Electrolyte Leakage from Stem Tissue as an Indicator of Hardwood Seedling Physiological Status and Hardiness

—It is important to identify rapid and accurate methods for assessing hardwood seedling quality and physiological status. Evaluation of electrolyte leakage (EL) from plant tissues is promising for this purpose. It has successfully predicted the physiological status of conifer seedlings and has been used experimentally on European hardwood species. Three species of hardwoods, northern red oak (Quercus rubra L.), black walnut (Juglans nigra L.), and black cherry (Prunus serotina Ehrh.), were evaluated for cold hardiness after being subjected to three storage methods (freezer, cooler, ambient) of varying duration. Higher EL values at longer durations represent a loss of dormancy and increase in cell damage over time. For all species, an increase in EL over time corresponded to a decrease in the number of days required for budbreak under greenhouse conditions. While trends were similar for all species and storage methods, DBB and EL levels did not appear to be related to greenhouse height growth. Further study is needed to assess the viability of EL as a predictor of seedling hardiness and quality for commonly produced hardwoods. The assessment of seedling quality is an important component of reforestation and afforestation programs. Use of low quality seedlings may result in low growth rates and plantation establishment failure (Sampson et al. 1996). It is important to identify high quality stock that has the potential for vigorous root and stem growth. New roots are more efficient in supplying the newly planted seedling with water, which is essential for withstanding transplant stress (Stone 1955, Nambiar et al. 1979, Rietveld 1989, Larcher 1995). Vigorous seedlings grow at increasingly faster rates compared to seedlings of low vigor (Vyse 1982; Burdett 1990) and growth differences evident shortly after transplanting may be maintained over the life of a planting (Paterson and Fayle 1984). Plantings established with high quality seedlings may ultimately require less maintenance (Paterson and Fayle 1984, Burdett 1990) and are more resistant to insect and disease stress (Schoeneweiss 1981, Cordell et al. 1989, Landis et al. 1989; Sutherland et al. 1989). Lifting procedures, post-lifting cold storage, and choice of planting site are important considerations in maintaining a high level of seedling quality. Transporting seedlings from the nursery to storage and then to the planting site subjects them to numerous physical and environmental stresses that lead to a reduction in vigor needed for establishment success (McKay 1996, Maki and Colombo 2001). Seedling vigor is associated with physiological activity of healthy tissue (Sampson et al. 1996). Therefore, the need for practical and efficient methods to monitor changes in seedling physiological status is apparent. The primary focus of most quality assessment research has been on conifer species, as these are produced in the greatest quantities (Moulton and Hernandez 2000). However, hardwood seedling demand is increasing, primarily as a result of ecological restoration and conservation practices (King and Keeland 1999, Stanturf et al. 2000). Consequently, research seeking to improve quality assessment methods for hardwood seedlings is increasing in significance. Cold hardiness assessment is one method for evaluating quality. It provides a measure of dormancy status (Ritchie 1984); predicts the ability of seedlings to withstand stresses associated with lifting, storing, and planting (O’Reilly et al. 1999); and provides an indication of field performance potential †Graduate Research Assistant (BCW), Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Purdue University, 195 Marsteller St., West Lafayette, IN 47907-2033; Assistant Professor (DFJ), Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Purdue University, 195 Marsteller St., West Lafayette, IN 47907-2033. BCW is corresponding author: to contact, call (765) 496-6686 or e-mail barrett@fnr.purdue. edu.