test the cohesion theory

Kai Liu KRL121 at psuvm.psu.edu
Fri Feb 23 15:36:19 EST 1996

Hi, everybody,

I am looking for some professor to support me to test the cohesion
Zimmermann's pressure proble technique cause some debate on the cohesion
theory. According to pressure proble technique, the negative pressure
in the xylem often is positive and the maximaum negative pressure is
about 0.7 MPa. However, according to cohesion theory, that can not be
true. The negative pressure measured by pressure is always negative and
the range is to -16 MPa. Here is the problems: there are some possitive
pressure exist in the xylem and in the leaves at night and raining days.

Kramer and Boyer's new book "water relation of plant and soil" also
state that there is possitive pressure. This caused by root pressure.
However, when we use pressure chamber technique, we can never achieve
negative pressure.
Canny (1995) annlysis that the pressure chamber is not really measure
the xylem tension.
Recent articles by Holbrook (science 11/95) and Sperry (12/95, nature)
using centrifuge technique to get artifical negative pressure in the
xylem seem support the pressure chamber technique and cohesion theory.
However, the cohesion theory still not be directly proved and fully
accepted (Steudle, Nature 12/95).

The present problems of cohesion theory is that there is not a technique
to directly mesure the xylem tension. I just sloved this problem.
I developed a new instrument to directly measure the xylem tension. We
can know how much it is the negative pressure in the xylem by using this
Furthermore, I developed an indirect technique to test the cohesion
theory. (J.A. Milburn also have his methods).

The present situtation of mine is that most professor that I have contacted
don't have money to support this project. I am just a student come from
China and can't afford this project. Another problem of mine is that
I will graduate from Penn State this May (Master). I want to continue
my Ph.D education in west countries.

If you have some interest and can support this project, you can contact
me at KRL121 at psuvm.psu.edu.

Following is the present research of mine:
1. I first quantify that there was a constant relationship between tree
morphology and hydraulic architecture in branch junction. I have developed
some equations to quantify the junction resistance in each pathway of a
junction. For a strong apical dominance pattern, the junction resistance
in lateral pathway is 5-60 time larger than terminal pathway (depend on
degree of apical domicance). For equal trifurcation pattern, the resistance
in each path is similar.
2. The LSC value of different branch pattern also have a realtionship
with hydraulic architecture.
3. I have given a general equation to quantify the junction resistance
of any branch pattern.
4. I first found there are structure difference in different side
of a same tree. This info not publish yet. I can tell too much detail
on this issue. The LSC, leaf stomata, guard cell length have difference.
The design of this experiment is very interesting.
5. I also measure leaf gas change rate of 5 provencance green ash that
represent different rainfall habitats. We didn't found valuable results.
6. I help some person measure the leaf water potential on seedling,
 and mature trees of black cherry. The result also related to cohesion
I also have several good research topic:
1. Get the maximum height of a plant from hydraulic aspect.
2. Quantify the embolism of plants at different degreee of water potential.
3. The ability of plants to abosrb water at drought stress by a simulation
   technique. We can get the reason why plants can absorb water-is it
   just osmotic potential or negative pressure works?

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