Inland aquatic systems play a crucial role in the global nitrogen (N) cycle. This study focused on the Shaying River Basin, which is characterized by intensive damming, base-flow deficiencies and high N loading. Metagenomics sequencing and molecular ecological network analysis were used to conduct a comparative analysis of N cycling and its coupling effects with carbon (C) and sulfur (S) cycling in different stagnant habitats. Our major findings are listed below. (1) Compared with free-flowing habitats, overlying water in stagnant habitats (reservoirs and sluices) had higher abundances of mineralization and organic nitrogen synthesis genes, and lower abundances of denitrification and nitrification genes. These results indicate that damming enhances the conversion between organic and inorganic N but weakens inorganic N removal. The superposition of high N concentrations also led to inhibition of N removal. (2) The topology of molecular ecological networks showed differentiated coupling effects between cycling of N with C or S. Specifically, methane metabolism in reservoirs with low N concentrations promoted N removal, and the co-occurrence between N and S cycling enhanced the simultaneous removal of N and S. Conversely, co-exclusion between N with C or S cycling functional groups hindered nitrification and denitrification in sluices with high N concentrations. (3) For sediment, a high N concentration enhanced the potential of mineralization, nitrification, denitrification, and anaerobic ammonium oxidation to facilitate inorganic N removal. The co-exclusion between C and N cycling consistently inhibited denitrification, anaerobic ammonium oxidation, and N fixation in different habitats. Co-occurrence of organic S transformation, S mineralization, S reduction genes and N mineralization, organic N synthesis, and denitrification genes promoted N removal. In conclusion, high N concentrations of overlying water and dam-induced stagnation impeded N removal, while the coupling of N with C or S cycling showed different effects on N removal in different stagnant habitats.

中文翻译：

---

集约坝控制河系氮循环的多元素耦合效应


内陆水生系统在全球氮 （N） 循环中起着至关重要的作用。本研究以沙颍河流域为研究对象，该流域具有密集筑坝、基流不足、氮负荷高等特点。采用宏基因组测序和分子生态网络分析对不同停滞生境中氮循环及其与碳 （C） 和硫 （S） 循环的耦合效应进行了比较分析。我们的主要发现如下。（1） 与自由流动的生境相比，停滞生境（水库和水闸）中的上覆水具有较高的矿化和有机氮合成基因丰度，而反硝化和硝化基因的丰度较低。这些结果表明，筑坝增强了有机氮和无机氮之间的转化，但削弱了无机氮的去除。高 N 浓度的叠加也导致 N 去除受到抑制。（2）分子生态网络拓扑结构显示氮与碳或硫循环之间的不同耦合效应，具体而言，低氮浓度储层中的甲烷代谢促进了氮的去除，而氮和硫循环的共现增强了氮和硫的同时去除，相反，氮与C或S循环官能团之间的共排斥阻碍了高氮浓度水闸中的硝化和反氮化作用。（3） 对于沉积物，高 N 浓度增强了矿化、硝化、反硝化和厌氧铵氧化的潜力，以促进无机 N 的去除。C 和 N 循环之间的共排斥始终抑制了不同生境中的反氮化、厌氧铵氧化和 N 固定。 有机 S 转化、S 矿化、S 还原基因和 N 矿化、有机 N 合成和反硝化基因共现促进了 N 的去除。综上，上覆水的高氮浓度和大坝诱导的停滞阻碍了氮的去除，而氮与碳或硫循环的耦合对不同停滞生境的氮去除表现出不同的影响。