It is well recognized that river-floodplain systems contribute significantly to riverine ecosystem metabolism, and that bacteria are key players in the aquatic organic carbon cycle, but surprisingly few studies have linked bacterial community composition (BCC), function and carbon quality in these hydrologically highly dynamic habitats. We investigated aquatic BCC and extracellular enzymatic activity (EEA) related to dissolved organic carbon quality and algae composition, including the impact of a major flood event in one of the last remaining European semi-natural floodplain-systems. We found that surface connectivity of floodplain pools homogenizes BCC and EEA, whereas low connectivity led to increased BCC and EEA heterogeneity, supported by their relationship to electrical conductivity, an excellent indicator for surface connection strength. Hydrogeochemical parameters best explained variation of both BCC and EEA, while the algal community and chromophoric DOM properties explained only minor fractions of BCC variation. We conclude that intermittent surface connectivity and especially permanent isolation of floodplain pools from the main river channel may severely alter BCC and EEA, with potential consequences for nutrient cycling, ecological services and greenhouse gas emissions. Disentangling microbial structure–function coupling is therefore crucial, if we are to understand and predict the consequences of human alterations on these dynamic systems.

中文翻译：

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沿多瑙河泛滥平原（维也纳，奥地利）时空连通性梯度的细菌群落组成和功能

众所周知，河流泛滥平原系统对河流生态系统代谢有显着贡献，细菌是水生有机碳循环的关键参与者，但令人惊讶的是，很少有研究将这些水文中高度相关的细菌群落组成 (BCC)、功能和碳质量联系起来。动态栖息地。我们研究了与溶解的有机碳质量和藻类组成相关的水生 BCC 和细胞外酶活性 (EEA)，包括在欧洲最后一个半天然洪泛区系统之一中发生的重大洪水事件的影响。我们发现漫滩水池的表面连通性使 BCC 和 EEA 均质化，而低连通性导致 BCC 和 EEA 异质性增加，这得到了它们与电导率的关系的支持，电导率是表面连接强度的极好指标。水文地球化学参数最好地解释了 BCC 和 EEA 的变化，而藻类群落和发色 DOM 特性仅解释了 BCC 变化的一小部分。我们得出的结论是，间歇性地表连通性，尤其是洪泛区池与主要河道的永久隔离，可能会严重改变 BCC 和 EEA，对养分循环、生态服务和温室气体排放产生潜在影响。因此，如果我们要理解和预测人类改变对这些动态系统的影响，解开微生物结构 - 功能耦合至关重要。我们得出的结论是，间歇性地表连通性，尤其是洪泛区池与主要河道的永久隔离，可能会严重改变 BCC 和 EEA，对养分循环、生态服务和温室气体排放产生潜在影响。因此，如果我们要理解和预测人类改变对这些动态系统的影响，解开微生物结构 - 功能耦合至关重要。我们得出的结论是，间歇性地表连通性，尤其是漫滩池与主要河道的永久隔离，可能会严重改变 BCC 和 EEA，对养分循环、生态服务和温室气体排放产生潜在影响。因此，如果我们要理解和预测人类改变对这些动态系统的影响，解开微生物结构 - 功能耦合至关重要。