Distribution Patterns of Abundance and Community Composition of Nitrogen-fixing and Denitrifying Bacteria along the Salinity Gradient in Coastal Soils
[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 NO3-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 N2O emission,and further influence global climate.
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