CARBON-ISOTOPE DISCRIMINATION IN QUERCUS-ILEX RESPROUTS AFTER FIRE AND TREE-FELL

Ecophysiological differences related to photosynthesis were compared i n helm oak Quercus ilex leaves from undisturbed helm-oak vegetation, r esprouts after fire and resprouts after tree-fell. No significant diff erences in any parameter measured were observed between the two kinds of resprout throughout the first growing season following disturbance. Resprouting leaves showed lower carbon isotope discrimination (Delta) and intercellular CO2 concentration (p(i)), and higher photosynthesis , leaf conductance and transpiration rates than leaves from undisturbe d stands. Nitrogen, soluble protein content and ribulose bisphosphate carboxylase (RuBP-Case) activity were 88%, 96% and 45% higher respecti vely, in both kinds of resprout. The results indicate that photosynthe tic capacity, rather than stomatal conductance, is the limiting factor in photosynthesis in resprouts. Chlorophyll content and chlorophyll a /b ratio did not differ between resprouts and undisturbed leaves, indi cating that the observed differences were not a result of differences in light environment during leaf development. Leaf mass per area (LMA) , was 80% higher in the resprouts, and was negatively related (r = -0. 86) to Delta and positively related (r = 0.87) to N content. Enhanced carbon assimilation after disturbances resulted in higher water use ef ficiency, as indicated by lower Delta values in the resprouts. We conc lude that the cause of defoliation was not relevant in the physiology of the resprouts, suggesting the importance of underground organs.