Factors Affecting Photosynthesis

In 1860, Julius Sachs proposed that any physiological process, including photosynthesis, is governed by three cardinal points - a minimum, an optimum, and a maximum value for each factor it depends on. In 1905, Frederick Blackman refined this idea into what is now called the Law of Limiting Factors, itself essentially a restatement, for physiological processes, of Liebig's earlier Law of the Minimum: Blackman put it that "when a process is conditioned as to its rapidity by a number of separate factors, the rate of the process is limited by the pace of the slowest factor." Put more simply, at any given moment, whichever essential factor is currently scarcest relative to what the process needs will set the process's actual rate, regardless of how abundant the other factors happen to be. A concrete example makes this concrete: even when light intensity is more than sufficient, the overall rate of photosynthesis can still be low if atmospheric CO2 is scarce, since CO2 is then acting as the limiting factor; raising CO2 concentration under these conditions does raise the rate of photosynthesis, but only up to the point where some other factor - most often light intensity itself - becomes the new limiting factor and further increases in CO2 stop producing any further benefit. The factors that can act as limiting factors for photosynthesis fall into two broad groups: external (or environmental) factors - light …