LI-COR LI-6400, Руководство пользователя

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Making Measurements
Leaks
4-44 Using the LI-6400
4
a linear relation when normalized leak is plotted against 1/flow rate. (The dif-
fusion leak is
; the normalizer is the gradient .)
To verify this model, we performed a simple experiment
7
. We used the CO
2
mixer to generate a variety of reference cell CO
2
concentrations, and recorded
the difference between the sample and reference cell concentrations at vari-
ous flow rates. (No leaf in the chamber.) We took the following steps to en-
sure the ambient CO
2
concentration was as stable as possible: 1) data
collection was done with an AutoProgram, so no one had to be standing there
breathing; 2) the instrument was set up in a vacant, well mixed greenhouse;
3) an external fan continually ventilated the chamber; 4) the ambient CO
2
concentration was monitored with a second gas analyzer. Sample cell CO
2
concentrations were measured by the reference IRGA using the match valve.
This eliminated any potential errors due to IRGA drift, since the same IRGA
7.
Simple in hindsight - it took a couple of weeks to get it right.
c
o
c
i
Ð
( )
c
a
c
o
Ð
( )
r
v
c
o
¶
t
¶
-------- uc
i
uc
o
Ð kc
a
kc
o
Ð + =
0 u c
i
c
o
Ð
( )
k c
a
c
o
Ð
( )
+ =
u c
o
c
i
Ð
( )
k c
a
c
o
Ð
( )
=
c
o
c
i
Ð
c
a
c
o
Ð
----------------
k
u
--- =
c
a
c
i
c
o
u u c
o
k
Figure 4-9. A model for diffusion in an open photosynthesis system, based on con-
servation of mass. The walls of the system have CO
2
leak rate k (mol s
-1
) . u is bulk
flow rate (mol s
-1
), and c
i
, c
o
, and c
a
are incoming, outgoing, and ambient CO
2
con-
centrations (mol mol
-1
). In steady state, the change of CO
2
with time in the system