Effects of temperature and substrate addition (glucose, ammonium or dissolved free amino acid) on bacterial growth were studied in short-term incubations of samples from north, mid and south Chesapeake Bay and a small salt marsh creek, in 1991 and 1992. Bacterial specific growth rates were exponentially and positively correlated with incubation temperature in all seasons studied. Relationships with temperature were consistently similar across different estuarine habitats and chlorophyll concentrations (2 to 5 0 pg I") at incubation temperatures ranglng from 3 to 25OC. Within this temperature range, the average Qlovalue for bacterial specific growth rates was 2.72 + 0.26. Substrate enrichment did not increase bacterial abundance, production and specific growth rate within 24 h when water temperature was <7 "C. At lugher temperatures (>20C), substrate enrichment effects occurred after 3 h incubation although the effect was not consistent across study areas. Temperature-substrate interaction experiments showed that temperature was more effective in regulating bacterial production and specific growth rate than substrate when compared on the same time scale. The substrate enrichment effect on bacterial growth appeared to be temperature dependent. High temperature dependency and the lack of substrate effect on bacterial growth at temperatures < 20C suggested that estuarine bacterial growth was not limited by substrate supply but by temperature during non-summer seasons. Response of bacteria to temperature was uniform across a range of time scales. There was no evidence of adaptation to in situ temperature by bacterial assemblages in different seasons. The seasonal cycle of bacterial growth rate can largely be explained as a physiological response to the in situ temperature by a eurythermal bacterial community.
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Shiah et al. (1994) studied this question.