REGULATION OF PLANKTONIC BACTERIAL-GROWTH RATES - THE EFFECTS OF TEMPERATURE AND RESOURCES

We examined the potential limitation of bacterial growth by temperatur e and nutrients in a eutrophic lake. Dilution cultures from winter and summer were incubated at both high (>20 degrees C) and low (4 degrees C) temperatures and enriched with various combinations of organic car bon (C), inorganic nitrogen (N), and inorganic phosphorus (P). Bacteri al abundance, H-3-thymidine incorporation, and H-3-leucine incorporati on were measured over the growth cycle. For both winter and summer ass emblages, low temperature limited growth even when resources (C, N, an d P) were added. When temperature was adequate, bacterial growth in di lution cultures was co-limited by C, N, and P. Additions of either C, P, or N and P alone provide little or only modest stimulation of growt h, suggesting that under in situ conditions both nutrients and organic carbon limit bacterial growth. Our results provide little evidence of seasonal adaptation to low temperatures for bacterial communities in temperate lakes. Instead, bacterial growth appears to be temperature l imited during winter and resource limited during summer. We propose th at, in general, bacterial growth rates are temperature dependent up to a threshold, but that the patterns of change across temperature gradi ents are resource dependent, such that temperature has little effect o n growth in resource-rich environments but a strong effect in resource -poor environments.