Benthic bacterial secondary production measured via simultaneous 3H‐thymidine and ¹⁴C‐leucine incorporation, and its implication for the carbon cycle of a shallow macrophyte‐dominated backwater system

Abstract

The role of the benthic bacterial community in the carbon cycle of a temperate, macrophyte-dominated oxbow was investigated in a 2-yr study from 1994 to 1996. Simultaneous incorporation of 3 H-thymidine into DNA and 14 C-leucine into proteins was monitored as a tool for the measurement of bacterial secondary production in the aerobic zone of the sediment along with bacterial numbers, morphotype composition, cell volumes, biomass, frequency of dividing cells (FDC), and abiotic variables. Bacterial numbers ranged from 2.5 ϫ 10 9 to 8.5 ϫ 10 9 cells ml Ϫ1 , corresponding to bacterial biomass values of 64 and 288 g C ml Ϫ1, respectively. Both bacterial production methods yielded similar and reliable results over the whole investigation period, varying between 42 and 2,350 g C L Ϫ1 h Ϫ1 for the thymidine method and between 67 and 2,490 g C L Ϫ1 h Ϫ1 for the leucine method, and also corresponded well with the FDC values. Only during late spring and early summer was the thymidine uptake uncoupled from leucine incorporation. Temperature was found to be of significant importance for the variation of all bacterial parameters. In addition carbon inputs from the water column were apparently crucial stimulators of benthic bacterial growth. The spring phytoplankton bloom together with higher temperatures led to a strong positive response of the bacterial community in the sediment. However, the planktonic algal production was not sufficient to cover the benthic bacterial C-demand and, as derived from mass-balance calculations, decaying macrophytes of the previous season seemed to provide the main energy source until the middle of spring. From the middle of August to the beginning of October, the period of maximal biomass of submerged macrophytes, all bacterial parameters exhibited their annual maximum. The benthic bacterial community was dependent on leachates and decay products of the submerged vegetation during this time. Temperature limitation was most probably the reason for the low biomass and production values observed during autumn and winter.

Benthic Bacterial and Fungal Productivity and Carbon Turnover in a Freshwater Marsh

“…Our high bacterial production rates in the aerobic sediment are within the range of rates measured in other freshwater sediments (36,41,75). Although comparable data are not available for naturally decaying plant litter in submerged conditions, data from litterbag studies show bacterial production rates 2 orders of magnitude lower (39,51,66).…”

“…Some estimates of bacterial production in sediments have highlighted the importance of carbon flows through benthic bacterial biomass (up to 160 g C m 2 year Ϫ1 ) (36,41). In macrophyte-dominated wetlands, additional biomass may be produced in epiphytic biofilms (46,67), the water column (43), and particularly plant litter (39).…”

Does Virus-Induced Lysis Contribute Significantly to Bacterial Mortality in the Oxygenated Sediment Layer of Shallow Oxbow Lakes?

“…The Lobau system has been separated from the main stream since the 1870s by a series of embankments, and only one downstream connection remains at the lowest part. A thick sediment layer with a mean depth of 39 cm fills the basin of the oxbow lake (23). Because of its shallowness, the Küh-wörter Wasser is strongly influenced by wind action.…”

Benthic and Pelagic Viral Decay Experiments: a Model-Based Analysis and Its Applicability

“…VDR 0-9 ranged from 0.0282 to 0.0696 h Ϫ1 (mean, 0.0464 h Ϫ1 ), VDR 0-24 ranged from 0.0179 to 0.0286 h Ϫ1 (mean, 0.0214 h Ϫ1 ), and VDR 9-24 ranged from 0 to 0.02 h Ϫ1 (mean, 0.01 h Ϫ1 ). VDR 0-9 as well as VDR [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] were not significantly differ- ent from the corresponding VDR calculated with the linear regression of log-transformed data (Mann-Whitney U test, P Ͼ 0.05; n ϭ 6) ( Table 1). Nevertheless, we favor the exponential decay function because it is derived from the realistic assumption that the decay is proportional to the viral population (see Materials and Methods).…”

“…In order to compare VDR calculated by using the exponential decay function with the other mathematical approaches and time periods previously used in studies concerning viral decay, VDR was calculated in three different ways: (i) with data from the initial 9-h period of the experiments (VDR 0-9 ), (ii) with data from the entire observation period (VDR 0-24 ), and (iii) with data from the period 9 to 24 h (VDR [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] ). VDR 0-9 ranged from 0.0282 to 0.0696 h Ϫ1 (mean, 0.0464 h Ϫ1 ), VDR 0-24 ranged from 0.0179 to 0.0286 h Ϫ1 (mean, 0.0214 h Ϫ1 ), and VDR 9-24 ranged from 0 to 0.02 h Ϫ1 (mean, 0.01 h Ϫ1 ).…”