Nitrogen fixation and the diazotroph community in the temperate coastal region of the northwestern North Pacific

[摘要] Nitrogen fixation in temperate oceans is a potentially important, but poorlyunderstood process that may influence the marine nitrogen budget. This studydetermined seasonal variations in nitrogen fixation and the diazotrophcommunity within the euphotic zone in the temperate coastal region of thenorthwestern North Pacific. Nitrogen fixation as high as 13.6 nmol N L⁻¹ d⁻¹was measured from early summer to fall when the surfacetemperature exceeded 14.2 °C (but was lower than 24.3 °C)and the surface nitrate concentration was low (≤0.30 μM),although we also detected nitrogen fixation in subsurface layers (42–62 m)where nitrate concentrations were high (> 1 μM). Clonelibrary analysis results indicated that nifH gene sequences were omnipresentthroughout the investigation period. During the period when nitrogenfixation was detected (early summer to fall), the genes affiliated withUCYN-A, Trichodesmium, and γ-proteobacterial phylotype γ-24774A11 werefrequently recovered. In contrast, when nitrogen fixation was undetectable(winter to spring), many sequences affiliated with Cluster III diazotrophs(putative anaerobic bacteria) were recovered. Quantitative PCR analysisrevealed that UCYN-A was relatively abundant from early to late summercompared with Trichodesmium and γ-24774A11, whereas Trichodesmium abundance was the highestamong the three groups during fall.

[学科分类] 地球化学与岩石