Community Characters And Functional Role In Litter Decomposition Of Soil Fauna In Fixed Dune In Songnen Sandy Land

Community characteristics of soil fauna are fundamental of research of soil fauna ecology. Ecological distribution, biodiversity and dynamic of soil fauna are included. Although some researches have been conducted in some regions, most of them are focused in forest ecosystem, while research in arid and semiarid ecosystems is still lack. Therefor, study on community characteristics of soil fauna in Songnen sandy lands is very important.Soil fauna are important components in ecosystems, due to their functional role in acceleration of organic matter decomposition and nutrient transformation. Although most decomposition is ultimately the result of catabolic activities of soil microbes (fungi and bacteria) associated with litter resources, soil invertebrates can alter microbial activity and the condition of decomposing litter. Soil fauna largely control decomposition process through breakdown of litter, digestion and stimulation of microbial activities. Mechanisms of soil faunal contribution to litter decomposition include digestion of substrates, increase of surface area through fragmentation and acceleration of microbial inoculation to litter. Soil fauna represent multiple trophic functions. Exclusion of soil fauna groups with special size indicates the significance of soil fauna community composition to control the litter decomposition rate. Soil fauna community composition changes affect litter decomposition and nutrient metabolism through global environmental changes. Consequently, knowledge on effects of macro-, mesofauna and microbial to litter decomposition is necessary.Research region was selected in Songnen sandy land in Jilin Province. Top, middle and bottom of sun slope of fixed dune were chosen. According to different purposes, two methods were taken in this experiment. Sampling of soil fauna in habitats was conducted in field. Soil macrofauna were picked up by hands in field and soil meso-microfauna were extracted by Tullgren method in laboratory. At the same time, soil samples of three habitats were collected to determine soil physical and chemical properties (pH, organic matter content, total nitrogen and total phosphor).Litterbags were selected to research the role of soil fauna in litter decomposition. According to classification to soil fauna, three types of nylon mesh size litterbags (15 cm×20 cm) were chosen: 0.01 mm (only microbe), 2 mm (include microbe and mesofauna) and 4.7 mm (include microbe, mesofauna and macrofauna). Dominant plant species litter of S. baicalensis, A. avinoides, L. davurica and A. cristatum were collected as decomposition materials during the peak litter fall period in October of 2006. Soil macrofauna were collected by hand from the litterbag first, then the materials of litterbags (4.7 mm and 2 mm) were placed in Tullgren extractors to remove the litter mesofauna. Results showed that 61 groups of soil fauna, average density was 2238.95 ind/m2, were obtained during two years. Significant characteristic of semiarid region has shown in soil fauna composition, which meant that there were more Coleoptera. For horizontal distribution, density of soil fauna showed bottom > middle > top of fixed dune and group numbers of soil fauna showed middle > bottom > top of fixed dune. Densities of soil fauna in 2007 were significant lower than in 2008; but, group numbers of soil fauna were in the opposition.Dynamic characteristics of Shannon-Wiener Diversity Index and Margalef Richness Index were same, while Pielou Evenness Index and Simpson Dominance Index were in the opposition. There was no significant relation between density and group number of soil fauna and soil physical and chemical properties in top of fixed dune, but there were some significant relation between them in middle and bottom of fixed dune.Some regularity was shown in dynamic of litter decomposition rate during two years. Process of decomposition of S. baicalensis and A. cristatum could be separated into two stages. First was the rapid decomposition stage and litter decomposition rate was very fast. Followed was the stable decomposition stage and mass loss of litter was relatively stable. Decomposition rates of three mesh size litterbags were 4.7 mm > 2 mm > 0.01 mm. Thus, decomposition rates were accelerated by soil fauna.For the community characteristics of soil fauna in litterbags, the same characteristics were shown in 4.7 mm and 2 mm mesh size litterbags. The highest individual number and group number of soil fauna were both in litterbags of S. baicalensis and the lowest were in litterbags of A. avinoides and L. davurica, respectively.There were differences in dynamics and in contributions of soil fauna to litter decomposition among litter. Contributions of soil fauna to litter decomposition were declined with time, except L. davurica which shown role of soil fauna in litter decomposition were declined with time. There were also differences among habitats in contributions of soil fauna to litter decomposition which were resulted from landform differentiation.