Stomatal Responses of Fraxinus pennsylvanica Seedlings during and after Flooding

Effects of flooding for 10, 20, 30, or 40 days on leaf diffusion resistance (r₁) of fraxinus pennsylvanica seedlings were studied during the period of flooding and continuing for 17 days after flooding. All Flooding treatments induced stomatal closure, as indicated by increased r₁. There was some evidence of stomatal adaptation to flooding, with stomata beginning to reopen after a critical period of flooding. After termination of flooding, stomata opened further within 6 to 10 days to near preflooding levels. The degree of stomatal opening was only slightly higher after 10 days than after 40 days of flooding. Some stomata may have been permanently damaged by flooding. The stomatal adaptation to flooding as well as rapid recovery of stomatal opening, even after prolonged flooding, appeared to be important factors in the flooding tolerance of Fraxinus petmsylvanica and are consistent with its distribution on wet sites.