呼伦贝尔草原不同退化梯度土壤细菌多样性季节变化

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

为了研究草地退化程度与土壤微生物多样性的关系,在呼伦贝尔草地上选取羊草草甸草原和贝加尔针茅草甸草原两个典型放牧点,按照轻度、中度和重度划分取样点,分别于6、8月份和10月份3个不同季节采集土壤样品。应用变性梯度凝胶电泳技术(PCR-DGGE)研究两个放牧地点不同退化程度、不同季节草地的细菌群落结构变化。结果表明,呼伦贝尔草地不同退化梯度的草地土壤中细菌种类较为丰富。从丰富度和Shannon-Winner指数的变化看,两个放牧点8月份丰富度和Shannon-Winner指数最高,8月份的丰富度平均为32.4,比6月和10月份分别高11%和7.4%;8月份Shannon-Winner指数平均为4.15,比6月和10月份分别高7.7%和5.4%。DGGE图谱聚类分析结果显示,随着季节变化和草地退化程度由轻至重的变化,土壤中的细菌优势种群没有受到明显的影响。回收DGGE图谱中10个条带进行测序分析,结果显示,所有序列与GenBank数据库中的相似度在87%100%之间。基于98%的相似度,可将其中的7个鉴定为Proteobacteria(变形菌门),将其中的1个鉴定为Actinobacteria(放线菌门)。另外2个同已知序列相似性较低,可能是未知的细菌。结果表明,Proteobacteria(变形菌门)为呼伦贝尔草原土壤中的优势细菌类群,尽管所选取样点草地植被有不同程度的退化,但土壤微生物优势种群并没有发生变化。

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.