a limiting factor in nature. Increase in Figure . Graph of light intensity on the rate of photosynthesis Rate of photosynthesis Light intensity A B C D E incident light beyond a point causes the breakdown of chlorophyll and a decrease in photosynthesis. .
. Carbon dioxide Concentration Carbon dioxide is the major limiting factor for photosynthesis. The concentration of CO is very low in the atmosphere (between . and .
per cent). Increase in concentration upto . per cent can cause an increase in CO fixation rates; beyond this the levels can become damaging over longer periods. The C and C plants respond differently to CO concentrations.
At low light conditions neither group responds to high CO conditions. At high light intensities, both C and C plants show increase in the rates of photosynthesis. What is important to note is that the C plants show saturation at about µ lL - while C responds to increased CO concentration and saturation is seen only beyond µ lL - . Thus, current availability of CO levels is limiting to the C plants.
The fact that C plants respond to higher CO concentration by showing increased rates of photosynthesis leading to higher productivity has been used for some greenhouse crops such as tomatoes and bell pepper. They are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields. . .
Temperature The dark reactions being enzymatic are temperature controlled. Though the light reactions are also temperature sensitive they are affected to a much lesser extent. The C plants respond to higher temperatures and show higher rate of photosynthesis while C plants have a much lower temperature optimum. The temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to.
Tropical plants have a higher temperature optimum than the plants adapted to temperate climates. . . Water Even though water is one of the reactants in the light reaction, the effect of water as a factor is