A recent study using Fe-limited phytoplankton strains, showed that iron (Fe) uptake rates normalized by cellular surface area were best related to dissolved iron (dFe) concentrations as the inorganic Fe (Fe’) supply rates were not sufficient to satisfy the Fe biological demand. Short-term (24 h) shipboard incubations with the in-situ phytoplankton community were used to measure Fe uptake rates that were normalized per biomass (as particulate organic carbon, POC). Fe uptake rates measured following ⁵⁵FeCl₃ additions (0.05 to 0.9 nM) were fitted to different Fe pools (dFe, Fe_labile, and Fe’) using the Michaelis-Menten equation. Data showed a similar high conditional stability constant for biological transporters across all sites and phytoplankton size classes, with only a 2-fold variation in the concentrations of cellular transporters. These observations are in line with previous reports that eukaryotic phytoplankton takes up Fe close to the limit imposed by transporters cellular density and uses similar high-affinity Fe uptake systems. To further explore the link between Fe uptake rates and Fe chemistry, we also studied the effect of Fe additions preequilibrated with different Fe-binding ligands (L) including: the siderophore desferrioxamine B, two carbohydrates (glucuronic acid and carrageenan) and two different bacterial exopolycarbohydrates (L₆ and L₂₂, referred as EPS). For all stations, phytoplankton were able to acquire Fe associated to DFB as previously reported, however, different Fe:L ratios prevent quantitative comparison with other studies. Iron bound to carbohydrates, glucuronic acid, carrageenan and EPS could enhance or decrease Fe uptake rates in comparison to equimolar FeCl₃ addition. These results illustrate that the effect of such L on Fe uptake rates will depend on the in-situ plankton community and their chemical structure. The variation of the Fe’ concentrations was able to explain up to 69% of the Fe uptake rates observed for the Antarctic communities. This relationship with Fe’ was related to the fact that the Fe’ maximal supply, due to the dissociation of FeL, was enough to satisfy the measured Fe uptakes rates. Calculations using previous reports in contrasted regions of the Southern Ocean, showed that Fe’ maximal supply was greater than Fe uptake rates measured in 80% of the cases. Moreover, considering photo- and redox-chemistry as well as kinetical situations prevailing in the field, Fe’ should not be overlooked as a pool able to satisfy most of the Fe biological demand. Finally, this study points towards the potential that the GEOTRACES Fe chemical speciation data represent to explore Fe uptake rates at a larger scale in this vast Fe-limited oceanic region.

最近一项使用有限Fe浮游植物菌株的研究表明，通过细胞表面积归一化的铁（Fe）吸收率与溶解的铁（dFe）浓度最相关，因为无机Fe（Fe'）的供应速率不足以满足Fe生物需求。在船上与原位浮游植物群落进行的短期（24小时）温育中，用于测量每个生物量（以颗粒有机碳，POC为标准）的铁摄取率。将^55种FeCl ₃加入（0.05至0.9 nM）后测得的Fe吸收率拟合到不同的Fe池（dFe，_不稳定的Fe），和Fe'）使用Michaelis-Menten方程。数据显示跨所有位点和浮游植物大小类别的生物转运蛋白具有相似的高条件稳定性常数，而细胞转运蛋白的浓度只有2倍的变化。这些观察结果与以前的报道相符，即真核浮游植物吸收的Fe接近转运蛋白细胞密度所施加的极限，并使用类似的高亲和性Fe吸收系统。为了进一步探索铁吸收速率与铁化学之间的联系，我们还研究了用不同的铁结合配体（L）预平衡的铁添加的影响，这些配体包括：铁载体去铁草胺B，两种碳水化合物（葡萄糖醛酸和角叉菜胶）以及两种不同的细菌外聚碳水化合物（L ₆和L ₂₂，称为EPS）。如先前所报道，对于所有站，浮游植物都能够获得与DFB相关的Fe，但是，不同的Fe：L比值妨碍了与其他研究的定量比较。与添加等摩尔的FeCl ₃相比，与碳水化合物，葡萄糖醛酸，角叉菜胶和EPS结合的铁可以提高或降低铁的吸收率。这些结果表明，这种L对铁吸收速率的影响将取决于原位。浮游生物群落及其化学结构。Fe'浓度的变化能够解释南极群落中69％的Fe吸收率。与Fe'的这种关系与以下事实有关：由于FeL的解离，Fe'的最大供给量足以满足测得的Fe摄取率。使用先前报告对南大洋的对比区域进行的计算表明，在80％的情况下，Fe的最大供给量大于Fe的摄取率。此外，考虑到光化学和氧化还原化学以及该领域中普遍存在的动力学情况，不应将Fe'视为能够满足大多数Fe生物需求的物质库。最后，