The main factors which affect the rate of photosynthesis are Carbon dioxide concentration, Light intensity and temperature. Any one of these could become the limiting factor (the factor which directly affects the rate of photosynthesis).
Limiting factor
The Law of limiting factors was created by Blackmann in 1905. The law states that the rate of a physiological process will be limited by the facotr which is in shortest supply.
Basicly, the rate of photosynthesis will decrease if Carbon dioxide, light intensity or tempearture is not sufficent.
For example, if light intenisty is right and the temperature is perfect for photosynthesis, the plant will still undergo photosynthesis efficiently if Carbon dioxide concentrations are low. This is shown in the graph bellow.
This is probably the most complex limiting factor in photosynthesis.
Light comes to earth in the form of photons. These photons oscillate along a path known as wave lengths. This is illustrated in the video to the right.
We know that chloroplast are filled with chlorophyll. However they are also filled with different forms of light catching chemicals, such as chlorophyll a, chlorophyll b and carotenoids. We can see these by doing a simple chromatography test. They do this to increase the amount of light energy they can capture from the specturm.
As you can see in the graph to the right, chlorophyll love to absorb Blue and Red light, however reflect green and yellow light.
As light intensity increases, the rate of the photosynthesis generally increases proportionately.
The more photons of light that fall on a leaf, the greater the number of chlorophyll molecules that are ionised and the more ATP and NADPH are generated.
Light dependent reactions use light energy and so are not affected by changes in temperature and Carbon dioxide concentrations.
As you can see in the graph above, the rate of photosynthesis will increase with light intensity. However after a point the rate of photosynthesis is eventually limited and at very high light intensity, chlorophyll are damaged causing a steep drop in the rate of photosynthesis.
The diagram bellow shows the entire light spectrum. Plants only use a very small amount of the spectrum, known as visible light.
As the concentration of carbon dioxide increases the rate of photosynthesis will increase (shown in the graph to the right).
This is because the plant can now incorperate more carbon into the carbohydrate formed, during the light independant stage.
Increasing the amount of Carbon dioxide will increase the rate of photosynthesis, and will eventually plateaue when the maximum rate of fixation is reached.
Carbon dioxide
The light independent stage requires enzymes. As we know enzymes are proteins. As the enzymes approach their optimum temperatures the overall rate increases. However above the optimum temperature the rate begins to decrease, as enzymes are denatured, until it stops.
