滨海盐度梯度土壤中固氮菌和反硝化菌的分布特征

Distribution Patterns of Abundance and Community Composition of Nitrogen-fixing and Denitrifying Bacteria along the Salinity Gradient in Coastal Soils

[目的]为探讨滨海土壤盐渍化过程对氮转化的影响,本研究分析了滨海盐土自然盐度梯度下固氮菌和反硝化菌的分布特征。[方法]在莱州湾南岸及黄河口采集自然盐度梯度(0.64%~5.18%)土壤样品,人为划分为低盐度(0.64%~0.76%)、中盐度(1.25%~2.39%)、高盐度(3.49%~5.18%)三个梯度,利用荧光定量PCR和末端限制性片段长度多态性(T-RFLP)技术分析不同盐度梯度土壤中固氮菌(nifH基因)和反硝化菌(nosZ、nirS、nirK基因)的丰度、多样性及群落结构。[结果]固氮菌丰度在低盐区显著高于中、高盐区(P<0.05)。Spearman相关分析显示,nifH基因拷贝数与土壤NO_(3)^(-)含量显著正相关(P<0.05),Shannon指数与土壤平均粒径(d0.5)显著正相关(P<0.05)。典范对应分析表明,nifH基因群落结构与土壤盐度显著相关(P=0.04)。反硝化菌在该区域盐土中以nirK基因型占主导,nirK、nirS和nosZ三种基因的拷贝数受盐度影响不大,但(nirK+nirS)/nosZ拷贝数比值随盐度升高而显著升高。无机氮营养是影响该区域盐土反硝化菌群落结构的关键环境因子。[结论]滨海土壤盐渍化程度显著影响固氮菌的丰度、群落结构和反硝化过程功能基因的比值,可能影响土壤氮循环过程及N_(2)O排放,进而对全球气候变化产生重要影响。

[Objective]To explore the influence of soil salinization on nitrogen transformation,the distribution patterns of nitrogen-fixing and denitrifying bacteria along a natural salinity gradient in coastal soils were analyzed in this study.[Method]The qPCR and terminal restriction fragment length polymorphism(T-RFLP)techniques were used to study the distributions of community abundance and composition of nitrogen-fixing(nifH gene)and denitrifying bacteria(nirS,nirK and nosZ genes)along the salinity gradient(0.64%~5.18%)in saline soils of the southern coast of Laizhou Bay and the estuary of the Yellow River.According to the range of soil salinity,the samples were divided into three gradients:low salinity(0.64%~0.76%),medium salinity(1.25%~2.39%),and high salinity(3.49%~5.18%).[Result]Nitrogen-fixing bacteria's abundance in the low salinity samples was significantly higher than those in the medium and high salinity(P<0.05).Spearman’s correlation showed that the copy number of nifH gene was significantly positively correlated with soil NO_(3)^(−) concentration(P<0.05),while Shannon index was significantly positively related to soil mean grain size(d0.5)(P<0.05).The canonical correspondence analysis(CCA)showed that nifH gene community structure was significantly controlled by salinity(P=0.04).NirK genotype dominated in denitrifying bacteria in the saline soils.Salinity had no significant effect on the copy numbers of nirK,nirS and nosZ genes,but the(nirK+nirS)/nosZ ratio significantly increased with the increasing salinity.Inorganic nitrogen was a key environmental factor affecting the community structure of denitrifying bacteria.[Conclusion]In summary,degree of soil salinization in coastal zones significantly affects the abundance and community composition of soil nitrogen-fixing bacteria and the ratios of functional genes in the denitrification,which may affect soil nitrogen transformation processes and N_(2)O emission,and further influence global climate.