Plants exposed to full sunlight seem to close stomata with a lower air saturation deficit (Fanjul et al.1985) than shaded plants (Hernandez et al. 1989), and photosynthesis is maintained for a longer period of time.
In the studies cited above, it was also evidenced that leaves at full sunlight with fast stomatal closure showed an increase in the leaf temperature, from 10 to 15°C above ambient temperature (Butler 1977; Kanechi et al. 1995). It is well known that high temperature affects the chemical reactions related to the incorporation of carbon in plants, since they are mediated by enzymes (Berry and Böjorkman 1980).
Low temperatures also affect photosynthesis. In assays in which the shoot of one yearold C. arabica seedlings were exposed to low temperatures only once, photosynthesis was considerably reduced, being more than 50% at 4°C (Bauer et al. 1985). At 0.5°C some injury occurred and the