MEPS 412:57-68 (2010)  -  DOI: https://doi.org/10.3354/meps08701

ABSTRACT: Understanding the response of diatoms to nutrient stress is important, both on its own terms and for the accurate portrayal of this key group of organisms in ecological and biogeochemical models. We therefore examined the growth and elemental composition of Thalassiosira weissflogii grown to nutrient depletion and then its recovery after nutrient readdition. During nitrate starvation, T. weissflogii continued dividing, producing cells with low quotas of N, P and Si. After nitrate readdition, cells immediately began taking up nitrate at relatively low net cell-specific rates and rebuilding cellular stores of all nutrients. More than 30 h elapsed before there was a visible increase in cell numbers. Cellular C/N and C/P ratios remained high and N/P ratios remained low for the remaining 45 h of the experiment. Cells in the silicon starvation experiment abruptly ceased dividing at 1 to 3 µM dissolved silicon (DSi) and immediately resumed dividing upon the resupply of DSi. Growth rates and net cell-specific rates of silicon uptake recovered to maximal values within 3 to 7 h, but net cell-specific rates of nitrate and phosphate never did, causing a decline in N and P content per cell during the whole experiment. Ratios of C/N and N/P remained close to Redfield values. While cell-specific rates of silicon uptake correlated strongly with DSi concentrations during all portions of the silicon starvation experiment, they were directly related to cellular growth rates during the nitrogen starvation experiment, suggesting that during nitrate starvation silicon acquisition was acting as the rate-limiting step for cell division.

KEY WORDS: Thalassiosira weissflogii · Nitrogen starvation · Silicon starvation · C/N · Si per cell