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 effects of soil moisture and temperature on earthworm physiology and ecology. The objective of this study was to evaluate the influence of soil moisture and temperature on the survival, growth and sexual development of an endogeic species, Aporrectodea tuberculata. Juvenile earthworms were grown at all possible combinations of four soil moistures (10, 15, 20 and 25 %, dry weight basis) and temperatures (5, 10, 15 and 20 degreesC). Logistic regression was used to determine the relationships between the proportion of surviving individuals with soil moisture and temperature, and time. Stepwise regression analysis was used to determine the various possible relationships between temperature, moisture and time on earthworm growth. Soil moisture accounted for 48 % of the variation in earthworm survival with the lowest survival associated with 10 % soil moistures. The interaction terms, time x temperature x moisture, and time x temperature, accounted for 63 % of the variation in earthworm growth. The greatest increase in earthworm weight was in soil incubated with 25 % moisture at 15 and 20 degreesC. There was also an obvious relationship between survival and growth linked to the interaction between 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 tumescences (GT). The results of the study showed that the effects of soil moisture on earthworm growth and survival are modified by soil temperature.