Microbial communities associated with Juncus roemerianus and Spartina alterniflora vegetated sediments in Louisiana saltmarshes

\"Saltmarshes are typically dominated by perennial grasses with large underground rhizome systems that can change local sediment conditions and be important in shaping the sediment microbial community. Factors that control plant zonation in saltmarshes (e.g. salinity) are also likely to influence the microbial community, but little is known as to whether microbial communities share distribution patterns with plants in these systems. To determine the extent to which microbial assemblages are influenced by saltmarsh plant communities, as well as to examine patterns in microbial community structure at local and regional scales, we sampled sediments at three saltmarshes in Louisiana, USA. All three systems exhibit a patchy distribution of Juncus roemerianus stands within a Spartina alterniflora marsh. Sediment samples were collected from the interior of several J. roemerianus stands as well as from the S. alterniflora matrix. Samples were assayed for extracellular enzyme activity and DNA extracted to determine microbial community composition. Denaturing gradient gel electrophoresis of rRNA gene fragments was used to determine regional patterns in bacterial, archaeal, and fungal assemblages, while Illumina sequencing was used to examine local, vegetation-driven, patterns in community structure at one site. Both enzyme activity and microbial community structure were primarily influenced by regional site. Within individual saltmarshes, bacterial and archaeal communities differed between J. roemerianus and S. alterniflora vegetated sediments, while fungal communities did not. These results highlight the importance of the plant community in shaping the sediment microbial community in saltmarshes, but also demonstrate that regional scale factors are at least as important.\"

盐沼通常以多年生草本植物为主，这些植物具有庞大的地下根茎系统，能够改变局部沉积物条件，并在塑造沉积物微生物群落方面发挥重要作用。控制盐沼植物分区的因素（如盐度）也可能影响微生物群落，但关于这些系统中微生物群落是否与植物具有相似的分布模式，目前知之甚少。为了确定盐沼植物群落对微生物组合的影响程度，并考察局部和区域尺度上微生物群落结构的模式，我们在美国路易斯安那州的三个盐沼采集了沉积物样本。这三个系统均表现出互花米草（Spartina alterniflora）沼泽中罗氏灯心草（Juncus roemerianus）群落的斑块状分布。沉积物样本采集自多个罗氏灯心草群落内部以及互花米草基质区域。样本检测了胞外酶活性，并提取DNA以确定微生物群落组成。通过rRNA基因片段的变性梯度凝胶电泳（Denaturing gradient gel electrophoresis）分析细菌、古菌和真菌组合的区域模式，同时利用Illumina测序考察单个站点上由植被驱动的局部群落结构模式。酶活性和微生物群落结构均主要受区域站点影响。在单个盐沼内，罗氏灯心草和互花米草植被覆盖的沉积物中细菌和古菌群落存在差异，而真菌群落则无差异。这些结果强调了植物群落在塑造盐沼沉积物微生物群落中的重要性，同时也表明区域尺度因素至少具有同等重要性。