Purpose: to determine how drought affects leaf water potential (Y ), transpiration (E), and photosynthetic assimilation rate (A) in tree seedlings.

Approach: Seedlings were grown in 8 L pots of a 1:1 peat-vermiculite mixture in a greenhouse. During a two-week period the seedlings will be weighed every other day and the water loss (WU) replaced for one half the seedlings (WET) while water will be withheld from the other half (DRY). At the end of the test all the seedlings will be measured for instantaneous Y (MPa), E (mmol H₂O m^-2 s^-1) and A (m mol CO₂ m^-2 s^-1). Each treatment will be replicated three times.

Results: Calculate a mean value for each of the variables - Y (MPa), E (mmol H₂O m^-2 s^-1), A (m mol CO₂ m^-2 s^-1) and WU (g). Be sure to report PPFD (photosynthetic photon flux density, m E m^-2 s^-1), temperature (° C) and humidity (RH, %).

Report: Show the mean values in a table for the WET and DRY treatment measurements. In addition show the data for Y , A and E in bar graphs. The water use data should be shown in a x-y graph. Answer the following questions:

1. Describe the results. What was the effect of drought on each variable?
2. Did A and E show the same effect due to drought? Describe and explain the changes due to drought.
3. Was WU linear with respect to days since the start of the experiment? Describe and explain the pattern of change in WU.
4. Did the seedlings change in appearance due to the drought? Describe and explain any differences.