Study of the temperature effect in three chestnut (Castanea sativa Mill.) cultivars' behaviour.

The aim of this work was to analyse the effect of temperature in three chestnut cultivars, Aveleira, Judia and Longal. For this purpose, gas exchange, thylakoid membrane potential, photosynthetic pigment and lipid content data in July, September and October under different temperatures (31, 26 and 18 degrees C) were determined. With respect to gas exchanges, significant changes in photosynthesis rate of Aveleira were observed between July and September (7mumol CO2m(-2)s(-1)). In contrast, Judia and Longal showed a strong increase in this period, 6.1-8.5 and 4.9-6.7 micromol CO2m(-2)s(-1), for Judia and Longal, which represent an increase of about 15% and 43%, respectively. Similar patterns were detected in daylight photosynthesis measurements for Judia and Longal, in which an almost 60% decrease was observed, in contrast to 40% for Aveleira, from morning to midday, when temperatures increased from 27 to 34 degrees C. In addition to high photosynthetic rates in the hottest month, Aveleira was also the sunniest cultivar according its highest value on chlorophyll a/b ratio (3.65). Cultivars also presented maximal thylakoid membrane potential at different temperatures, with their values being 20.8, 17.8 and 17.2 degrees C for Aveleira, Longal and Judia, respectively. These results were also supported by thylakoid fatty acid composition which indicated that the unsaturation index of Aveleira (158) was the lowest in comparison with other two cultivars, 168 and 175, for Longal and Judia, respectively.