Ecology of VAM fungi in tropical agrosystems

Abstract

The known edaphic and climatic stress situations in the tropics imply that agronomic crops depend, for nutrition and growth, on vesicular arbuscular mycorrhizae (VAM). VAM fungal populations in tropical agrosystems may be high in quantity (concentration of infective propagules) when soils are cultivated after a fallow period, or when low levels of agronomic inputs are applied. The quality (effectiveness) of VAM populations varies among sites. Quality may be related to the composition of VAM fungal species within the native populations. Agronomic inputs to agrosystems, such as cropping practices, fertilization, weeding, pesticide applications etc. may decrease the diversity of VAM fungi and/or change the quantitative composition of fungal species due to improvement of the competitive ability of certain fungi. Possible results may also be preferential associations between certain plant and certain fungal species. The significance of differential abilities of VAM fungal species to tolerate edaphic conditions and to infect crop plants, as well as the significance of preferential associations and diversity of VAM fungi are presented. The necessity to introduce VAM fungi to disturbed tropical soils and the feasibilities to inoculate tropical agroecosystems are discussed.