WATER VAPOUR AND CARBON DIOXIDE EXCHANGE OF LEAVES AS AFFECTED BY DIFFERENT ENVIRONMENTAL CONDITIONS
Many environmental factors affect the gas exchange of leaves (Tab. 1A). In the environment of the shoot those are light, the water vapour and CO2 concentrations in the air, temperature and the concentrations of pollutants. In the root environment (Tab. 1A) these factors are mainly water and nutrients, salinity and soil temperature.
Leaves show different response types of gas exchange to these environmental factors (Tab. 1B). Short-term responses occur in seconds or minutes, and they are usually caused by light flecks (10) and consecutive leaf temperature changes. They are typical for many natural environments, depending on clouds or on the movement of leaves caused by wind and within-canopy convection. Of the steady-state responses of leaf gas exchange to light (11), water vapour (3, 30), temperature (12, 13, 30) and CO2 (4), we have quite a good knowledge. Investigating those responses it is possible to learn about the long-term effects of pollutants (14, 74), climate and photoperiod (15), leaf ontogeny (16), soil water availability (17, 18) and nutritional factors (19), which are related to growth conditions and which determine the carbon (20) and water balances (21) at the leaf and the whole plant level. In the following, examples of these responses will be presented. They are qualitatively similar in the field and in protected cultivation. Differences between natural and controlled growth conditions are of quantitative nature. Their relevance in terms of energy saving in protected cultivation is discussed.