Photosynthesis, Harsh Temperatures and Variable Elevations

Daryl Goldman, Logan Loeb, Tara Galanski

We tested the effects of colder temperatures on rates of photosynthesis in plants that grow at different elevations. Because plants that live at high elevations are better adapted to the climate at that elevation, we thought that these high elevation plants would adapt to cold temperatures and therefore be able to function well at cold temperatures. In contrast, we thought that plants at low elevations would not be adapted to such severely cold temperatures because such temperatures are rare at lower elevation climates. We wanted to compare the rate of photosynthesis in cold temperature of plants found at high elevations to the rate of photosynthesis at cold temperature of plants found at lower elevations. If the enzymes of higher elevation plants are better adapted for cold temperatures, then cold temperatures will affect the rate of photosynthesis in high elevation plants less than that of lower elevation plants. In addition, we examined the effects of temperature on photosynthetic rates.

To test this hypothesis we measured CO₂ rates in pinyon pine, Pinus edulis, in three trees from high elevations and three trees from low elevations. For each tree we determined the rate of photosynthesis at room temperature and at freezing temperature. We predicted that the rate of photosynthesis would be greater in the plants found at high elevations at cold temperatures than the rate of photosynthesis of plants found at low elevations at cold temperatures.

Our results indicated that although the rates of photosynthesis of the low elevation plants at cold temperatures (mean = -11.033 ppm/min/g) were greater than the rates of photosynthesis of the high elevation plants at cold temperatures (mean = -7.727 ppm/min/g), there was no significant difference in the means (p = .19). Interestingly we found that, at room temperature, high elevation plants had a significantly lower rate of photosynthesis (mean -10.157 ppm/min/g) than low elevation plants (-15.28 pmm/min/g, p = .04). Additionally, for both high and low elevation plants temperature did significantly affect photosynthesis rates; plants found at colder temperatures had lower photosynthetic rates (High elevation plants: room temperature mean = -10.157 ppm/min/g, cold temperature mean of -2.43 ppm/min/g, p=02; Low elevation plants: cold temperature mean = -4.25 ppm/min/g, room temperature mean -15.28 ppm/min/g, p =.01).

Our results are inconsistent with our perditions about how elevation affects photosynthetic rates at cold temperatures. When comparing high elevation vs. low elevation plants, there is not a significant difference in their rates of photosynthesis at cold temperatures. However, at room temperature there was a difference in photosynthetic rates at high elevation vs. low elevation pinyon pine. Plants at lower elevations seemed to photosynthesize at higher rates. These results indicate that elevation may indeed affect photosynthetic rates however, in extreme conditions, such as freezing temperatures, metabolic processes may slow or shut down indicating why we did not see differences in our cold temperature experiments. These interpretations are supported by our results that indicated that plants in colder temperatures had significantly lower rates of photosynthesis. Green and Hua, 2005, examined the effects of temperature extremes on photosynthesis. Their results yielded a lower rate of photosynthesis at cold temperatures than at room temperature. This supports our contention that at colder temperatures metabolic processed may be slowed. This evidence gives a possible explanation to why we did not see a significant difference between photosynthetic rates at cold temperatures in high vs. low elevation plants but we did see a significant difference in photosynthetic rates at room temperature. Elevation affects photosynthetic rates at room temperature but not at extreme cold temperatures.

Although our experiment is reliable, we would like to test plants from a greater elevational difference. Our high elevation trees were from an elevation of 8500 ft and the low elevation trees were from an elevation of 5400 ft. It is very likely that testing a more extreme elevational difference might add information to our interesting results.