Effects Of The Interaction Between Two Earthworm Species On Soil Availability In An Alpine Meadow, Northwestern Sichuan, China

Earthworm ecology is increasingly receiving attentions from ecologists. Earthworms have been viewed as an ecosystem engineer due to their important impact on properties of soil system. Most previous studies have been focused on the effects of earthworm on soil organic matter, soil nutrient, and interaction between earthworm and soil microorganism. However, few studies on the interaction between earthworm species have been reported. The interaction between earthworm species is an important factor that affects species coexistence and ecosystem functions. Thus, the studies on the interaction between earthworm species may contribute to the understanding of the mechanism of earthworm species coexistence and their roles in soil ecosystem, and hence provide a theoretical basis for the management and protection of ecosystem.In this study, two earthworm species (small earthworms: Megascolecidae Amynthas sp1; large earthworms: Megascolecidae Amynthas sp2), which dominate the alpine meadow, northwestern Sichuan Province, were chosen to explore the effect of the interaction on dung-soil system. The number, distribution and reproduction of the two earthworm species, as well as cattle dung decomposition and soil nutrient content, were examined for the treatments where the species were added into dung-soil system individually and together. The main results are as follows.1) When they were added individually, most small earthworms were in the upper soil (0-10cm) during the experiment period, which significantly reduced the upper soil moisture and highly but not significantly accelerated the decomposition of cattle dung relative to controls without earthworm addition, while the number of large earthworms in the upper and lower (10-20cm) soil was almost equal, which significantly decreased the upper and lower soil moisture and increased cattle dung loss. However, soil organic matter and nutrient content were unaffected by small or large earthworms.2) When they were added together, the interaction not only altered both number and distribution, but also affected their reproduction. The mortalities of both species increased and the epigeic small earthworms had a higher mortality than the epianecic large earthworms; the numbers of two earthworm species in the upper soil both decreased when they coexisted. Although the upper soil was still dominated by the small earthworms, large earthworms tended to move into the lower soil; the larvae number of large earthworm was significantly decreased, while the larvae number of small earthworm increased.3) An additive effect of two earthworm species on available nitrogen in lower soil was found when they coexisted in the dung-soil system and the available nitrogen content in lower soil significantly increased.