We investigated dinitrogen (N₂) fixation activity and diazotroph community composition across the Cape Verde Frontal Zone (CVFZ), from photic epipelagic waters (0-200 m) to aphotic meso- (200–1000 m) and bathypelagic (> 1000 m) waters. The highest N₂ fixation rates of 4.1 ± 2.2 nmol N l^− 1 day^− 1 and 7.8 ± 2.3 nmol N l^− 1 day^− 1 were in epipelagic waters south of the front. We detected aphotic N₂ fixation in 5 out of 32 samples, primarily south of the front, and sporadically down to 3,000 m, with rates ranging from 0.03 ± 0.01 nmol N l^− 1 day^− 1 to 0.07 ± 0.01 nmol N l^− 1 day^− 1. Cyanobacteria dominated the diazotroph community and nitrogenase gene (nifH) expression profiles in surface waters and, surprisingly, in aphotic waters. The detection of cyanobacterial nifH genes by DNA sequencing and quantitative PCR in the aphotic zone, together with nifH expression in meso- and bathypelagic waters, indicates a downward flux of metabolically active cyanobacteria, and points to a contribution to the observed aphotic N₂ fixation rates. In the photic zone, UCYN-A dominated north of the front, whereas Trichodesmium was mainly found in the southern region. However, our results also show that cross-frontal advection of cyanobacterial diazotrophs can occur via intrusions of surface water. Salinity, temperature, and mixed layer depth were the main determinants of the diazotroph composition and distribution of the key cyanobacteria. Thus, the front appeared to act as a dynamic barrier controlling the distribution of cyanobacterial diazotrophs.

我们调查了整个佛得角前缘带 (CVFZ) 的二氮 (N ₂ ) 固定活性和固氮菌群落组成，从有光的表层水域 (0-200 m) 到无光的中层 (200-1000 m) 和深海 (> 1000 m)水域。^{4.1 ± 2.2 nmol N l - 1}天^{- 1}和 7.8 ± 2.3 nmol N l ^{- 1}天^{- 1}的最高 N ₂固定率位于前沿以南的远洋水域。我们在 32 个样本中的 5 个样本中检测到无光 N ₂固定，主要在前部以南，偶尔下降到 3,000 m，速率范围为 0.03 ± 0.01 nmol N l ^{- 1} day ^{- 1}到 0.07 ± 0.01 nmol N l ^{- 1}天^{- 1}。蓝细菌在地表水中以及令人惊讶的是在无光水域中的固氮菌群落和固氮酶基因 ( nifH ) 表达谱中占主导地位。在无光区通过 DNA 测序和定量 PCR检测蓝藻nifH基因，以及在中海和深海水域中的nifH表达，表明代谢活跃的蓝藻向下流动，并指出对观察到的无光 N ₂固定率的贡献. 在光带中，UCYN-A 在锋面北部占主导地位，而Trichodesmium主要分布在南部地区。然而，我们的研究结果还表明，蓝藻固氮菌的交叉正面平流可以通过地表水的侵入发生。盐度、温度和混合层深度是固氮菌组成和关键蓝藻分布的主要决定因素。因此，前沿似乎充当了控制蓝藻固氮菌分布的动态屏障。