Root and shoot responses of Taxodium distichum seedlings subjected to saline flooding

Variation among progeny of five half-sib family collections of baldcypress ( Taxodium distichum) from three freshwater and two brackish-water seed sources subjected to saline flooding was evaluated. Mini-rhizotrons (slant tubes) were used to monitor root elongation for a period of 99 days. Salinity level produced significant effects across all baldcypress half-sib families, with root elongation averaging 1594.0, 956.8, and 382.1 mm, respectively, for the 0, 4, and 6 g l −1 treatments. Combined mean root elongation for families from brackish-water seed sources was greater (1236.7 mm) than for families from freshwater seed sources (794.6 mm). Considerable variation occurred at the highest salinity treatment, however, with one freshwater family maintaining more than 28% more root growth than the average of the two brackish-water collections. Hence, results indicate that short-term evaluation of root elongation at these salinity concentrations may not be a reliable method for salt tolerance screening of baldcypress. Species-level effects for height and diameter, which were measured at day 62, were significant for both parameters. Height increment in the control (7.4 cm), for example, was approximately five times greater than height increment in the 6 g l −1 salinity treatment (1.5 cm). Family-level variation was significant only for diameter, which had an incremental range of 0.2 to 1.5 mm across all salinity levels.