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

Extracellular enzymes are very important to leaf litter decomposition. Timberline ecotone is one of the most sensitive area of terrestrial ecosystems response to climate change. To research the enzyme activity and its influence factors in the process of litter decomposition of this area is of great significance for deeply understanding and predicting the effects of global climate change on the alpine ecosystem. Enzyme activities involved in the degradation of lignin, cellulose and hemicellulose were studied in timberline ecotone of Western Sichuan in the process of litter decomposition by using litterbag decomposition method. The impact of seasonal snow cover on enzyme activities and relationships between enzyme activities and environmental factors and the initial quality of leaf litter were also explored. The results showed that:1) Overall, the correlations between enzyme activities and mass loss rate were significantly or very significantly positive (P<0.05;P<0.01). The correlations between mass loss rates of leaf litter and enzyme activities were not consistent among three vegetation types. On alpine meadow, enzyme activities and mass loss rates correlated significantly and positively (P<0.05; P<0.01). Enzyme activities except laccase activity, correlated with mass loss rates significantly and positively (P<0.05; P<0.01). While in the coniferous forest, only cellobiohydrolases and endo-1,4-β-xylanase activity and mass loss rate correlated significantly (P<0.05).2) Initial litter quality had a significant effect on enzyme activities. Initial litter quality had a significant effect on enzyme activities. Lignocellulose enzyme activities were mainly affected by lignin content, lignin/N, C/N and cellulose content. Especially, lignin and lignin/N regulated the enzyme activities.3) Seasonal snow cover had a profound effect on litter decomposition process. Except the laccase and manganese peroxidase activities, the average thickness of the snow cover had a significant influence on enzyme activities (P<0.01). Overall, the moisture content and average leaf litter decomposition temperature and freeze-thaw cycles affected enzyme activities significantly, moisture content of leaf litter had a greater effect on laccase and manganese peroxidase activities than leaf litter decomposition temperature. The responds of different kinds of enzymes to temperature changes were different.4) During the early stage of decomposition of leaf litter, most kinds of enzymes activities were the highest in coniferous forest. With the gradual decomposition of leaf litter, the freeze-thaw cycle, leaching and other physical processes of fragmentation increased decomposability of leaf litter. Therefore the enzyme activities of leaf litter increased in alpine meadows and timberline with the high frequency of freeze-thaw cycles.5) Decomposition period had a significant effect on enzyme activities, and the response of different kinds of enzymes to decomposition periods are different. Lignin peroxidase, cellobiohydrolase enzymes and β-glucosidase activities were the highest in the first growing season and endoglucanase and endo-1,4-β-xylanase activities were the highest in the second snow cover period.In summary, lignocellulose enzyme activities were affected by seasonal snow cover. The average thickness of the snow cover, the moisture content, average decomposition temperature and freeze-thaw cycles can have different level of influence on enzyme activities. The enzyme activities were regulated by leaf litter initial quality. Lignin and lignin /N were the most important quality factors. The change of seasonal snow cover caused by the future climate change will have a profound effect on the activity of lignocellulose enzyme in the process of the decomposition of the leaf litter.