Seasonal variation of soil bacterial community under different degrees of degradation of Hulunbuir grassland

The goal of this study was to detect the links between grassland degradation and bacterial communities in soil.Grasslands under different degrees of degradation(heavily degraded grassland,HDG;moderately degraded grassland,MDG;and light degraded grassland,LDG) were selected from the Leymus Chinensis and Stipa baicalensis Meadow Steppe of Hulunbuir.Soil samples of each location were collected in June,August,and October respectively.Bacterial communities were characterized by analysis of PCR-amplified 16S rRNA genes using the fingerprinting method of denaturing gradient gel electrophoresis(DGGE).The results showed that the soil of Hulunbuir grasslands were rich with different bacterial species.Based on the PCR-DGGE banding patterns,Shannon Weaver diversity indices and species Richness were calculated.The average calculated species Richness values were 11% and 7.4% greater in August(32.4) than in June and October respectively.Similarly,August samples had the greatest Shannon-Weaver diversity index(4.15);7.7% and 5.4% greater than in June and October respectively.Cluster analysis of DGGE profiles indicated that different seasons and degradation gradients had no significant impacts on dominant soil bacterial community structure.Ten bands were excised from the DGGE gel and re-amplified for 16S rRNA sequencing.The partial 16S rRNA sequences have 87% 100% similarity compared against those available in the NCBI database.Based on the sequencing results,seven bands can be identified as related to Proteobacteria(98% 100%),one close to Actinobacteria(99%),the other two are unknown bacteria.These results provide evidence that although the grassland vegetation is degrading,the domain bacterial communities in the grassland soil has not changed.