包气带反硝化菌多样性和群落结构垂向分布规律与主控环境因子研究:以北京市潮白河冲洪积扇为例

Vertical Distribution Patterns and Controlling Environmental Factors of Denitrifying Bacterial Diversity and Community Structure in the Vadose Zone:A Case Study of Chaohe River Alluvial Fan in Beijing

近年来,我国农田氮肥施用量增加,给地下水天然屏障“包气带”带来了威胁,而微生物反硝化作用对包气带中氮素的去除具有重要意义.为探究包气带深度和理化性质对反硝化菌组成和结构的影响,本研究选择北京市地下水水源地潮白河洪积扇区2个典型包气带剖面(编号为S6和S8)为研究对象,采用高通量测序方法分析潮白河10.0 m内包气带剖面nirS、nirK和nosZ型反硝化菌多样性和群落结构的垂向分布规律,通过Spearman非参数分析方法识别反硝化菌多样性主控因素,通过冗余分析方法、随机森林分析方法和曼特尔检验相关性分析方法,探究影响反硝化菌组成结构主控因素.结果表明:S6剖面反硝化菌的α多样性整体高于S8剖面,同时不同类型反硝化菌的α多样性表现为nirK>nirS>nosZ.S8和S6剖面反硝化菌的α多样性和包气带深度为非线性的关系,S6剖面α多样性变化相比S8剖面更加明显.nirS、nirK和nosZ基因主要来源于变形菌门和放线菌门中参与氮循环的属,且不同剖面的反硝化菌群落结构差异显著(P<0.05).与反硝化菌多样性存在明显正相关性的环境因子包括pH、氨氮和黏粒含量,存在负相关性的环境因子包括亚硝酸盐、硝酸盐含量和反硝化速率.不同深度范围内影响微生物群落结构的环境因子数量不同,在浅层包气带(S8剖面(0.2~1.0 m),S6剖面(0.2~0.8 m))下,与反硝化菌群落结构呈显著相关的因子包括黏粒含量、深度、pH以及有机质、碳酸盐、亚硝酸盐含量等;深层包气带〔S8剖面(1~5.0 m),S6剖面(0.8~10.0 m)〕,与反硝化菌群落结构呈显著相关的环境因子包括钙、镁、硝酸盐、总有机碳含量等.研究显示,不同深度包气带中的反硝化菌对环境的响应存在差异,多种环境要素共同影响了反硝化菌的多样性和群落结构.因此,持续关注包气带中的反硝化功能基因,对于合理应对包气带及地下水环境氮污染、调节生物地球化学氮循环具有指导意义.

In recent years,the increasing use of nitrogen fertilizer in Chinese farmland has posed a threat to the natural groundwater barrier known as the‘vadose zone’,where denitrification microbial processes play a crucial role in nitrogen removal.In order to investigate the influence of redox potential zone depth and physicochemical properties on the composition and structure of denitrifying bacteria in the vadose zone,this study selected vertical sections(S6 and S8)of diluvial fans of the Chaobai River in Beijing as the representative research object.High throughput sequencing was used to analyze the vertical distribution of the marker genes(including nirS,nirK and nosZ)of denitrifying bacteria in the vadose zone at a depth of 10.0 m of diluvial fans.The main components affecting the diversity of denitrifying bacteria were determined through non-parameter Spearman test,and the main components affecting the composition and structure were investigated by the Redundancy Analysis,Random Forest analysis method,and Mantel test.The results showed that the overallα-diversity of denitrifying bacteria in the S6 was higher than that in the S8,and their diversity follows the order:nirK>nirS>nosZ.Theα-diversity of both S6 and S8 shows non-linear relationship with vadose zone depth.Compared to S8,the diversity of S6 was more evident.The species containing nirS,nirK and nosZ genes mainly belonged to Proteobacteria and Actinomycetes phyla,which are involved in nitrogen cycle.The structure and composition of denitrifying bacteria were significantly different between the two sections(P<0.05).The main components showing positive relationship with diversity of denitrifying bacteria included pH,ammonium,and clay content,while the main components showing negative relationship included nitrite,nitrate,and denitrification rate.The number of environmental factors varied with depth:at shallow depth(0.2-0.8 m for S6,and 0.2-1.0 m for S8),the factors significantly correlated with the community structure of denitrifying bacteria included clay content,depth,pH,organic matter(OM),carbonate and nitrite;at deeper depth(0.8-1.0 m for S6,and 1.0-5.0 m for S8),the factors significantly related to community structure included calcium,magnesium,nitrate,and total organic carbon content.The study shows that the denitrifying microorganisms in the vadose zone respond differently to the environment at different depths,and various environmental factors jointly affect the diversity and community structure of denitrifying bacteria.Continuous attention to denitrification genes in the vadose zone is of great significance for solving nitrogen pollution in the vadose zone and groundwater environment and regulating the biogeochemical nitrogen cycle.