Effect of nitrogen source on the thermal tolerance of different strains of the symbiotic dinoflagellate Breviolum minutum in culture and within a cnidarian host

Capista, Jessica
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University of Delaware
Symbiotic cnidarians often occupy oligotrophic environments but are able to thrive due to their dinoflagellate symbionts, however, rising temperatures and changing nutrient regimes put this symbiosis at risk of bleaching. Bleaching response is highly dependent on nutrient concentration, nitrogen form, and stoichiometry, as moderate NO3- enrichments, especially in the absence of balanced phosphorus additions have been linked to increased bleaching while moderate NH4+ enrichments are associated with increased thermal tolerance. Despite these differential responses, the underlying mechanisms driving these outcomes are not well understood. Since algal photosystem II (PSII) is a central target of bleaching, I hypothesized the additional energy requirement of reducing NO3- to NH4+ in the chloroplast was driving electrons away from photosynthesis and slowing PSII protein repair rates, thus leading to increased damage. I investigated how NO3- and NH4+ in tandem with heating effected Breviolum minutum in culture and within the cnidarian host, Exaiptasia diaphana. Contrary to previous work on coral hosts, I did not find a clear differential response based on nitrogen form in culture or within a sea anemone host. Additionally, a bleaching response was observed as a loss of algal cells in culture and in hospite but PSII did not appear to be damaged. My findings highlight the importance of assessing multiple cnidarian hosts and closer examining how both the algae and the host respond to better predict how these organisms will respond to future climate conditions.
Nitrogen , Symbionts