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 26.
The impact of the environment on photosynthesis is of
interest to plant physiologists, ecologists, and agronomists.
From a physiological standpoint, we wish to understand
how photosynthetic rate responds directly to environmental
factors such as light, ambient CO2 concentrations, and temperature,
or indirectly, through the effects of stomatal control,
to environmental factors such as humidity and soil
moisture. The dependence of photosynthetic processes on
environment is also important to agronomists because plant
productivity, and hence crop yield, depend strongly on prevailing
photosynthetic rates in a dynamic environment. To
the ecologist, the fact that photosynthetic rates and capacities
show differences in different environments is of great interest
in terms of adaptation.
In studying the environmental dependence of photosynthesis,
a central question arises: How many environmental