耕作方式和秸杆还田对纤维素降解细菌多样性的影响

Effects of Tillage and Straw Mulching on Diversity of Cellulose-decomposing Bacteria in Fluvo-aquic Soil

免耕和秸秆还田是培肥地力的重要措施,明确其对土壤纤维素降解细菌群落的影响对于土壤质量提升具有重要意义。选择中国科学院封丘农业生态国家试验站耕作秸秆还田(WtS)、免耕秸秆还田(WntS)、耕作秸秆不还田(Wt)和免耕秸秆不还田(Wnt)4种处理小区并采集土壤样品,用CMC-Na刚果红培养基对纤维素降解细菌计数,采用PCR-RFLP技术研究保护性耕作和秸秆还田对纤维素降解细菌群落的影响。结果表明,秸秆还田与免耕处理均不同程度提高了纤维素降解细菌数量。WtS、WntS、Wt和Wnt4个纤维素降解细菌基因文库中,OTUs数量分别为23、26、20和19个,秸秆还田加免耕处理多样性指数最高。本文获得的纤维素降解细菌共属于11个属,秸秆还田土壤中Streptomycetaceae、Flavobacterium、Sphingobium相对丰度明显多于秸秆不还田处理土壤;免耕处理土壤中Pseudomonas、Phyllobacterium、Paenibacillus、Promicromonosporaceae、Sphingobacterium相对丰度明显高于耕作处理土壤。典范对应分析显示四种处理纤维素降解细菌群落结构发生了较大变化,p H、全磷、有机碳和全钾与免耕处理呈显著正相关性,全氮、碱解氮、速效钾、速效磷和有机碳与秸秆还田处理呈显著正相关性。免耕和秸秆还田能提高土壤中纤维素降解细菌数量及多样性,改变纤维素降解细菌群落结构。

【Objective】No-tillage and straw mulching are two important techniques in soil building. It is,therefore,of great significance to understand effects of the two on diversity of the cellulose-decomposing bacteria（CDB）community in the soil. To this end,analyses were done of effects of long-term no-tillage and straw mulching on diversity of CDB,microbial community structure,and richness and dominance of CDB,so as to provide a theoretical basis for the study and demo-extrapolation of the technique of conservation tillage. 【Method】A long-term experiment,designed to have four tillage treatments,i.e. tillage with mulching（WtS）,no-tillage with mulching（WntS）,tillage without mulching（Wt）and no-tillage without mulching（Wnt）,was conducted at the State Experimental Station for Agro-Ecology in Fengqiu,Henan Province. Soil samples were collected from the plots of the four treatments,incubated in CMC-Na Congo red medium for counting of CDB and analyzed with PCR-RFLP for effects of no-tillage and straw mulching on CDB community. 【Result】The results of plate counting show that the population of CDB was 8.40×107（WtS）,11.4×107（WntS）,4.57×107（Wt）and 5.27×107（Wnt）,indicating that both No-tillage and straw mulching increased the number of CDB to a varying extent. Out of the soil samples collected from the four treatment plots,a total of 425 strains of CDB were isolated,4 CDB gene libraries built based on treatment,and a total of 33 OTUs obtained. The number of OTUs of CDB in the treatments range from 19 to 26,among which 7 were found common in all the 4 treatments. 8 particular in the treatments with straw mulching soil and 3 in the treatments of no-tillage,which indicates that the practices of straw mulching and no-tillage did have some effects on CDB community structure in the soil. The 4 clone libraries varied sharply in CDB diversity index,which was the highest in Treatment WntS,and higher in the two treatments with straw mulching than in the two without straw mulching,which indicates that compared with tillage,notillage is more conducive to diversity of the CDB in the soil. Phylogenic analysis shows that the CDB in the soils varied in the range of 80%~99% in 16 S r DNA homology. The 33 OTUs could be sorted into 4 phyla,7 classes,11 orders,15 families and 20 genera. Proteobacteria is the dominant phylum,composed of 15 OTUs,which could be sorted into 11 genera. In Treatment WtS,Sphingobium,Streptomycetaceae,Sinorhizobium and Promicromonsporaceae are the dominant groups,accounting for 67.92%,in Treatment WntS,Streptomycetaceae,Promicromonosporaceae and Flavobacterium are,accounting for 48.15%,in Treatment Wt,Sinorhizobium,Promicromonosporaceae and Acinetobacter are,accounting for 54.29%,and in Treatment Wnt,Rhizobium,Phyllobacterium,Pseudomonas and Promicromonosporaceae are,accounting for 63.21%. The treatments with straw mulching are significantly higher than the treatments without straw mulching in relative abundance of Streptomycetaceae,Flavobacterium and Sphingobium,which indicates that straw mulching is conducive to growth of these bacteria,which play an important role in straw decomposition. And the treatments of no-tillage are apparently higher than the treatments of tillage in relative abundance of Pseudomonas,Phyllobacterium,Paenibacillus,Promicromonosporaceae and Sphingobacterium,which indicates that no-tillage is conductive to growth of these bacteria. Canonical correspondence analysis shows that great changes have taken place in CDB community structure in all the four treatments,that p H,TP,organic carbon and TK is significantly and positively related to no-tillage and that TN,analyzable N,readily available K,readily available P and organic carbon is significantly and positively related to straw mulching. 【Conclusion】It is quite clear that no-tillage and straw mulching can significantly raise the number and diversity of cellulose-decomposing bacteria in the soil,and alter cellulose-decomposing bacteria community structure. Conducted as key techniques for sustainable agriculture to improve soil quality by increasing the number and variety of microorganisms,no-tillage and straw mulching or incorporation do have some theoretical significance and enormous potential for extrapolation.