Production of Sterols and Alkenones in Typical Marine Phytoplankton under Ocean Related Global Change

Ocean global change will concurrently alter environmental factors and profoundly influence marine ecosystems. It remains unclear how the changes in multiple environmental factors affect the biochemical composition of marine phytoplankton, hindering our understanding of the consequences of global change on marine ecosystems. In this study, the diatom Phaeodactylum tricornutum, the cryptophyte Rhodomonas sp. and the haptophyte Emiliania huxleyi were grown under a full-factorial combination of three temperatures, three N:P supply ratios and two pCO₂ levels. The responses of sterols and alkenones were tested and further compared with previous published findings on fatty acids (FAs). Overall, imbalanced N:P supply ratios had a stronger effect on carbon-normalized contents of sterols, total alkenones and FAs than warming and enhanced pCO₂. P deficiency caused an overall increase in most of the three lipid classes, while N deficiency, warming and high pCO₂ caused non-systematic changes. Under future ocean scenarios, we predict an overall decrease in sterols and polyunsaturated fatty acids (PUFAs) in E. huxleyi and P. tricornutum, and a contrasting change in sterols and PUFAs in Rhodomonas sp. The variable contents of major lipid classes indicate a diverse carbon reallocation between marine phytoplankton species in response to the changing environmental conditions. Thus, it is necessary to consider the changes in major lipid classes and their consequences for food webs, when predicting the influence of global change on marine carbon cycle and ecosystem functions.