Effects of salinity on leaf characteristics and CO2/H 2O exchange of Kandelia candel (L.) Druce seedlings

Effects of salinities on leaf characteristics and CO2/H 2O exchange of mangrove species Kandelia candel seedlings were studied in a pot experiment. The seedlings grown in salinity of 50‰ caused a strong reduction in the rate of growth, but their leaves were black-green, smaller and less expanded or distorted than those of plants in the control and treatment of 25‰. As compared with control plants, leaves of plants treated with salinity of 25‰ were shiny and smooth. Stomatal number and density under the epidermis in leaves were reduced with the increase of salinity. Mesophyll cells in plants grown in salinity of 50‰ were smallest, 25‰ ranked the second and 0‰ were largest. Their arrangement was compact in 50‰, while in the control it was loose. Cells of the upper epidermis in leaves of control plants were loose and the cell wall was thin while that of 50‰ was more compact and the cell wall was thicker than that of 25‰. Chlorophyll (Chl) (a + b) content (uμmol/cm 2) in plants grown in 50‰ salinity increased significantly compared with that in 0‰, and Chl a/b was also reduced. Carotenoid pigments (Car) increased significantly in different treatments. Photosynthesis (Pn) was significantly inhibited by higher salinity, and the light compensation point of higher salinity leaves increased. Net photosynthetic rate (Pn), stomatal conductance (Cs), and transpiration rate (Tr) were reduced with the increase of salinity while dark respiration (Rd) increased.