RELATIONSHIPS BETWEEN CASTS OF GEOPHAGOUS EARTHWORMS (LUMBRICIDAE, OLIGOCHAETA) AND MATRIC POTENTIAL .1. CAST PRODUCTION, WATER-CONTENT, AND BULK-DENSITY

Laboratory experiments were conducted to investigate the effects of matric potential on the rate of cast production, and water content and bulk density of casts. Fresh, subsurface, and surface casts were collected from Aporrectodea caliginosa, A. rosea and A. trapezoides kept in reconstituted soil cores at matric potentials between -25 and -2 kPa. Rates of cast production and water contents of fresh casts, subsurface casts, and surface casts increased as the matric potential of soil cores increased from -25 kPa to -2 kPa. The bulk density of fresh casts decreased as the matric potential of soil cores increased from -8.6 to -2 kPa. Aestivating earthworms were found in soil cores at all matric potentials except -2 kPa. The rate of cast production at the drier matric potentials may have been related to the water balance of the earthworms. As the matric potential of the soil cores decreased, the amount of water egested per cast remained constant, but overall the water egested per day decreased due to a reduction in the number of casts produced. Differences between the three species were identified in rates of cast production, with A. rosea generally producing more casts than either A. caliginosa or A. trapezoides, and in water contents and bulk densities of fresh casts.