The physiology of vesicular–arbuscular endomycorrhizal symbiosis

Abstract

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 hyphae, which tap the soluble P in soil beyond the phosphate-depletion zone near the root surface. This mechanism can explain the many corrrelations between root geometry and mycotrophy and other nutritional effects of VA mycorrhizae such as increased uptake of zinc and copper ions. Recently VA mycorrhizae have been shown to increase the levels of chlorophyll and some hormones in plants and to alleviate water stress. Legumes are now receiving considerable attention because VA mycorrhiza affects nitrogen fixation in them indirectly by its action on P uptake. In this review the physiology of the VA mycorrhizal symbiosis is discussed in categories reflecting successive stages in its formation and function: (i) activation of the VA mycorrhizal propagules; (ii) penetration and initial infection of the host plant; (iii) spread of infection in roots; (iv) response of the plant; the components and mechanisms of VA mycorrhizal systems; (v) benefits to the fungus; carbon sinks; and (vi) imbalances in the symbiosis. It is suggested that studies on the physiological complexities of VA mycorrhizal associations should take more account of the biological diversity of VA mycorrhizal fungi and the wide range of host–endophyte–soil specificities.

Mineral nutrition in the tripartite interaction between Frankia, Glomus and Alnus at different soil phosphorus regimes

“…The results confirm that VAM associations have a marked influence on growth and nitrogen fixation of actinorhizal plants, as is also seen in legumes, especially in soils with low P availability (Smith, Nicholas & Smith, 1979;Hayman, 1983;. In this experiment VAM did not greatly improve growth in the most P-deficient soils, a result previously reported by Plenchette, Fortin & Furlan (1983) and Davis, Youngberg & Rose (1984).…”

Hongo endomicorrízico y bacteria fijadora de nitrógeno inoculadas a Coffea arabica en vivero.

“…muchos autores han demostrado que las plantas micorrizadas absorben fósforo del suelo más eficientemente que las plantas no colonizadas (stribey 1987, aguirre-medina y Kohashi 2002) debido a la capacidad de las hifas para explorar mayor volumen de sustrato y con más eficiencia en comparación con un sistema radical no micorrizado (Bolan 1991). Las hifas fúngicas tienen mayor afinidad por el ion fosfato cuando su concentración es baja en la solución (Hayman 1983, gianinazzi-Pearson y gianinazzi 1986) y las raíces micorrizadas se mantienen funcionales por más tiempo (Hayman 1983).…”

Vesicular arbuscular mycorrhizae-mediated uptake and translocation of P and Zn by wheat in a calcareous soil

“…This result is very interesting but the reason is not clear. However, it is usually reported that degrees of VAM colonization, and the beneficial effects associated with VAM colonization, decrease as the supply of soil P increases (Abbott and Robson 1982;Hayman 1983). Moreover, inoculation of VAM has sometimes depressed plant growth, especially when P supply is not limiting (Buwalda and Goh 1982;Hays et al 1982).…”