Limitation by Fe, Zn, Co, and B12 Results in Similar Physiological Responses in Two Antarctic Phytoplankton Species

Abstract

In many areas of the world's ocean such as the Southern Ocean (SO), primary production is low despite an abundance of macronutrients. In these high nutrient low chlorophyll (HNLC) regions the trace metal (TM) iron (Fe) limits phytoplankton biomass and subsequently the biological carbon pump. Besides Fe, the TMs zinc (Zn), cobalt (Co), and the vitamin cobalamin (B 12) have also been shown to limit biomass and/or influence plankton species composition. While the impacts of Fe limitation and, to a lesser degree of Zn and Co, on the cellular physiology of Antarctic phytoplankton have been investigated, studies focusing simultaneously on several TMs and vitamins are still lacking. This study measured the impacts of Fe, Zn, Co, and B 12 limitation on the Antarctic diatom Chaetoceros simplex and Fe and Zn limitation on the Antarctic cryptophyte Geminigera cryophila. Both species responded to all limitation scenarios by reducing their growth and particulate organic carbon (POC) production rates. For both algae limitation by Fe and Zn resulted in a reduction of light harvesting pigments, a significant reduction in the photosynthetic yield (F v /F m) and increase in the C:N ratio. Most interestingly, with a few exceptions, limitation by one TM also resulted in a significant decrease of the cellular quotas of other TMs measured. These observations suggest that one consequence of limitation by one TM may be a secondary and perhaps more fatal limitation by another.

Nutrient Distribution in East Antarctic Summer Sea Ice: A Potential Iron Contribution From Glacial Basal Melt

“…Our positive Fe* values suggest organic ligands should be present in sea ice in excess relative to DFe concentrations, therefore preventing Fe precipitation. Fe does not seem to limit primary production in summer sea ice, although we cannot rule out a potential co‐limitation imposed by other essential micronutrients such as manganese and cobalt (Corami et al., 2005; Koch & Trimborn, 2019; Pausch et al., 2019; Schoffman et al., 2016).…”

Changing Biogeochemistry of the Southern Ocean and Its Ecosystem Implications

“…Iron-manganese co-limitation of phytoplankton growth has been shown for P. antarctica in the Ross Sea in late summer (Wu et al, 2019) and in the Antarctic diatom Chaetoceros debilis (Pausch et al, 2019). The future status of iron-manganese co-limitation may depend in part on the poorly understood effects of ocean acidification on the availability of these metals (Koch et al, 2019). Cobalt in the form of cobalamin (vitamin B 12 ) can also co-limit, with iron, some Southern Ocean phytoplankton species (Moore et al, 2013;Bertrand et al, 2015).…”

“…Because cobalamin can only be produced by bacteria and archaea, as is the case for some strong iron ligands, this points to a critical role for complex phytoplankton−bacteria interactions in regulating Southern Ocean primary productivity. Laboratory experiments investigating the interactions among all of these factors and their combined physiological and biogeochemical implications suggest that a complex and seasonally varying mosaic of limitation scenarios may apply in various subregions of the Southern Ocean and Antarctic shelf waters (Koch and Trimborn, 2019).…”

Efficient zinc/cobalt inter‐replacement in northeast Pacific diatoms and relationship to high surface dissolved Co : Zn ratios

“…In eukaryotes such as diatoms, the transition metal zinc (Zn) is a component of nearly 300 enzymes involved in virtually all aspects of metabolism (Vallee and Auld 1990). In addition to its important role in alkaline phosphatase (Dyhrman and Ruttenberg 2006), zinc‐finger transcription factors (Klug 2010), Cu/Zn superoxide dismutase (Alscher et al 2002; Twining and Baines 2013), and photosystem II efficiency (Koch and Trimborn 2019), Zn 2+ fulfills a catalytic role in carbonic anhydrase enzymes (CAs). It is well established that diatoms and most other aquatic photoautotrophs possess an inorganic carbon‐concentrating mechanism (CCM) in which accumulated inorganic carbon is kept in the chloroplast as HCO 3 − and is rapidly interconverted with CO 2 in a process catalyzed by chloroplastic CAs in the vicinity of ribulose‐1,5‐biphosphate carboxylase/oxygenase (Rubisco).…”