秸秆还田与施肥对稻田土壤微生物生物量及固氮菌群落结构的影响

利用氯仿熏蒸法和变性梯度凝胶电泳法(PCR-DGGE)研究了秸秆覆盖还田与施肥对灰棕冲积水稻土0—10cm和10—20cm土层土壤微生物生物量碳、氮和固氮菌群落结构的影响。结果表明:土壤微生物量碳、氮和固氮菌多样性从0—10cm土层到10—20cm土层均呈现降低趋势。无秸秆覆盖处理(对照组)的土壤微生物生物量碳(SMB-C)和微生物生物量氮(SMB-N)量最小。在秸秆覆盖还田处理中,低氮和无钾处理的SMB-C和SMB-N都显著低于全量氮磷钾肥处理。虽然无磷处理的SMB-N低于全量氮磷钾处理,但差异不显著。说明秸秆覆盖还田配施充足氮磷钾肥能显著提高土壤微生物生物量碳、氮。由DGGE图谱多样性指数分析得知,配施充足氮磷钾肥的处理土壤的固氮菌多样性最丰富。UPGMA聚类分析显示,10种不同处理的聚类图也不同,对照(无秸秆)处理0—10cm和10—20cm的微生物不同于其它处理单独聚在了一个群里。DGGE条带测序得知,14个条带的近缘种大部分为非培养细菌nifH基因片段,主要优势菌群其归属于变形菌门(Proteobacteria)的β-变形菌纲(Betaproteobacteria)。应用PCR-DGGE技术可以解释灰棕冲积水稻土秸秆覆盖不同肥料用量固氮菌分子群落结构特点。

Effect of different fertilizer combinations and straw return on microbial biomass and nitrogen-fixing bacteria community in a paddy soil

Chloroform fumigation and denaturing gradient gel electrophoresis(DGGE) were employed to study the influence of different fertilizer treatments with crop residue return on microbial biomass and nitrogen-fixing bacteria community in a gray brown alluvial paddy soil at soil depth of 0-10 cm and 10-20cm. Results show that soil microbial biomass carbon (SMB-C), microbial biomass nitrogen (SMB-N) and diversity of nitrogen-fixing bacteria decreased with soil depths. The control treatment with straw removal had the lowest amounts of SMB-C and SMB-N. Among the treatments receiving straw return, the quantity of SMB-C and SMB-N in the treatments with low nitrogen rate and omitting was significantly lower than the full rate NPK treatment. Omission of phosphate on the basis of NPK nonsignificantly reduced the SMB-N compared to the NPK treatment. It shows that straw mulching with addition of adequate NPK fertilizers can significantly increase the SMB-C and SMB-N. The diversity indices of DGGE profiles indicate that the treatment with adequate NPK had the most abundant nitrogen-fixing bacterial diversity. According to UPGMA cluster analysis, dendrogram of the 10 treatments were different, and the micro-organisms at the 0-10cm and 10-20cm in the control treatment differed from all the other treatments and stood alone in a separate group. DGGE bands sequencing further revealed that the 14 closely related species were largely uncultured bacteria nifH gene fragment with the predominant community falling in the class of Proteobacteria in Betaproteobacteria. Application of PCR-DGGE can well interpret the community structure characteristics of the nitrogen-fixing bacteria molecules in the gray-brown alluvial paddy soil with straw return and different fertilizer treatments.