Flood and salinity stress of wetland woody species, buttonbush (Cephalanthus occidentalis) and swamp tupelo (Nyssa sylvatica var.biflora)

Abstract

Buttonbush (Cephalanthus occidentalis) and swamp tupelo (Nyssa sylvatica var.biflora) seedlings were exposed to flooding and salinity conditions simulating the chronic exposure of sea-level rise and the acute exposure of hurricane storm surge. Chronically exposed seedlings were either watered or flooded with 0, 2, or 10 ppt salinity. Those in the acute experiment were watered or flooded with freshwater until exposed to a 21-ppt salinity surge for 48 hours. Freshwater flooding reduced photosynthesis (A), water pressure potential (Ψ), height, and stem and root biomass for swamp tupelo while biomass of buttonbush roots decreased and stem increased. Chronic watering with 2 ppt salinity reduced height, basal diameter, and stem and root biomass for swamp tupelo but did not significantly affect buttonbush. Both species were negatively affected by watering with 10 ppt salinity, with total mortality of swamp tupelo. Flooding with 2 ppt salinity also caused a 100% mortality for swamp tupelo. All buttonbush seedlings survived with reducedA, Ψ, and stem and root biomass. Plants chronically flooded with 10 ppt salinity were more affected, with drastically decreasedA, stomatal conductance (g s ), and Ψ within the first day of treatment and all dying within three weeks. Watering with 21 ppt salinity reducedA andg, of both species during the second day of the surge, but buttonbush recovered within the next 20 days. Flooding with 21-ppt saline water also greatly impacted buttonbush, which did not recover as when watered with 21 ppt salinity. Swamp tupelo was already stressed due to flooding and showed no further reduction in A org s due to the 21-ppt salinity flood surge. Buttonbush seedlings were more tolerant of salinity and flooding conditions than swamp tupelo seedlings, although it is unlikely that either species could survive long-term exposure to 10-ppt salinity flooding.