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Ecogenomic sensor reveals controls on N2-fixing microorganisms in the North Pacific Ocean

  • Author(s): Robidart, JC
  • Church, MJ
  • Ryan, JP
  • Ascani, F
  • Wilson, ST
  • Bombar, D
  • Marin, R
  • Richards, KJ
  • Karl, DM
  • Scholin, CA
  • Zehr, JP
  • et al.
Abstract

Nitrogen-fixing microorganisms (diazotrophs) are keystone species that reduce atmospheric dinitrogen (N2) gas to fixed nitrogen (N), thereby accounting for much of N-based new production annually in the oligotrophic North Pacific. However, current approaches to study N2fixation provide relatively limited spatiotemporal sampling resolution; hence, little is known about the ecological controls on these microorganisms or the scales over which they change. In the present study, we used a drifting robotic gene sensor to obtain high-resolution data on the distributions and abundances of N2-fixing populations over small spatiotemporal scales. The resulting measurements demonstrate that concentrations of N2fixers can be highly variable, changing in abundance by nearly three orders of magnitude in less than 2 days and 30 km. Concurrent shipboard measurements and long-term time-series sampling uncovered a striking and previously unrecognized correlation between phosphate, which is undergoing long-term change in the region, and N2-fixing cyanobacterial abundances. These results underscore the value of high-resolution sampling and its applications for modeling the effects of global change. © 2014 International Society for Microbial Ecology. All rights reserved.

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