Coulometric carbonߚbased respiration rates and estimates of bacterioplankton growth efficiencies in Massachusetts Bay

Abstract

Heterotrophic bacterioplankton production rates have been measured in many aquatic ecosystems over the last two decades, whereas measurements of bacterioplankton respiration rates have been scarce. This paper reports and discusses measurements of carbon-based plankton respiration rates made in a coastal ecosystem over an annual cycle. The coulometric technique was used to measure total inorganic carbon (TCO 2 ) production rates in 0.8-m filtered and unfiltered Massachusetts Bay surface seawater. Bacterioplankton respiration rates, defined as respiration in 0.8-m filtered seawater, varied from 0.01 to 0.15 mol C kg Ϫ1 h Ϫ1 (0.07 Ϯ 0.01 mol C kg Ϫ1 h Ϫ1 ) (mean Ϯ 1 SE) and accounted for a high proportion (median 70%) of respiration in unfiltered seawater. Microplankton (unfiltered seawater) respiration rates varied from 0.04 to 0.24). Bacterioplankton growth efficiencies (BGEs), estimated with concurrent measurements of bacterial production and respiration rates, varied from 0 to 69% (median 22%) and were well correlated with specific production rates (r 2 ϭ 0.67). To assess carbon flow in aquatic ecosystems, BGEs should be measured when possible because of their high variability. Compared with bacterioplankton specific production rates, bacterioplankton specific respiration rates were relatively constant (0.05 Ϯ 0.01 fmol CO 2 cell Ϫ1 h Ϫ1 ). Given the apparent uncertainty in the values of respiratory quotients (Toolan 1996; Robinson and Williams 1999), carbon-based comparisons of microbial respiration and primary production rates will improve evaluations of the role of the coastal ocean in the global carbon cycle.Relative to the plentiful literature on microbial productivity (growth rates of autotrophs and heterotrophs), respiratory activity in marine ecosystems has been understudied (Williams 1984;Biddanda et al. 1994;Jahnke and Craven 1995). Measurement of respiration rates in seawater has challenged oceanographers for decades because of the high precision required to measure small changes of 0.01-1 mol kg Ϫ1 h Ϫ1in O 2 or total inorganic carbon (TCO 2 ) relative to the naturally high background concentrations of O 2 (ϳ200 mol O 2 kg Ϫ1 ) and TCO 2 (ϳ2,000 mol C kg Ϫ1 ). Advances in endpoint detection and automation have increased the precision of the Winkler titration and made O 2 utilization rates in seawater measurable (Pomeroy et al. 1994 and references therein). It is now possible to estimate carbon-based respiration rates with the highly precise coulometric technique, wherein a seawater sample is acidified, and evolved CO 2 reacts with ethanolamine to form hydroxyethylcarbamic acid; the number of moles of OH Ϫ that are generated to titrate the acid is related by the Faraday constant to the product of current and

Relationship of bacterial growth efficiency to spatial variation in bacterial activity in the Hudson River

“…Most studies of BR to date have assumed that the filtered fraction represents the majority of microbial metabolism (i.e. Biddanda et al 1994, 2001, Pomeroy et al 1994, Obernosterer et al 2003, Reinthaler & Herndl 2005, but our results show that the approach tends to significantly underestimate BR. Further, because retention of bacterial activity in filters is not uniform and probably depends on the particulate load, size and attachment of bacteria, DOC and colloidal matrix, and type of filter used, key aspects of microbial carbon dynamics in situ might be masked or entirely changed by filtration artifacts.…”

“…Since their paper, there has been a renewed interest in BGE and a large increase in the number of measurements reported for a wide range of aquatic ecosystems. It is now clear that BGE is, as Jahnke & Craven (1995) argued, variable, and that most values are generally well below 40% (del Giorgio & Cole 1998, Toolan 2001, Pradeep Ram et al 2003, Reinthaler & Herndl 2005. In spite of these advances, the fundamental problem posed by Jahnke & Craven (1995) has never been adequately answered: 'To what extent are the spatial and temporal variations in the magnitude of BP in aquatic ecosystems driven by environmental processes that control overall carbon availability and consumption by bacteria, versus processes that control how this carbon is processed, i.e.…”

Planktonic community production and respiration and the impact of bacteria on carbon cycling in the photic zone of Lake Kinneret

“…Others have quantified BR directly by following the increase in ambient dissolved inorganic carbon (Cole et al 1989) or, more frequently, by determining O 2 uptake in water samples that were pre-filtered in order to exclude phytoplankton and protozoans (e.g. Hopkinson et al 1989, Biddanda et al 1994, 2001, Roland & Cole 1999, Sherry et al 1999, Rivkin & Legendre 2001, Smith & Kemp 2003. Unfortunately, the method of estimating BR using filtration followed by a lengthy (usually ~24 h) incubation step radically changes the environment in which BR determinations are made by altering the patterns of organic carbon cycling in these samples.…”

“…Recently, Toolan (2001) successfully applied coulometric respiration measurement on filtered and unfiltered samples to directly estimate BR and CR with onlỹ 10 h incubation. Measurements of electron transport system (ETS) activity (Packard 1971) have also been used to quantify planktonic respiration.…”

Thermal effects on heterotrophic processes in a coastal ecosystem adjacent to a nuclear power plant

“…Of organisms < 300 µm, heterotrophic bacteria have been considered to be the major consumers of O 2 , due to their larger surface area to volume ratio. Bacterial respiration (BR) alone has been shown to contribute as much as > 70% to the total microplankton CR (Toolan 2001). High BR values have been suggested to be the major factor determining the heterotrophic status of many coastal and even oceanic ecosystems (Smith & Hollibaugh 1993, del Giorgio et al 1997, Duarte & Agusti 1998.…”