Benthic microalgae play important roles in energy flow and biogeochemistry of coastal ecosystems; however, factors influencing community composition remain largely unknown. Our purpose was to identify and compare spatial and environmental influences on benthic diatom biogeography at regional scales. In summer 2018, we sampled sediment at various spatial scales (0.0001–180 km) from five saltmarshes in South Carolina, USA, and characterized diatom assemblages using DNA metabarcoding. Twenty-three environmental variables from marsh sediments, adjacent creeks, and atmosphere were recorded. Multivariate analyses revealed that the saltmarsh communities were clearly distinct. Community dissimilarity was compared to both geographic distance and environmental differences to determine influences on community structure. Mantel tests and redundancy analysis revealed that spatial influences, in addition to several environmental factors (phosphate, grain size, sediment sorting, sediment moisture, and creek salinity), were significant. Variation partitioning revealed that 26% of community variation was explained by geographic distance alone, whereas 60% could be explained by combined spatial/environmental factors. In contrast, the independent explanatory power of individual environmental factors was negligible. Our findings suggest that spatially structured environmental variation mainly conditioned the saltmarsh diatom biogeography in this region. Dispersal limitation, as evinced by the large pure spatial effect and distance-decay pattern, was also important. Spatial effects were stronger relative to that previously observed in other microbial groups (marine bacteria and phytoplankton) and detected at finer spatial scales. Results support prior studies that suggest body size and dispersal mode are important drivers of metacommunity structure and therefore must be considered when studying aquatic microbial biogeography.

底栖微藻类在沿海生态系统的能量流和生物地球化学中起着重要作用。但是，影响社区组成的因素仍然未知。我们的目的是在区域范围内识别和比较对底栖硅藻生物地理学的空间和环境影响。在2018年夏季，我们从美国南卡罗来纳州的五个盐沼采样了各种空间尺度（0.0001至180 km）的沉积物，并使用DNA元条形码对硅藻组合进行了表征。记录了沼泽沉积物，邻近小溪和大气中的23个环境变量。多变量分析表明，盐沼群落明显不同。将社区差异与地理距离和环境差异进行比较，以确定对社区结构的影响。壁炉架测试和冗余分析表明，除了几个环境因素（磷酸盐，颗粒大小，沉积物分选，沉积物水分和小溪盐度）外，空间影响也很重要。变异分区显示，仅通过地理距离可以解释26％的群落变异，而可以通过空间/环境综合因素来解释60％。相反，单个环境因素的独立解释力可忽略不计。我们的发现表明，空间结构化的环境变化主要是该地区盐沼硅藻生物地理的条件。如大的纯空间效应和距离衰减模式所示，色散限制也很重要。相对于以前在其他微生物组（海洋细菌和浮游植物）中观察到并在更精细的空间尺度上检测到的而言，空间效应更强。结果支持先前的研究，这些研究表明体型和扩散模式是元社区结构的重要驱动力，因此在研究水生微生物生物地理学时必须考虑。