University of Colorado at Boulder

Brent Burgie, Jeffrey Gold, and Sonya Golden

In this study we examined whether coniferous plants are better photo-synthesizers than deciduous plants under colder temperatures. We know that leaves are the site of photosynthesis in coniferous and deciduous plants, and that, during the Winter, the leaves of coniferous plants retain their needles, while the leaves of deciduous plants often die. Our hypothesis was---if coniferous plants are better photo-synthesizers than deciduous plants under colder temperatures, then they will consume more C0₂. We placed three species of coniferous plants and three species of deciduous plants in respiration chambers, and ran four trials on each of the six samples. Each sample was placed under light at a cold temperature (about 0 degrees C) and at room temperature (about 22 degrees C), and, as a control, under no light at the same two temperatures. We compared the C0₂ consumption of the coniferous plants to the deciduous plants at the two temperatures. The variation in mean rates of photosynthesis among individual species for deciduous was -8.57 and coniferous was -12.15. This data has a non-significant relationship. For this reason, we fail to accept our active hypothesis. It is evident that there were problems with our experimental design. First, one of the coniferous samples is not an appropriate measurement because the total weight, 3g, included stem weight. Thus the rate in change of CO₂ will be affected by the stem size and the decreased mass of leaves. Second, under freezing and room temperatures, the rates of CO₂ change in individual coniferous species, A: -29.861/ -72.296; B: -68.428/ -49.524; C: -11.071/ -9.332, varied more between species than among deciduous species, D: -36.788/ -73.969; E: -28.487/ -40.687; F: -11.921/ -33.489. The range for coniferous is -11.071 to -68.428 and the range for deciduous is -11.921 to -73.969. These wide spread ranges decrease the probability of attaining a significant mean difference between groups. Also, 2 out of 3 Coniferous plants had increased rates of photosynthesis under freezing temperatures, while 3 out of 3 Deciduous plants had increased rates of photosynthesis under room temperatures. These varying results suggest that testing variations among individual species of coniferous and deciduous may have been more compatible and conclusive than mean differences between groups. Last and most obvious, physiologically, coniferous and deciduous plants undergo the same C3 photosynthesis, and thus, one should not be a better photo-synthesizer than another. In this regard our hypothesis was flawed. A more effective variable to test would have been light since deciduous and coniferous plants differ structurally, it can be inferred that varying leaves may absorb light differently in reduced light conditions due to differences in surface area, volume, and outer-covering. Thus a design varying light conditions may have been a better indicator of difference in leaf structure to explain coniferous leaf retention in the Winter.