Physiological control on carbon isotope fractionation in marine phytoplankton

[摘要] One of the great challenges in biogeochemical research over thepast half a century has been to quantify and understand the mechanismsunderlying stable carbon isotope fractionation ( ε p ) inphytoplankton in response to changing CO 2 concentrations. This interest is partly grounded in the use of fossil photosynthetic organismremains as a proxy for past atmospheric CO 2 levels. Phytoplanktonorganic carbon is depleted in 13 C compared to its source because ofkinetic fractionation by the enzyme RubisCO during photosynthetic carbonfixation, as well as through physiological pathways upstream of RubisCO.Moreover, other factors such as nutrient limitation, variations in lightregime as well as phytoplankton culturing systems and inorganic carbonmanipulation approaches may confound the influence of aquatic CO 2 concentrations [CO 2 ] on ε p . Here, based onexperimental data compiled from the literature, we assess which underlyingphysiological processes cause the observed differences in ε p for various phytoplankton groups in response to C-demand/C-supply, i.e., particulate organic carbon (POC) production  /  [CO 2 ]) and test potential confounding factors.Culturing approaches and methods of carbonate chemistry manipulation werefound to best explain the differences in ε p betweenstudies, although day length was an important predictor for ε p in haptophytes. Extrapolating results from culturing experiments tonatural environments and for proxy applications therefore require caution,and it should be carefully considered whether culture methods andexperimental conditions are representative of natural environments.

[学科分类] 大气科学