Abstract:Microorganism plays an irreplaceable role in litter decomposition, and the dynamics of microbial activity in litters is of ecological significance in understanding the mechanism of litter decomposition. Microbial biomass serves their important statuses as a sensitive bio indicator of microbial activity in respond to environmental change. Seasonal freezing and thawing is one of the most significant environmental changes in many high latitude/altitude areas such as in alpine regions. The significant temperature fluctuations with related freezing, thawing and freeze thaw cycles could exhibit a strong effect on microbial biomass during litter decomposition in the cold season. As yet, more attentions have been given to the growing season, only a few studies have focused on litter decomposition and the related microbial activities in winter. Moreover, far less information has been available on the dynamics of microbial biomass in litter decomposition at different critical ecological stages as the growing period, the freezing period, completely frozen period as well as the thawing period. Therefore, litters of fir (Abies faxoniana), birch (Betula albosinensis) and spruce (Picea asperata), which are three dominant tree species in the alpine and subalpine forest of Western China, were put into the nylon bag and placed on the forest floor of a primary fir alpine forest in November, 2008. Litterbags were sampled in March (completely frozen period), April and May (thawing period), June, August, September and October (growing period), and November (freezing period, one-year decomposition), 2009, according to the monitored soil temperatures. Microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) in litters were measured to characterize the dynamics of microbial biomass during litter decomposition in an alpine forest, and explore the microbial processes during litter decomposition in winter time. Similar to the general view, the highest MBC and MBN during litter decomposition were detected in growing period (June and August). Meanwhile, relative higher MBC and MBN during litter decomposition were also observed in the freeze-thaw season (March, April, May and November) compared with that in September. Just after the thawing period, significantly sharp increase of MBC and MBN were found in June during the decomposition of all three sampled litter. However, in disagreement with the dynamics of MBC and MBN, MBP showed the lower values in the mid-growing period (August), completely frozen period (March) and early freezing period (November) compared with the other periods. The higher MBP was detected in the thawing period (April and May) and later growing period (September) compared with other periods. In addition, MBC, MBN and MBP during birch litter decomposition were higher than those during fir and spruce litter decomposition in the whole first year decomposition process, except for the abnormal increase of MBP during spruce litter decomposition in April. The results provided efficient data to understand the process and mechanism of litter decomposition in the high-frigid forest ecosystem, and further understand the structure and function of terrestrial ecosystems. Moreover, the results suggested more attention should be paid to the ecological processes in winter time, especially for alpine and subalpine forest.