The starch content of roots and the osmotic concentration of expressed xylem sap as predictors of Douglas-fir seelding quality Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/12579v809

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  • The goal of this study was to evaluate the ability of two seedling quality evaluation methods to predict the field survival of Douglas-fir (Pseudotsuga menziesii) seedlings. The starch reserves in seedlings have been suggested as a possible predictor of seedling quality. Starch reserves have been shown to decrease during cold storage, but there has been no concentrated evaluation of their relationship to seedling quality and field survival. This study has investigated the correlation between starch reserves in Douglas-fir seedling roots (and needles) and subsequent field survival. It has also evaluated the ability of measurements of the osmotic concentration of expressed xylem sap to detect seedling damage and predict field survival. Results show that neither the starch content of roots nor the osmotic concentration of xylem sap is a reliable predictor of Douglas-fir seedling quality. The study also suggested that the starch content of Douglas-fir needles has no significant relationship to seedling quality. Starch content of roots increased considerably throughout the winter in seedlings growing in nursery beds. Seedlings lifted and cold stored showed large reductions in root starch reserves due to respiration, but did not necessarily exhibit reduced survival potential in the field. Even some seedlings with very low root starch reserves were able to survive on the field site. Any relationship between starch reserves and overall seedling quality is weak at best. The osmotic concentration of xylem sap also failed to exhibit a significant correlation with field survival. The test was unable to reliably detect seedling damage, especially damage resulting from cold storage or root desiccation. The study demonstrated that severe freezing damage often results in significantly elevated solute concentrations in expressed xylem sap, apparently due to leakage of cell solutes through ruptured cell membranes. However, osmotic concentration of xylem sap below the level associated with severe freezing damage does not necessarily indicate that the seedlings are healthy. The method may be a quick and easy way to detect seedlings damaged by freezing. The "standard" root growth potential and stress (OSU vigor) tests are still the most reliable techniques to estimate Douglas-fir seedling quality. The best single predictor of field survival in this study was the mean total length of new roots after one month, which accounted for 51 percent of the variability in field survival.
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