Daily and seasonal trends of gas exchange in Pistacia lentiscus L.

The spring-summer photosynthetic behaviour of Pistacia lentiscus, a spontaneous evergreen bush of the Mediterranean macchia, was followed during two consec- utive years. Outdoor measurements were carried out monthly in the period from May to September in the years 2004 and 2005. Mean values of net photosynthesis (P N )of external tests show a typical daily trend: a rise until the maximum followed by a decline of assimilation with lower values maintained until the end of day. External data were validated by light-response curves, obtained under different thermal regimes in controlled conditions. External trials and measures in controlled conditions confirm an elevated photosynthetic activity below 30 C and a decrease over that limit. The results obtained evidence that the CO 2 assimilation of the P. lentiscus is influenced by stressful temperatures. The ecophysiological response to this limit- ing factor is an adaptation that concentrates on the photo- synthetic activity in the hours of the day and in the periods of the year in which temperatures are more favourable.