Carbohydrate dynamics and kernel oil in pecan: Alternate bearing drivers and post-ice-storm management

Pecan (Carya illinoinensis (Wangenh.) K. Koch) is a perennial nut crop whose productivity, kernel quality, and resilience to disturbance are strongly influenced by whole-tree carbohydrate management and the physiological processes regulating oil biosynthesis. This thesis combines basic and applied research in three related chapters to (1) summarize the current knowledge on carbohydrate storage, mobilization, and alternate bearing, (2) assess the impacts of nitrogen fertilization and epicormic shoot removal after severe ice-storm damage, and (3) quantify seasonal oil accumulation, kernel percentage, and soluble-sugar and starch dynamics in nuts and shoots to assess how resource allocation influences nut quality and orchard recovery. The first chapter summarizes site-specific and seasonal variances of non-structural carbohydrates (NSCs). The synthesis highlights both cultivar and environmental influences on oil contents (generally 62 - 77%) and when the majority of lipid deposition occurs (about 120-150 DAF), with implications for developing a carbohydrate-based approach to the management of nut production. The second chapter describes a two-year factorial field study in an ice-damaged 'Kanza' orchard, indicating that nitrogen was the primary determiner of oil percentage and fatty-acid composition. Full nitrogen (70 lb N acre⁻¹) consistently increased total oil, and fatty acid profiles shifted to include greater proportions of linoleic and linolenic fatty acids and less oleic acid. The removal of epicormic shoots caused a modest increase in oil percentage without significantly altering fatty acid composition. A significant nitrogen × shoot removal interaction indicated that the highest oil quality occurred with a 75% removal of shoots with full N fertilization. The third chapter characterizes a seasonal oil accumulation rate, nut sugars, nut starch, shoot sugars, and shoot starch that was collected across multiple sampling events. Data indicated year-dependent yet physiologically coherent patterns in which oil accumulation increased late in the season while kernel percentage remained relatively stable and NSC pools in nuts and shoots responded to crop load, canopy condition, and nitrogen treatment. Collectively, this work provides a physiological interpretation and management insight into the stabilizing nut quality for better post-storm recovery and enhancing the long-term productivity of pecans.