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THE CONVERSION OF SOLAR ENERGY to the chemical energy of organic compounds is a complex process that includes electron transport and photosynthetic carbon metabolism (see Chapters 7 and 8). Earlier discussions of the photochemical and biochemical reactions of photosynthesis should not overshadow the fact that, under natural conditions, the photosynthetic process takes place in intact organisms that are continuously responding to internal and external changes. This chapter addresses some of the photosynthetic responses of the intact leaf to its environment | Chapter 9 Photosynthesis Physiological and Ecological Considerations THE CONVERSION OF SOLAR ENERGY to the chemical energy of organic compounds is a complex process that includes electron transport and photosynthetic carbon metabolism see Chapters 7 and 8 . Earlier discussions of the photochemical and biochemical reactions of photosynthesis should not overshadow the fact that under natural conditions the photosynthetic process takes place in intact organisms that are continuously responding to internal and external changes. This chapter addresses some of the photosynthetic responses of the intact leaf to its environment. Additional photosynthetic responses to different types of stress are covered in Chapter 25. The impact of the environment on photosynthesis is of interest to both plant physiologists and agronomists. From a physiological standpoint we wish to understand how photosynthesis responds to environmental factors such as light ambient CO2 concentrations and temperature. The dependence of photosynthetic processes on environment is also important to agronomists because plant productivity and hence crop yield depends strongly on prevailing photosynthetic rates in a dynamic environment. In studying the environmental dependence of photosynthesis a central question arises How many environmental factors can limit photosynthesis at one time The British plant physiologist F. F. Blackman hypothesized in 1905 that under any particular conditions the rate of photosynthesis is limited by the slowest step the so-called limiting factor. The implication of this hypothesis is that at any given time photosynthesis can be limited either by light or by CO2 concentration but not by both factors. This hypothesis has had a marked influence on the approach used by plant physiologists to study photosynthesis that is varying one factor and keeping all other environmental conditions constant. 172 Chapter 9 TABLE 9.1 Some characteristics of limitations to the rate of photosynthesis .
