Abstract: In this experiment , we investigated sex-related heterogeneity in stomatal distribution and gas exchange on leaves of male and female trees of Populus cathayana using grids measurement and 2-D contour maps . There were significant differences in stomatal length (SL), stomatal width (SW) and stomatal ratio (SR) between leaves of female and male and the significant variations were P= 0.000, P= 0.000 and P= 0.002, respectively. Compared with leaves of male trees, SL and SW in leaves of female trees increased 51 . 86% and 67 . 06% , respectively , while SR in which decreased 11 .46% .
Moreover , the patterns for stomatal density (SD) as“middle zones > apical zones > basal zones”and for SL as“apical zones > middle zones > basal zones”were found in both male and female leaves. The patterns for SW were observed as“middle zones > apical zones > basal zones”in female leaf and“apical zones > middle zones > basal zones”in male leaf . It was also detected that the patterns for SR in female leaf as“basal zones > apical zones > middle zones”was opposite to that in male leaf . Significant difference was found in distribution pattern of net photosynthetic rate ( Pn) between female and male leaves . Pn of female leaf was lower in base regions (2 . 00 - 3. 00μmol m^{- 2} s ^{- 1} ) while higher in front regions (8.00
- 9 . 00μmol m^{- 2} s ^{- 1} ), and increased gradually from basal to apical zones . However , Pn of male leaf didn′t show certein pattern. The transpiration (Tr) and stomatal conductance (Gs) showed significant lower value in basal zones on male leaf comparing with famale leaf . Furthermore, CO2 concentration (Ci ) showed pattern as“basal zones > middle zones > apical zones, which was opposite to stomatal limiting value (Ls) , were observed on female leaf . Only Ls was found increased gradually from apical to basal zones although Ci and Ls varied obviously in each zones . To summarize , our result showed
that there were significant differences in heterogeneity of stomatal distribution and gas exchange on male and female Populus cathayana leaves.

Key words: Populus cathayana