Date of Award

1994

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

First Advisor

Jim L. Chambers

Abstract

This study evaluated genotypic variation in responses of baldcypress (Taxodium distichum) seedlings to combined flooding and salinity stress. Two experiments form the core of this dissertation. In the first experiment, seedlings of 15 open-pollinated families of baldcypress were exposed to combined salinity and flooding stress under greenhouse conditions. Ten of the families were from coastal locations that were slightly brackish. The other families were from freshwater locations. Five salinity levels were investigated--0, 2, 4, 6, and 8 g l$\sp{-1}$ artificial seawater--all with shallow flooding. Substantial variation was found among salinity levels and families for most of the response variables assessed. In general, families from brackish sources had greater biomass, leaf area, and tolerance index values than families from freshwater sources at the highest salinities, but mean survival did not differ by source. Striking differences in seedling morphology were noted between seedlings that appeared to be salt tolerant and those that were not. More tolerant seedlings had larger mean leaf sizes and retained leaves at the top of the seedling. Less tolerant seedlings exhibited partial stem dieback and near total defoliation, in some cases followed by partial refoliation with smaller leaves. In the second experiment, a subset of seedlings from the greenhouse trial were periodically placed indoors under artificial light, and measurements were made of gas exchange, water potential and chlorophyll fluorescence. Also, an analysis of tissue concentrations of $\rm Cl\sp-,\ Na\sp+,\ K\sp+,\ and\ Ca\sp{2+}$ following harvest of the greenhouse study was included in the chapter summarizing this experiment. Significant variation was found for nearly all the physiological parameters evaluated, but only shoot concentrations of Na$\sp+$ and Cl$\sp-$ were related to family-level differences in salt tolerance. An important conclusion drawn from this study is that there appears to be adequate evidence of genotypic variation in combined flooding and salt tolerance to justify a selection and breeding program. The development of planting material with improved tolerance, combined with efforts to restore original hydrologic regimes where feasible, may be an effective strategy for restoration of coastal forests dominated by baldcypress.

Pages

183

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