Thalassiosiroid diatom responses to silicon stress and ocean acidification

Atmospheric CO2 has risen dramatically since the industrial revolution. This rise in atmospheric and oceanic pCO2 has perturbed ocean carbonate chemistry and led to ocean acidification. Diatoms are phytoplankton that account for 40% of oceanic primary production through photosynthetic carbon fixation, which is aided by their carbon concentrating mechanism (CCM). The CCM uses the bicarbonate transporters (BCTs) and carbonic anhydrases (CAs). Our current understanding of how diatoms might respond to ocean acidification is based on experiments using model diatoms or assessing the response of the bulk diatom community, rather than assessing a diversity of diatoms in a complex environment. This dissertation aims to expand our knowledge regarding diatom response to CO2 in ecologically important, non-model diatoms and their response in laboratory experiments and field mesocosms to alterations in CO2 concentration.

Diatoms’ primary production is a function of their growth, which is constrained by the availability of nutrients in the surface ocean. Silicon is a nutrient that is particularly important for diatoms, as they are unique in their requirement for silicon to build their cell walls. Silicon limitation has been observed in low iron high nutrient low chlorophyll (HNLC) regions and the North Atlantic Ocean, although these studies have focused on the whole diatom community rather than specific diatom groups that may not uniformly experience silicon limitation. Genetic markers have been used to probe species-specific iron status in the field, and similar molecular markers of silicon status could be powerful tools to probe the silicon status of different co-existing diatom species. However, current studies of silicon limitation have relied on model diatoms rather than species that are likely to be found in HNLC regions or the North Atlantic Ocean, limiting the ability to develop appropriate molecular markers. This dissertation aimed to fill in these knowledge gaps using transcriptomic studies of Thalassiosiroid diatom isolate cultures as well as incubations of mixed diatom assemblages.

Wallace J., 2018. Thalassiosiroid diatom responses to silicon stress and ocean acidification. PhD thesis. University of Rhode Island. Thesis (restricted access).

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