小麦-甘薯轮作长期增施有机肥对碱性土壤固氮菌群落结构及多样性的影响

生物固氮为农业生态系统提供天然的氮素来源,探究长期增施有机肥对土壤固氮菌群落的影响,为合理增施有机肥和维持土壤固氮微生物群落多样性提供科学依据。选取小麦-甘薯轮作中连续37a不施肥对照(CK)、单施化肥(NPK)、化肥+有机肥(NPKM)处理的甘薯季碱性土壤样品为研究对象。采用Illumina MiSeq高通量测序技术,研究土壤固氮菌群落的组成、多样性及其与土壤特性的关系。结果表明:与对照和单施化肥相比,长期增施有机肥降低土壤固氮菌群落丰富度和多样性,且丰富度与土壤pH显著正相关,与有机碳、全氮和有效养分(硝态氮、有效磷和速效钾)显著负相关。主坐标分析表明长期施肥显著改变土壤固氮菌群落结构,与对照相比,增施有机肥比单施化肥对固氮菌群落结构的影响更大。冗余分析表明土壤有机碳和速效钾是影响固氮菌群落结构改变最主要的因素。长期增施有机肥显著降低变形菌门、蓝藻菌门、Beta-变形菌和固氮弧菌属的相对丰度,显著增加硝化螺旋菌门、酸杆菌门和硝化螺菌属的相对丰度,这与土壤pH、有机碳和有效养分显著相关。因此,在碱性土壤上长期增施有机肥对固氮菌群落结构的改变更大,对群落多样性的抑制作用更强。

Effects of long-term organic fertilization on soil diazotrophic community structure and diversity under wheat-sweet potato rotation system

Biological nitrogen fixation provides a natural source of nitrogen for agro-ecosystems. Exploring the effects of long-term organic fertilization regime on soil diazotrophic communities can provide scientific basis for rational application of organic fertilizer and maintenance of soil diazotrophic community diversity. In this study, the long-term fertilization experiment under wheat-sweet potato system has been established in an alkaline soil since 1981. Soil samples were collected from without fertilizers control (CK), chemical fertilizer alone (NPK), and chemical fertilizer plus organic fertilizer (NPKM). The Illumina Miseq high throughput sequencing technologies was employed to study soil diazotrophic community composition, diversity, and its relationship with soil environmental factors. The results showed that long-term (37 year) application of organic fertilizer decreased the diversity and richness of soil diazotrophic community compared to CK and NPK treatment. The richness index Chao1 and observed species was significantly positively correlated with pH, and significantly negatively correlated with soil organic carbon, total nitrogen and soil nutrients (i.e., NO₃^--N, available phosphorus and available potassium). Principal coordinate analysis (PCoA) indicated that long-term fertilization significantly altered community structure of soil diazotrophic, and the application of organic fertilizers had a greater impact on the structure of diazotrophic than application of chemical fertilizers alone compared to without fertilizer control. Redundancy analysis (RDA) suggested that soil organic carbon and available potassium were main influential factors on changes of diazotrophic community structure. Long-term addition of organic fertilizer reduced the relative abundance of Proteobacteria, Cyanobacteria, Betaproteobacteria and Azoarcus, and increased the relative abundance of Nitrospirae, Acidobacteria and Nitrospira, which was closely related to soil pH, organic carbon and available nutrients. Therefore, this study revealed that organic fertilizer addition had a greater change than chemical fertilizer alone on diazotrophic community structure, and it increased also the inhibition of diazotrophic community diversity.