Carbon isotope discrimination in Quercus ilex resprouts after fire and tree-fell

Ecophysiological differences related to photosynthesis were compared in helm oak Quercus ilex leaves from undisturbed helm-oak vegetation, resprouts after fire and resprouts after tree-fell. No significant differences 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 undisturbed stands. Nitrogen, soluble protein content and ribulose bisphosphate carboxylase (RuBP-Case) activity were 88%, 96% and 45% higher respectively, in both kinds of resprout. The results indicate that photosynthetic 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, indicating 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 efficiency, as indicated by lower Delta values in the resprouts. We conclude that the cause of defoliation was not relevant in the physiology of the resprouts, suggesting the importance of underground organs.