Physiological Characteristics of Acacia auriculiformis A. Cunn. ex Benth., Acacia mangium Willd. and Pterocarpus indicus Willd. in the La Mesa Watershed and Mt. Makiling, Philippines

The physiological responses of nitrogen-fixing species (Acacia auriculiformis A.Cunn. ex Benth., Acacia mangium Willd. and Pterocarpus indicus Willd.) were determined using 2-year-old, 10-year-old and 20-year-old age classes. Parameters obtained were stomata size and number, leaf anatomical characteristics, total leaf nitrogen and carbon concentrations, net photosynthesis rate (P-N), photosynthetic nitrogen utilization efficiency (PNUE), transpiration rate (E), stomatal conductance (g), water use efficiency (WUE), net CO2 assimilation rate vs calculated internal CO2 concentrations (A/C-1 curve), rate of maximum Rubisco carboxylation (V-cmax) and photosynthetic photon flux density saturated rate of maximum electron transport (J(max)). In all the studied species and age classes, significant differences in P-N were observed (p<0.001) and was higher in 20-yr-old A. mangium (12.4 mu mol CO2 m(-2) s(-1)) and A. auriculiformis (11.5 mu mol CO2 m(-2) s(-1)). Also, PNUE, g(s), and WUE were significantly higher (p<0.050) in 20-yr-old A. auriculiformis (4.57 mu mol g(-1) s(-1), 0.71 mol H2O m(-2) s(-1), and 7.71 CO2 m(-2) s(-1/)mmol H2O m(-2) s(-1), respectively) and A. mangium (5.93 mu mol g(-1) s(-1), 0.86 mol H2O m(-2) s(-1), and 7.94 mu mol CO2 m(-2) s(-1)/mmol H2O m(-2) s(-1), respectively). A. auriculiformis and A. mangium showed better physiological attributes, which could be important features for species to be used for rehabilitating degraded areas of the country.