Im a genetics degree student and thought I would correct or answer a statement/ question made by yourself.You said:
From these statements, we must conclude that the concentration of oxygen in the atmosphere is significantly higher in hot, dry climes than in cool, wet ones. Do you have some references to back up this inference?
The reason why plants specifically xerophytes are thought to have evolved C4 and CAM pathway to overcome Rubisco's afinity for Oxygen is not due to higher oxygen levels in the atmosphere of hot arid environments, but due to the fact that plants in these environments close their stomata to reduce water loss(by transpiration)and so also reduce the amounts of CO2 that they can take in, effectively starving the Calvin cycle of CO2.As the levels of CO2 begin to decrease due lack of intake and use in Calvin cycle, the ratio of O2 to CO2 inside the leaf increases, increasing the chances that rubisco will bind O2 rather than CO2.
This however is rerely a problem for plants in more temperate climates so there has been little or no selection pressures to evelove this kind of pathway in these environments.
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