HNLC (High Nutrient Low Chlorophyll) regions account for approximately 30% of the ocean.  In which the extremely low iron concentration may limit the growth of marine phytoplankton, which require relatively large amounts of iron to meet their physiological needs. To acquire iron from the surface seawater in which iron exists as various chemical forms, different marine phytoplankton are suggested to take up iron through different efficient pathways. Amoung these, three major pathways have been propsed, that is uptake of labile Fe, reduction-dependent iron uptake pathway, and siderophore-mediated iron uptake pathway. However, the relative importance of these pathways under differental environmental conditions across the ocean remains poorly understand. Here, we use growth inhibition assays with BPDS to investigate the importance of reduction-dependent iron uptake pathway in different marine phytoplankton grown in medium with different Fe substartes. To verify the laboratory culture results and investigate the importance of reduction-dependent iron uptake pathway in field population, we performed a series of microcosm experiements. Combined laboratory and microcosm experiments suggest the prevalence and importance of reduction-dependent iron uptake pathway in marine phytoplankton.