Castellano-Hinojosa Antonio, Correa-Galeote David, Carrillo Presentación, Bedmar Eulogio J, Medina-Sánchez Juan M
Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, Consejo Superior de Investigaciones Científicas, Granada, Spain.
Instituto Universitario de Investigación del Agua, Universidad de Granada, Granada, Spain.
Front Microbiol. 2017 Oct 6;8:1911. doi: 10.3389/fmicb.2017.01911. eCollection 2017.
Wet deposition of reactive nitrogen (Nr) species is considered a main factor contributing to N inputs, of which nitrate ([Formula: see text]) is usually the major component in high-mountain lakes. The microbial group of denitrifiers are largely responsible for reduction of nitrate to molecular dinitrogen (N) in terrestrial and aquatic ecosystems, but the role of denitrification in removal of contaminant nitrates in high-mountain lakes is not well understood. We have used the oligotrophic, high-altitude La Caldera lake in the Sierra Nevada range (Spain) as a model to study the role of denitrification in nitrate removal. Dissolved inorganic Nr concentration in the water column of la Caldera, mainly nitrate, decreased over the ice-free season which was not associated with growth of microbial plankton or variations in the ultraviolet radiation. Denitrification activity, estimated as nitrous oxide (NO) production, was measured in the water column and in sediments of the lake, and had maximal values in the month of August. Relative abundance of denitrifying bacteria in sediments was studied by quantitative polymerase chain reaction of the 16S rRNA and the two phylogenetically distinct clades I and II genes encoding nitrous oxide reductases. Diversity of denitrifiers in sediments was assessed using a culture-dependent approach and after the construction of clone libraries employing the I gene as a molecular marker. In addition to genera , , , , , , and , which were present in the clone libraries, , , and were also detected in culture media that were not found in the clone libraries. Analysis of biological activities involved in the C, N, P, and S cycles from sediments revealed that nitrate was not a limiting nutrient in the lake, allowed NO production and determined denitrifiers' community structure. All these results indicate that denitrification could be a major biochemical process responsible for the N losses that occur in La Caldera lake.
活性氮（Nr）物种的湿沉降被认为是导致氮输入的主要因素，其中硝酸盐（[化学式：见原文]）通常是高山湖泊中的主要成分。反硝化细菌菌群在很大程度上负责陆地和水生生态系统中硝酸盐还原为分子态二氮（N），但反硝化作用在高山湖泊中去除污染物硝酸盐方面的作用尚未得到充分了解。我们以西班牙内华达山脉贫营养的高海拔拉卡尔德拉湖为模型，研究反硝化作用在硝酸盐去除中的作用。拉卡尔德拉湖水柱中溶解的无机Nr浓度（主要是硝酸盐）在无冰季节下降，这与微生物浮游生物的生长或紫外线辐射的变化无关。通过测量湖泊水柱和沉积物中一氧化二氮（N₂O）的产生来估算反硝化活性，其在8月份达到最大值。通过对16S rRNA以及编码一氧化二氮还原酶的两个系统发育不同的I和II类基因进行定量聚合酶链反应，研究了沉积物中反硝化细菌的相对丰度。使用依赖培养的方法并构建以I基因作为分子标记的克隆文库后，评估了沉积物中反硝化细菌的多样性。除了克隆文库中存在的属、、、、、、和外，在克隆文库中未发现的、和也在培养基中被检测到。对沉积物中参与碳、氮、磷和硫循环的生物活性分析表明，硝酸盐不是该湖泊中的限制养分，允许N₂O产生并决定了反硝化细菌的群落结构。所有这些结果表明，反硝化作用可能是导致拉卡尔德拉湖氮损失的主要生化过程。
