不同年限毛竹林土壤固氮菌群落结构和丰度的演变

应用变性梯度凝胶电泳(denaturing gradient gel electrophoresis,DGGE)和荧光定量PCR(real time fluorescent quantitative PCR,q PCR)方法研究了不同年限毛竹林土壤固氮菌群落结构和丰度的变化。结果表明:土壤p H、有机质、有效磷、速效钾和铵态氮含量在马尾松林改造成毛竹林5 a后明显提高,而后逐渐降低,并趋于稳定;土壤固氮菌多样性和nif H基因丰度也呈现相似的趋势。条带测序分析表明,毛竹林土壤固氮菌均为不可培养的固氮菌,与慢生根瘤菌(Bradyrhizobium sp.)具有较高的相似度。冗余分析结果表明,不同栽培年限毛竹林地土壤固氮菌群落组成发生了明显变化,长期栽培毛竹林引起的土壤养分变化对土壤固氮菌多样性具有重要影响。

Evolvement of structure and abundance of soil nitrogen-fixing bacterial community in Phyllostachys edulis plantations with age of time

Soil nitrogen-fixing bacterial communities play a key role in nitrogen recycling in phyllostachys edulis plantations forest soils. However, so far little has been reported on changes in structure and abundance of the nitrogen-fixing bacterial community in phyllostachys edulis plantations with age of cultivation. In this study, soil samples were collected from the topsoil (0~20 cm) layers of four phyllostachys edulis plantations different in cultivation history (5 a, 9 a, 15 a and 18 a, respectively) and a pinus massoniana plantation similar in ecological background (as control, CK). Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and real-time fluorescent quantitative PCR (qPCR) were employed to characterize changes in structure and abundance of the soil nitrogen-fixing bacterial communities in the soils, separately. Factors affecting structure of the nitrogen-fixing bacterial communities in soils were analysed using the redundancy analysis method. Results show that soil pH and contents of readily available potassium, available phosphorus, organic matter and ammonium nitrogen in the soil increased greatly 5 years after the transformation of pinus massoniana stand into phyllostachys edulis stand, but then decreased gradually and leveled off with the plantation going on. Shannon and richness indices and nifH gene copies of the soil nitrogen-fixing bacterial communities show similar trends. Sequencing of DGGE bands reveals that in the soils under phyllostachys edulis plantations, the N2-fixing bacteria are all unculturable azotobacteria that are quite similar to Bradyrhizobium sp. Redundancy analysis (RDA) shows that age of cultivation clearly affected structure of the soil nitrogen-fixing bacterial communities in phyllostachys edulis plantations and the community structures in the soils after 5YR and 9YR of cultivation differed sharply from that in control. However, differences between the plots of 15YR and 18YR and control were not so significant. Besides, soil readily available potassium, available phosphorus, organic matter and pH were the main factors affecting nitrogen-fixing bacterial community in soils under phyllostachys edulis plantations. Therefore, changes in soil fertility induced by long-term phyllostachys edulis plantations can potentially influence diversity of the soil nitrogen-fixing bacteria and alter their community structure.