Interactions between limiting factors

Plant structures and their functions · Photosynthesis and limiting factors · note 4 of 6

Spec 6.4Higher tierDownload these notes (PDF)6 pages

Interactions between limiting factorsSpec 6.4

Temperature, light intensity and carbon dioxide concentration all act at the same time. At any moment, the rate of photosynthesis is limited by whichever factor is in shortest supply.

To explain a graph, find where the line levels off. At that point the factor on the x-axis is no longer limiting. Something else is, and it will be a factor that is not being increased.

If a graph for light intensity has two lines, the line with a higher plateau has more of the other factor, for example a higher carbon dioxide concentration or a better temperature.
The two lines are the same at low light intensity because light is the limiting factor for both.
At the plateau, the lower line is limited by the factor that differs between the two conditions.
If increasing one factor makes no difference to the rate, a different factor is limiting.

Graph of rate of photosynthesis against light intensity with two curves that overlap at low light (limited by light intensity); the lower carbon dioxide curve levels off lower, limited by carbon dioxide concentration, and the higher carbon dioxide curve levels off higher, limited by temperature. — Where each line levels off, light is no longer limiting. The factor in shortest supply sets the plateau.