Two-way and multiple-factorial effects of OA and other environmental Drivers on the physiology and gene expression of marine coccolithophore Emiliania huxleyi

Chair: Alistair Hobday

Yuanyuan Feng (1), Michael Roleda (2), Evelyn Armstrong (3), Cliff Law (4), Philip Boyd (5), Catriona Hurd (5)

1 College of Marine and Environmental Science, Tianjin University of Science and Technology, Tianjin, 300457, China
2 Bioforsk Norwegian Institute for Agricultural and Environmental Research, Bodø, 8094, Norway
3 NIWA/University of Otago Research Centre for Oceanography, Department of Chemistry, University of Otago, Dunedin 9054, New Zealand
4 NIWA, Greta Point, Wellington 6023, New Zealand
5 Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, 7005, Australia

Background
Concurrent changes in multiple environmental drivers affect the physiology of marine phytoplankton, both individually and interactively, in a complex way. Emiliania huxleyi, the most abundant and widely-distributed coccolithophore in the ocean, is a model organism for understanding the marine carbon cycle.

Methods
Southern Hemisphere E. huxleyi strain NIWA1108, isolated from the Chatham Rise, New Zealand, was subjected to a two-way (OA plus changes in either nitrate concentration, phosphate concentration, irradiance or temperature) and multiple factorial (manipulation of all the five environmental drivers) manipulation experiment. The degree of change for each environmental driver was based on the model-projected conditions for year 2100 in the Chatham Rise area.

Findings
The results suggest that interaction of OA and a 33% decrease in nitrate concentration had the largest synergistic negative effects on most of the E. huxleyi physiological metrics among all the two-way factorial manipulations. The simultaneous manipulation of all the five environmental drivers to the projected future (2100) conditions had the most prominent negative effects on E. huxleyi growth, photosynthetic and calcification rates. The gene expression study suggests that changing pCO2 probably affects E. huxleyi photosynthesis and calcification through regulating carbon concentrating mechanism (CCM) and pH homeostasis at the molecular level. Furthermore, the substantial down-regulation of most of the investigated genes associated with inorganic carbon acquisition and calcification by multi-factorial manipulation of all the five environmental drivers indicate a link between significant suppress of functional genes and the substantially decreased physiological rate processes (growth, photosynthetic and calcification rates) in E. huxleyi.

Conclusions
This study reveals that interplay between OA and other environmental drivers is likely to have antagonistic, additive or synergistic effects on different physiological metrics of E. huxleyi. The findings contribute to our understanding of how the physiology of E. huxleyi will respond to the concurrent changes of multiple environmental drivers.