Question 1
Start at preindustrial CO2 levels and run the first simulation at 30°N. Note how photosynthesis changes over the course of the year, and the annual quantum yield. Now rerun the simulation for 40° to 60° North at ten degree intervals. Plot annual yield by latitude for both photosynthetic types. Which photosynthetic type will dominate? At what range of latitudes do you predict C4 dominance, mixed prairie (both C3 and C4), C3 dominance?

Question 2
Now change the CO2 level to current (350 ppmV) and run the same range of latitudes noting the relative growth rate of both photosynthetic types at each latitude. Plot annual yield by latitude for both photosynthetic types. Which photosynthetic type will dominate? At what range of latitudes do you predict C4 dominance, mixed prairie (both C3 and C4), C3 dominance?

Run the same series of simulations for a future CO2 level (500 ppmV). Run the same range of latitudes noting the relative growth rate of both photosynthetic types at each latitude. Plot annual yield by latitude for both photosynthetic types. Which photosynthetic type will dominate? At what range of latitudes do you predict C4 dominance, mixed prairie (both C3 and C4), C3 dominance?

Question 3
Considering all three of your graphs, how is the mix of C3 and C4 plants likely to change with future changes in CO2 levels? Explain why. Note that we are only considering changes in CO2 and not corresponding temperature change. How might higher temperatures affect the relative growth of these two photosynthetic types?