Photosynthesis and antioxidant enzymes of phyllodes of Acacia mangium

Physiological processes are influenced by environmental factors and plant characteristics. The distribution of photosynthetic capacity of phyllodes of Acacia mangium Willd. seedlings was studied in relation to the in vivo photosystem II (PSII) function, photosynthetic gas exchange, chlorophyll fluorescence and activities of antioxidant enzymes (superoxide dismutase (SOD) and ascorbate peroxidase (APX)) of phyllodes at different positions on seedlings. There was a vertical gradient in photosynthetic capacity of phyllodes along the shoot. Phyllode 1 (at the apex) showed negative carbon uptake at PPFD lower than 400 µmol m(-2) s(-1). High photosynthetic capacities, chlorophyll concentrations, DeltaF/F'(m), and q(P) were observed in phyllodes 4, 6 and 8. The high photosynthetic capacities of mature phyllodes could be attributed to the enhanced availability of CO(2) and the high efficiency of PSII in energy absorption and utilization. Total SOD and APX activities (on a dry weight basis) were highest at phyllode 1 and decreased as the phyllodes matured. The high photosynthetic capacity and low respiration loss in mature phyllodes could be important factors, responsible for the rapid establishment and fast growth of A. mangium in reforestation programs.