Table_1_Diel Patterns of Variable Fluorescence and Carbon Fixation of Picocyanobacteria Prochlorococcus-Dominated Phytoplankton in the South China Sea Basin.docx

<p>The various photosynthetic apparatus and light utilization strategies of phytoplankton are among the critical factors that regulate the distribution of phytoplankton and primary productivity in the ocean. Active chlorophyll fluorescence has been a powerful technique for assessing the nutritional status of phytoplankton by studying the dynamics of photosynthesis. Further studies of the energetic stoichiometry between light absorption and carbon fixation have enhanced understanding of the ways phytoplankton adapt to their niches. To explore the ecophysiology of a Prochlorococcus-dominated phytoplankton assemblage, we conducted studies of the diel patterns of variable fluorescence and carbon fixation by phytoplankton in the oligotrophic South China Sea (SCS) basin in June 2017. We found that phytoplankton photosynthetic performance at stations SEATS and SS1 were characterized by a nocturnal decrease, dawn maximum, and midday decrease of the maximum quantum yield of PSII (Fv(′)/Fm(′), which has been denoted as both F_v/F_m and Fv′/Fm′) in the nutrient-depleted surface layer. That these diel patterns of Fv(′)/Fm(′) were similar to those in the tropical Pacific Ocean suggests macro-nutrient and potentially micro-nutrient stress. However, the fact that variations were larger in the central basin than at the basin's edge implied variability in the degree of nutrient limitation in the basin. The estimated molar ratio of gross O₂ production to net production of carbon (GOP:NPC) of 4.9:1 was similar to ratios reported across the world's oceans. The narrow range of the GOP:NPC ratios is consistent with the assumption that there is a common strategy for photosynthetic energy allocation by phytoplankton. That photo-inactivated photosystems or nonphotochemical quenching rather than GOP accounted for most of the radiation absorbed by phytoplankton explains why the maximum quantum yield of carbon fixation was rather low in the oligotrophic SCS.</p

Physical-Biological Coupling in the Western South China Sea: The Response of Phytoplankton Community to a Mesoscale Cyclonic Eddy - Fig 8

<p><b>The linear relationship between (A) NO</b>_<b>2</b>^<b>-</b><b>+NO</b>_<b>3</b>^<b>-</b><b>[</b>μ<b>M], (B) TChl <i>a</i> biomass of the upper 100 m water column integration [mg m</b>^<b>-2</b><b>], (C) TChl <i>a</i> biomass at DCML [mg m</b>^<b>-3</b><b>], (D) TChl <i>a</i> biomass at surface layer [mg m</b>^<b>-3</b><b>] and the temperature at the 50 m depth layer.</b> The two red dashed lines in Fig 8A indicate 23.0°C and 26.0°C, which were the frontal temperature gradients. The solid line shows the linear regression, and the two dashed lines the 95% upper confidence limit and lower confidence limit.</p

Vertical distribution of hydrologic parameters, nutrients and <i>in situ</i> fluorescence along the Y0 during the cruise.

<p>(A) Temperature [°C], (B) Salinity, (C) potential density anomaly [kg m^-3], (D) fluorescence [relative units]. The bright contour denotes the euphotic depth [m], and the gray one denotes the mixed layer depth [m].</p

The hydrologic parameters of the three blocks of C2.

<p>The hydrologic parameters of the three blocks of C2.</p

Development of an Integrated Syringe-Pump-Based Environmental-Water Analyzer (<i>i</i>SEA) and Application of It for Fully Automated Real-Time Determination of Ammonium in Fresh Water

The development of a multipurpose integrated syringe-pump-based environmental-water analyzer (<i>i</i>SEA) and its application for spectrophotometric determination of ammonium is presented. The <i>i</i>SEA consists of a mini-syringe pump equipped with a selection valve and laboratory-programmed software written by LabVIEW. The chemistry is based on a modified indophenol method using <i>o</i>-phenylphenol. The effect of reagent concentrations and sample temperatures was evaluated. This fully automated analyzer had a detection limit of 0.12 μM with sample throughput of 12 h^–1. Relative standard deviations at different concentrations (0–20 μM) were 0.23–3.36% (<i>n</i> = 3–11) and 1.0% (<i>n</i> = 144, in 24 h of continuous measurement, ∼5 μM). Calibration curves were linear (<i>R</i>² = 0.9998) over the range of 0–20 and 0–70 μM for the detection at 700 and 600 nm, respectively. The <i>i</i>SEA was applied in continuous real-time monitoring of ammonium variations in a river for 24 h and 14 days. A total of 1802 samples were measured, and only 0.4% was outlier data (≥3 sigma residuals). Measurements of reference materials and different aqueous samples (<i>n</i> = 26) showed no significant difference between results obtained by reference and present methods. The system is compact (18 cm × 22 cm × 24 cm), portable (4.8 kg), and robust (high-resolution real-time monitoring in harsh environments) and consumes a small amount of chemicals (20–30 μL/run) and sample/standards (2.9 mL/run)

Vertical distribution of TChl <i>a</i> and major phytoplankton groups in terms of TChl <i>a</i> biomass [mg m^-3] along section Y0 during the cruise.

<p>(A) TChl <i>a</i>, (B) Diatoms, (C) Prasinophytes, (D) <i>Synechococcus</i>, (E) Haptophytes_8, and (F) <i>Prochlorococcus</i>. The bright contours denote the isopycnals bordered between 22.0 kg m^-3 and 25.0 kg m^-3, and the intermediated red line is the euphotic depth [m].</p

The upper 150 m profiles of potential temperature (°C) for the survey stations to distinguish the three blocks of the C2 (IN, EDGE and OUT).

<p>The upper 150 m profiles of potential temperature (°C) for the survey stations to distinguish the three blocks of the C2 (IN, EDGE and OUT).</p

Evolution of the cyclonic eddy C2 in the western SCS during the cruise.

<p>The weekly merged data of the SLA product from the French AVISO data project, from 15 August to 19 September 2007.</p

The water column integrated phytoplankton group composition in term of group-average TChl <i>a</i> biomass within the euphotic zone [mg m^-3].

<p>The group OUT was treated as the control in the multiple comparison using one-way ANOVA. * implied significantly different in the level of p<0.050, ** for p<0.010 and *** for p<0.001.</p

The comparison of TChl <i>a</i> biomass and the contribution of major phytoplankton groups to the TChl <i>a</i> biomass among the three blocks.

<p>The comparison of TChl <i>a</i> biomass and the contribution of major phytoplankton groups to the TChl <i>a</i> biomass among the three blocks.</p