Temperature effects on steady-state growth, phosphorus uptake, and the chemical composition of a marine phytoplankter

The marine chrysophyteMonochrysis lutheri was grown in phosphorus-limited continuous cultures at temperatures of 15°, 18.8° and 23°C. The effect of temperature on the maximum growth rate was well-defined by the Arrhenius equation, but the Q10 for this alga (1.7) was somewhat lower than has been determined previously for many other phytoplankton species (2.0-2.2). The minimum phosphorus cell quota was relatively unaffected by temperature at 18.8°C and 23°C, but doubled in magnitude at 15°C. As a result, the internal nutrient equation of Droop described the relationship between specific growth rate and phosphorus cell quota well at 18.8° and 23°C, but was less successful at 15°C. The major limitation in using the Droop equation is that the ratio between the minimum and maximum cell quotas must be known, thus necessitating the need to establish the true maximum growth rate by the cell washout technique. In addition, the phosphorus uptake rate on a cell basis at a given steady state growth rate (=specific uptake rate) increased dramatically at 15°C, whereas the turnover rate of total available phosphorus was unaffected by temperature. Both the nitrogen and carbon cell quotas were relatively unaffected by growth rate at a given temperature, but the average values increased slightly with decreasing temperature. The overall conclusion is that phytoplankton growth and limiting-nutrient uptake rates are only synchronous at or near the optimum temperature. Because these types of responses are species specific, much additional data on temperature effects will be required before the importance of including such effects in phytoplankton-nutrient models can be determined.