Physiological Ecology: An Introduction to Methods

Dr. Drenovsky explaining
components of the LICOR-6400

On the 31^st of October 2013, the BL 435/535 class became acquainted with the LICOR-6400 and the pressure bomb so that for next week’s lab we will be able to harvest and record data of our greenhouse experiment.  The purpose of the LICOR-6400 is to measure gas exchange in plants while the Scholander-type pressure bomb measures leaf water potential. 

Students taking measurements
with the LICOR-6400

In order to collect data using these two machines, learning how to set them up was important.  Our professor gave us a thorough explanation for each machine.  The class was split in two groups to use the two LICOR-6400 machines, affectionately known as LUCY and OSCAR.  We were able to gain hands-on experience as our professor explained how to connect the parts of the instrument.  Although the LICOR-6400 can be easily set up, there is a pre-checklist that must be done before using the machine.  Noting the chamber, the cables, the console, and the chemical tubes were instructions given to us so that we become more aware of the machine before beginning our measurements. We were then able to begin measurements.  Extra samples of the study species for our greenhouse experiment were used.  Due to overcast weather conditions, additional lighting was used to increase photosynthetic rates.  The leaf of a specimen was placed in the chamber, which was held there until the conditions inside the chamber equilibrated.  Upon equilibration, the data was logged in the machine.  We had to repeatedly check during measurements that the Infrared Gas Analyzers (IRGAs) were matching to ensure accuracy.  This simply means to ensure that the carbon dioxide reference and sample are read as equivalent as when a balance is zeroed before weighing something.

Preparing specimens for
 pressure bomb measurements

Before the lab groups were able to use the pressure bombs, samples of our study species in the greenhouse experiment were extracted and placed in a plastic bag inside a cooler until needed.  The cut end of the specimen was placed inside the narrow chamber; this required patience to guarantee that the cut end was exposed on the other side of the chamber.   While one person took charge of the pressure dial for recording the measurements, the other person ensured that the rate valve was never closed completely and controlled the arrow dial while observing the pressurized specimen.  In addition, safety was stressed during this experiment.  When using the pressure bomb, all students had to wear goggles for protection.

The final part of collecting sample data on both machines was practice for our next lab, where we will be using the plants that we have been growing throughout the semester.  Prior knowledge of using these machines in this lab session increases the accuracy of data collection for our greenhouse experiment next week.

For more information on the LICOR-6400:  http://hydrology1.nmsu.edu/teaching/soil698/student_material/photosynthesis/6400.html

For more information on the Scholander pressure bomb:  http://www.pmsinstrument.com/resources/making-the-measurement-of-the-plant-sample

Written by:  Danny Dlugos

                    Jaylan Craig