Limiting Factors of Photosynthesis

The rate of photosynthesis depends on several factors: light intensity, carbon dioxide concentration and temperature (water availability matters too, but water stress closes stomata before it limits the reactions directly).A limiting factor is the factor that is in shortest supply and so limits the rate of a process. If the level of the limiting factor is increased, the rate increases. Increasing any other factor has no effect until the limiting factor is raised.Photosynthesis has two stages that depend on different factors. Light intensity controls the light-dependent stage (production of ATP and reduced NADP). Carbon dioxide concentration and temperature mainly affect the light-independent stage (the Calvin cycle), where RuBisCO fixes carbon dioxide. The slowest step sets the overall rate.On a graph of rate against one factor, the rising part of the curve shows that factor is limiting. Where the curve levels off (plateaus), a different factor has become limiting. If the plateau is higher when, for example, carbon dioxide concentration is raised, then carbon dioxide was the limiting factor on the plateau.In nature, the limiting factor changes during the day: light is usually limiting at dawn and dusk, while carbon dioxide concentration is often limiting on bright summer days. Temperature is often limiting in winter.