Subsurface microbial communities mediate biogeochemical transformations that drive both local and ecosystem-level cycling of essential elements, including nitrogen. However, their study has been largely limited to the deep ocean, terrestrial mines, caves, and topsoils (< 30 cm). Here, we present regional insights into the microbial ecology of aerobic ammonia oxidation within the terrestrial subsurface of five semi-arid riparian sites spanning a 900-km N-S transect. We sampled sediments, profiled communities to depths of ≤ 10 m, and compared them to reveal trends regionally within and surrounding the Upper Colorado River Basin (CRB). The diversity and abundance of ammonia-oxidizing microbial communities were evaluated in the context of subsurface geochemistry by applying a combination of amoA (encoding ammonia monooxygenase subunit A) gene sequencing, quantitative PCR, and geochemical techniques. Analysis of 898 amoA sequences from ammonia-oxidizing archaea (AOA) and bacteria (AOB) revealed extensive ecosystem-scale diversity, including archaeal amoA sequences from four of the five major AOA lineages currently found worldwide as well as distinct AOA ecotypes associated with naturally reduced zones (NRZs) and hydrogeochemical zones (unsaturated, capillary fringe, and saturated). Overall, AOA outnumber AOB by 2- to 5000-fold over this regional scale, suggesting that AOA may play a prominent biogeochemical role in nitrification within terrestrial subsurface sediments.

地下微生物群落介导了生物地球化学转化，从而推动了包括氮在内的必需元素在局部和生态系统层面的循环。但是，他们的研究主要限于深海，陆地矿山，洞穴和表土（<  30厘米）。在这里，我们介绍了跨越900公里长的NS断面的五个半干旱河岸站点的陆地地下有氧氨氧化微生物生态的区域性见解。我们对沉积物进行了采样，对≤10 m深度的群落进行了剖析，并对它们进行了比较，以揭示科罗拉多河上游流域（CRB）内和周围区域的趋势。通过应用amoA的组合，在地下地球化学的背景下评估了氨氧化微生物群落的多样性和丰度。（编码氨单加氧酶亚基A）基因测序，定量PCR和地球化学技术。对来自氨氧化古细菌（AOA）和细菌（AOB）的898 amoA序列的分析揭示了广泛的生态系统规模多样性，包括目前在全球范围内发现的五个主要AOA谱系中的四个的古细菌amoA序列以及与自然减少的AOA生态型相关的独特AOA生态型区域（NRZs）和水文地球化学区域（不饱和，毛细管边缘和饱和）。总体而言，在该区域范围内，AOA的数量比AOB多2到5000倍，这表明AOA在陆地地下沉积物中的硝化作用中可能起着重要的生物地球化学作用。