This thesis research examines the effects of film-forming antidesiccants applied to dormant pondexosa pine (Pinus ponderosa Dougl.) seedlings after being lifted and to actively growing seedlings. The basic proposition was that antidesiccants would have a positive effect on reducing water loss in ponderosa pine seedlings. In order to evaluate the effects of six different antidesiccant treatments on the physiology, morphology, and phenology of ponderosa pine seedlings, four experiments were conducted and four hypotheses tested. Eleven variables were studied: survival, height and diameter growth, budbreak, budset, foliar damage, root growth potential, water loss, stomatal conductance, electrolyte leakage, and chlorophyll fluorescence.
None of the antidesiccants or concentrations tested affected survival or height and diameter growth. However, several antidesiccant treatment did cause temporary reductions in stomata! conductance of outplanted seedlings in June 1992. Seedlings treated with AntiStress® 2000 (1:20 and 1:40) had the lowest reduction in stomatal conductance. In another experiment in a controlled environment, antidesiccants did reduce water loss but failed to significantly affect height growth.
Antidesiccant application to actively growing seedlings subjected to different periods of wind exposure reduced foliar damage as measured by the amount of electrolyte leakage released from the fascicles but increased stomatal conductance. In a separate experiment under greenhouse conditions antidesiccants did not reduce stomatal conductance but they did damage seedling foliage.
The film-forming antidesiccants had a negative effect on the growth of new roots. A 46% reduction in new root growth was observed. When antidesiccants were used, budbreak activity was also delayed. Moreover, in several experiments antidesiccants had no effect on photochemical efficiency. Antidesiccants also did not affect light absorption or emission.
In this thesis research the proposition was that antidesiccants would have a positive effect on ponderosa pine seedlings. Based on the preponderance of evidence from the four experiments conducted, it is concluded that under the conditions of this study, antidesiccants tested had little overall effect on ponderosa pine seedlings. However, had seedlings been subjected to greater water stress, the outcome of this research might have been different
