AME 20:31-38 (1999)  -  doi:10.3354/ame020031

ABSTRACT: Bacterial secondary production transforms organic C from the environment into new bacterial biomass. Bacterial respiration generates energy and converts assimilated organic C into CO₂. Two decades of research have given us a good understanding of the magnitude and regulation of bacterial production in pelagic ecosystems, but much less is known about bacterial respiration. Bacterial growth efficiency [BGE = BP/(BP + BR)] relates measurements of bacterial production and respiration. Recent reviews demonstrate a large range in BGE among and within systems; the regulation of this variance is not well understood. We made direct measurements of both BP and BR over a full seasonal cycle in the Hudson River, New York, and in a series of manipulative experiments. BGE was well correlated with BP and ranged from 0.04 to 0.66, with a majority (69%) between 0.2 and 0.5. BR and BP were correlated (r = 0.65; p < 0.0001) but BR was less variable than BP. Thus, much of the variation in BGE could be explained by the variation in BP. The relationship (based on 24 h bioassays) between BP and BGE fit a rectilinear hyperbola [BGE = 0.10 + 0.68BP(5.21 + BP)] and explained 70% of the variation in BGE (p < 0.001). During the relatively long incubation (24 h) required to measure BR, conditions diverge from ambient. BP, BR and BGE all increase during this incubation period. We used the relationships between BGE and BP and BR (above) to calculate realistic ambient estimates of BGE from short-term measurements (<1 h) of BP. Based on this approach, modeled BGE for the Hudson averaged 0.16 ± 0.05 (range = 0.07 to 0.23), about 50% lower than the values based on 24 h bioassays. Using this relationship we estimate pelagic BR in the tidal, freshwater Hudson River to be between 176 and 229 g C m^-2 yr^-1.

KEY WORDS: BGE · Bacterial metabolism · Production · Respiration · Estuary · River · Ecosystems