PHYSIOLOGICAL, MORPHOLOGICAL AND ANATOMICAL RESPONSES OF FRAXINUS-MANDSHURICA SEEDLINGS TO FLOODING

Two-year-old Fraxinus mandshurica Rupr, var. japonica Maxim. seedlings were flooded to 8 cm above soil level for 70 days. The flooding treat ment altered the growth, morphology, stem anatomy and ethylene product ion of the seedlings. Although flooding did not affect height growth, it stimulated diameter growth of the submerged stems by increasing bot h the number and size of wood fibers produced; however, the thickness of the cell walls of the wood fibers was reduced by flooding, In respo nse to the flooding treatment, the seedlings formed abundant hyperhydr ic tissues, originating from the vicinity of lenticels on the surface of the flooded stems, and adventitious roots, which grew through the h yperhydric tissues. Aerenchyma tissues were observed in the bark of th e adventitious roots. The flooding treatment did not affect dry weight increment of leaves and stems, but it reduced the total dry weight in crement of the root system even though it promoted adventitious root f ormation. Flooding also enhanced ethylene production in the submerged portions of stems. The potential roles of flood-induced ethylene in ca mbial growth and adventitious root formation in flooded plants are dis cussed.