Fk. Shiah et Hw. Ducklow, REGULATION OF BACTERIAL ABUNDANCE AND PRODUCTION BY SUBSTRATE SUPPLY AND BACTERIVORY - A MESOCOSM STUDY, Microbial ecology, 30(3), 1995, pp. 239-255
Daily bacterial abundance and production, heterotrophic nanoflagellate
s (HNAN) abundance, chlorophyll, and NH4+ concentrations were measured
in four indoor 400-liter tanks over 13 days to study the role of hete
rotrophic bacterioplankton in NH4+ cycling and to identify the success
ion of top-down and bottom-up processes in regulating bacterial biomas
s and production. Ammonium (NH4+) was added to these four tanks daily
whenever its concentration in tanks was < 4 mu M. Tanks 3 and 4 (treat
ment tanks) also received 4 mu M of glucose daily till the end of expe
riment. Lower NH4+ concentrations and higher bacterial specific growth
rate and production observed in the treatment tanks indicated that ba
cteria might take up NH4+ with the addition of labile organic carbon.
Bacterial biomass was controlled by substrate supply and HNAN grazing
from day 7 to day 13, when phytoplankton declined. Bacterial size dist
ribution patterns were determined primarily by substrate supply, with
HNAN grazing playing a less important role. Certain variabilities exis
ted between the control (and the treatment) tanks. These inconsistenci
es could be due to differences in time of expression of given variable
s. However, the total amounts of bacterial biomass accumulated in the
four tanks were very similar. The inconsistency in timing of expressio
n of variables was probably due to different initial conditions in eac
h tank. The ecological meanings of the inconsistency in timing and ove
rall consistency were discussed.