Biomass, production, and specific growth rate of bacterioplankton and coupling to phytoplankton in an oligotrophic lake

Abstract

Production of bacterioplankton and phytoplankton was analyzed in oligotrophic Lawrence Lake, Michigan, over a 2‐yr period. Variables examined were temperature, bacterial numbers and biovolumes, bacterial production and specific growth rates (µ), phytoplanktonic biomass and production, and alkaline phosphatase activity. Algal and bacterial production varied similarly on temporal and spatial scales; some differences in vertical patterns were evident during summer stratification. Values for µ ranged from 0.2 d‒1 during winter to 2.6 d‒1 in midsummer. Decreases in specific growth rates of bacteria coincided with the onset of heavy CaCO3 precipitation and with increased alkaline phosphatase activities. µ was close to predicted maximal values during periods of mixing but was depressed in upper layers during summer. Temperature showed significant bivariate rank correlations with all variables. With temperature controlled, µ did not show significant partial correlations with algal chlorophyll or production, consistent with a minor role of dissolved organic carbon from phytoplankton for bacterial growth. Low and high estimates of bacterioplanktonic production over 2 yr exceeded that of phytoplankton by factors of 1.33 and 3.35. Net metabolism in the pelagic zone was heterotrophic, a state likely maintained by littoral macrophytic and periphytic production. Apparent coupling between phyto‐ and bacterioplankton stemmed mainly from similar responses of each component to common regulating factors rather than from direct metabolic links.