Chemical composition of earthworm casts as a tool in understanding the earthworm contribution to ecosystem sustainability - a review

Earthworms dominate the soil biota, and different structural and functional features of their biology and ecology have been studied and exploited to evaluate their contributions as ecosystem services. Due to their feeding ecology, burrowing and casting activity, earthworms are involved in the nutrient cycles, and therefore it is opportune to be considered when the biogeochemical cycles of the terrestrial ecosystems are analysed. All structural, microbiological and biogeochemical impacts of earthworms in soil start with their feeding and digestive functions, which end in casting. The casting activity consisting of the excretion of the ingested soil and organic matter after digestion processes depends on earthworm feeding behaviours and ecology, even described in the current literature as a new ecological feature: the casting ecology. The complexity of the chemical relationships occurring inside earthworm casts between main nutrients (organic carbon, nitrogen, phosphorus, potassium, calcium) highlights the complexity of the biogeochemical cycles and the great earthworms' contribution to these cycles in the ecosystems towards a better understanding of the soil sustainability through the soil biodiversity contribution. Due to this great contribution, the earthworms' casts should be included as indicators in the integrative conservation management of the ecosystems, as a re-thinking of the concept of ecosystem sustainability.