Abstract：
While satisfying the demands of social and economic development, dams act as physical barriers affecting both abiotic and biotic factors in large rivers. These altered factors can interact with each other and gradually reshape the local ecosystem state. The reshaped state may spread downstream and affect ecosystem states on a large scale. However, the spread extent and characteristics of ecosystem states along large rivers remain understudied. To address this problem, alternative microbiota states and their responses to environmental conditions in the Yangtze River were investigated, considering the preponderance of alternative stable states theory in explaining the response of ecosystem states as well as the role of benthic microorganisms in indicating ecosystem states. In this study, flow discharge was identified as the main hydrological factor that clustered benthic microbiota into two types, and these two microbiota types were bistable and characterized by differential enrichment of the Cyanobacteria phylum. Potential analysis demonstrated that reducing flow discharge beneath a threshold (i.e., flow discharge < 12,900 m3/s) could shift benthic microbiotas to a state where benthic cyanobacteria would become the dominant species (the Microbiota State B). In the bistable region (i.e., 12,900 < flow discharge < 28,000 m3/s), both the ecological resilience and the contribution of deterministic process were found weak by relative potential depth calculations and neutral community modeling, suggesting that this region is susceptible to the microbiota state of its upstream and thus deserves more scientific attention to prevent the unfavorable state from spreading downstream. In addition, high denitrification potential at sites of the Microbiota State B was likely responsible for the low N:P ratio, further benefiting the dominance of N-fixing cyanobacteria. This study empirically showed the response of alternative microbiota states to flow gradients, and explored the distribution and characteristics of the microbiota states along the mainstream of the Yangtze River, therefore providing insights into environmental flow design and reservoir regulation of large rivers.
摘要：
在满足社会经济发展要求的同时,水坝是影响大型河流非生物和生物因素的物理屏障。这些改变的因素可以相互作用，并逐渐重塑当地的生态系统状态。重塑的状态可能会向下游扩散并大规模影响生态系统状态。然而,大型河流生态系统状态的传播范围和特征仍未得到充分研究。为了解决这个问题,研究了长江中替代微生物群状态及其对环境条件的响应，考虑替代稳定状态理论在解释生态系统状态响应方面的优势以及底栖微生物在指示生态系统状态方面的作用。在这项研究中,流量排放被确定为将底栖微生物群聚集为两种类型的主要水文因素，这两种微生物群是双稳态的，其特征是蓝细菌门的富集差异。潜在分析表明，将流量排放减少到阈值以下(即，流量排放<12,900m3/s）可能会将底栖微生物转移到底栖蓝细菌将成为优势物种的状态（微生物区系B）。在双稳态区域(即，12,900<流量排放<28,000m3/s)，通过相对潜在深度计算和中性群落建模，发现生态韧性和确定性过程的贡献都很弱，这表明该区域易受其上游微生物群状态的影响，因此值得更多的科学关注，以防止不利状态向下游传播。此外,B州微生物区系的高反硝化潜力可能是低N：P比的原因，进一步有利于固氮蓝藻的优势。这项研究凭经验显示了替代微生物群状态对流动梯度的响应，并探讨了长江干流微生物群的分布和特征，因此，为大型河流的环境流量设计和水库调节提供见解。
