1. Diagram the pathways of water leaving a leaf. Which are variable, and which constant? Calculate, using electrical resistance theory, the total leaf conductance for a leaf in which the abaxial stomatal conductance is twice that of the adaxial stomatal conductance. Note: abaxial is the lower side.  Don't forget to include the boundary layer conductance.

2. Suppose a hypostomatous leaf has the following resistances: cuticular = 2.0 s/cm; stomatal = 0.5 s/cm; boundary layer = 1.0 s/cm. What is the total leaf resistance? Note: these units are the 'old' units, and are not used anymore, but they work well for doing these kinds of problems. Conductance would simply be the inverse.

Addendum: the 'old' units for conductance would be cm/s, a velocity measurement if you think about it. But these units do not take into consideration variation due to temperature or pressure. Thus, if you reported a conductance measurement in cm/s from a sea level measurement, it would not be the same if you did the same measurement in Boone, at 1000 m elevation. The new units (mmol m^-2 s^-1) take temperature and pressure into account, and are thus more versatile, and the ones you should use. Just remember, the new units have been used for only the past 15 years, and older literature probably contains just the old units.

3. Given a leaf conductance of 400 mmol m^-2 s^-1, and a VPD of 0.025 kPa/kPa (note: units cancel out for VPD since we have divided by the barometric pressure), what would be the estimated transpiration rate?

4. Explain the relationship between VPD and transpiration, given that leaf conductance remains constant. If leaf conductance decreases as VPD increases? Draw a graph showing both lines.

5. Could a leaf transpire less in very dry air compared to more moist air? How? Could a leaf transpire in air with a relative humidity of 100%?

6. What is the water potential of air at 100% RH? 99% RH? 90% RH? 75% RH?  Assume an air temperature of 25^oC.

7. Given a transpiration rate of 10 mmol m^-2 s^-1, a leaf temperature of 23^oC, an air temperature of 25^oC, and a relative humidity of 60%, what would be the estimated stomatal conductance? Assume a barometric pressure of 101.3 kPa.  How would your estimate of stomatal conductance in question 7 change if you performed your experiment in Boone, where the barometric pressure is 91.3 KPa?

8. Suppose you have a transpiration rate of 10 mmol m^-2 s^-1, a stomatal conductance of
700 mmol m^-2 s^-1, and a relative humidity of 70% at an air temperature of 30^oC. What is your estimated leaf temperature for these conditions?  If the air temperature suddenly increased by 5^oC, the stomatal conductance decreased by half, and E dropped to 5 mmol m^-2 s^-1, how would leaf temperature change, if at all?

9. If you have 75% RH at 20^oC, what is it at 30^oC? What is the VPD if leaf T = 23^oC, and you have 65% RH at 27^oC? If the leaf temperature increases by 2^oC, what is the new VPD?