Inorganic Phosphorus Stimulation of Bacterioplankton Production in a Meso-Eutrophic Lake

Abstract

Experiments were conducted to determine whether production of heterotrophic bacterioplankton in a small meso-eutrophic lake was influenced by the dissolved inorganic phosphorus (DIP) supply. DIP may indirectly limit bacterial production by limiting phytoplankton, which in turn may limit the carbon available to bacteria. Direct DIP limitation of bacteria occurs where the availability of DIP for bacteria is insufficient to maintain growth. This work examined direct DIP limitation of bacteria by removing phytoplankton and incubating flasks with or without added P in the dark. Bacterial production was measured via the rate of incorporation of [3lH]thymidine ([3HlTdR) into DNA. Bacterial abundance was followed with epifluorescent direct counts. Rates of [3HjTdR incorporation were significantly greater in flasks with added DIP, and changes in cell abundances generally paralleled increases in [3HjTdR incorporation. Even very small additions of P (0.05 ,uM) were sufficient to stimulate production. DIP addition to whole lakewater also stimulated [3H]TdR incorporation relative to that in zero-addition controls, but there was not a concurrent increase in bacterial cell numbers. The stimulation of [3H]TdR incorporation after DIP addition to whole lakewater was significantly less than the stimulation due to DIP addition to 1-jim-pore-size-filtered lakewater. In this study, addition of DIP caused as much as an eightfold stimulation of [3H]TdR incorporation.

Influence of phytoplankton on the response of bacterioplankton growth to nutrient enrichment

“…Inorganic P and N enrichments stimulated bacterioplankton specific activity in four of our five 6.0 treatments regardless of the presence or absence of phytoplankton activity (Figs lb,2a,b & c), indicating that inorganic P and N can directly limit bacterioplankton growth in our study lake. Such results are supported by recent reports of inorganic P stimulation of bacterioplankton growth in an oligotrophic lake (Coveney & Wetzel, 1992) and in a mesoeutrophic lake (Toolan et al, 1991). Our results, in concert with those of others, do not support the common view that the growth of bacterioplankton in nutrientdeficient lakes is always limited by the availability of reduced carbon substrates (Currie & Kaiff, 1984).…”

“…Such a relationship is supported by the positive correlations observed between bacterioplankton production and phytoplankton biomass (Fuhrman, Ammerman & Azam, 1980;Cole, Findlay & Pace, 1988;White et al, 1991). Recent studies have shown that bacterioplankton growth rates can be stimulated directly by inorganic P enrichment in both oligotrophic (Coveney & Wetzel, 1992) and mesotrophic lajfe water (Toolan, Wehr & Findlay, 1991). These reports are consistent with the fact that bacterioplankton inorganic P and N uptake systems have higher affinities for P and N than those of phytoplankton (Currie & Kalff, 1984;Currie, Bentzen & Kalf, 1986;Vadstein & Olsen, 1989).…”

Seasonal differences in bacterial community composition following nutrient additions in a eutrophic lake

“…Past studies indicate that P generally limits microbial growth in lakes (reviewed by Vadstein, 2000), including eutrophic lakes like Lake Mendota (Toolan et al, 1991). In our study, the SRP pool (often considered the most bioavailable fraction) was not exhausted and the APA [a proxy for P starvation (Jurgens et al, 1999)] changed little in each season following P amendment ( Fig.…”

Impacts of suspended sediment on the ecosystem in Lake Michigan: A comparison between the 1998 and 1999 plume events

“…This feature remained unchanged from 1998 to 1999, although the sediment resuspension frequencies, spatial distributions and intensities of plumes between these 2 years were significantly different. The role of bacteria in freshwater ecosystems has received a great deal of attention in recent field measurements [Toolan et al, 1991;Coveney and Wetzel, 1992;Morris and Lewis, 1992;Cotner, 2000]. Moreover bacteria are important competitors with phytoplankton for dissolved inorganic phosphorus (DIP) [Currie and Kalff, 1984;Cotner and Wetzel, 1992;Vadstein et al, 1993].…”