Chapter 11 - 3 Photosynthesis : Limiting Factors

Limiting Factors "The actual magnitude of assimilation in a leaf at any moment is determined by one or other of the main controlling conditions, light, temperature, or CO2-supply, acting as a limiting factor." That was the conclusion of Blackman and Smith (1910-1911) in the ninth of their series of papers on vegetable assimilation and respiration. We know that water is another important parameter, but we are still trying to understand completely just how these parameters limit bryophyte photosynthesis. Perhaps Blackman and Smith again best sum it up in their statement that studies on photosynthesis "are more harmoniously interpreted from the point of view of interacting limiting factors than by the conception of optima." Gerdol et al. (1998) illustrated this principle of interacting factors in their study of sphagnum capillifolium. They found that low nighttime temperatures could lower growth five-fold, that nutrients limited growth when nighttime temperatures were high, that N and P limited growth at optimum temperatures. Different enzymes are turned on at different temperatures and different pH levels, and Gerdol et al. suggested that enzymatic reactions could be limited at unfavorable temperatures.