Making Measurements
Light Response Curves
Using the LI-6400
4-25
approach. This has the advantage of being fairly quick, yet has equilibrated
values The potential for difficulty comes from using multiple leaves, thus
bringing age differences and other factors into the response curve. The survey
approach is better suited for some species than others. In deciduous trees, for
example, leaf age is not particularly related to position in the canopy. With
this approach you can achieve a range of light levels by selecting leaves that
are tilted with respect to the sun, and in varying degrees of shade. The orien-
tation of the sunlit leaves is a problem, however, unless you are using a light
source when you clamp onto them. With a clear chamber top, leaves that are
tilted with respect to the sun will be shaded by the chamber wall, and this is
to be avoided at all costs. If, however, you use a light source, you can set the
appropriate value first, or have it automatically track the ambient light as
measured by an eternal PAR sensor.
Sunfleck / Shade Method
The fourth approach offered here is to separate each new light level with the
starting light value, with time to equilibrate. That is, use a sequence such as:
1800, 1000, 1800, 500, 1800, 300, 1800 µmol m
-2
s
-1
. (The starting point
neednÕt be high; you could work the other direction with shade leaves.) Data
collected in this manner might be most appropriate for addressing questions
of light dynamics in canopies.
Operational Considerations
Once you decide on the strategy you wish to take, you then need to decide on
how the chamber controls should be set, and on how data is to be collected.
Light
The best light source for light response curves is the red+blue 6400-02B. The
red only 6400-02 source has the potential problem of allowing excessive (that
is, more than normal) stomatal closure as light decreases, or delaying sto-
matal opening as light increases.
Without the LED light source, a light curve cannot be automated, but is still
possible. Neutral density filters, for example, can provide means to reduce
sunlight or other sources by known amounts. The survey technique discussed
above could be done without a light source.
CO
2
It is important to maintain the chamber CO
2
concentrations as constant as
possible while measuring a light response curve. Otherwise, the effects of
CO
2
on photosynthesis will be confounded with the effects of light. If you
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 ...