A measurement example using a
twelve flask system
A twelve flask system was constructed following the
methods outlined above and used to measure CO
2
efflux
from navel oranges. Flask air temperature was monitored
during the measurements with an 8150-203 soil tem-
perature thermistor installed in each flask as described
above. Fluxes were calculated on a fresh weight basis and
a volume correction was used to account for the flask
volume occupied by the fruit. The flux measurements
were made over a 3 minute period (observation length =
3 min). Due to significant carryover of CO
2
from one
flask to the next (Figures 11 and 12) the first 60 seconds
of each measurement were ignored in the flux calcula-
tions (deadband = 60 sec).
Figure 11.
Chamber CO
2
mole fraction during
measurement of navel orange respiration. Data shown are
for one flask over one three minute measurement. The
initial decrease in CO
2
mole fraction is due to mixing of the
high mole fraction air trapped in the measurement loop
from the previous measurement with the air in the flask.
Figure 12.
The change in CO
2
mole fraction with time
calculated for various deadband lengths using the data
shown in Figure 13. dC/dt is calculated as the slope of a
straight line fit to the CO
2
mole fractions. Due to carryover
of CO
2
in the measurement loop, an appropriate estimate
of dC/dt cannot be made without excluding the first 60
seconds of data.
Figure 13.
Navel orange respiration measured with a
multiplexed flask system.
A.
Respiration rates for ten
oranges measured over a 24 hour period. The number
given for each symbol indicates the port where the flask
was connected.
B.
The fluxes for port 2 (solid circles)
plotted with chamber airtemperature (open circles).
C.
The
fluxes shown in panel B plotted as a function of
temperature.
Flux (µmol kg
-1
s
-1
)
Time of Day
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
1
1
:30
15:30
13:30
17:30
19:30
23:30
21:30
1:30
3:30
7:30
9:30
5:30
9:30
Flux (µmol kg
-1
s
-1
)
Chamber T
emp.
(°C)
Time of Day
Flux (µmol kg
-1
s
-1
)
Chamber Temp. (°C)
A.
B.
C.
Chamber CO
2
concentration
(µmol mol
-1
)
Time (seconds)
Deadband length (seconds)
dC/dt (µmol mol
-1
s
-1
)
9
