The End of Photosynthesis


ChantŽ Karimkhani, Justin Maki, and Julian Hirschbaum


CU Boulder, 2007


Faced with the increasing impacts of global climate change, we were curious about the effects of environmental temperature changes on the photosynthetic rates of plants.  Our initial understanding of global warming led us to hypothesize that severe fluxes in temperature will cause a plant to decrease its photosynthetic rate.  This major shift in photosynthetic efficiency presents a serious danger to the life on planet earth. This threat inspired our experiment, which we performed using samples from a Colorado pine tree.  We predicted that severe deviations from room temperature would cause a pine tree to take in less carbon dioxide (CO2), until at some point, the cellular respiration process of emitting CO2 would dominate over the photosynthetic process.  Specifically, we expected to observe an increase in CO2 levels by the pine tree in both hot and cold environments.

            To test our hypothesis, we weighed a pine tree sample and placed it in a sealed container along with a CO2 gas probe.  We performed the experiment at three different temperatures: 46 ĄC, 2 ĄC and 28 ĄC (room temperature).  For 46 ĄC and 2 ĄC we submerged the container containing the pine tree into the hot or cold water. To measure the CO2 produced through photosynthesis, we performed each trial in both light and dark environments.  The light environment was simulated with three lamps.  The dark environment was simulated by covering the pine tree container with aluminum foil.  We performed three replicates at the hot and cold temperature, and only one at room temperature (due to time constraints).  Each trial was run for five minutes in the light and five minutes in the dark.  We determined the change in CO2 for each trial by subtracting the slope of the line in the dark from the slope of the line in the light.

            Our results support our hypothesis and indicate that there was a significant increase in CO2 levels at both the hot and cold temperatures, compared to room temperature (P = .0104).  From our linear regression, we can predict the point of maximum photosynthesis falls between 28ĄC and 35 ĄC.  In addition, an R2 value of 0.762 indicated that our data points fit the linear regression line fairly well. To improve the experiment we could prolong the hot environment using a hot plate because our hot sink water gradually lost heat, and performing more replicates would have likely given a higher R2 value. Experimental results from the Grassland Research Institute and the University of Sydney reinforce our conclusions.  These experiments determined that Ňthe maximum rate of net photosynthesis peaked at around 30 or 35 ĄC,Ó and that photosynthesis decreased in temperature deviations from 30-35 ĄC.  The combined results from our experiment and numerous studies performed throughout the world indicate that global climate change may have a drastic impact on plant photosynthesis and may change life as we know it on planet earth.