Effects Of Soil Fauna On Litter Decomposition In The Subalpine And Alpine Forests Of Western Sichuan, China

Decomposition of plant litter is influenced by climate condition, substrate quality and decomposer community. At a global scale, climate is the best predictor for the decomposition constants of the litter, while substrate quality is the main determinant of litter decomposition within a given climatic region. As one of the most important decomposer organisms, soil fauna largely controls the decomposition process. However, under the effect of climate condition and substrate quality, it is not clear that the effects of soil fauna on litter decomposition in cold regions. In addition, under a warming climate, the seasonal freezing and thawing pattern will be changed, the litter quality and the soil fauna composition will be effected in cold forests. All of above will act on the process of soil fauna effecting litter decomposition, lack of further understanding. A field litterbag experiment was conducted in subalpine and alpine forests of western Sichuan, China, from November 2011 through October 2013. Samples of air-dried leaf litter for Salix paraplesia, Sabina saltuaria, Betula albosinensis, and Abies faxoniana were placed in nylon litterbags of 3.00 mm and 0.04 mm mesh sizes. The structure and diversity of soil fauna community, the mass loss rates driven by soil fauna, the rates of organic carbon decomposition, the rates of nitrogen and phosphorus released, and the rates of lignin and cellulose degradation through soil fauna were investigated at different stages during decomposition process, i.e., onset of freezing period, deep freezing period, thawing stage, early growing season, mid-growing season, and late growing season both of the two years.A total of 12164 individuals of soil fauna were collected, according to preliminary identification, they belonged to 2 phyla 9 classes 15 orders and 57 families, the individuals were A. faxomana(33.8%)>B. albosinensis(29.3%)>S. paraplesia(21.6%)>S. saltuaria(15.3%). The individuals of soil fauna in growing season(76.8%) was significantly greater than that in freeze-thaw season(23.2%). The dominant group of soil fauna was mainly Collembola. Moreover, climate condition and substrate quality had a significant effect on the structure of soil fauna community during litter decomposition process. The Shannon-Wiener diversity index of soil fauna consistent basically with the temperature and precipitation changed.During the research period, the mass loss rates were 42.5-72.0%, while the organic carbon decompositin rates were 49.1-78.2%, and both of them showed the order as S. paraplesia>B. albosinensis>A. faxoniana>S. saltuaria. The N dynamics were of a release-enrichment-release-enrichment pattern in S. paraplesia and B. albosinnsis, and of a release-enrichment pattern in A.faxoniana and S. saltuaria. The P generally displayed a declining trend, but with an obvious enrichment process in the mid-growing season of the first year. Besides, the rates of lignin degradation were 16.3-45.4%, while the rates of cellulose degradation were 68.1-86.4%.The mass loss rates driven by soil fauna showed S. saltuaria(13.0%)>A. faxoniana(12.3%)>B. albosinensis(11.4%)>S. paraplesia(9.9%). Higher mass loss rates of all the four species driven by soil fauna were observed in the first year compared with the second year, and growing season were much greater than freeze-thaw season in both of the two years. During the process of litter decomposition, soil fauna imposed a positive effect on organic carbon decompositin and N release of all the four species, the same on P release of S. paraplesia and B. albosinensis, while a negative effect on P release of A. faxoniana and S. saltuaria. In addition, the rates of lignin degradation through soil fauna were 16.3-45.4%, and the rates of cellulose degradation through soil fauna were 68.1-86.4%.In conclusion, climate condition and substrate quality affected significantly on the structure and the diversity of soil fauna community during litter decomposition in subalpine and alpine forests of western Sichuan. Soil fauna affected more on broadleaf litters than coniferous litters in mass loss. No matter the litter of broadleaf trees or the litter of coniferous trees, soil fauna imposed a positive effect on organic carbon decompositin and N release. Besides, soil fauna imposed a positive effect on P release of the litter of broadleaf trees, while a negative effect on P release of the litter of coniferous trees. Moreover, soil fauna had a significant effect on lignin and cellulose degradation during litter decomposition. These results found that soil fauna largely controlled the litter decomposition process in subalpine and alpine forests of western Sichuan, and been for understanding the material recycling process sucha as litter decomposition in cold forest ecosystem of great significance.