View Abstract

IN SITU DIAZOTROPH NET GROWTH RATES UNDER DIFFERENT RESOURCE RATIOS AT STATION ALOHA

Biological nitrogen fixation supports up to 50% of new primary productivity in the North Pacific Subtropical Gyre. However, it remains poorly understood how environmental factors control the observed spatial and temporal patterns in abundances of nitrogen-fixing organisms (diazotrophs) in this region. To quantify diazotroph net growth rates and determine whether rates can be correlated to environmental factors or microbial population structure we conducted a bioassay using in situ incubation arrays in the vicinity of Station ALOHA during March 2016. Net growth rates for diazotroph taxa were quantified under high (H) and low (L) nitrate:phosphate (NP) ratio conditions at four depths in the water column using quantitative PCR. Changes in microbial community composition were characterized using 16S rRNA tag sequencing. The diazotroph community was dominated by two unicellular taxa, the prymnesiophyte symbiont UCYN-A1, and a Cyanothece-like organism (UCYN-C). Net growth rates for these taxa after 48h were not stimulated by LNP conditions, as expected. However, enhanced net growth rates were measured in HNP conditions at 25m and 100m for UCYN-C and UCYN-A1, respectively. Interestingly, net growth rates for UCYN-A1, UCYN-C, Crocosphaera and the diatom symbiont Richelia, were uniformly high at a single depth independent of NP ratio (45m; 1.6 +/- 0.5 d-1), suggesting all taxa were growing optimally at the onset of the experiment at this depth. Quantification of diazotroph growth rates and understanding how the microbial community responds to changes in the diazotroph population are important steps for advancing predictive models.

Authors

Turk-Kubo, K. A., UCSC, USA, kturk@ucsc.edu

Hogan, M. E., UCSC, USA, hulk@ucsc.edu

Zehr, J. P., UCSC, USA, jpzehr@gmail.com

Munoz-Marin, M., UCSC, USA, mmunozma@ucsc.edu

Details

Poster presentation

Session #:040
Date: 03/01/2017
Time: 15:30 - 16:30
Location: Poster/Exhibit Hall

Presentation is given by student: No

PosterID: 357