高山森林凋落物分解过程中的微生物生物量动态

凋落物分解过程中的微生物生物量动态对于深入了解森林凋落物分解机理具有重要意义。为了解高山森林典型树种凋落物分解过程中的微生物生物量特征，采用凋落物分解袋法，研究了土壤冻结期(3月)、融冻期(4月-5月)、生长季节(5-10月)和冻结初期(11月)红桦(Betula albosinensi)、岷江冷杉(Abies faxoniana)和粗枝云杉(Picea asperata)凋落物分解过程的微生物生物量C(MBC)、微生物生物量N(MBN)和微生物生物量P(MBP)动态。四个关键时期，凋落物的MBC、MBN以生长季节最高，但非生长季节的三个关键时期也检测出较高的MBC、MBN。在融冻期结束后，三类凋落物分解过程中MBC和MBN均出现爆发性增长。然而，MBP在生长季节中期(8月)、完全冻结期(3月)和冻结初期(11月)均相对较低，但在融冻期和生长季节后期(9月)相对较高。另外，红桦凋落物的MBC、MBN和MBP含量均高于岷江冷杉和粗枝云杉凋落物(除4月粗枝云杉凋落物MBP异常升高外)。这些结果为更加清晰地认识高寒森林凋落物分解过程及机理，以及进一步理解陆地生态系统结构和功能提供了一定基础数据。

Dynamics of microbial biomass during litter decomposition in the alpine forest

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.