lab designs

Scott Shumway Scott_Shumway at
Tue Feb 27 16:36:07 EST 2001

I am designing two labs for my plant ecology class.  I'd appreciate help
with some questions.

Lab 1 - experiment to measure photosynthetic and water potential responses
to salt stress in seaside golenrod, Solidago sempervirens.  This is a plant
which somehow can grow on dry sand dunes and in salt marshes.

5 yr-old plants growing in 6 inch pots will be watered with freshwater, 25%
seawater (instant ocean), and 50% seawater.  After one to two weeks (or at
longer weekly intervals?) plants will be measured for photosynthesis using
an IRGA and water potential using a pressure bomb.

Question:  How frequently should the salt treatments be watered with
saltwater versus freshwater?  I want to avoid accumulation of large amounts
of salt in the soil.  In the past I've monitored soil salinity by squeezing
water from soil wrapped in cheesecloth onto a refractometer.  ARe there
better methods?

Lab 2 - exercise to teach students how to use an IRGA (the relatively new
"miniature" LCi by ADC).  I am thinking of having them compare light curves
for several species found in our greenhouse.  I'll choose plants native to
sunny habitats (Bougainvillea, Solidago sempervirens) and shady habitats
(Colocasia, Monstera).

Question:  Can someone recommend a protocol for creating a light curve?  I
could either use ambient light and shade screens or an external light
source that attaches to the IRGA chamber head.  Is it best to increase
light levels as you go (avoid photoinhibition?) or start off high and go
low?  Is there a standard range of light intervals?

Question:  How might these results be influenced by the New England winter
lighting that these plants have been experiencing?

Question:  I plan to supplement light (sodium lamps) to achieve a 14 hr day
photoperiod for the 1st experiment.  Is it advisable to ease plants into
this photoperiod or should I just turn the lights on one day and jolt them
into summer? (I'd like to run this latter experiment on myself!!)

Thanks for your help.

Scott Shumway
Associate Professor of Biology
Dept. of Biology
Wheaton College
Norton, MA 02766
"Scott_Shumway at"
fax 508-285-8278


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