Rate of photosynthesis:
Measured by the net CO2 uptake: photosynthetic uptake – photorespiratory evolution – respiratory evolution
There are 4 main factors affecting the rate of photosynthesis in plants:
1) Light Intensity
When there is no light, net CO2 production is negative due to cellular respiration.
Light-compensation point - when the amount of CO2 used is equal to the CO2 produced: net CO2=0
Light Limited phase - For sometime, the rate of photosynthesis increases in direct proportion to light (the relationship is linear). The reaction is speeding up as substrate concentration is increasing until the enzymes are working at full potential.
Light Saturation point - carbon fixation has reached maximum rate: enzyme concentration in limiting.
40 + degrees: the enzymes which catalyze the reactions within photo synthesis become denatured and are no longer able to function. This causes the rate to decrease after this point.
3) Carbon dioxide Concentration
The enzyme rubisco involved in the Calvin Cycle also has a high affinity for oxygen. The greater the carbon dioxide concentration, the less chance RuBP will oxidized.
Once again, this increase in rate of photosynthesis is only until the enzymes involved are working at full potential.
4) Water Concentration
Water is another reactant in photosynthesis, and therefore causes an increase in reaction rate also until the enzymes are working at their full potential.
Can a plant get too much water?
Yes, in large plants, root cells are responsible for carrying water to upper cells for photosynthesis. They, themselves, perform cellular respiration to survive which requires oxygen which they absorb from air pockets in the soil. If the soil is completely saturated with water, no oxygen will be absorbed by these cells, and they will die. This may eventually lead to the death of the entire plant.