There is growing evidence that the composition of river microbial communities gradually transitions from terrestrial taxa in headwaters to unique planktonic and biofilm taxa downstream. Yet, little is known about fundamental controls on this community transition across scales in river networks. We hypothesized that community composition is controlled by flow‐weighted travel time of water, in combination with temperature and dissolved organic matter (DOM), via similar mechanisms postulated in the Pulse‐Shunt Concept for DOM. Bacterioplankton and biofilm samples were collected at least quarterly for 2 yr at 30 sites throughout the Connecticut River watershed. Among hydrologic variables, travel time was a better predictor of both bacterioplankton and biofilm community structure than watershed area, dendritic distance, or discharge. Among all variables, both bacterioplankton and biofilm composition correlated with travel time, temperature, and DOM composition. Bacterioplankton beta‐diversity was highest at shorter travel times (< 1 d) and decreased with increasing travel time, showing progressive homogenization as water flows downstream. Bacterioplankton and biofilm communities were similar at short travel times, but diverged as travel time increased. Bacterioplankton composition at downstream sites more closely resembled headwater communities when temperatures were cooler and travel times shorter. These findings suggest that the pace and trajectory of riverine bacterioplankton community succession may be controlled by temperature‐regulated growth rate and time for communities to grow and change. Moreover, bacterioplankton, and to a lesser extent biofilm, may experience the same hydrologic forcing hypothesized in the Pulse‐Shunt Concept for DOM, suggesting that hydrology controls the dispersal of microbial communities in river networks.

中文翻译：

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温带大流域的温度、水流时间和溶解有机物结构河流微生物群落


越来越多的证据表明，河流微生物群落的组成逐渐从源头的陆地类群转变为下游独特的浮游生物和生物膜类群。然而，人们对河流网络中跨尺度的社区过渡的基本控制知之甚少。我们假设群落组成由水的流量加权旅行时间结合温度和溶解有机物 (DOM) 控制，通过 DOM 脉冲分流概念中假设的类似机制。两年内至少每季度在康涅狄格河流域的 30 个地点采集浮游细菌和生物膜样本。在水文变量中，与流域面积、树突距离或流量相比，旅行时间是浮游细菌和生物膜群落结构更好的预测因子。在所有变量中，浮游细菌和生物膜组成均与传播时间、温度和 DOM 组成相关。浮游细菌β多样性在较短的旅行时间（< 1 d）时最高，并随着旅行时间的增加而减少，随着水流向下游而逐渐均质化。浮游细菌和生物膜群落在短旅行时间内相似，但随着旅行时间的增加而出现分歧。当温度较低且传播时间较短时，下游地点的浮游细菌组成更接近于源头群落。这些发现表明，河流浮游细菌群落演替的速度和轨迹可能受到温度调节的生长速度以及群落生长和变化的时间的控制。 此外，浮游细菌以及较小程度的生物膜可能会经历与 DOM 脉冲分流概念中假设的相同的水文强迫，这表明水文控制着河流网络中微生物群落的扩散。