Groupe de recherche interuniversitaire en limnologie, Département de sciences biologiques, Université de Montréal, Montréal, Québec, Canada.
Groupe de recherche interuniversitaire en limnologie, Department of Biology, Concordia University, Montréal, Québec, Canada.
PLoS One. 2019 Mar 20;14(3):e0213748. doi: 10.1371/journal.pone.0213748. eCollection 2019.
We investigated the variability in ammonia oxidation (AO) rates and the presence of ammonia-oxidizing archaea and bacteria (AOB and AOA) over an annual cycle in the water column of a small, seasonnally ice covered, temperate shield lake. AO, the first step of nitrification, was measured in situ using 15N-labelled ammonium (NH4+) at 1% and 10% of photosynthetic active radiation during day and at the same depths during night. AO was active across seasons and light levels, ranging from undetectable to 333 nmol L-1 d-1 with peak activity in winter under ice cover. NH4+ concentration was the single most important positive predictor of AO rates. High NH4+ concentrations and reduced chlorophyll a concentrations under ice, which favoured AO, were coherent with high nitrate concentrations and super saturation in nitrous oxide. When targeting the ammonia monooxygenase (amoA) gene in samples from the photic zone, we found AOA to be omnipresent throughout the year while AOB were observed predominantly during winter. Our results demonstrate that AO is an ongoing process in sunlit surface waters of temperate lakes and at all seasons with pronounced nitrification activity observed during winter under ice. The combination of high NH4+ concentrations due to fall overturn, reduced light availability that limited phytoplankton competition, and the presence of AOB together with AOA apparently favoured these elevated rates under ice. We suggest that lake ice could be a control point for nitrification in oligotrophic temperate shield lakes, characterized as a moment and place that exerts disproportionate influence on the biogeochemical behaviour of ecosystems.
我们研究了一个小而季节性被冰覆盖的温带盾牌湖中水柱中氨氧化（AO）速率的变异性以及氨氧化古菌和细菌（AOB 和 AOA）的存在，该湖具有年度周期。在白天，在 1%和 10%的光合有效辐射下，以及在夜间在相同深度，使用 15N 标记的铵（NH4+）原位测量 AO，这是硝化作用的第一步。AO 在整个季节和光照水平下都是活跃的，其范围从不可检测到 333 nmol L-1 d-1，冬季在冰盖下达到峰值。NH4+浓度是 AO 速率的最重要的单一正预测因子。冰下高 NH4+浓度和减少的叶绿素 a 浓度有利于 AO，这与高硝酸盐浓度和一氧化二氮的过饱和相一致。当针对光区样本中的氨单加氧酶（amoA）基因时，我们发现 AOA 全年普遍存在，而 AOB 主要在冬季观察到。我们的研究结果表明，AO 是温带湖泊中透光地表水的持续过程，在冬季冰下观察到明显的硝化作用。由于秋季翻转而导致的高 NH4+浓度、限制浮游植物竞争的光照可用性降低以及 AOB 和 AOA 的存在，显然有利于这些在冰下的高速率。我们认为，湖泊冰是贫营养温带盾牌湖中硝化作用的控制点，其特征是对生态系统生物地球化学行为产生不成比例影响的时刻和地点。
