Partial Pressure of CO2 and it effect on photosynthesis.

An inquiry of the possible effect of altitude on the photosynthetic process of Douglas Fir Needles.

G Greenfield and T. Lynch

Fall, 2008

How does elevation affect the photosynthetic rate of Douglas Fir needles?  In order to address this question we designed a simple experiment that would allow us to test a fundamental difference in the partial pressure of CO2, at the different altitudes of the Douglas Fir inhabits. In general, the partial pressure of CO2 decreases as the altitude increases. As a result of this difference in the concentration of CO2 , we hypothesized that if the partial pressure of CO2is increased, the rate of photosynthesis of Douglas Fir Needles will increase. Thus, if we increase the concentration of CO2 in a controlled environment, we predicted that the rate of carbon dioxide uptake would increase.

            To test this hypothesis we placed two grams of Douglas Fir needles inside a gas chamber at the prevailing concentration of CO2 of our laboratory (350 ppm).  Then proceeded to measure the reduction of CO2 gas with a CO2 gas sensor for a time period of 10 minutes for a total of 3 trials with new needles for each trail.  In each trial, containers of water were used for heat reduction. Three lights surrounded the chamber for the facilitation of photosynthesis.  Next, we repeated the trials but increased the amount of CO2 available for fixation by exhaling into the gas chamber just before attaching the gas sensor. We attempted to reach 2000 ppm of CO2, which was intended to simulate the elevated partial pressure of CO2 that can be found at lower altitudes.

            Our results clearly show that the rate of carbon fixation was higher in the chamber with the higher level of CO2.  After analyzing the data we found that the mean rate of CO2 uptake in the elevated chamber was -14.34ppm/min/g while the mean rate of CO2 uptake in the prevailing lab environment was  -2.86ppm/min/g.  Further more, a P-Value of .0177 show that the rate of CO2 update in 2000 ppm of CO2 was significant higher than that in 350 ppm of CO2.

            Our results were consistent with our prediction, and then failed to reject our hypothesis, in which the rate of CO2 update increases as the concentration of CO2 increases. Therefore, we conclude that Douglas Fir needles may have low photosynthesis rate at the high altitude. Potential problems with our experimental design include the countless variables that can affect the uptake of CO2 of Douglas Fir needles in a given location, such as moisture level, relative proximity to the ground, temperature, and light availably.  The preceding variables could have a possible impact on the stomata openings on the needles, changing the rate of CO2 uptake.  As stated by J. Gale of Hebrew University of Jerusalem, “In considering the effect of altitude on whole plant physiology and ecology all factors of the environment must be taken into account, not only leaf gas exchange.”