There are many other techniques out there.
Gross morphological response is a good, general technique that
can take into account everything from reduction in lamina surface area,
lamina mass, lamina thickness, stem mass, root mass,....
Using these measurements in the form of a ratio will give you some decent
numbers to compare/contrast the two taxa. Competitive advantages
including larger root mass:shoot mass (or better yet, root mass:lamina
surface area), larger xylem diameter:lsa, etc...
Also, comparing the specific leaf mass of droughted and control plants of
both taxa can also be informative (if the droughted plants of one cultivar
increase the density of the leaves, perhaps suggesting solute accumulation).
Growth analyses, accomplished by comparing gross morphology over
time by way of a series of destructive harvests will provide you with Net
Assimilation Rate, Lamina Area Ratio and Relative Growth Rate. These
will put into perspective the efficiency and capacity of the plants as
Measurements of stomatal conductance (with a steady-state
porometer) can also yield interesting information. Comparing stom. cond.
among the two cultivars under the same level of stress will show you if
one is able to maintain 'adequate' photosynthesis while the other is not,
Also, examining the osmotic potential would show you if
(typically after prolonged drought exposure) a plant is osmotically
adjusting (aka osmotolerance).
Is this for a class demonstration/lab experiment or is it for research?
If for class, an nice correlation can be drawn using Water Potential
(determined from the pressure bomb) and Stomatal Conductance (with the
Porometer). I you had 5 or 6 different irrigation levels (easily
detectable by the pressure bomb) students could correlate these with
stom. cond. The two taxa could then be compared.
Michael S Dosmann
dosmann at iastate.edu . . .
Graduate Research Assistant . .
Department of Horticulture . . .
Iowa State University