Key Laboratory of Water and Sediment Sciences of Ministry of Education, State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China.
School of Oceanography, University of Washington, Seattle, WA, USA.
Water Res. 2020 Apr 15;173:115589. doi: 10.1016/j.watres.2020.115589. Epub 2020 Feb 4.
Ammonia-oxidizing bacteria (AOB) and archaea (AOA) as well as complete ammonia oxidizers (comammox) aerobically catalyze ammonia oxidation which plays essential roles in riverine nitrogen cycle. However, performances of these ammonia oxidizers in high-elevation river sediments have rarely been documented. This study investigated the abundance, community, and activity of ammonia oxidizers in five high-elevation rivers of the Qinghai-Tibet Plateau (QTP). Comammox were dominant ammonia oxidizers in 23% of studied samples and the clade B was principal comammox type. amoA gene abundances of AOA and AOB in these high-elevation rivers were comparable to those in low-elevation rivers. However, in contrast to most studied low-elevation rivers, AOB amoA gene abundance outnumbered AOA in 92% samples, which might be caused by the lower temperature and more intense solar radiation of the QTP. Potential nitrification rates (PNRs) ranged from 0.02 to 2.95 nmol-N h g dry sediment. Ammonia concentration was the limiting factor to PNRs at some sites, and when ammonia was not limiting, the PNR: ammonia ratio was greater at higher temperatures. There was no apparent variation in ammonia oxidizer community compositions along the elevation gradient due to the high elevation (2687 to 4223 m) of our entire study area. However, compared with low-elevation rivers, the lower temperature, huge diurnal temperature change, and lower nutrient conditions in the QTP rivers shaped distinctive communities for ammonia oxidizers; the unique community characteristics were significantly correlated to PNRs. These results suggest that ammonia oxidizers in the five high-elevation rivers have adapted to high-elevation conditions; more research should be conducted to study their adaptation mechanisms and their roles in riverine nitrogen cycle.
氨氧化细菌（AOB）和古菌（AOA）以及完全氨氧化菌（comammox）有氧催化氨氧化，在河流氮循环中发挥着重要作用。然而，高海拔河流沉积物中这些氨氧化菌的性能很少有文献记载。本研究调查了青藏高原（QTP）五条高海拔河流中氨氧化菌的丰度、群落和活性。在研究的样本中，有 23%的样本中 comammox 是主要的氨氧化菌，且 clade B 是主要的 comammox 类型。这些高海拔河流中 AOA 和 AOB 的 amoA 基因丰度与低海拔河流相当。然而，与大多数研究的低海拔河流不同，92%的样本中 AOB amoA 基因丰度超过了 AOA，这可能是由于 QTP 的低温和更强的太阳辐射造成的。潜在硝化速率（PNRs）范围为 0.02 至 2.95 nmol-N h g 干沉积物。在一些地点，氨浓度是限制 PNRs 的因素，而当氨不成为限制因素时，PNR：氨的比值在较高温度下更大。由于我们整个研究区域的海拔较高（2687 至 4223 米），氨氧化菌群落组成没有沿海拔梯度明显变化。然而，与低海拔河流相比，QTP 河流的低温、巨大的昼夜温差和较低的营养条件塑造了氨氧化菌独特的群落；独特的群落特征与 PNRs 显著相关。这些结果表明，五条高海拔河流中的氨氧化菌已经适应了高海拔环境；应该进行更多的研究来研究它们的适应机制及其在河流氮循环中的作用。
