Chlorophyll fluorescence of stem cambial tissue reflects dormancy development in Juglans nigra seedlings
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Assessment of chlorophyll fluorescence (CF) of forest tree seedlings can provide important insight into physiological function, dormancy status, and stress resistance. This evaluative tool has been measured routinely using foliage on conifer seedlings to assess seedling physiological status during winter dormancy. Absence of foliage during dormancy has thus far precluded the potential application of CF to seedling quality assessment of temperate deciduous hardwood seedlings. Because stems contain chlorophyll, however, assessment of CF using stem tissue may serve as an effective alternative tissue type to facilitate CF measurements. We collected Juglans nigra L. (black walnut) seed from two provenances (Alabama and Indiana, USA) and subjected 1-year-old container seedlings from these provenances to a simulated hardening regime (i.e., progressively decreasing temperatures and photoperiods) in a growth chamber environment over an 18-week period; CF of stem tissue (evaluated as ΦPSII, efficiency of photosystem II) was sampled periodically at seven time intervals. Though both provenance and measurement period significantly affected ΦPSII, measurement period had a much more pronounced effect. Values for ΦPSII fluctuated (ranging from 0.45 to 0.72) during the simulated growth and hardening regimes, generally decreasing over time for both provenances. Our results suggest that physiological status of temperate deciduous seedlings may be effectively evaluated during dormancy by assessing CF of stem tissue.
KeywordsBlack walnut Dormancy Forest restoration Seedling physiological status Stress resistance
Funding support for this research was provided by the USDA Forest Service State and Private Forestry and Purdue University. We appreciate constructive comments from a Guest Associate Editor, two anonymous reviewers, and J. Sloan that helped to improve the manuscript.
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