| Microbial community plays an important and irreplaceable role in the processes of litter decomposition, but the dynamics of microbial community during litter decomposition may be affected by the snow cover in alpine forest ecosystems in winter. In order to understand the effects of forest gap and snow patches on the litter decomposition in alpine forests, PCR-DGGE and real-time quantitative PCR were used to investigate the number of bacterial16s rDNA and its diversity and community structure during litter decomposition. Four widely distributed species were selected as larch(Larix mastersiana), fir(Abies faxoniana), cypress(Sabina saltuaria) and birch(Betula albo-sinensi). Five kinds of snow patch (thick snow cover, thicker snow cover, medium snow cover, thin snow cover, no snow cover) with different snow depths in winter were chose to simulate the changing process of snow cover in the ongoing climate change. The results were expected to provide a scientific data to understand the affecting mechanisms of climate change on litter decomposition in the alpine forest ecosystem.1. There were obvious differences in the number of bacterial16s rDN A during litter decomposition of different species in conditions of snow cover at different critical periods, but the number of bacteria displayed a decreasing trend as litter decomposition proceeded. The number of bacteria showed the tendency as decreased, increased, decreased and then increased trend in the first decomposition year, but it was lower in the later growing period than the early growth period in the second decomposition year.The number of bacteria was significantly affected by snow patch in both non-growing season and growing season. The number of bacteria was lower under thin snow cover and no snow cover than other snow patches in the early stage of snow cover (OF I). The number of bacteria was minimum under thin snow cover and no snow cover in the peak of snow cover (FP I), and it was maximum under thin snow cover in the stage of snow thaw (TP I). In early growth period (EGP I), the number of bacteria showed an increase trend with the decrease of snow depth, but the trend was contrary in later growth period (LGP I). The minimum numbers of bacteria were observed under thick snow cover and thicker snow cover in OF II in the second year, and the maximum ones were observed under no snow cover in TP II. In EGP II, the minimum numbers of bacteria16S rDNA were observed under thick snow cover and thicker snow cove, but which were observed under thin snow cover and no snow cover in LGP II.Number of bacteria in different species of litter showed different responses to the depths of snow cover, the minimum numbers of bacteria were observed in the litter of fir under thin snow cover in OF I, and which were observed under no snow cover for the other species. The minimum numbers of bacteria in litter of larch and birch were observed under thin snow cover, but which were observed under no snow cover for fir and cypress. During the litter decomposition of larch and birch, the minimum numbers of bacterial were observed under thin snow cover in FP I, but which were observed for fir and cypress under no snow cover. The maximum numbers of bacteria in fir were observed under thick snow cover in TP I, and which were observed for the other species under thin snow cover. The minimum numbers of bacteria were observed for larch and fir under thick snow cover in EGP I, and which were observed under thin snow cover for cypress, or thicker snow cover for birch. The maximum numbers were observed for larch and cypress under thin snow cover, but maximum numbers were observed under thick snow cover and thicker snow cover for fir and birch, respectively. The minimum numbers of bacteria were observed in larch under thicker snow cover, but which for the other species were observed under thicker snow cover in OF II. The maximum numbers of bacteria were observed in four species of litter under no snow cover in TP II, but the minimum numbers were observed under thick and thicker snow cover in EGP II, and minimum numbers were observed under thin snow cover for cypress and under no snow cove for the other species in LGP II.2. The community richness and diversity index of bacteria was different under different snow patches with different depths. Snow patches did also change the structure of bacterial community. The diversity index of bacteria showed increased and decreased at first and then increased and decreased trend during critical periods in the first year, but it was decreased in second year.The diversity index of bacteria was significant affected by snow patches. The two-year study showed that Shannon-Wiener index of bacteria under no snow cover and thin snow cover in the non-growing season is generally lower than the other snow patches, but it was similar under all of five snow patches during the growing season. The Shannon-Wiener index and Simpson index fluctuations were significant varied throughout the course under no snow cover and thin snow cover.Bacterial diversity index had different responses to snow thickness in different species of litter decomposition. In the non-growing season, Shannon-Wiener index was lower in larch and fir under no snow cover and thin snow cover, but which was higher in cypress and birch under no snow cover in OF I. Shannon-Wiener index showed minimum value under no snow cover in FP I. The Shannon-Wiener index of bacteria in larch and birch under no snow cover was higher than snow-covered patches, but which were higher in fir and cypress respectively under thick and thicker snow cover in TP I. Maximum Shannon-Wiener index was detected under no snow cover in coniferous species but which was detected under thin snow cover in birch in EGP I. Shannon-Wiener index showed minimum value under thicker snow cover in fir and birch, but which was under thick snow cover and no snow cover, respectively, in larch and cypress in LGP I. Minimum Shannon-Wiener index was detected under no snow cover and thin snow cover in OF II in the second year. Minimum value was observed under thin snow cover in larch and fir, but which was in birch and cypress under thick and no snow cover in FP II, respectively. The Shannon-Wiener index of bacteria showed minimum value under no snow cover in TP II, and which were also low in fir and cypress in EGP II, but which were observed under middle snow cover in larch, and thick snow cover in birch in EGP II, respectively. The index of bacteria showed minimum value under no snow cover in cypress and birch, but which were observed in larch and fir under thick snow cover in LGS II.3. The bacterial groups during litter decomposition dominated by Proteobacter, Bacteroidetes, Actinobacteria, Gemmatimonadetes and Firmicutes. The structure of bacterial community in the process of litter decomposition showed significant seasonal variations, and it was significantly different in different periods during litter decomposition. The dominant populations were Proteobacter, Bacteroidetes.Structure of bacterial community was significantly different under different snow patches with different thickness in non-growing period, but the difference was smaller during the growing season. In non-growing season of the first year, the dominant population in the larch was y-Proteobacteria, and Bacteroides was the dominant population in the subsequent period. Bacteroides was the dominant population in LGP I, TP â…¡ and later growing season of the second fir decomposition year, but the dominant population in non-growing season was different in snow patches with different depths.The bacterial community during cypress litter decomposition was significantly different as the decomposition proceeded rather than larch and fir. Bacteroides was the dominant population in all snow patches in the non-growing season of the first decomposition year, y-Pacteroides was the dominant population in OF II and FP â…¡, and Bacteroides was the dominant polulation in TP II; but y-Proteobacteria was the dominant population in EGS â…¡ and Bacteroides was in LGS â…¡. In the first decomposition year, y-Proteobacteria dominated the bacterial community under snow-covered patches in OF I and EGP â… /â…¡ in birch, but Bacteroides was the dominant population under no snow and thin snow cover in the other periods; a-Proteobacteria was the dominant population under snow-covered patches and y-Proteobacteria dominated bacterial community under no snow in OF II, and Bacteroides was the dominant population in the subsequent periods.In summary, both the number of bacteria and the structure of bacteria community were affected by snow patches with different thickness. Different decomposition substrate controlled the activity of bacteria, which may be the main reason for the differences of dominated bacterial groups of bacteria in larch, fir, cypress and birch. Compared with the snow-covered environment, the number of bacteria, bacterial populations and community diversity displayed more obvious changes as litter decomposition proceeded under no snow-covered environment. These results could provide an efficient data to understand the processes of litter decomposition in alpine forest. |
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