Dominance of bacterial metabolism in oligotrophic relative to eutrophic waters

Abstract

Heterotrophic bacteria are a key component driving biogeochemical processes in aquatic ecosystems. In 1998, we examined the role of heterotrophic bacteria by quantifying plankton biomass and bacterial and planktonic respiration across a trophic gradient in several small Minnesota lakes as well as Lake Superior. The contribution of bacteria (<1‐ µm fraction) to total planktonic respiration ranged from ~10 to 90%, with the highest contribution occurring in the most oligotrophic waters. The bacterial size fraction constituted a substantial reservoir of planktonic carbon, nitrogen, and phosphorus (14‐58%, 10‐49%, and 14‐48%, respectively), being higher in oligotrophic than in eutrophic waters. However, we saw no clear evidence for the selective enrichment of either nitrogen or phosphorus in the bacteria size fraction relative to total plankton. Carbon : nitrogen and carbon : phosphorus ratios in both the total particulate matter and <1‐ µm fractions were similar and above Redfield values in oligotrophic waters, but approached them in eutrophic waters. Carbon‐based bacterial growth efficiencies (BGE) were variable (4‐40%) but were lowest in oligotrophic systems and increased in eutrophic systems. BGE varied negatively with carbon : nitrogen : phosphorus ratios, suggesting increased maintenance costs in low‐nutrient waters. In oligotrophic waters most of the organic matter is dissolved, supporting a predominantly microbial food web, whereas in eutrophic waters there is an increased abundance of particulate organic matter supporting a food web consisting of larger autotrophs and phagotrophic heterotrophs.

Nutrient and light availability regulate the relative contribution of autotrophs and heterotrophs to respiration in freshwater pelagic ecosystems

“…1) were statistically significant (Table 2). These results are qualitatively similar to those of Biddanda et al (2001) except that, in their study, BR was positively correlated with Chl a concentrations only at low (Ͻ15 g Chl a L Ϫ1 ) concentrations. Their findings suggested that BR attains a maximal rate along a trophic gradient after which it either levels off or decreases (Biddanda et al 2001).…”

“…The use of larger (1.0 m) nominal cutoff filters in the current study minimizes the extent of this problem. Several other studies (e.g., Cimberlis and Kalff [1998] and Biddanda et al [2001]) have successfully used the Ͻ1.0-m-size fraction to quantify heterotrophic bacteria respiration rates. In fact, Biddanda et al (2001) found that Ͼ95% of heterotrophic bacteria found in unfiltered samples consistently passed through the 1.0-m pore-size filters in their study along a trophic gradient in north temperate lakes similar to those in the current study.…”

“…Several other studies (e.g., Cimberlis and Kalff [1998] and Biddanda et al [2001]) have successfully used the Ͻ1.0-m-size fraction to quantify heterotrophic bacteria respiration rates. In fact, Biddanda et al (2001) found that Ͼ95% of heterotrophic bacteria found in unfiltered samples consistently passed through the 1.0-m pore-size filters in their study along a trophic gradient in north temperate lakes similar to those in the current study. Because bacterial abundance and biomass were not determined for either size fraction in this study, we consider the respiration rates observed in the Ͻ1.0-m-size fraction as conservative estimates of heterotrophic bacteria respiration.…”

Body size, energy consumption and allometric scaling: a new dimension in the diversity?stability debate

“…As already mentioned, in stable ecosystems of open ocean and lakes the share of energy consumption by bacteria exceeds 90% (Del Giorgio et al, 1997;Biddanda et al, 2001). The available data on soil bacteria agree with these figures.…”

“…Sprules and Munawar (1986) A similar difference between energy partitioning patterns in stable versus unstable ecosystems can be traced within separate trophic groups. Biddanda et al (2001) measured bacterial respiration in Lake Superior and several small Minnesota lakes, differing greatly in the degree of eutrophy (chlorophyll content from 0.57 to 53 g l −1 ). In the most stable ecosystem of Lake Superior and other oligotrophic lakes bacterial respiration accounts for more than 90% (from 91 to 98%) of the total planktonic respiration.…”