Equipment and methods    For this research project we get to use a lot of fun gadgets (also known as very expensive scientific research equipment), such as the High pressure flow meter, the Li6200, the Sap Flow meter, the leaf bomb (haven't blown it up yet) and the leaf area meter, not to mention the microtome, tree corer and high-tech razor blades, (well not really but we couldn't research without them.)

LI6200  an instrument that measures physiological activity of individual leaves.  A leaf on one of the sample trees is sealed in the Li6200's clear plastic chamber with a foam gasket.  The air from the chamber is cycled through the machine (specifically the IRGA or infrared gas analyzer),  which measures the change in CO2 concentrations.  Transpiration and photosynthetic rates are calculated from measurements of CO2 concentration, relative humidity, and flow rates.  A sensor on the chamber records leaf and air temperature along with the relative humidity and the current quantum readings,  Meanwhile, the operator just stands there and watch's the small screen of the machine until the CO2 concentration is bellow 370ppm and is dropping steadily, showing that the leaf is indeed photosynthesizing, before pressing the log button, at which time the machine will begin to record on set of three observations for that particular leaf.  Four beeps later from the LI6200 and the measurement is done. BACK

    The next step is to find the water potential of the observed leaf and requires a little more effort on our part.  First the leaf is cut from the branch using a razor blade ( a leaf torn from the branch gives inaccurate readings for water potential.)  The leaf is scanned with the leaf area meter and its area in square centimeters in entered into the LI6200.  Then it is quickly placed into the pressure bomb and its water potential is taken. The leaf is sealed in a chamber with its petiole extending through a gasket in the lid.  Pressurized nitrogen is run into the chamber and the pressure at which a small bead of water can be seen on the end of the petiole is recorded and converted to water potential  for that leaf (number is multiplied by  - 0.1).  This number is recorded and we are ready to take another reading.         BACK
    The pressure bomb is also used in the lab to make water release curves for oak leaves.  A small branch is cut from the selected tree, a Gary Oak in our case.  The end is then cut again below water and a plastic sack is placed over the leaves.  This is done to bring the leaves to full turgor by capturing the transpired moisture.  This increases the relative humidity  which decreases the water gradient between the air in the bag and the leaves.  The branch is left covered for a few hours.
     Sap flow probes were inserted into the four trees of study.   Probes were attached to the north and the south side of each tree.  The sap flow meter functions by measuring the difference between the two sap probes.  The upper sap probe contains a small heating element which creates a temperature gradient between the two probes.  As the sap flows upwards, heat is carried away from the upper probe, and the difference in heat is measured and used to calculate the rate of flow.  Theoretically, if the sap were to flow infinitely fast, the two probes would be the same temperature.    Cables were run from the sap probes to the sap flow meter, which was connected to the Data Logger.  Measurements were recorded every two minutes.
    The High Pressure flow meter is used in the lab to measure conductance of the xylem vessels in branches.  Degassed water is forced through the vessels of the branch, and the rate at which it travels( or the difference in pressure between two pressure meters is calculated and recorded on a computer.  A best fit line is then found through a least squares regression, and the slope of this line is the conductance for that branch.
    Slides of oak sections were also made.  At first the microtome was used to slice thin sections of xylem tissue, but making oak sections proved  to be "exasperatingly difficult."  We made the sections using razor blades instead.  The sections of oak were then mounted and dyed and the average vessel size was calculated using the computer.             BACK