Changes in respiration rate and some physicochemical properties of soil during gut transit through Allolobophora molleri (Lumbricidae,Oligochaeta)

Summary Some physicochemical and biological measurements were carried out on the gut content and casts of Allolobophora molleri, an earthworm which lives in humid soils of Northern Spain. In the anterior part of the gut, water (22% of moist weight of soil) and soluble organic matter (27.4%) had been added to the ingested soil and pH had increased from 5.75 to 7.0. The amount of water-soluble compounds decreased sharply in the middle and posterior parts of the gut and were hardly detectable in control soil or casts. The average O₂ consumption, measured at 28° and 21°C, indicated respectively 2.75-to 12-fold increases in microbial respiration in the gut content compared to the non-ingested soil. These results extend the hypothesis of a mutualistic digestion in earthworms previously proposed for tropical endogeic species.