Graduate Thesis Or Dissertation
 

Influence of Limited Water Access on Douglas-fir Seedling Root Systems, Physiology, and Growth

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  • Nursery-grown seedlings are critical for attaining reforestation and restoration success in many ecosystems, including mixed-conifer forests in the Northwest, which is the native range for Douglas-fir (Pseudotsuga menziesii). Seedling establishment after planting depends on coordinated responses in seedling growth, physiology, and hydraulic function. The chapters in this dissertation review growth targets for seedling morphology, test methods to describe root growth and function, and evaluate how water limitation and experimental manipulations of seedling root morphology impact root hydraulic function and whole-plant responses of Douglas-fir seedlings. Results show that root hydraulic function changes in response to water limitation due to drying soil, but not in response to water limitation created through removal of portions of the root system. Aboveground physiological functions of seedlings, including photosynthesis and growth, change along with root hydraulic function, as predicted by a conceptual model of seedling establishment. However, the results described within these chapters challenge some of the assumptions about root growth after planting and its role in seedling establishment. Specifically, greater initial root volume did not lead to greater root growth and an increase in root growth was not proportional to increase root hydraulic conductance in water-limiting conditions. From this dissertation, one can conclude that classifying hydraulic characteristics of nursery-grown seedlings and assessing functional responses after planting will help with planning for and troubleshooting reforestation and restoration challenges.
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  • Funding for this research was provided by PotlatchDeltic and Oregon State University’s College of Forestry.
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