We used spruce and aspen seedlings, and allowed the roots to air-dry. Water
potential and transpiration were measured at 20 minute intervals.
We also used the spruce and aspen in an excercise which determined the light
saturation and light compensation points for the two species. Just set up
the plant in the IRGA and increase the light intensity in steps. Record
photosynthetic rate and light intensity, and plot the results. I have found
that this excercise works well to demonstrate the difference in the ecology
of the two species.
Department of Renewable Resources
University of Alberta
"Bill Williams" <WEWilliams at osprey.smcm.edu> wrote in message
> >I am teaching a course on plant ecology this semester and would welcome
> >suggestions for lab exercises, particularly on water relations (using a
> >pressure chamber) and photosynthesis (using an IRGA). Thanks.
> >Scott Shumway
>> We often begin our plant-physiology course labs with a survey of the
> differences between shade- and sun-grown sunflowers. (We just grow
> the sun-grown on top of a greenhouse bench and the shade-grown on the
> floor underneath the same bench.) They show very obvious differences
> in overall morphology, chl a:b ratios, and photosynthetic light
> curves (we've been using O2 electrodes, but an IRGA would be at least
> as good -- what are you using?). Water relations are a bit trickier
> because, as you undoubtedly know,it's very difficult to water-stress
> a plant growing in a small pot without killing it. We sometimes see
> pretty clear differences between noon and pre-dawn water potentials
> in the sun-grown sunflowers, though; you might try that.
> William E. Williams
> Biology Department
> Saint Mary's College of Maryland
> 18952 E. Fisher Rd.
> Saint Mary's City, MD 20686-3001