380
conditions or from nutrient depletion, incubations of both surface and deep samples were
carried out at the same intermediate light level, but with different nutrient additions. The
results suggested that the original surface samples were nutrient limited, while the samples
from the chlorophyll maximum were not (Fig. 18).
Q)
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u
10
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ell
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5b Q)
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Q)
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80
160
240
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Relative Integrated Biovolume
Figure 18. Relationship between integrated red fluorescence and biovolume of chlorophyll-containing cells, as
estimated with a flow cytometer equipped with a Coulter-type volume analyzer. The data lie along one of
two slopes: initial samples from the surface (+ 's) and samples from both the surface and the subsurface
chlorophyll maximum that were incubated without added N or P (circles) have relatively low Chi
fluorescence per biovolume; initial samples from the subsurface chlorophyll maximum (x's) and all samples
incubated with added Nand P (squares) have higher Chi per biovolume. After Demers et al. (1989).
Knowledge of cell activity is more useful than that of biomass alone. Biomass, as determined
by counting and sizing cells with chlorophyll fluorescence, can be misleading because the
activity of the cells can vary and all cells may not even be viable. Fluorescein diacetate (FDA)
is a fluorescent probe which in combination with flow cytometry offers a quick and relatively
easy way to assess cell viability without the use of radioactive isotopes. FDA is lipophilic
(thus able to cross the plasma membrane) and non-fluorescent until it is cleaved by
conditions or from nutrient depletion, incubations of both surface and deep samples were
carried out at the same intermediate light level, but with different nutrient additions. The
results suggested that the original surface samples were nutrient limited, while the samples
from the chlorophyll maximum were not (Fig. 18).
Q)
g
Q)
u
10
•
ell
•
Q)
•
I-<
0
;:j
8
G::
•
+
+
"0
•
~
6
•
.. • •
"0
B
4
K
• •
~
K
5b Q)
•
....
• • •
~
2
""' "'
Q)
>
.....
0
....
~
...... Q)
0
80
160
240
~
Relative Integrated Biovolume
Figure 18. Relationship between integrated red fluorescence and biovolume of chlorophyll-containing cells, as
estimated with a flow cytometer equipped with a Coulter-type volume analyzer. The data lie along one of
two slopes: initial samples from the surface (+ 's) and samples from both the surface and the subsurface
chlorophyll maximum that were incubated without added N or P (circles) have relatively low Chi
fluorescence per biovolume; initial samples from the subsurface chlorophyll maximum (x's) and all samples
incubated with added Nand P (squares) have higher Chi per biovolume. After Demers et al. (1989).
Knowledge of cell activity is more useful than that of biomass alone. Biomass, as determined
by counting and sizing cells with chlorophyll fluorescence, can be misleading because the
activity of the cells can vary and all cells may not even be viable. Fluorescein diacetate (FDA)
is a fluorescent probe which in combination with flow cytometry offers a quick and relatively
easy way to assess cell viability without the use of radioactive isotopes. FDA is lipophilic
(thus able to cross the plasma membrane) and non-fluorescent until it is cleaved by