Study On Characteristics Of Soil Fauna Community And Their Function In Litter Decomposition In Leymus Chinensis Steppe, Songnen Plain

Litter decomposition is an important part of ecosystem progress. Based on the review of history of soil fauna ecology, the thesis summarized the four topics, including ecological distribution of soil fauna community and the relationship between soil fauna community and environmental factors; bioindictor of soil fauna; the function of the diversity of soil fauna in litter decomposition and nutrient cycle as well. As the case of function of soil fauna in the litter decay and element cycle, most researches were performed in forest ecosystem, and few of them carried in grassland ecosystem. The characteristics of vegetation, soil and other environmental factors in grassland ecosystem are different from those in forest ecosystem. And the function of soil fauna in litter decomposition and nutrient release in grassland ecosystem should be different from that in the forest ecosystem. Consequently, soil fauna's function in litter decomposition and nutrient cycle in grassland ecosystem should be eager to perform more researches, which will enrich the fundamental and theoretics of soil fauna ecology. The results that had gotten in a few researches about the function of the diversity of soil fauna were not consisted. There are few studies on the longer time of litter decomposition in grassland ecosystem that performed to study the function of soil fauna, especially in China. The goal of this study is discussing the function of different groups of soil fauna in litter decomposition and nutrient cycle in grassland ecosystem. And the effects of litter qulities and environmental factors on the litter decomposition rate and nutrient release are also discussed in the thesis. The present study will not only be a great performance of the theory of soil fauna ecology, but also give leading help in ecological restoration and management of Songnen grassland ecosystem. The thesis was financially supported by National Natural Science Foundation of China (No. 40871120 ).The thesis had been studied the decomposition and nutrient release of the above-ground litter of the Leymus chinensis, Chloris virgata, Calamagrostis epigejos, Puccinellia chinampoensis, and Kochia sieversiana by litterbag standard method in Leymus chinensis steppe ecosystem in Songnen plain(44°40′- 44′N and 123°44′-47′E). The four different mesh sizes of litterbag, including 4mm, 2mm, 0.15mm, and 0.01mm, were used to control the different body size of soil fauna in the litterbag. The litterbags of L. chinensis, C. virgata, C. epigejos are located in their situ (called typical situ), and the litterbags of P. chinampoensis and K. sieversiana are located in their situ (called degraded situ). Starting from 23rd October 2006 to 23rd September 2007, at monthly intervals, litter samples were carefully retrieved from the field to laboratory. Based on the data of decay rate and dynamics of the N, P, K of litter and soil fauna community, the thesis discussed the function of different fauna groups in litter decomposition and nutrient release and analysized the relationship between soil fauna community and environmental factors at the same time.The results showed that soil fauna community in litter had seasonal dynamics with the seasonal fluctuation of temperature and moisture. The density and diversity indexes of soil fauna community in June 2007~ September 2007 were higher than those in November 2006~ May 2007. In the open (mesh size=4mm) litterbag, the individual numbers of soil fauna in the five litter were in the sequence of C. virgata> L. chinensis > C. epigejos > P. chinampoensis > K. sieversiana. The individual numbers of soil fauna in the litter of typical situ are higher than that of in degraded situ through all litterbags. The phytophagous, saprophagous, and omnivorous groups of soil fauna were more common in litter than those in soil. But the number and dominance of predacious group of soil fauna were lower than those in soil.The decay rate of litter also showed seasonal dynamics in all mesh size litterbags. The loss rate of litter in summer and autuman are higher than that in winter and spring. After decomposition of eleven months, the percent of litter mass remained from 61% to 84%. The decay rates of P. chinampoensis and K. sieversiana litter in the degraded situ are higher than those of C. virgata, L. chinensis and C. epigejos litter in the typical situ. The decay rates of litter in litterbags were not consistent with the mesh size of the litterbag, which indicated that the different groups of soil fauna in litterbags had different effects on the litter decomposition.The remaining percent of N, P, K in the open litterbags of litter were all decreased to 4%~45%, 26%~63%, 72%~89%, respectively, at the end of study stage. There are great changes in the other mesh size litterbags had great changes. The loss percent of N, P, K of litter in degraded situ were higher than that of in typical situ. The different groups of soil fauna in litterbags had different effects on the nutrient release of litter.Soil fauna had great contribution on litter decay rate. There were significant positive relations between density, diversity of soil fauna community and litter decay rate. Soil fauna have great influences on the element cycle in ecosystems. The decay rate and loss percent of nutrient of litter in the open litterbags were higher than that in the other mesh size litterbags, which also indicated that soil fauna community had great effects on litter decomposition and nutrient release. The groups of soil fauna as decomposers in litter had changes in different seasons. In winter and spring, Prostigmata, Thysanoptera were the main decomposers, and Diptera, Psocoptera, Araneae, Coleoptera as well. In summer and autumn, the groups included Collembola, Hemiptera, Lepidoptera larvae, Hymenoptera, Homoptera, Coleoptera larvae, Oribatida, Astigmata, Isopoda, Gastropoda were also founded in the litter. The number and diversity of soil fauna in litter in summer & autumn are higher than those in winter & spring. At the end of autumn (September 2007), the number of soil fauna in litter decreased than before (August 2007). The effects of physical and chemical leaching on litter decay and nutrient release possibly explained that the decay rates and dynamics of nutrient concentration in litter were not consistent with the mesh size of litterbag. The results of ANOVA analysize showed that there are significant effects of litter species, mesh size of litterbag, sampling time and the interactions of them on litter decay rates. Litter species, mesh size of litterbag, sampling time had significant effects on P and K release.The density of soil fauna in litter were influenced significantly by litter species, sampling time and their interactions. There were little relativity between temperature, precipitation and the individual number and group number of soil fauna. There was positive relationshiop between the individual number of soil fauna and total N in soil in typical situ. And the individual number of soil fauna was mainly influenced by temperature in degraded situ.