Effect Of Seasonal Snow Cover On Leaf Litter Decomposition In Timberline Ecotone

Plant leaf litter decomposition is the principal way of material cycle and energy conversion in terrestrial ecosystems. Alpine timberline ecotone is one of the most sensitive area of terrestrial ecosystems response to climate change. Researching the mass loss, elements release and component degradation in the process of leaf litter decomposition in timberline ecotone for deeply understanding and predicting the effects of global climate change on the alpine ecosystem has the vital significance. Therefore, mass loss, the release of dissolved organic carbon, carbon, nitrogen, phosphorus and total phenol and the degradation of cellulose and lignin in the process of 12 dominant species leaf litter 2 years (2 snow seasons+2 growing seasons) decomposition were studied were studied in alpine timberline ecotone (coniferous forest-timberline-alpine meadow) of Western Sichuan by using litterbag decomposition method. Discussed the effects of seasonal snow cover on mass loss, element release and component degradation, and analysised the relationship between mass loss and initial quality, leaf litter dynamic quality and the environmental factors. The results showed that:1) From coniferous forest, timberline to alpine meadow in alpine timberline ecotone, environmental temperature fluctuation was gradually increasing, the average temperature rised gradually, freezing and thawing frequency increased in turn. The consequence of seasonal snow cover in alpine timberline ecotone was obvious. Snow cover duration, and snow cover thickness in the second year were higher than in the first year. Two years together, the snow thickness size sequence was timberline, coniferous forest and alpine meadow.2) Decomposition period (four decomposition phases), vegetation type, species factors were significantly affected the litter mass loss process. The initial nitrogen content, phosphorus content, cellulose content and lignin content, C/N and L/N of leaf litter were associated significantly with decomposition rate. Leaf litter k value ranged of 0.096-0.928, Epilobium angustif decomposed fastest, decomposition 3-4 years essential complete. But Actinothuidium hookeri and Rhododendron lapponicum decomposed slowly, decomposition more than 20 years essential complete. And, other 9 kinds of leafs litter decomposed half demanding about a year and a half and essential complete decomposed demanding 5-7 years. Most litters residual rates plummeted and decomposition speeded at the beginning of the first growing season. Leaf litters mass loss concentrated in the first year, especially in the first growing season. Two snow season mass loss together accounted for nearly forty percent of two years.3) Different types of leaf litter quality have taken place different level changes. The change of leaf litter quality in different decomposition period responsed differently to seasonal snow. The change trend of dissolved organic carbon, nitrogen, phosphorus and phenols content were relatively consistent in three vegetation, nitrogen and phosphorus content rose slightly, dissolved organic carbon and phenols content reduced greatly. The change tendency of carbon, cellulose and lignin content were different clearly in three vegetation, the carbon content is slightly lower, cellulose content remain basically stable, the lignin content increased slightly.4) Different elements (components) of leaf litter occurred in different degrees of release (degradation). Seasonal snow cover had a significant influence on the release (degradation) of different elements (components). Carbon, nitrogen, phosphorus, cellulose and lignin were release (degradation) approximately in 50-65%, while the soluble carbon and total phenols released up to 90%. All of the elements (components) were release (degradation) mainly in the first year. Carbon, soluble carbon and total phenols were release (degradation) mainly in growing season of the first year, while the release (degradation) of nitrogen, phosphorus, cellulose and lignin in two seasons each accounted for about 1/2 in the first year. The release (degradation) of carbon, nitrogen, phosphorus, cellulose and lignin in the second snow cover period were accounted for about 60% of the second year. The release (degradation) of nitrogen, soluble carbon and cellulose were the highest in the dark coniferous forest. The release (degradation) of carbon and total phenols were the highest in the alpine timberline, while the release (degradation) of phosphorus and lignin were the highest in the alpine meadow.5) Temperature, snow, L/N, C/N, and cellulose had a significant effect on the litter mass loss rate. The correlation between mass loss rate and was temperature positive very significantly, and the correlation between mass loss rate and snow thickness was negative very significantly, and the correlation between mass loss rate and cellulose dynamic content were positive very significantly, the correlation between mass loss rate rate and C/N, L/N ratio were negative very significantly. The effects of temperature, snow, L/N, C/N and cellulose on mass loss rate decreases in turn. L/N, C/N, cellulose quality factor had important effects on leaf litter mass loss, but the role of the temperature and snow environmental factors was more critical.Decomposition process of leaf litter in four period has respective characteristic in alpine timberline ecotone region, and seasonal snow cover is not only direct control litter decomposition process of leaf in snow season, but also indirectly affect litter decomposition process in growing season. Leaf litters mass loss concentrated in the first year, especially in the first growing season. After the rapid weight loss in the first year, decomposability of leaf litter significantly reduced, and the role of the seasonal snow cover started to become outstanding from the second year, mass loss, elements release and component degradation of leaf litter began to concentrate in snow period. L/N, C/N, cellulose quality factor had important effects on leaf litter mass loss, but the role of the temperature and snow environmental factors was more critical. Therefore, under the background of global warming, temperatures rising and seasonal snow cover continuing shrinking in the future, litter decomposition process could obviously accelerated in alpine timberline ectone region.