>Do you know of any techniques used to quantify or compare plants'
>responses to water stress other than the pressure bomb, psychrometer or
>actual field experiments? I am planning to examine a cultivar (species yet
>to be determined) classified as drought tolerant (relatively) and
>compare it with an 'average/non-drought tolerant' control.
Since the subject could be of interest to the others, I reply to the whole
Try these two papers
Pockman et al., (1995) Nature 378:715-716.
Holbrok et al., Science (1995)270:1193-1195
Essentially they measure water potential with a centrifuge. They find that
the potential at which one gets cavitation is species specific and lends
support to the air-seeding theory for cavitation. More about this:
Sperry et al., Plant, Cell & Env. (1996)19:427-436
Tyree and Sperry Ann Rev. Plant Phys. Mol. Biol. (1989) 40:19-38.
I use the first two cited paper for teaching. I assume they settle the
disputes over presure probe and pressure bombs measurements.
>Another question that distantly, since simplified, relates to plants: what
>are the forces acting on a pipe/tube when put vertically, its bottom
>immersed in a tank of water and a pump attached on its top which is
>powerful enough to raise a water-column through the pipe. It is assumed
>that the weight of the pump is negligible and that the water supply is not
>limiting. The latter point is important since I am particularly interested
>in whether the pipe experiences any of the forces which cause the pipe to
>collapse in the absence of water and significant 'suction' generated by
>the pump. In other words: can the 'negative' pressure generated by the
>pump be completely transferred onto the column? What about the weight of
>the water column itself? Is the water completely 'held' by the pump in
>such a case or do the lower parts of the pipe nonetheless experience an
>outward pressure due to the weight of the water?
Try first to see: Nobel "Physicochemical and environmental Plant Phys."
(1991) Academic p.
I'd say no collapse without water since the pressure would go at most to
zero and never reach negative values as with water under tension (assuming
of course that the pipe resist at pressure 0).
If there is water AND the pump is working AND there is no cavitation
occurring (which is probably untrue for large diameter pipes (>1 cm) and
columns above 10 m in height) I assume there will NOT be positive pressure
in the pipe.
Biology Department "L. Gorini"
Plant Physiology and Biochemistry Section
University of Milan
Via Celoria 26, Torre 4C,
Milan 20133 Italy
tel: +39-2-2660-4394 Email: pm1 at imiucca.csi.unimi.it