6533b870fe1ef96bd12d04ab

RESEARCH PRODUCT

Activity and role of the enchytraeid worm Cognettia sphagnetorum (Vejd.) (Oligochaeta: Enchytraeidae) in organic and mineral forest soil

subject

description

Summary Site preparation following clear felling of coniferous forest creates a mosaic of different kinds of habitats for soil decomposers, ranging from bare mineral soil to thick layers of organic soil and felling residues. To study whether the impact of enchytraeids on nutrient mineralisation processes is different in residues, organic layer, and mineral soil, a microcosm experiment was conducted in the laboratory. Microcosms contained mineral soil (sand) alone or with soil organic layer (humus and F-layer materials) and spruce needles, either separately or together. Enchytraeids (Cognettia sphagnetorum) were introduced to the half of the microcosms. Numbers of enchytraeids, their gut content, and soil pH and mineral nitrogen were determined twice, 8 and 13 weeks from the start. Population increase of C. sphagnetorum was found only in the soil organic layer. In the mineral soil, enchytraeids ingested sand grains together with bacteria and protozoans. In the organic soil enchytraeid intestines were filled with dark coloured humus material in which plant fragments, fungal hyphae and bacterial colonies were recognized. Enchytraeids significantly increased the amount of NH 4 -N in the bare mineral soil. When a soil organic layer was present on the mineral soil, enchytraeids decreased NH 4 -N in the presence of needles but had no effect when needles were absent. Enchytraieds did not affect the pH of the mineral soil, but they slightly increased that of the soil organic layer. The results of this experiment revealed that C. sphagnetorum is able to maintain its population and its functional importance also in resource poor mineral soil. Its effect on nitrogen dynamics appears to be dependent on environmental conditions, resource quality and development of a population, i.e. acceleration, no effect and inhibition of nitrogen mineralisation are all possible.