13 Photosynthesis as a Tool
for Indicating Temperature Stress Events
w. Larcher
13.1 Introduction
Photosynthesis is a major topic in the biophysical and biochemical approaches to plant physiology, as well as in molecular biology. Photosynthesis
forms the central theme in the ecophysiology of carbon assimilation and
carbon budgets of plants and plant stands, and is the basis upon which
heuristic and prognostic production models are constructed. Additionally,
photosynthesis provides an indicator for the quantitative characterization of
states of stress and of functional limitations imposed by environmental
factors.
It is with good reason that methods for studying photosynthesis are
frequently employed in stress physiology. A deterioration in environmental
conditions quickly leads to decreased photosynthesis, resulting either from
reduced CO2 uptake due to narrowing of the stomata or from direct inhibition of primary and secondary processes in the chloroplasts. It has long
been recognized that changes in photosynthesis provide an earlier indication
of stress caused by cold and heat than other criteria of cell stress
and damage, such as abnormal respiration and leakiness of biomembranes
(Alexandrov 1964; Kislyuk 1964).
In this chapter it is not the intent to explain the mechanisms leading
to impairment of photosynthetic function, but rather to present examples
demonstrating how, by means of measuring photosynthetic parameters, the
impact of extreme temperatures can be identified and quantified.
13.2 Development of Temperature Stress and Characteristic Responses
of Photosynthesis
Temperature is an important limiting factor for vigor and distribution of
plants. Each individual process is geared to an optimal temperature, above
and below which its performance drops. At temperatures too high or too
low the photosynthetic yields decrease steadily until CO2 uptake ceases.
After a small and short-lived deviation from the favorable temperature