Phosphorus transformations in two P-sorption contrasting tropical soils during transit through Pontoscolex corethrurus (Glossoscolecidae : Oligochaeta)

Abstract Individuals of Pontoscolex corethrurus Muller, a geophagous tropical earthworm, were fed with two soils that have P-sorption contrasting characteristics. Water-soluble and exchangeable-P contents increased significantly in casts produced after ingestion of the low P-sorption soil, meaning that an important change occurred in the P-sorption complex. This increment was maintained for 4 days of cast aging and it could be ascribed to changes in the sorption reactive surfaces induced by competition for sorbing sites between orthophosphate and carboxyl groups of a (mucus-produced) glycoprotein. The increment in P availability in casts derived from the higher P-sorption soil decreased after 96 h perhaps due to an aging effect. The results presented, coupled with the high population of Pontoscolex corethrurus recorded in natural grasslands and cultivated agroecosystems suggest that these earthworms could be important in affecting P cycling in humid tropical soils.