Why Do Weeds Overcome Indegenous Plants:

An Investigation Into Varying Rates of Photosynthesis

Wendy Billington, Christina Best, Talia Brown

University of Colorado at Boulder, Fall 2004

Our goal was to investigate why weeds flourish in natural, intended conditions more so than native platns. A crucial constituent for plant survival is its ability to photosynthesize. A possible cause for variation in the ability of different plant species to grow is the rate in which these plants photosynthesize. We hypothesized that if weeds photosynthesize at a greater rate than their native plant counterparts, then they will thrive more and display more growth than native plant.

To test this hypothesis, we measured the rate of photosynthesis, as tested by CO2 output, in a weed, a native plant, and in the absence of any plant species, as an experimental control. Photosynthesis was measured using separate gas chambers and a CO2 gas sensor, which was attached to a computer with a program that measured the CO2 output. The CO2 output, measured in ppm/min/g, was measured separately for the plant, weed, and in the absence of a plant for 5 minutes while exposed to light, followed by 5 minutes in the absence of light, then again in the light. We predicted that the overall photosynthesis would be greatest in the weed chamber.

Our results indicated that photosynthesis was, indeed, greatest in the weed. While the overall CO2 ouput in the native plant was ≠17.7 ppm/min/g. the CO2 ouput from the weed was ≠20.05 ppm/min/g, with a p-value of 0.2777, indicating that difference in the data was not significant.

From the data collected, we found that our results were cinsistent with our hypothesis, but the difference could not be considered statistically significant. One potential problem with our experiment was the presence of an unspecified fungus observed on the native plant, which should have hindered the ability of the plant to photosynthesize. In the furure, it would be useful to test several different invasive plant species versus several indigenous plant species, and to compare the average rate of photosynthesis between those two groups. Such studies would increase the validity of the results, and with more tials, the data may become increasingly significant.