The influence of soil moisture and temperature on the survival, aestivation, growth and development of juvenile Aporrectodea tuberculata (Eisen) (Lumbricidae)

Soil moisture and temperature are the primary factors determining earthworm survival and growth. Few studies, however, have examined the combined effe cts of soil moisture and temperature on earthworm physiology and ecology. T he objective of this study was to evaluate the influence of soil moisture a nd temperature on the survival, growth and sexual development of an endogei c species, Aporrectodea tuberculata. Juvenile earthworms were grown at all possible combinations of four soil moistures (10, 15, 20 and 25 %, dry weig ht basis) and temperatures (5, 10, 15 and 20 degreesC). Logistic regression was used to determine the relationships between the proportion of survivin g individuals with soil moisture and temperature, and time. Stepwise regres sion analysis was used to determine the various possible relationships betw een temperature, moisture and time on earthworm growth. Soil moisture accou nted for 48 % of the variation in earthworm survival with the lowest surviv al associated with 10 % soil moistures. The interaction terms, time x tempe rature x moisture, and time x temperature, accounted for 63 % of the variat ion in earthworm growth. The greatest increase in earthworm weight was in s oil incubated with 25 % moisture at 15 and 20 degreesC. There was also an o bvious relationship between survival and growth linked to the interaction b etween soil temperature and moisture. After 10 wk the only post-clitellate individuals were observed in the 25 % and 20 degreesC treatment. Clitellate earthworms weighed 1.5 times more than individuals having only genital tum escences (GT). The results of the study showed that the effects of soil moi sture on earthworm growth and survival are modified by soil temperature.