Abstract：
Nitrification is an important control on the form and distribution of nitrogen in freshwater ecosystems. However, the seasonality of nitrogen pools and the diversity of organisms catalyzing this process have not been well documented in oligotrophic lakes. Here, we show that nitrogen pools and nitrifying organisms in Flathead Lake are temporally and vertically dynamic, with nitrifiers displaying specific preferences depending on the season. While the ammonia-oxidizing bacteria (AOB) Nitrosomonadaceae and nitrite-oxidizing bacteria (NOB) Nitrotoga dominate at depth in the summer, the ammonia-oxidizing archaea (AOA) Nitrososphaerota and NOB Nitrospirota become abundant in the winter. Given clear seasonality in ammonium, with higher concentrations during the summer, we hypothesize that the succession between these two nitrifying groups may be due to nitrogen affinity, with AOB more competitive when ammonia concentrations are higher and AOA when they are lower. Nitrifiers in Flathead Lake share more than 99% average nucleotide identity with those reported in other North American lakes but are distinct from those in Europe and Asia, indicating a role for geographic isolation as a factor controlling speciation among nitrifiers. Our study shows there are seasonal shifts in nitrogen pools and nitrifying populations, highlighting the dynamic spatial and temporal nature of nitrogen cycling in freshwater ecosystems.
摘要：
硝化作用是对淡水生态系统中氮的形态和分布的重要控制。然而,在贫营养湖泊中，氮库的季节性和催化这一过程的生物多样性尚未得到充分记录。这里,我们表明，平头湖中的氮库和硝化生物是时间和垂直动态的，硝化氮显示特定的喜好取决于季节。虽然氨氧化细菌（AOB）亚硝唑科和亚硝酸盐氧化细菌（NOB）亚硝唑在夏季的深度占主导地位，氨氧化古细菌（AOA）亚硝基细菌和NOB亚硝基螺旋体在冬季变得丰富。鉴于铵的季节性明显，夏季浓度较高，我们假设这两个硝化基团之间的演替可能是由于氮亲和力，当氨浓度较高时，AOB更具竞争力，当AOA较低时，AOA更具竞争力。平头湖中的硝酸盐与其他北美湖泊中报道的硝酸盐具有超过99％的平均核苷酸同一性，但与欧洲和亚洲不同。表明地理隔离作为控制硝化者物种形成的因素。我们的研究表明，氮库和硝化种群存在季节性变化，强调了淡水生态系统中氮循环的动态时空性质。
