The influence of Enchytraeidae (Oligochaeta) on the soil porosity of small microcosms

Abstract

Tunneling and burrowing activities of soil organisms affect structure and porosity of soils, but the role of enchytraeids as a soil burrowing organism is unclear. This study was initiated to evaluate the effect of enchytraeids on soil porosity in two soils with different texture and similar, low organic matter contents. In small microcosms, the burrowing activities of Enchytraeus minutus were followed during a 51 day period. The microcosms consisted of two glass plates with a bottom of plaster of Paris and sides of Plexiglas. Sieved (<1 mm), enchytraeid-free soil was added between the glass plates and two litter placement treatments were simulated by the addition of rye to the surface or by incorporating it into the soil. The soil in the microcosms was wetted from the bottom through the capillary action of the plaster and soil. Twenty enchytraeids were added to the microcosms and every 17 days the distribution of pores was determined under a stereomicroscope by a point counting technique and with image analysis. At least 65% of the enchytraeids survived in the microcosms, and in the surface litter treatments, the population expanded. Enchytraeids increased porosity in the microcosms at 17 days. At later times the porosity of the microcosms decreased to levels below the starting values. This decrease in porosity was attributed to consolidation of the soils as a result of overburden pressure and destabilization of soil aggregates caused by the egestion of the soil by enchytraeids. Porosity estimates by image analysis were much lower than by point counting, but a strong correlation was found between the two.