Effect of Root and Shoot Manipulation on the Morphology and Physiology of Oregon White Oak (Quercus garryana) Seedlings in the Nursery and Following Outplanting
Oregon white oak, or Garry oak (Quercus garryana), has been adversely affected by land-use conversion, landscape fragmentation, and anthropogenic fire suppression. Its historical range has contracted significantly to the point where an estimated 1-5% remains intact. Natural regeneration is difficult due to a lack of seed sources and the physiological characteristics of the seed. Because of this, artificial regeneration has become essential for helping to sustain current populations. However, seedlings can be difficult to establish due to high mortality from post-planting water stress. Nursery cultural practices can improve future field survival in reforestation projects by manipulating a seedling’s morphology and physiology. The primary objective of this study was to evaluate the effect(s) of container size in combination with pruning treatments on Oregon white oak seedlings. The experiment began in the greenhouse and then transitioned to a field experiment and determined the effect of seedling morphology and physiology on growth, water stress and field survival after planting. Overall, seedlings cultivated in the three container sizes showed similar height (HT), shoot dry mass (SDM), root dry mass (RDM), root-to-shoot ratio (R:S) and root volume (RV) but differed in root collar diameter (RCD) and root length (RL) after one greenhouse growing season. Compared to seedlings cultivated in a D27 container, seedlings cultivated in both D40 and D60 containers had smaller RCD but greater RL. Both container size and top pruning impacted net photosynthesis (A), transpiration (E), stomatal conductance (gs), water use efficiency (WUE) and pre-dawn water potential (ΨPD) at various times throughout the field growing season. While end-of-season RCD and survival were not statistically significantly different among container size or between pruning treatments, end-of-season HT was impacted by both container size and pruning treatment. Seedling HT was greater for seedlings cultivated in D27 containers compared to seedlings cultivated in a D40 container, where D60 seedlings displayed an intermediate HT. Additionally, seedling HT was greater among unpruned seedlings compared to pruned seedlings. This study showed that nursery-based decisions such as container size and field treatments such as top pruning can impact Oregon white oak seedling morphology and physiology, which can aide in offsetting the stresses of low water availability in the field
