Flow is an important physical driver of biofilm communities. Here, we tested the effects of the near bed flows in two mountainous stream reaches on the structure of biofilm microbial guilds (autotrophs, heterotrophic bacteria, and heterotrophic protists) within and across trophic levels. Near bed flow velocity and turbulent kinetic energy were important physical drivers for structuring the communities within and across guilds of the multitrophic fluvial biofilms. The effects of flow were nested in a seasonal and spatial (across‐streams) context. Changes in physicochemical factors (temperature, light, dissolved carbon, and nutrients) along the reaches were alike in both streams suggesting that environmental boundary conditions at larger temporal scales were responsible for the seasonal differences of biofilm communities, whereas locally microbial diversity was shaped by near bed flow. Typically, the abundance of autotrophs increased with flow, indicating that biofilms shifted toward increasing autotrophy with increasing shear forces. Filamentous autotrophs seemed to provide protected habitats from the shear forces for smaller sized bacteria. Heterotrophic protist abundance decreased with flow leading to decreasing grazer to prey ratio. Bacteria thus benefitted from a reduction in grazing pressure at faster flowing, more turbulent sites. Our results suggest that near bed flow can impact the magnitude and direction of matter fluxes through the microbial food web and possibly affect ecosystem functioning of fluvial biofilms.

中文翻译：

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河流生物膜中营养层内和营养层附近的河床流动使微生物行会成形

流量是生物膜群落的重要物理驱动力。在这里，我们测试了两个山区河流附近河床水流对营养层内和营养层之间生物膜微生物行会（自养生物，异养细菌和异养生物）的结构的影响。近床流速和湍动能是构造多营养性河流生物膜行会内和跨行会的重要物理驱动力。流量的影响嵌套在季节性和空间（跨流）环境中。两条河流沿线的理化因素（温度，光，溶解的碳和营养素）的变化相似，这表明较大时间尺度的环境边界条件是生物膜群落季节性差异的原因，而局部微生物多样性是由近床水流形成的。通常，自养生物的丰度随着流量的增加而增加，表明生物膜随着剪切力的增加而向着自养的方向移动。丝状自养生物似乎为较小尺寸的细菌提供了受剪切力保护的栖息地。异养原生生物的丰度随着流量的增加而降低，从而导致放牧者与猎物的比率降低。因此，细菌得益于更快流动，更湍流的部位的放牧压力降低。我们的结果表明，床层附近的水流会影响通过微生物食物网的物质通量的大小和方向，并可能影响河流生物膜的生态系统功能。表明生物膜随着剪切力的增加而向着自养的方向转移。丝状自养生物似乎为较小尺寸的细菌提供了受剪切力保护的栖息地。异养原生生物的丰度随着流量的减少而降低，从而导致放牧者与猎物的比率降低。因此，细菌得益于更快流动，更湍流的部位的放牧压力降低。我们的结果表明，床层附近的水流会影响通过微生物食物网的物质通量的大小和方向，并可能影响河流生物膜的生态系统功能。表明生物膜随着剪切力的增加而向着自养的方向转移。丝状自养生物似乎为较小尺寸的细菌提供了受剪切力保护的栖息地。异养原生生物的丰度随着流量的增加而降低，从而导致放牧者与猎物的比率降低。因此，细菌得益于更快流动，更湍流的部位的放牧压力降低。我们的结果表明，床层附近的水流会影响通过微生物食物网的物质通量的大小和方向，并可能影响河流生物膜的生态系统功能。因此，细菌得益于更快流动，更湍流的部位的放牧压力降低。我们的结果表明，床层附近的水流会影响通过微生物食物网的物质通量的大小和方向，并可能影响河流生物膜的生态系统功能。因此，细菌得益于更快流动，更湍流的部位的放牧压力降低。我们的结果表明，床层附近的水流会影响通过微生物食物网的物质通量的大小和方向，并可能影响河流生物膜的生态系统功能。