The physiological response of an Antarctic key phytoplankton species to low iron and manganese concentrations

Abstract

Iron (Fe) and manganese (Mn) availability and the divergent requirements of phytoplankton species were recently shown to be potential important drivers of Southern Ocean community composition. Knowledge about Antarctic phytoplankton species requirements for Fe and Mn remains, however, scarce. By performing laboratory experiments and additional calculations of the photosynthetic electron transport, we investigated the response of the ecologically important species Phaeocystis antarctica under a combination of different Fe and Mn concentrations. Fe deprivation alone provoked typical physiological characteristics of Fe limitation in P. antarctica (e.g., lowered growth and photosynthetic efficiency). In comparison, under Mn deprivation alone, the growth and carbon production of P. antarctica were not impacted. Its tolerance to cope with low Mn concentrations resulted from an efficient photoacclimation strategy, including a higher number of active photosystems II through which fewer electrons were transported. This strategy allowed us to maintain similar high growth and carbon production rates as FeMn‐enriched cells. Due to its low Mn requirement, P. antarctica performed physiologically as Fe‐deprived cells under the combined depletion of Fe and Mn. Hence, our study reveals that different from other Southern Ocean phytoplankton species, P. antarctica possesses a high capacity to cope with natural low Mn concentrations, which can facilitate its dominance over others, potentially explaining its ecological success across the Southern Ocean.

The Southern Ocean Hub for Nutrients, Micronutrients, and Their Isotopes in the Global Ocean

“…A consequence is the well-known limitation of Southern Ocean productivity by Fe (Martin et al, 1990;Moore et al, 2013), demonstrated in situ by Fe enrichment experiments carried out around the turn of the millennium (e.g., Boyd et al, 2000;Gervais et al, 2002;Coale et al, 2004). More recently, evidence has emerged that the low Mn concentrations of the surface Southern Ocean can also lead to (co-)limitation of productivity by Mn (Wu et al, 2019;Pausch et al, 2019;Browning et al, 2021;Latour et al, 2021;Balaguer et al, 2022Balaguer et al, , 2023.…”