Log response ratio of observed versus expected growth rates of Antarctic phytoplankton in response to temperature and nitrogen:phosphorus supply interactions

Data were obtained from a laboratory growth experiment conducted from April to May 2021 at the Institute for Chemistry and Biology of the Marine Environment (University of Oldenburg). Three Antarctic phytoplankton species (Chaetoceros simplex, Phaeocystis antarctica (single cell culture) and Geminigera cryophila) were grown in monocultures and a mixture of all three species. We used a factorial design including four different N/P treatments (control plus three different N/P levels) and 10 different temperatures (-2, -1, 0, 1, 2, 3, 4, 6, 8 and 10°C). The detailed experimental setup is explained in doi:10.1594/PANGAEA.971329. In order to analyze whether the temperature and nutrient response of the mixed assemblage differs from expectations based on the monoculture performance, we calculated the log response ratio between the observed specific growth rate (µobs) of the mixed phytoplankton assemblage and the expected growth rate based on monocultures (µexp) as ln(µobs/µexp). Therefore we calculated an abundance weighted specific growth rate for the expected performance in the mixed assemblage (µexp) based on the monoculture performance as µexp = (a1µ1) + (a2µ2) + (a3*µ3) / (a1+a2+a3) where a is the abundance of each species at exponential growth in the mixed assemblage and µ is the specific growth rate of the corresponding monoculture. Positive deviations from 0 indicate higher observed growth in the mixed assemblage (µobs) than expected from monoculture performance (µexp).