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									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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