Earthworms, microbial biomass and enzymatic activities as useful bioindicators of agroecosystem sustainability in protected and deteriorated savannas
Instituto de Zoología y Ecología Tropical/Facultad de Ciencias/ Universidad Central de Venezuela, Caracas, Apartado postal 47058, Caracas 1041-A, Venezuela.
* Corresponding author: Danilo López-Hernández, Instituto de Zoología y Ecología Tropical/Facultad de Ciencias/ Universidad Central de Venezuela, Caracas, Apartado postal 47058, Caracas 1041-A, Venezuela, E-mail: email@example.com
We studied soil parameters and the earthworm biomass and density in a protected savanna (PS) from fire and cattle raising for more than fifty years located at Estación Biológica de los Llanos, Venezuela (EBLL), and an adjacent natural savanna (NS) under frequent burning and agricultural activities. Earthworm sampling was carried out at the end of the dry season (April), and at the peak of the wet season (July-August. The main physical, chemical, microbial (biomass) and enzymatic activities of soils in both systems were estimated. The establishment of tree canopies and the presence of litter layer at PS have increased the soil water retention capacity. In the PS also have increased the organic-C, C-microbial biomass, dehydrogenase activity and fertility levels respect NS. The presence of earthworms, in turn, affects the physical properties of the soil through the construction of channels and galleries.The average density of earthworms in the PS ranged between 25.6 and 85 individuals m-2, and average biomass varied between 6.92 and 23.23 g m-2. In the NS earthworms only were found in the wet season, with a mean density of 22.40 individuals m-2 and a mean biomass of 5.17 g m-2. Results suggest that, agricultural management in savannas can decrease their earthworm communities and microbial and enzymatic activities. However, earthworm populations and soil quality indicators can be restored after long-term protection. Therefore, we can emphasise the potential use of the density and biomass of earthworms as bioindicators of soil fertility and as active actors in the regeneration of deteriorated savanna’s soil.
Key words: Macrofauna, Glossoscolecidae, Microbial biomass, Dehydrogenase, Fire