Photosynthesis, growth and structural characteristics of holm oak resprouts originated from plants grown under elevated CO₂

The physiological characteristics of holm oak ( Quercus ilex L.) resprouts originated from plants grown under current CO 2 concentration (350 μl l −1 ) (A‐resprouts) were compared with those of resprouts originated from plants grown under elevated CO 2 (750 μl l −1 ) (E‐resprouts). At their respective CO 2 growth concentration, no differences were observed in photosynthesis and chlorophyll fluorescence parameters between the two kinds of resprout. E‐resprouts appeared earlier and showed lower stomatal conductance, higher water‐use efficiency and increased growth (higher leaf, stem and root biomass and increased height). Analyses of leaf chemical composition showed the effect of elevated [CO 2 ] on structural polysaccharide (higher cellulose content), but no accumulation of total non‐structural carbohydrate on area or dry weight basis was seen. Four months after appearance, downregulation of photosynthesis and electron transport components was observed in E‐resprouts: lower photosynthetic capacity, photosystem II quantum efficiency, photochemical quenching of fluorescence and relative electron transport rate. Reduction in ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCo) activity, deduced from the maximum carboxylation velocity of RuBisCo, accounts for the observed acclimation. Increased susceptibility of photosynthetic apparatus to increasing irradiance was detected in E‐resprouts.