Photoperiod manipulation during nursery culture: Effects on Quercus rubra seedling development and responses to environmental stresses following transplantation

Anthony S Davis, Purdue University

Abstract

With over 1.5 billion forest tree seedlings produced annually in the USA, use of high quality nursery stock is critical to ensure afforestation and reforestation success. Northern red oak (Quercus rubra L.) is an economically and ecologically important forest tree species naturally occurring in the Central Hardwood Forest Region, however physiological conditioning of nursery-grown seedlings to optimize responses under given environmental conditions is relatively unexplored. Photoperiod manipulation, a nursery cultural practice employed to manage conifer seedling development, was investigated to evaluate affects on seedling physiological and morphological status of northern red oak during nursery culture and post-transplanting into limiting environmental conditions. A series of experiments revealed: (i) seedling development during nursery culture is affected in terms of both morphology and physiological status; and (ii) photoperiod manipulation during nursery culture alters seedling development following transplanting after winter storage. During nursery culture, seedling height growth, along with the number of growth flushes, was reduced indicating greater control over seedling morphology with photoperiod manipulation. Net photosynthesis showed an early decrease along the same pattern typically associated with seasonal variation with extensive (28 d) photoperiod manipulation. A corresponding higher tolerance to freezing was detected in those seedlings when tested using stem sections, with seedlings that received 28 d of photoperiod manipulation most cold hardy (e.g., LT 50 < -33°C) and control seedlings least cold hardy (LT50 = -21.49°C). Upon removal from cold storage, faster bud break of seedlings treated with shortened photoperiods occurred. All seedlings exposed to photoperiod manipulation produced more new roots than control seedlings at low (10°C) root-zone temperatures, indicating a predisposition to early growth resumption. When exposed to drought conditions, control seedlings maintained higher leaf xylem water potential (ΨL) than seedlings that received shortened photoperiods during nursery culture. This potential long-term negative effect of photoperiod manipulation could be attributed to faster bud break of those seedlings, which may have led to longer exposure of the actively growing seedlings to drought conditions thereby potentially depleting internal moisture levels. Outcomes are discussed in terms of the differences in responses to optimal and limiting environmental conditions and the potential implications for seedlings quality testing. With most current seedling quality testing conducted under favorable conditions, results may not be readily transferable to the field, where conditions are less favorable.

Degree

Ph.D.

Advisors

Jacobs, Purdue University.

Subject Area

Horticulture|Forestry

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