Effects of temperature on growth rate, cell composition and nitrogen metabolism in the marine diatom Thalassiosira pseudonana (Bacillariophyceae)

Abstract

Although temperature effects on phytoplankton growth and photosynthesis can be clearly demonstrated in the laboratory, their relevance in the field is much harder to establish. Recently, however, it has been recognized that temperature has a significant influence on nitrogen uptake. In particular, temperate marine diatom species may be limited by their ability to acquire nitrate at temperatures above approximately 16°C. In order to explore this idea, we grew the diatom Thalassiosira pseudonana at 8, 17 and 25°C, and compared cell composition, and rates of growth (µ), 15 N incorporation, calculated nitrate incorporation (the product of µ and cell N content), and the activity of nitrate reductase (NR), a key enzyme involved in nitrate incorporation. Cell N content, protein and volume remained relatively constant across different temperatures, but cell C, chlorophyll a (chl a), and C:N ratio increased with increasing temperature, suggesting that C metabolism was affected more strongly than N metabolism. Classical temperature models suggested that growth and various indices of nitrate metabolism all responded to temperature, with Q 10 values of close to 2 over the whole temperature range. However, Q 10 values over the interval from 8 to 17°C were higher than 2 and much lower than 2 between 17 and 25°C. Limitations to the Q 10 concept are considered. Temperature effects on different measures of nitrate metabolism were very similar, supporting the hypothesis that the effects of temperature on diatom nitrate metabolism are mediated at the level of NR activity. Recent biochemical data for NR also supports this idea.

The Response of Diatom Central Carbon Metabolism to Nitrogen Starvation Is Different from That of Green Algae and Higher Plants

“…For the purpose of this study, this point is considered to be the onset of nitrogen starvation. Furthermore, assuming a total nitrogen content of 1 pg per T. pseudonana cell (Berges et al, 2002;S. Chollet, personal communication), we calculate that, based on cell numbers, the medium of the low-nitrate cultures would have been completely depleted of nitrate and that to support the cell density achieved the total cell nitrogen must be reduced, as suggested by the decline in the cellular content of nitrogenous compounds reported.…”

Nitrate Assimilation: The Role of In Vitro Nitrate Reductase Assay as Nutritional Predictor

“…Nitrate reductase activity is temperature sensitive over a narrow range, with several optimum temperatures for the various species, depending on the habitat. For temperate macroalgae, this ranges from 10 to 25 °C (Gao et al, 2000;Berges et al, 2002;Chow et al, 2004). Activities at low temperatures may require a larger amount of NR protein or higher catalytic rates to so maintain the same catalytic activity, as during low winter temperatures enzymes function below the optimum.…”

Phytoplankton community response to Fe and temperature gradients in the NE (SERIES) and NW (SEEDS) subarctic Pacific Ocean

“…Only a few degrees change in temperature significantly influences the growth and nitrogen metabolism of phytoplankton (Berges et al, 2002;Kudo et al, 2002, Lomas andGlibert, 1999;Suzuki and Takahashi, 1995).…”