| Three Taxodium salinity studies and one Taxodium genotype study were conducted from 2007 to 2009. The purpose of the salinity studies was to evaluate growth and ion uptake of Taxodium genotypes--two varietal collections and one hybrid--exposed to acute and chronic application of saline solutions. The purpose of the genotype study was to evaluate growth and performance of Taxodium genotypes, varieties, and seedlings at the SFA Gardens, Stephen F. Austin State University, Nacogdoches, TX.;In the first Taxodium salinity study, beginning July 11, 2007, four sea salt concentrations (0, 204, 408, and 612 moles·m-3) were applied one time per week for eight weeks to container plants. When no salt damage was visually evident, the treatment frequency was changed to two times per week and that regime continued for the final eight weeks of the sixteen-week project. In spite of doubling the application frequency in midcourse of this study, all plants survived and few exhibited salt damage. However, there were significant effects of the salt treatments on leaf tissue elemental concentrations and growth (plant height change and relative growth rate). Increasing salt rates reduced growth in all three genotypes. Leaf Na concentrations reached elevated levels in the sea salt treatments.;In the second Taxodium salinity study, BC, MC, and T302 were subjected to acute salt applications for eight weeks in a container study to test the effect of NaCl and KCl/CaCl2 on the leaf water potential and tissue elemental concentrations. In the KCl/CaCl2 solution, T302 exhibited the highest content of Ca and K; BC had the lowest content of K. In the NaCl solution, T302 exhibited the highest content of K and leaf Na. BC had the lowest content of K. All three genotypes had higher contents of Ca, K and lower contents of Na, Mg in KCl/CaCl2 solution than in NaCl solution. BC showed the most damage, followed by MC, T302 showed the least. The leaf water potential in Taxodium decreased as the salt rates increased. T302 had the highest leaf water potential, BC had the lowest, and MC was in between. This may indicate that MC and T302 have more salt tolerance than BC. In the NaCl solution, the concentration of Na in Taxodium significantly increased as the salt rates increased. In the KCl/CaCl2 solution, the concentration of K and Ca in Taxodium increased as the salt rates increased.;In a third salinity study, BC and T302 were subjected to salt exposure of four rates of NaCl solution (0, 51, 102, and 153 moles·m -3) in a container study. There was no significant salt rate effect on Ca, Mg, S, and P in T302. The ratio of Na to K in both genotypes significantly increased as the salt rates increased. Leaf, stem, root Na in BC increased as the salt rates increased. Based on the salt damage symptoms and the apparent capacity for excluding Na, it appears that the salt tolerance of T302 was higher than BC.;In these acute and chronic application salt tolerance studies, it was found that variation existed in Taxodium genotypes (BC, MC, and T302) for salt tolerance. There were significant effects of salt rates on leaf tissue nutrient levels and growth. Increasing salt rates reduced growth in Taxodium genotypes. The concentration of Na in the leaf tissue increased as the sea salt concentration increased. The salt tolerance of Taxodium was improved in a hybrid cross between T. distichum var. distichum (BC) and T. distichum var. mexicanum (MC) genotypes. The benefits of using a hybrid cross (T302) that maintains greater biomass than BC or MC across a range of salinities must be weighed against the negative effects created by plagiotropic growth form relative to BC and MC, and reduced flood tolerance relative to BC.;Seventeen Taxodium genotypes were evaluated for growth performance. No significant difference in height growth was found among genotypes during the period from 2006 to 2010. However, based on leaf color retention in the fall and the time for leaf emergence, it was concluded that the overall performance of the hybrid T302 was the best of all 17 Taxodium genotypes under natural plantation conditions without imposed stress. (Abstract shortened by UMI.)... |
