Growth rate relationships to physiological, indices of nutrient status in marine diatoms

The growth of two species of marine diatom, Thalassiosira weissflogii (Grun ow) and Thalassiosira pseudonana (Hustedt), was followed in batch cultures at four concentrations of dissolved inorganic carbon from N- and C-replete lag phase into N- and/or C-deplete stationary phase. Results describe the r elationship between carbon-specific growth rate (mu (C)) and chi EI:carbon (chl a:C) and glutamine:glutamate (gln:glu) ratios with changes in the cell s' nutritional status (N:C), during the utilization of either NO3- or NH4+. The use of the gln:glu ratio as an index of N:C requires further clarifica tion. For both species and N sources, N stress resulted in a decrease in mu (C), chi a:C, and N:C relative to mu (Cmax) values, whereas C stress resul ted in a decrease in mu (C) and an increase in chi a:C and N:C relative to mu (Cmax) values. Both species attained a chi a:C ratio of approximately 15 mug.g(-1) at mu (Cmax) using either N source. However, this value was not necessarily an indicator of maximal growth rate. NC colimitation resulted i n decreased mu (C) to values less than 20% of mu (Cmax) with only minor cha nges in chi a:C and N:C relative to mu (Cmax) values. Chi a:C results sugge st a similarity between the light stress and C stress responses of marine d iatoms, The potential for C stress in the marine environment needs to be ad dressed.