Abstract: Owing to climate change and human activities, evident degradation of permafrost has happened in the upstream regions of the Shule River Basin, such as increasing depth of active layer and vegetation degradation. However, little is known about the effects of permafrost degradation on soil microbes. In this study, we investigated the effects of soil properties on bacterial community during the process of permafrost degradation by analyzing the culturable bacterial quantity of 12 soil samples from four permafrost types \[i.e., substable permafrost (SSP), transition permafrost (TP), unstable permafrost (UP) and extremely unstable permafrost (EUP)\] in different seasons (April, June and September). The results showed that the quantity of culturable bacteria varied between 0.4×10⁷-5.3×10⁷ CFU·g^-1, and the quantity of culturable bacteria decreased significantly during the process of permafrost degradation in each season, and the bacterial quantity reached the highest level for each permafrost type in June. However, the seasonal variation of the bacterial quantity in the different types of permafrost did not exhibit the same trend. Correlation analysis showed that soil bacterial quantity was significantly positively correlated with soil moisture, total nitrogen, and organic carbon contents. These results indicated that there existed huge environmental heterogeneity such as heterogeneity in soil moisture, organic carbon and total nitrogen content between different permafrost types during retrogressive succession of vegetation along with permafrost degradation, and this heterogeneity may further affect the microbial quantity. The results provide a reference for the comprehensive evaluation of ecological environment of different types of permafrost in QinghaiTibet Plateau.

Key words: starch, Horqin sandy land, carbon starvation, plant organ, soluble sugar