Making Measurements
Some Simple Experiments
4-18 Using the LI-6400
4
Question #15: Suppose you want to do some sun / shade dynamics measure-
ments, and you a) want the sample cell CO
2
concentration to be as consistent
as possible, and b) donÕt want the slower time response of the sample cell CO
2
control algorithm to be interfering with your measurements. How could you
do it? (Answer on page 4-54.)
7 Change to a shade adapted leaf
Change to a leaf that has been in the shade for some time. If you are using an
LED source, donÕt forget to adjust the light to a low value, before putting the
leaf in the chamber. Change to CO
2
control back to constant reference mode.
8 Provide a brief sunfleck
Give the leaf full sun for 30 or 40 seconds, and observe the response of Photo,
Cond, and Ci.
9 Provide a long sunfleck
Now give it full sun, and see how long (if ever) it takes for Photo and Cond
to reach the values that you found for the sunlit leaf.
Experiment #6 Sun And Shade Leaf Survey
This experiment uses the LI-6400 in a survey mode in which a succession of
leaves is measured, and each measurement lasts a minute or less.
Should you use the LED light source for this experiment? If you have this
choice, here are some things to consider. This experiment will measure sun
and shade leaves that are adapted to their radiative environment. If you donÕt
use the light source, you wonÕt be affecting that environment very much when
you clamp onto the leaf with the clear chamber top. If you are using the light
source, youÕll have to be sure and set the light to match this ambient value be-
fore clamping onto each leaf. If you have an external quantum sensor and a
Points to Remember
¥ Light changes produce immediate photosynthetic rate changes. These
changes can be compensated by controlling sample cell CO
2
, but some ad-
justment time is necessary, typically 1 minute or less.
¥ Light changes will cause stomatal changes, but only after many minutes.
These changes are continuously compensated when using constant humid-
ity control.
Equilibrium is reached faster by decreasing light on a sun-adapted leaf,
than by increasing light on a shade-adapted leaf.
To Next Page
Loading...
