Using Fe chemistry to predict Fe uptake rates for natural plankton assemblages from the Southern Ocean

Exopolymeric Substances Control Microbial Community Structure and Function by Contributing to both C and Fe Nutrition in Fe-Limited Southern Ocean Provinces

“…This suggests that EPS can promote natural plankton growth as previously reported in the Sub-Antarctic Zone [ 21 ]. During the same expedition as this study, Cabanes et al [ 23 ] showed that Fe chemical speciation could explain the different Fe uptake rates determined for the same experimental treatments as used here ( Supplementary Tables S11 and S12 ). The latter study showed that inorganic Fe concentrations (Fe’) could explain up to 70% of the Fe uptake rates measured following short-term (24 h) incubations.…”

“…During the same expedition, Fe uptake rates also support strong Fe limitation for the Drake Passage sites (Bio 1 and 3) and milder Fe limitation in the coastal WAP (Bio 2) [ 23 ]. Moreover, “mild” to strong Fe-limiting conditions at all study sites are further supported by the comparison of phytoplankton requirements for growth typically reported for Fe-limiting conditions (Kµ; Antarctic Polar Frontal zone, Indian sector, 410–450 pM, [ 43 ]; in and south of the Antarctic Polar Frontal Zone, Pacific sector, 90–110 pM, [ 44 ]) with inorganic and labile (e.g., highly reactive) Fe concentrations determined at our study sites (1–3 pM, 21–63 pM, respectively; Supplementary Table S11 ).…”

“…Incubations aimed to test the response of plankton communities to identical total Fe enrichments, but with different Fe chemistry and Fe accessibility to phytoplankton. The impact of FeL treatments on Fe chemistry and Fe uptake rates was assessed using short-term incubations (24 h) and is presented in a companion paper [ 23 ]. In this study, incubations were performed over six days at 2 °C with a 15:9 h light:dark cycle.…”

“…Samples for macronutrients (nitrate, nitrite, ammonium, phosphate, and dissolved silicate) were collected for each experimental bottle at the beginning and the end of incubation, 0.2 µm filtered (Sartorius Stedium, Göttingen, Germany), and stored at −20 °C in 15 mL polycarbonate vials (Falcon) until further analysis. Colorimetric determination was performed using a QuAAtro Continuous Segmented Flow Analyzer (SEAL Analytical, Norderstedt, Germany) as described in Cabanes et al [ 23 ].…”

“…Specifically, experiments were conducted to evaluate the impact of carbohydrates, EPS, and a siderophore using shipboard incubations of natural communities from three distinct regions of the Drake Passage (DP) and Western Antarctic Peninsula (WAP). This represents the first study south of the Polar Front to verify whether EPS enhances phytoplankton growth as reported in the Coral Sea [ 21 ] and identifies whether effects on primary producers can be related to Fe uptake rates published in a companion manuscript [ 23 ]. Moreover, we investigated how these ligands control microbial and viral abundances as well as community diversity in order to identify whether these communities were affected by changes in Fe chemistry, C sources, or changes in primary productivity.…”