Intraspecific variation in the response of Taxodium distichum seedlings to salinity

Seedlings of 15 open-pollinated families of baldcypress (Taxodium distichum) were tested for their tolerance to combined salinity and flooding strees. Ten of the families were from coastal locations in Louisiana or Alabama, USA, that were slightly brackish. The other families were from locations not affected by saltwater intrusion. Five salinity levels were investigated — 0, 2, 4, 6, and 8 g l⁻¹ artificial seawater—all with flooding to approximately 5 cm above the soil surface. Survival, height growth, leaf area and total biomass all declined with increasing salinity. Significant variation was found among salinity levels, families, and salinity×family interactions for leaf area and total biomass. Two tolerance indices were also developed to compare family response with salinity. In generalm families from brackish sources had greater total biomass, leaf area, and tolerance index values than families from freshwater sources at the higher salinity levels. A selection and breeding program designed to develop moderately salt-tolerant baldcypress seedlings for use in wetland restoration projects and other applications appears to be well-justified.