| Propagules of Bruguiera gymnorrhiza and Aegiceras corniculatum were collected at various stages of development while still on the parent plant, separated into pericarp and hypocotyl. Length, diameter, density, fresh weight, dry weight, water content, osmotic potential and element concentrations (Ca, Mg, Na, K, Cl) were determined for each. Seedling of B. gymnorrhiza and A. corniculatum were cultured for 60 days on various salinity of seawater (0, 5, 10, 15, 20, 30, 40, 50‰) in green house. Samples were taken at 3, 7, 11, 15, 22, 30, 45 and 60 days after planting, separated into root, hypocotyl, stem and leaf. Length (height), fresh weight, dry weight, water content, osmotic potential and element concentrations (Ca, Mg, Na, K,Cl) were determined for each. Leaf area and photosynthetic characteristics were measured on various salinity. The paper also studied the survivorship, early growth and leaf photosynthetic characteristics of kandelia candel seedlings planted in the tidal mangrove area of Zhangjiang estuary of Yunxuao, Fujian.The propagules of B. gymnorrhiza and A. corniculatum undergo some growth before becoming detached from the parent plant. They accumulated large amounts of ions during the development while the level of ion concentrations are consistently lower in their embryos compared to leaves of parent plant. Before detachment, the growth of hypocotyls were reduced, the water content declined, while the osmotic potential was approaching to or more negative than that of the solution on which their parent plant vegetating. Thus help the seedlings survive better in the flooding and saline conditions. The density of mature hypocotyls of B. gymnorrhiza was close to or lower than seawater, thus the propagules can float and be dispersed by tide. On the contrary, the density of mature hypocotyls of A. corniculatum was much higher than seawater, they tend to sinking and grow around their parent plant.When the substrate salinity was higher than 30 ‰, the germination rate of A. corniculatum declined sharply with increasing salinity, whereas the germination rate of B. gymnorrhiza was independent of salinity. Both species grew poorly in the culture medium absent of salt, especially to A. corniculatum. Moderate salt stress (from 5‰ to 20‰) can stimulate the growth of both species, and the optimum salinity for growth was from 10‰ to 15‰. When the substrate salinity was higher than 30‰, stem height, root length, dry mass increment, net photosynthetic rate fell remarkably for both species. With the increase of substrate salinity, the accumulated sodium and chloride increased. As a result, all tissues had considerablly lower osmotic potentials than that of the solution on which they were grown at60 day after planting. Changes in length, dry weight, water content, ion concentrations, osomotic potential, ion content of hypocotyls during culture indicated that viviparous hypocotyls not only afforded nutrition for seedling growth, but also reserved ions, thus charged the balance of ion concentration and osmotic potential of the seedling.We investigated early growth and mortality of K. candel seedlings under the mangrove canopy and bare tide flat across a tidal gradient. After 1 year, the survival rates of seedlings planted in K. candel forest, Avicennia marina forest and at bare tidal flat were 54.7%, 13.7% and 76.0%, respectively. Insect and crab feeding were the main cause of lower survivorship of K. candel seedlings under A. marina forest. Among the surviving K. candel seedlings, seedlings at bare tidal flat grew much better in terms of height, diameter, leaf production and biomass than did under the A. marina forest and K. candel forest. Seedlings at bare tidal flat had relatively larger leaf area and leaf number and higher net photosynthetic rate than did under the A. marina forest and K. candel forest. There were higher Chi content and lower Chi a/b ratio in leaves of seedling growing under K. candel forest than those growing at bare tidal flat. On the contrary, there was the lowest Chi conten...
|
PDF Full Text Request