Trophic relationships between the earthworm Pontoscolex corethrurus and three tropical arbuscular mycorrhizal fungal species

Abstract

Earthworms and arbuscular mycorrhizal fungi (AMF) are essential for nutrient cycling and organic matter dynamics in terrestrial ecosystems. In soils, they tightly interact especially in the rhizosphere. Therefore, the objective of this study was to evaluate the trophic relationship between the earthworm Pontoscolex corethrurus and three species of AMF (Rhizophagus clarus, Claroideoglomus etunicatum, and Gigaspora margarita). We performed bioassays with different experimental designs and treatments, to evaluate cast production by P. corethrurus in the three different substrates, the number of AMF propagules after ingestion by earthworms, the germination capacity of ingested spores, the earthworm feeding preferences, and the influence of AMF species on earthworm growth. P. corethrurus produced more casts when R. clarus and C. etunicatum was present in the food source. Spore number, percentage of germinated spores and most probable number of infective propagules of R. clarus and C. etunicatum were higher in earthworm casts than in soil inocula, whereas opposite trend of results was found with G. margarita, suggesting that the digestion of AMF propagules by P. corethrurus varies with the AMF species. Earthworm weight increased when they were fed with R. clarus and G. margarita soil-inocula, but individuals showed no clear preference for different AMF species. Roots colonized by R. clarus were more attractive to P. corethrurus. Findings of this study have important implications for the roles of P. corethrurus in mycorrhizal potential of R. clarus e C. etunicatum and in the reduction of the propagules of G. margarita in soil.