The Photosynthesis and Water Use Efficiency of Eight Garden Tree Species

Gas exchange parameters in leaves of eight 2 to 3 year old garden tree species growing in the institute nursery were measured during the summer in 1999, by using LCA 4 portable photosynthesis and transpiration system. The results are as follows: (1) the daily variation of the net photosynthesis rate( Pn, μmol·m-2 ·s-1), stomatal conductance(gs, mol·m-2 ·s-1), transpiration rate( E, mmol·m-2 ·s-1), and instantaneous water use efficiency(Pn/E, μmol CO2·mmol-1O H2O) are remarkable and differ among species. (2) the daily average P n are 11.2, 9.7, 8.6, 8.5, 6.3, 5.8, 5.6 and 3.4 μmol·m-2 ·s-1 for Erythrina crista galli, Cleistocalyx operculata, Pterocarpus indicus, Ficus celebensis, Sterculia lanceolata, Pachira aquatica, Jatropha pandurifolia, Saraca dives pierre,respectively, showing that the first four species have relatively higher capacity for CO 2 assimilation. (3) the daily mean values of transpiration rate are 3.40, 2.79, 2.55, 2.32, 2.32, 2.25, 2.25 and 1.57 mmol·m-2 ·s-1 for Erythrina crista galli, Ficus celebensis, Cleistocalyx operculata, Sterculia lanceolata, Pachira aquatica, Saraca dives pierre, Pterocarpus indicus, Jatropha pandurifolia, respectively, indicating that the former 3 species consume greater amount of water than other species. (4) The daily average WUE are 3.97, 3.73, 3.68, 3.48, 3.84, 3.03, 2.79, 2.64 and 2.50 μmol CO2·mmol-1O H2O for Pterocarpus indicus, Cleistocalyx operculata, Jatropha pandurifolia, Erythrina crista galli, Ficus celebensis, Sterculia lanceolata, Pachira aquatica, Saraca dives pierre, respectively,suggesting that the first four species have relatively higher water use efficiency than the others. Information presented here is helpful for understanding the differences among species in aspects of growing and productivity. It might also be useful to guide garden practices in water management.