Sensitivity of life history parameters in the earthworm Aporrectodea caliginosa to small changes in soil water potential

Abstract

The effects of decreasing soil water potential on cocoon production, cocoon development and growth of juveniles were investigated in the earthworm Aporrectodea caliginosa. The earthworms were subjected to water potentials between −2 and ca. −300 kPa, using two soil types with various wetness. The duration of the drought exposure was 14 days, whereafter the earthworms were returned to ideal moisture conditions. Cocoon production was negatively affected when the water potential was lower than −12 kPa, and below −40 kPa cocoon production was completely arrested. The negative effect on cocoon production persisted for at least 2 weeks after the worms were moved back to soil with optimal moisture conditions. For those worms that were exposed to the most severe drought level, −330 kPa, cocoon production was still significantly impaired two months after drought exposure. Juvenile growth was sensitive to decreasing water potential. Even at −6 kPa the growth of juveniles was significantly lower than in controls and at ca. −20 kPa there was no growth at all. Cocoon development was less sensitive to water potential than growth and cocoon production. Thus, development seemed not to be affected by a 14 day exposure at water potentials above ca. −700 kPa, whereas at higher levels there was an increasing effect. When cocoons were exposed to ca. −3 MPa the development was immediately arrested.