Planktonic bacterial respiration as a function of C:N:P ratios across temperate lakes

Abstract

Bacterioplankton and total planktonic community respiration were measured in 14 Canadian lakes during the summer. Total planktonic community respiration (O2 consumption and CO2 production) was best predicted by total phosphorus (TP), with respiratory rates increasing at higher TP levels. The bacterioplankton respiration alone was less well linked to nutrient concentrations. Yet, the rates of both planktonic and bacterial CO2 production changed similarly with changes in the C:N ratio, with the bacterial fraction, on average, contributing about 42% of the total planktonic respiratory rates. Bacterial carbon respired was uncoupled from oxygen consumption, with resultant average planktonic respiratory quotient (RQ) close to 2. Bacterioplankton respiratory rates are affected by a negative relationship between specific aerobic respiration and bacterial biomass. Higher bacterial specific oxygen consumption rates (µg O2 cell-1 d-1) were observed with increasing C:N and C:P ratios, suggesting an increase in maintenance cost at the low cell densities observed in oligotrophic waters. Phosphorus appeared as the limiting nutrient in these lakes and determined total planktonic respiratory rates, however, epilimnetic bacterial respiration was mainly related to the DOC: nutrient ratios.