AUTHOR=Glibert Patricia M. , Wilkerson Frances P. , Dugdale Richard C. , Parker Alexander E. , Alexander Jeffrey , Blaser Sarah , Murasko Susan 

TITLE=Phytoplankton communities from San Francisco Bay Delta respond differently to oxidized and reduced nitrogen substrates—even under conditions that would otherwise suggest nitrogen sufficiency

JOURNAL=Frontiers in Marine Science

VOLUME=1

YEAR=2014

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2014.00017

DOI=10.3389/fmars.2014.00017

ISSN=2296-7745

ABSTRACT=<p>The effect of equivalent additions of nitrogen (N, 30–40 μM-N) in different forms (ammonium, NH<sup>+</sup><sub>4</sub>, and nitrate, NO<sup>−</sup><sub>3</sub>) under conditions of different light exposure on phytoplankton community composition was studied in a series of four, 5-day enclosure experiments on water collected from the nutrient-rich San Francisco Bay Delta over 2 years. Overall, proportionately more chlorophyll <italic>a</italic> and fucoxanthin (generally indicative of diatoms) was produced per unit N taken up in enclosures enriched with NO<sup>−</sup><sub>3</sub> and incubated at reduced (~15% of ambient) light intensity than in treatments with NO<sup>−</sup><sub>3</sub> with high (~60% of ambient) light exposure or with NH<sup>+</sup><sub>4</sub> under either light condition. In contrast, proportionately more chlorophyll <italic>b</italic> (generally indicative of chlorophytes) and zeaxanthin (generally indicative of cyanobacteria) was produced in enclosures enriched with NH<sup>+</sup><sub>4</sub> and incubated under high light intensity than in treatments with low light or with added NO<sup>−</sup><sub>3</sub> at either light level. Rates of maximal velocities (<italic>V</italic><sub><italic>max</italic></sub>) of uptake of N substrates, measured using <sup>15</sup>N tracer techniques, in all enclosures enriched with NO<sup>−</sup><sub>3</sub> were higher than those enriched with NH<sup>+</sup><sub>4</sub>. Directionality of trends in enclosures were similar to phytoplankton community shifts observed in transects of the Sacramento River to Suisun Bay, a region in which large changes in total N quantity and form occur. These data substantiate the growing body of experimental evidence that dichotomous microbial communities develop when enriched with the same absolute concentration of oxidized vs. reduced N forms, even when sufficient N nutrient was available to the community prior to the N inoculations.</p>