Relationship between photosynthetic activity and chlorophyll content in an isolated Quercus ilex L. tree during the year

The relationship between chlorophyll (Chl) content and net photosynthetic rate (P-N) in an isolated Quercus ilex tree, growing inside Villa Pamphili Park in Rome, was explored. The highest P-N was in March, May, and September (10.1 mu mol m(-2) s(-1), maximum rate). P-N decreased by 65 % (with respect to the yearly maximum) when leaf temperature reached 34 degrees C, and by 50 % when leaf temperature was 9 degrees C. The highest Chi contents were in April, October [1.47 g kg(-1)(d.m.), maximum value], and December. The lowest Chi content was found in July (0.78 g kg(-1)). The decrease of P-N in July was in close connection with the decrease of Chi content. On the contrary, the high Chi content during winter did not correspond with P-N of this season. Discordances between Chi content and P-N over the year influenced the regression analysis, which although positive did not show very high correlation coefficients (r = 0.7). The high Chi (a+b) content during most of the year indicated that the photosynthetic apparatus remained basically intact also during stress periods.