01767naa a2200217 a 450000100080000000500110000800800410001910000180006024500750007826000090015330000120016252012070017465000120138165000140139365000090140765000230141665300110143965300180145070000180146877300630148616464041994-01-05       1991    bl ---       0--  u    #d1 aABBOTT, L. K.  aFactors influencing the occurrence of vesicular-arbuscular mycorrhizas  c1991  a121-150  aVesicular-arbuscular (VA) mycorrhizas are widely distributed but there is limited knowledge of the occurrence of indivudual species in relation to soil, climate and vegetation. Recent developments in methods for identifuing VAM fungi, both in soil and within roots, should the clearer definition of the factors that influence their distribution. Careful attention must be paid sampling procedures to avoid bias and subjectivity. Soils commonly contain more than one VAM fungus. The development of VA mycorrhizas varies with soil type and depth, season and vegetation. The dynamics of root colonization by individual species within a population have not been adequately explored. Minor or gradual disturbances in agricultural and natural ecosystems may, or may not, lead marked changes in the environment without abrupt changes in the extent of colonization. In contrast, more extreme, or rapid environmental changes such as those associated with mining or erosin, may markedly decrease mycorrhiza formation. The restorarion of populations of mycorrhizal fungi will depend on the availability of accessible sources of propagules and on the suitability of the disturbed soils for plant and fungal growth.  aDoença  aMicorriza  aSolo  aVariação Sazonal  aFungos  aGigaspora spp1 aROBSON, A. D.  tAgriculture Ecosystems and Environment, 35 (1991) 121-150.