滨海盐渍化土壤中蓝细菌多样性及分布

【目的】蓝细菌在贫瘠土壤的固氮、固碳中发挥着重要作用，然而土壤盐渍化对蓝细菌多样性及群落结构的影响还不清楚。本研究以莱州湾南岸及黄河口海水入侵盐渍化土壤为例，研究蓝细菌的多样性、群落结构及丰度沿盐度梯度的分布情况。【方法】利用自动核糖体间隔基因分析(ARISA)技术与群落相似性分析(ANOSIM)探究蓝细菌群落的差异与空间分布格局；通过16S rRNA基因克隆文库、测序与系统进化分析解析了3个典型盐度梯度样品中蓝细菌的群落组成；实时定量PCR测定蓝细菌16S rRNA拷贝数(丰度)；BEST多元分析探寻影响蓝细菌分布的主要环境因子。【结果】蓝细菌在莱州湾南岸盐土中分布广泛，其群落结构在低(0.63%?1.27%)、中(1.55%?2.00%)、高盐度(2.39%?5.11%)样品组之间差异显著(P=0.03)，而在不同含水量样品组间则不显著(P=0.09)。总体来看，群落结构主要受土壤盐度与含水量这两个因子联合控制(P=0.02)。低盐样品中蓝细菌多样性和丰富度最低，并以Halomicronema和Acaryochloris为优势类群。Leptolyngbya在中、高盐土中占优势。Arthrospira与Geitlerinema仅在低盐土中检测到，而Oscillatoria则仅出现在高盐土中。随盐度升高蓝细菌丰度呈下降趋势，低盐土样中蓝细菌丰度(2.14×105 copies/g干土)显著高于中盐土(1.25×105 copies/g干土)(P<0.05)；高盐度土为1.20×105 copies/g干土。【结论】盐渍化程度是调控莱州湾南岸滨海土壤中蓝细菌群落结构与丰度的最重要环境因子，可能对滨海土壤微生物碳氮循环产生重要影响。

Diversity and distribution of cyanobacteria in coastal saline soils

Objective] Little is known about the diversity and distribution of cyanobacteria in salinized soils. In this study, we determined soil properties (pH, salinity and water contents, ammonium, nitrite, nitrate, total organic carbon and nitrogen), and investigated the molecular diversity and distribution patterns of soil cyanobacteria at 12 sites near the mouth of Yellow River and in the southern coastal plain of Laizhou Bay (Shandong province), typical salinized coastal regions in China. Salinity gradients were devided into three ranges: low (0.63%?1.27%), medium (1.55%?2.00%), and high saline (2.39%?5.11%). Methods] Automated ribosomal intergenic spacer analysis (ARISA), clone libraries and real-time quantitative PCR were used to determine the cyanobacterial community structure, composition and abundance, respectively. Results] Based on ARISA fingerprints, we found cyanobacterial phylotype richness increased with salinity; multiple dimensional scaling and hypothesis testing (ANOSIM) indicated that the community structure of cyanobacteria generally clustered by salinity (P=0.03) more than by water content (P=0.09). Biota-Environment correlation (BEST) analysis further revealed that a combination of two factors, salinity and water content of soils, could mostly explain the changes in cyanobacterial community structure (P=0.02). Clone libraries of 16S rRNA gene were constructed for 3 representative samples. Sequencing and classification following phylogenetic analysis showed that Halomicronema and Acaryochloris dominated in the low saline samples, whereas Leptolyngbya was the most abundant in both medium and high saline soils. Another two taxa, Arthrospira and Geitlerinema, were only found in the samples of low salinity, while Oscillatoria was detected once from the high salinity. Cyanbacterial 16S rRNA genes were much more abundant in low salinity (2.14×105 copies/g dry soil) than in medium (1.25×105 copies/g dry soil) and high salinity samples (1.20×105 copies/g dry soil). Conclusion] This study demonstrates that salinity shapes the diversity, community structure and abundance of cyanobacteria in the saline soils, which has implications for carbon and nitrogen cycling contributed by these microorganisms in coastal terrestrial ecosystems.