External and Internal Factors Regulating Photosynthesis

This chapter discusses the external and internal factors regulating photosynthesis. Photosynthesis is simultaneously regulated by many factors. Environmental factors, consisting primarily of light, water, heat, carbon dioxide, and other gases, can have direct effects on photosynthesis when they alter rates of chemical processes in the photosynthetic pathway. Environmental factors along with nutrients and sink demands for carbohydrates may also have indirect effects on photosynthesis. Indirect effects are the result of changes in nonphotosynthetic processes that, in turn, alter the rate of photosynthesis. A final category of regulators, photosynthetic framework, consists of substances that compose the physiologically active compounds and structures that form the basis of the light and dark reactions responsible for photosynthesis. The framework determines the photosynthetic capacity of a plant or organ, that is, the rate of photosynthesis achievable when direct and indirect effects are non-limiting. The main components of the photosynthetic framework are the physical structure and arrangement of photosynthesizing organs, and the nutrients involved in the photosynthetic pathway.