CO2, temperature, light, N and P are necessary factors for growth of phytoplankton. Rising carbonate dioxide (CO2) levels in the atmosphere lead to increasing CO2 concentration and declining pH in seawater, as well as ocean warming. This enhances stratification and shoals the upper mixed layer (UML), hindering the transport of nutrients from deeper waters and affect light intensity exposed by phytoplankton. Effect of one environmental factor on physiological processes is modulated by other environmental factors. This report will show combined effects of CO2, temperature, light intensity, dissolved inorganic nitrogen (DIN) and phosphate (DIP) concentrations on physiological rates of coccolithophore, and effects of rising temperature and CO2 on photosynthetic carbon fixation of phytoplankton community in western South China Sea.
In all incubations in the laboratory, high temperature increased growth of coccolithophore and high CO2 level inhibited growth of coccolithophore. High CO2 level, low dissolved inorganic nitrogen and phosphate concentrations synergistically reduced growth rates of coccolithophore. High light intensity and low dissolved inorganic phosphate concentration increased particulate organic carbon quota. High temperature, high light intensity and low nutrient concentrations synergistically increased calcification rates of coccolithophore.
In the shipboard culture experiment, rising temperature and CO2 individually increased primary productivity of phytoplankton assemblages in all sites, whereas high temperature and high CO2 level did not increase primary productivity synergistically. Rising temperature increased primary productivity at low CO2 level whereas decreased primary productivity at high CO2 level. High temperature decreased the Chl a concentrations in the off-shore waters at low CO2 level, and did not affect Chl a concentrations in the coastal waters at both LC and HC conditions. These results suggest that we should investigate the combined effects of changes in multiple environmental factors on physiological rates of phytoplankton and the mechanisms behind physiological processes in order to understand the responses of phytoplankton functional groups to marine environmental changes.