Dataset: Vitacopss: nutrients and microbial cell counts

Water samples were collected from 3 meters depth at the San Pedro Ocean Time-series (SPOT) station (33°33'N, 118°24'W) off the coast of Southern California in March 2015. Six treatments were used: control, nitrate, nitrate+B1, nitrate+B7, nitrate+B12, and nitrate+B1+B7+B12 with triplicate 10L incubations. Growth was tracked daily. Samples were collected initially, and at two points during the experiment: exponential growth and stationary phase. Exponential growth occurred at day 7 and stationary growth varied between treatment ranging from 10-12 days. The incubations were co-limited by nitrate and B12. Samples were flash frozen and stored at -80C until analysis. For further details on the methodology, see Suffridge et al (2017).

Cell counts were made with using flow cytometry. Samples for flow cytometry were collected, fixed with 2% formalin, and frozen at -80C. Analysis for the cellular abundance of heterotrophic bacteria, Synechococcus, and pircoeukaryotes was conducted using a BD Accuri C6 flow cytometer (Becton Dickerson and Company).

Elemental ratios were obtained by measuring particulate organic nutrients: carbon and nitrogen (POC and PON), and particulate organic phosphorus (POP). For particulate organic carbon and nitrogen (POC and PON), 100 ml was filtered onto pre-combusted POC and PON were analyzed on a Costech Elemental Analyzer using methionine and acetanilide as references to calibrate the system at the beginning of the measurements (Fu et al. 2007).

For particulate organic phosphorus (POP) samples, 40 mls were filtered onto precombusted (500°C, 2 h) GF/F filters and rinsed twice with 2 ml 0.17 mol L-1 Na2SO4 solution. The filters were placed in 20 ml borosilicate scintillation vials (pre-combusted at 500°C, overnight) to which was added 2ml 0.017 mol L-1 MgSO4 solution. The vials were then covered with aluminum foil and dried at 95 °C, followed by combustion at 450-500 °C for 2 h. After cooling to room temperature, 5 ml of 0.2 mol L-1 HCl solution was added to each vial, which were then tightly capped and heated at 80°C for thirty minutes to digest POP into inorganic phosphate. The standard molybdate colorimetric method was used to analyze the samples (Solorzano and Sharp 1980). Three GF/F filters were treated in the same way as the samples for blank determinations. POP quantification was done using a Shimadzu UV-1800 UV/Visible Scanning Spectrophotometer.

Chl-a concentrations were measured using the protocol described by Welschmeyer (1994). 40 ml of water samples from each replicate were filtered through GF/F glass fiber filters, 3.0-μm and 8.0-μm polycarbonate membrane for size fractionated Chl-a analyses. After adding 6 ml of 90% acetone, Chl-a was extracted in the freezer at -20°C and measured using the non-acidification method with a Turner Designs 10-AUTM fluorometer after 24 hours.