Vertical distributions of nitrogen-fixing phylotypes at Stn Aloha in the oligotrophic North Pacific Ocean

Aquatic Microbial Ecology

Bethany D. Jenkins¹  Jonathan P. Zehr¹  Matthew J. Church¹  David M. Karl¹ 

关键词: Nitrogen fixation;    Bacterial diversity;    Quantitative PCR;    Hawaii Ocean;    Time-series;   

DOI  :  10.3354/ame038003

学科分类：生物科学（综合）

来源: Inter-Research

【 摘 要 】

ABSTRACT: In large areas of the world’s oceans, biological dinitrogen (N₂) fixation supports a significant fraction of ecosystem productivity; to date, however, there is little information on the abundances of specific diazotrophs in theocean. In this study, the vertical distributions of several different groups of N₂-fixing bacteria were examined using quantitative polymerase chain reaction (QPCR) amplification of group-specific dinitrogenase reductase (nifH)genes from Stn ALOHA in the subtropical North Pacific Ocean. Depth distributions (<200 m) of 3 cyanobacterial nifH phylotypes and 1 previously uncharacterized Cluster III nifH phylotype were evaluated. The nifH-containingcyanobacteria included sequence-types similar to Trichodesmium spp.and 2 nifH sequences closely related to unicellular cyanobacteria (termed Groups A and B). The Group A cyanobacteria (most closely related to Cyanothecesp.) were the most abundant of all phylotypes examined, comprising 2 × 10⁵ nifH gene copies l^-1 in the high-irradiance (>700 µmol quanta m^-2 s^-1), nitrate-depleted(<10 nmol l^-1) upper-ocean waters. Group B cyanobacterial phylotypes (most closely related to Crocosphaera watsonii) demonstrated a depth distribution similar to Group A, but Group B nifH abundance was considerably lower,averaging 2 × 10³ nifH gene copies l^-1 in the upper photic zone. The abundance of Trichodesmium spp. ranged from 1 × 10³ to 7 × 10³ nifH gene copiesl^-1 in the upper ocean, declining to <100 nifH gene copies l^-1 below the mixed layer (~82 m). The Cluster III nifH phylotype was the most abundant nifH phylotype in the dimly lit (<12 µmolquanta m^-2 s^-1) lower photic zone (>100 m). These results revealed differences in the depth distributions of N₂-fixing plankton at Stn ALOHA, and suggest that unicellular diazotrophs comprise a significantcomponent of plankton biomass in this oligotrophic marine ecosystem.

【 授权许可】

Unknown