Analysis of photosynthesis-water relationship between simple- and compound-leafed leguminous trees

To investigate the influence of leaf form on the relationship between water and photosynthesis of leaves and branches, we measured the stomatal conductance, leaf water conductance, water potential, and relative water content of 11 compound-leafed species and six simple-leafed species in Fabaceae. Results showed no significant differences in midday water potential between leaf rachises (-0.91 MPa) of compound-leafed trees and branches of simple-leafed trees (-0.88 MPa). However, the midday water potential of the branches of compound-leafed trees (-0.60 MPa) was significantly higher than that of simple-leafed trees. The percent decrease in midday stomatal conductance of compound-leafed trees was significantly higher than that of simple-leafed trees (55.3% vs. 34.1%). We found significantly positive correlations between leaf and stem midday water potentials in all 17 species, and between the rachis and stem midday water potentials in the 11 compound-leafed species. There was no correlation between midday water potential of leaflets, leaf rachises, and branches and midday stomatal conductance. There was a significant positive correlation between leaf hydraulic conductance and midday stomatal conductance across the 17 species (r=0.79, P<0.001), and a significant negative correlation between leaf hydraulic conductance and percent decrease in midday stomatal conductance (r=-0.81, P<0.001), indicating the important role of leaf hydraulic conductance in maintaining diurnal stomatal conductance. There were significant differences in the photosynthesis-water relationship among simple-and compound-leafed tree species, reflecting their different adaptive strategies to environmental conditions.