Host specificity

AM associations occur in a wide range of distribution among the tropical and temperate regions. They are known not to occur only in a few plants, namely members of the families Amaranthaceae, Pinaceae, Betulaceae, Cruciferae, Chenopodiaceae, Cyperaceae, Juncaceae, Proteaceae, and Polygonaceae. The ectomycorrhizas, on the other hand, occur primarily in temperate forest species, although they have been reported to colonize a limited number of tropical tree species.

Functions of mycorrhizal fungi

AM fungi absorb N, P, K, Ca, S, Cu, and Zn from the soil and translocate them to associated plants. However, the most prominent and consistent nutritional effect of AM fungi is in the improved uptake of immobile nutrients, particularly P, Cu, and Zn. The fungi enhance immobile nutrient uptake by increasing the absorptive surfaces of the root through diffusion.
Enhanced nutrient uptake by AM fungi is often associated with dramatic increase in dry matter
yield, typically amounting to several-fold increases for plant species having high dependency on mycorrhiza.
AM fungi may have biochemical capabilities for increasing the supply of available P and other immobile nutrients. These capabilities may involve increases in root phosphatase activity, excretion of chelating agents, and rhizosphere acidification.
AM fungi are often implicated in functions which may or may not be related to enhanced nutrient uptake. For example, they have been associated with enhanced chlorophyll levels in leaves and improved plant tolerance of diseases, parasites, water stress, salinity, and heavy metal toxicity. Moreover, there is increasing evidence that hyphal networks of AM fungi contribute significantly to the development of soil aggregates, and hence to soil conservation.