Biodiversity and Ecosystem Function

The beneficial effects of mycorrhizae on plant growth have often been related to the increase in the uptake of immobile nutrients, especially phosphorus (P). In this review the mechanisms for the increase in the uptake of P by mycorrhizae and the sources of soil P for mycorrhizal and non-mycorrhizal plants are examined. Various mechanisms have been suggested for the increase in the uptake of P by mycorrhizal plants. These include: exploration of larger soil volume; faster movement of P into mycorrhizal hyphae; and solubilization of soil phosphorus. Exploration of larger soil volume by mycorrhizal plants is achieved by decreasing the distance that P ions must diffuse to plant roots and by increasing the surface area for absorption. Faster movement of P into mycorrhizal hyphae is achieved by increasing the affinity for P ions and by decreasing the threshold concentration required for absorption of P. Solubilization of soil P is achieved by the release of organic acids and phosphatase enzymes. Mycorrhizal plants have been shown to increase the uptake of poorly soluble P sources, such as iron and aluminium phosphate and rock phosphates. However, studies in which the soil P has been labelled with radioactive 32P indicated that both mycorrhizal and non-mycorrhizal plants utilized the similarly labelled P sources in soil.

A critical review on the role of mycorrhizal fungi in the uptake of phosphorus by plants

A check-list of mycorrhiza in the british flora*

The enhanced growth of plants infected by vesicular–arbuscular (VA) mycorrhizal fungi results primarily from improved uptake of soil phosphate. Extra phosphate reaches the root through the fungal h...

The physiology of vesicular-arbuscular endomycorrhizal symbiosis

Publisher Summary A grass-legume association has been used in many countries of the world because a greater total herbage yield may be obtained by growing a grass and a legume in association, rather than in individual swards, where no fertilizer N is applied. Interferences and competition between legumes and associated grasses are of great importance in world pasture production. Such interspecific interferences are likely to be a dominating factor in the nonequilibrium, man-made and -managed pasture vegetation. It is generally accepted that grasses normally have a competitive advantage over legumes, and they tend to dominate pastures but to maintain high pasture productivity, a balance between grasses and legumes is desirable. This chapter examines the competitive relationships between grasses and legumes and also considers the way in which pasture management techniques alter the balance of legumes and grasses by manipulating the environment, which results in a competitive advantage to the legume component.

D. S. Hayman

Papers

Plant growth responses to vesicular-arbuscular mycorrhiza. ix. interactions between va mycorrhiza, rock phosphate and symbiotic nitrogen fixation