THE POTENTIAL ROLE OF EARTHWORMS APORRECTODEA CALIGINOSA AND PHERETIMA CALIFORNICA IN REGULATING THE DENSITY AND DIVERSITY OF SOIL MICROARTHROPODS AND SOIL TRANSFORMATION

Abstract

Mesocosm experiments were performed to investigate, whether the presence of endogeic earthworms; Aporrectodea caliginosa and Pheretima californica together influence the population density and diversity of soil microathropods also to determine whether their influence may change the physical habitat and the soil essential elements. The effects of earthworms on oribatids at the genus level were further examined. The experiment included five treatments 1) a control treatment with soil only; 2) soil+earthworms; 3) soil+microarthropods; 4) soil+microarthropods+Aporrectodea caliginosa and 5) soil+microarthropods+Aporrectodea caliginosa+Pheretima californica and lasted for six months. Then after, the mesocosms were tested and microarthropods were extracted, identified and counted. The concentrations of essential elements were measured at the beginning and at the end of the experiment, in each treatment. The detected results indicated that, the population density of the grouped microarhropods was significantly lower in the treatments containing the two earthworm species compared with other treatments. The population density of oribatid mites, prostigmata and Collembola follow the same order: treatments with the two earthworm species < treatments with one earthworm species < treatments with microarthropods only. In contrast, the presence of the two tested earthworm species reflected an increased density of the number of mesostigmated mites followed by the treatments with one earthworm species and then after comes the treatments with microarthropods only. In spite of the recorded negative effect of the earthworms on the density of microarthropods, the presence of microarthropods and earthworms leads to a significant increase in the net level of soil elements. The increase in N, C, K and P concentrations of soil at the end of the experiment followed the pattern: soil with earthworms < soil with micro arthropods < soil with microarthropods and earthworms; A. caliginosa < soil with microarthropods and both earthworm species. However, no significant differences in pH were reported in both of the treatments with earthworms only and that with earthworms and microarthropods. However, more studies must be carried out to explain the effects of these fauna on the soil nutrient cycles.