BIOLOGICAL AND PHYSICOCHEMICAL PROCESSES IN EXCREMENTS OF SOIL ANIMALS

Soil animals, especially saprophagous species, ingest large amounts of organic and/or mineral materials. The undigested material is voided as excrements, which are physical structures with specific microenvironmental conditions that may dramatically influence the biological and physico-chemical processes as compared to those occurring in the initial material. In this paper, we emphasize firstly some critical constraints that have to be taken into account in studies of processes in soil fauna excrements, such as (i) the diversity in composition, size and stability of excrements, (ii) the difficulty in sampling excrements in field studies, and/or (iii) the difficulty in defining a relevant reference material for comparative approaches, and (iv) a relevant time-scale for dynamic studies. A review of recent literature enlightens some specific aspects of biological processes in soil fauna excrements, e.g., the composition of the microbial community, microbial activity, decomposition and nutrient release in addition to specific physico-chemical conditions, e.g., aggregation, clay/organic matter interactions and fluid movements. This synthesis emphasizes the close relationship between physical and biological processes that need to be investigated through interactive approaches.