus mosseae, on the adverse effects of soil compaction on growth and phosphorus (P) uptake of red clover was studied in a model experiment. The pots used in the experiment had three compartments, a central one with a soil bulk density of 1.3 g.cm(-3) and two outer compartments with three different levels of soil bulk density (1.3, 1.6, or 1.8 g.cm(-3)). The soil in the outer compartments was fertilized with P and was either freely accessible to roots and hyphae, or separated by nets and accessible to hyphae only. At a soil bulk density of 1.3 g.cm(-3), mycorrhizal plants did not absorb more P than nonmycorrhizal plants except when access of roots to the outer compartments was restricted by nets. At high soil bulk density, root growth was drastically decreased. However, hyphae of G. mosseae absorbed P even from highly compacted soil, and induced a P-depletion zone of about 30 mm from the root surface. In consequence, at higher soil bulk density shoot P concentration and the total amount of P in the shoot were higher in mycorrhizal than in nonmycorrhizal plants. This experiment showed that hyphae of G. mosseae are more efficient in obtaining P from compacted soil than mycorrhizal or nonmycorrhizal roots of red clover.