Gas Exchange,Leaf Structure,and Hydraulic Features in Relation to Sex,Shoot Form,and Leaf Form in An Evergreen Shrub Sabina vulgaris in the Semi-Arid Mu Us Sandland in China

We examined differences in net photosynthetic rate (P_N), transpiration rate (E), water use efficiency (WUE), ratio of substomatal to atmospheric CO₂ concentration (C_i/C_a), cuticle thickness (CT), epidermis cell size (ECS), mesophyll cell size (MCS), vascular bundle size (VBS), tissue density (TD), and coefficient of water loss (k) in Sabina vulgaris as related to sex, shoot form, and leaf form. P_N, E, WUE, C_i/C_a, MCS, VBS, and k varied with sex, whereas CT, ECS, and TD did not. These differences in physiology and anatomy between the female and male plants may be closely related with their reproduction behaviour. P_N, E, C_i/C_a, CT, ECS, MCS, and VBS were significantly smaller in the erect shoots than in the prostrate shoots, WUE was just opposite; TD and k did not vary with shoot form. These changes in physiology with shoot form indicate that erect shoots may be more tolerant of water stress than prostrate shoots. P_N, E, C_i/C_a, TD, and k were significantly greater in the spine leaves than in the scale leaves, whereas WUE, CT, ECS, MCS, and VBS followed the opposite trends. The changes in physiology and anatomy with leaf form suggest that scale leaves have higher drought-resistant and water-holding capacities than spine leaves. Measurements of field gas exchange showed that three-year-old seedlings had lower drought-resistance and higher water loss than five-year-old seedlings, which provides some evidence that seedling survival decreases with decreasing plant age.