LONG-TERM AND SHORT-TERM FLOODING EFFECTS ON SURVIVAL AND SINK-SOURCERELATIONSHIPS OF SWAMP-ADAPTED TREE SPECIES

About 95% of swamp tupelo (Nyssa sylvatica var. biflora (Walt.) Sarg.) sweetgum (Liquidambar styraciflua L.) seedlings survived continuous r oot flooding for more than two years, whereas none of the swamp chestn ut oak (Quercus michauxii Nutt.) and cherrybark oak (Q. falcata var. p agodifolia Ell.) seedlings survived one year of flooding. Death of oak seedlings occurred in phases associated with periods of major vegetat ive growth, e.g., after bud burst in spring, after summer stem elongat ion, and during the winter deciduous stage, suggesting that stored res erves and sources were inadequate to maintain the seedlings when veget ative sinks were forming. Additional evidence that flooding induced a source deficiency in oak was that leaves of flooded oak were 65 to 75% smaller than leaves of nonflooded oak. Flooded swamp tupelo seedlings had a normal leaf size and patchy stomatal opening compared with nonf looded seedlings. Flooding caused increases in alcohol dehydrogenase ( ADH) specific activity in taproot cambial tissues and increases in sta rch concentrations of swamp tupelo seedlings that were reversed when s eedlings were removed from flooding. Flooding had little effect on sol uble sugar concentrations in swamp tupelo or sweetgum. In the long-ter m flood-dry-flood treatment, in which all species had survivors, upper canopy leaf photosynthetic rates were higher in all species during th e dry period than in nonflooded controls, whereas their starch and sol uble sugars concentrations were similar to those of nonflooded control s. Based on seedling survival and the sink-source relationships, the o rder of flood tolerance was: swamp tupelo > sweetgum > swamp chestnut oak > cherrybark oak.