The effect of elevated oxygen levels on photosynthesis in C3 vs. C4 plants Gary Larsen Al Wallace Michelle Jordan College of Charleston Team Far Darwin Bulls Introduction As the world warms, how will elevated temperatures affect photosynthetic productivity in plants and alter the structure of natural and agricultural plant communities? Source: Intergovernmental Panel on Climate Change (IPCC) for the Third Assessment Report (TAR) in 2001 Possible effects of global warming… Plants adapted to higher temperatures, lower rainfall, or elevated CO2 may fare better in a warmer world. Implications? Crop yields? Structure of natural plant communities? An alternative photosynthetic pathway (C4 plants) Hypothesis: Plants that use the C4 photosynthetic pathway will be better able to meet their energy demands and will therefore be more successful than C3 species. Experimental hypothesis & predictions… If the photosynthetic pathway used by a plant affects its photosynthetic rate during periods of elevated oxygen levels then… Photosynthetic rate (ppm/min/g) [O2] will have no (or minimal) influence on photosynthetic rate C4 plant C3 plant Atmospheric O2 concentration (ppm) Methods • Leaves (4g samples) from 6 species of plants were collected from a the Cof C campus and the herbarium. C3 Plants C4 plants Live Oak (Quercus virginiana) Blue Stem grass (Andropogon gerardii) Dwarf Nandina (Nandina domestica) Centipede grass (Eremochloa ophiuroides ) Tea olive (Osmanthus fragrans) Corn (Zea mays ) Samples were placed in a sealed chamber and the rate of change of CO2 was measured in both the light and the dark under varied oxygen concentrations. Total Photosynthetic Rate (PR) calculation: Total PR = Rate of Change[CO2]light - Rate of Change[CO2]dark Results Ho: There is no significant relationship between PR and [O2] in C3 plants. Relationship between atmospheric [O2] Linear Regression photosynthetic rate (PR) Analysis: • F=26.20; df=17; p<0.0001 • Reject Ho Conclusion Increasing [O2] significantly decreases PR in C3 plants. *Negative PR values reflect uptake of CO2, so as values of PR become more negative, PR is increasing. Results Ho: There is no significant relationship between PR and [O2] in C4 plants. Relationship between atmospheric [O2] photosynthetic rate (PR) Linear Regression Analysis: • F= 0.113; df=17; p= 0.74 • Fail to reject Ho Conclusion Increasing [O2] does not significantly affect PR in C4 plants. *Negative PR values reflect uptake of CO2, so as values of PR become more negative, PR is increasing. Discussion The photosynthetic pathway employed does affect photosynthetic rate in response to oxygen stress! Discussion Why do C4 plants harness more of the sun’s energy than C3 plants in hot /arid environments? C4 photosynthesis C3 photosynthesis Conclusions Global warming could lead to increased heat and oxygen stress and decreased photosynthesis in C3 plants. This may alter natural plant community structure. Conclusions Global warming may shift agriculture away from C3 crop plants and more towards corn, or bioengineering C3 crops to better withstand the effects of heat and oxygen stress.
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