Contribution Of Soil Fauna To Litter Decomposition In The Alpine/Subalpine Forests

Litter decomposition is an important component of material cycles in terrestrial ecosystem. The decomposition process is regulated by environmental conditions, litter quality and soil organisms. Many focuses have been paid on how much contribution of soil fauna to litter decomposition in high-elevation and high-latitude ecosystems which are extremely sensitive to global change? Whether litter decomposition is influenced by soil fauna in winter? Meanwhile, there are four key periods (OF:the onset of the freeze-thaw season, DF:the deep frozen period, TS:the thawing stage and the growing season) in the ecological processes, and how about the contribution of soil fauna to litter decomposition among these periods? Whether the soil fauna community changes are responding to dynamics of the four periods, and they could differently contribute to litter decomposition among the periods? These unresolved questions limit our understanding of soil ecological processes in the areas with seasonal soil frozen.The alpine/subalpine forest of Western Sichuan is the representative forest in southwest China, which is an optimal ideal site to study soil ecological processes in wintertime since its vertical distribution characteristic of climate, and obviously seasonal freezing of soil with a length of5-6months. So far, researches on changes of the contributions from soil fauna due to temperature changing during the three stages of the freeze-thaw season in the alpine/subalpine forests of western Sichuan have not been well documented. Additionally, global climate warming can influence the structure and function of soil fauna community, and in turn change the pattern of wintertime litter decomposition and the following process in cold biomes. Thus, a field experiment using litterbags was conducted in primary fir (Abies faxoniana) forest, fir and birch (Betula albo-sinensis) mixed forest and secondary fir forest, which were three representative and widely distributed forests along an elevation gradient from3000to3600m in the eastern Tibet Plateau, during the freeze-thaw seasonal and growing season from26October2010to9November2011. We investigated mass loss rates and nutrient releases of birch and fir leaf litters in litterbags with different mesh sizes (0.020,0.125,1.000and3.000mm) and simultaneously analyzed contributions of micro-, meso-and macro-fauna to leaf litter decomposition. The results are helpful to deeply understand soil ecological processes of the alpine and subalpine forest ecosystem and its relationship between the processes in winter and growing season.Contributions of soil fauna to mass losses of birch and fir leaf litters increased with the increase of body size of soil fauna during the freeze-thaw season and the three different stages. The contributions of macro-fauna were significantly higher than that of micro-and meso-fauna regardless of elevation during the freeze-thaw season and the three different stages (except the contribution to fir leaf litter during the OF stage at site3000m). There were little differences in the contributions regardless of elevation during the freeze-thaw season. However, contributions of micro-and meso-fauna to mass losses of birch leaf litter were significantly higher at site3600m than that of at site3000m, while the contribution of micro-fauna to fir leaf litter was obviously lower at site3600m than that of at site3000m.Contributions of soil fauna to mass losses of birch and fir leaf litters increased with the increase of body size of soil fauna, and there were no significant differences in the contribution regardless of elevation during non-growing season and growing season. The contributions of different body-size soil fauna regardless of elevation during non-growing season were higher compared to the growing season. Particularly, the contributions of different body-size soil fauna to birch (except for the contribution of micro-fauna at site3000m) and macro-fauna to fir leaf litter at the three elevations during non-growing season were significantly higher than that of growing season.Contributions of soil fauna to mass losses of birch and fir leaf litters increased with the increase of body size of soil fauna during the1-year decomposition period. There were little differences in the contributions regardless of elevation during the1-year decomposition period. Macro-fauna contributed more to mass losses of birch and fir leaf litters than that of micro-fauna and meso-fauna regardless of elevation during the1-year decomposition period. Particularly, we observed that the significant differences in the contributions of micro-, meso-and macro-fauna to birch leaf litter at site3000m.In conclusion, soil fauna with different body sizes made significant contributions to the decomposition of fir and birch litter, and freeze-thaw cycles significantly affect soil fauna litter decomposition processes during the freeze-thaw period in alpine/subalpine forests. The changes in soil fauna community structures in litterbags with0.125,1.000and3.000mm mesh size are dependent on climate warming, but the contributions of soil fauna with different body sizes to litter decomposition do not respond to the simulated warming during winter and growing season in alpine/subalpine regions. Similarly, we detected the consistent results with the winter and growing season during the1-year decomposition period, which suggested that the contributions increasing with a raised of latitude in a range of large-scale area. Therefore, these results could be contributed to understand the wintertime ecological processes, and the interaction in freeze-thaw season and growing period.