Making Measurements
Operational Hints
Using the LI-6400
4-47
cant, and failure to account for it will lead to a large relative overestimation
of assimilation rate.
A protocol for measuring at concentrations well away from ambient is:
¥
Minimize the gradient
Keep high CO
2
(breath) away from the chamber. Keeping the chamber well
ventilated will help do this. If possible, collect data with AutoPrograms, so an
operator doesnÕt need to be nearby.
¥
Use the diffusion corrected formula for photosynthesis
Implement the correction in the Compute List.
Operational Hints
Air Supply Considerations
An open system, such as the LI-6400, is only as good as the incoming air
stream is stable, especially with respect to CO
2
concentration. When the in-
coming air is fluctuating in CO
2
concentration, there will be phase differences
as those fluctuations pass through the reference IRGA and the sample IRGA,
resulting in fluctuations in the CO
2
differential - even with no leaf in the
chamber.
There are essentially three options for making the incoming air stable:
Table 4-2.
Typical values of the three terms of the net photosynthesis equation under two sets of conditions
Term
Equation
Near Ambient
Near
CO
2
Compensation
CO
2
Uptake
Transpiration
Correction
Diffusion
Correction
Net Photosynthesis
F C
r
C
s
Ð
(
)
100
S
---------------------------
300 380
340
Ð
(
)
100
6
´
--------------------------------------
20
=
200 50
48
Ð
(
)
100
6
´
--------------------------------
0.67
=
C
s
E
340
0.005
´
1.7
=
48
0.007
´
0.33
=
k C
a
C
s
Ð
(
)
100
S
---------------------------
0.4 370
340
Ð
(
)
100
6
´
------------------------------------
0.02
=
0.4 370
48
Ð
(
)
100
6
´
---------------------------------
0.21
=
20
1.7
Ð
0.02
+
18.32
=
0.67
0.33
Ð
0.21
+
0.55
=
Summary of Contents for LI-6400
Page 1: ...Using the LI 6400 Portable Photosynthesis System ...
Page 15: ...Part I The Basics ...
Page 16: ......
Page 174: ...Making Measurements Answers to Questions 4 56 Using the LI 6400 4 ...
Page 175: ...Part II Useful Details ...
Page 176: ......
Page 200: ...Standard Tools Power ON Hooks 5 24 Using the LI 6400 5 ...
Page 214: ...Real Time Data Real Time Graphics 6 14 Using the LI 6400 6 ...
Page 234: ...Environmental Control Light Control 7 20 Using the LI 6400 7 ...
Page 244: ...Light Sensor Considerations Gallium Arsenide Phosphide GaAsP Sensor 8 10 Using the LI 6400 8 ...
Page 288: ...Data Logging Making Your Own AutoPrograms 9 44 Using the LI 6400 9 ...
Page 289: ...Part III Working With Files ...
Page 290: ......
Page 312: ...The LPL File System Troubleshooting 10 22 Using the LI 6400 10 ...
Page 340: ...Downloading Files Using a Data Capture Program 11 28 Using the LI 6400 11 ...
Page 375: ...Part IV Configuration Issues ...
Page 376: ......
Page 420: ...Defining User Variables Old Style vs New Style 15 18 Using the LI 6400 15 ...
Page 454: ...Using an Energy Balance Further Reading 17 12 Using the LI 6400 17 ...
Page 455: ...Part V Maintenance Troubleshooting ...
Page 456: ......
Page 572: ...Troubleshooting Useful Information 20 46 Using the LI 6400 20 ...
Page 593: ...Part VI Programming ...
Page 594: ......
Page 622: ...Programming with LPL Compiler Directives 22 28 Using the LI 6400 22 ...
Page 846: ...Index I 16 Using the LI 6400 ...