AGRICULTURAL INTENSIFICATION, SOIL BIODIVERSITY AND AGROECOSYSTEM FUNCTION IN THE TROPICS - THE ROLE OF EARTHWORMS

Earthworm biodiversity is modified when forests and natural savannas a re replaced by agroecosystems; these changes can be studied from the t axonomic and functional point of view. In the first case the number an d origin (native or exotic) of species is important, as well as the ge ographic scale of the study (local or regional), The functional approa ch considers the ecological groups (epigeic, endogeic, anecic), which have different effects on soil function, Studies in Mexico, Peru and I ndia reveal that agroecosystem earthworm communities (as compared with those in the undisturbed ecosystem) have lower species richness, lowe r number of native species, lower number of ecological groups and a pr edominance of endogeics, Therefore the role of endogeic species in int ensifying agroecosystems is likely to be more important for soil funct ion, especially because they act as ecosystem engineers and through th eir mutualistic interactions with microflora, selective ingestion of s oil particles, high rates of ingestion and production of casts, galler ies, burrows and chambers can affect nutrient and organic matter dynam ics and other pedological processes. Epigeic and anecic species do not appear to be as widespread in agricultural systems and their dependen ce on a litter layer for survival implies that litter management pract ices must be implemented for their role in soil function to be of impo rtance. The role of earthworms in enhancing primary production depends on the synlocalization (in the same place) and the synchronization (a t the same time) of their activities with the period and the sphere of active root growth and nutrient demands. Several field studies have f ound significant yield increases with earthworm inoculation, though mo re research is needed. Incorporation of information on earthworm life histories, field population variations, ecological strategies and shor t and long term effects on soil properties, in addition to plant and e nvironmental factors (climate, soil, cropping period and management of the agroecosystem), are essential to properly assess the potential ro le of a particular earthworm species on plant production.