Effects of total submergence in saltwater on growth and leaf ion content of preflooded and unflooded Taxodium distichum saplings

Preconditioning by hypoxic condition would contribute higher tolerance to anoxic condition in physiological and metabolic aspects of various plant species. In expectation of improvement of salinity tolerance, effects of preconditioning with soil flooding on growth responses and photosynthetic activity in relation to Na⁺ content in leaves and roots were studied using 2-year-old Taxodium distichum saplings. A submergence experiment was performed at three salt concentrations (0, 4000, and 8000 ppm NaCl), and preconditioning was started 2 months prior to the beginning of submergence treatments. Continuous soil flooding with freshwater as a control did not inhibit growth in height and stimulated diameter increment of the saplings. Saplings submerged in saltwater and freshwater also showed no morphological changes during submergence treatments. However, leaf injury and shoot dieback were observed in drained saplings that had been submerged in saltwater. Na⁺ and K⁺ ion contents increased with increases in salt concentration in both preconditioned and unconditioned saplings, whereas ion contents in preconditioned saplings tended to be higher than those of unconditioned saplings.