This experiment investigated the effect of different plug-tray cell designs on root development of red maple (Acer rubrum), red oak (Quercus rubra), and quaking aspen (Populus tremuloides) seedlings. In April of 2015, seeds of each species were sown into three plug trays with different substrate volumes and grown for 17 weeks. Two trays had permeable walls for air-pruning, one with vertical ribs and one without. The third tray had impermeable plastic cell walls. Harvested seedlings were analyzed for root dry weight, length, volume, surface area and number of deflected roots. Root length per volume was highest in the impermeable-walled tray for red maple and quaking aspen. The total numbers of deflected root systems were higher for all species in the impermeable-walled tray. Seedlings grown in the air-pruning trays had smaller proportions of deflected root masses. Greater substrate volume did not influence root deflection development. The air-pruning tray without vertical ribs had the lowest total number of root masses with misdirected roots and lower proportions of root masses with misdirected roots for all species. These results indicate that improved root architecture in root-air pruning tray designs is achievable in tree propagation; however, vertical plastic structures in air-pruning trays can still cause root deflections. Index words: Deflected roots, air-pruning, seedling, propagation, plugs, root architecture. Species used in the study: red maple (Acer rubrum L.); red oak (Quercus rubra L.); quaking aspen (Populus tremuloides Michx.).

This study evaluated the effects of low, moderate and high substrate exposure air-pruning propagation trays on eastern cottonwood (Populus deltoides W. Bartram ex Marshall ssp. deltoides) and black cherry (Prunus serotina Ehrh.) seedling root system quality and overall performance. Root system quality was characterized primarily by proportion of coarse root defects within the container imprint. Seedlings were evaluated after a nearly four-month commercial greenhouse production phase and one year after transplanting into a nursery field. Above and below-ground growth were measured at both time points. Proportions of coarse root defects, indicating degree of root deflection in container production, were persistent between greenhouse and field production phases. The Open (high substrate exposure) tray produced seedlings with roughly three times less deflected coarse root weight compared to the Closed Wall (low substrate exposure) tray for both species in both production phases. At neither production phase were there significant differences in above-ground growth among trays. This corroborates findings from other research studies that have found that variable root system quality does not always result in above-ground growth differences; and that when it does, differences in growth may take several years to manifest. Index words:, tree seedling quality, root defects, transplant performance, above-ground growth. Species used in this study: eastern cottonwood (Populus deltoides W. Bartram ex Marshall ssp. deltoides), black cherry (Prunus serotina Ehrh.).

Air-pruning can improve tree seedling root quality in propagation by subjecting root tips to desiccation, thereby avoiding deflections, but also increases substrate dry-out rates. Several studies have indicated that coconut (Cocos nucifera L.) coir dust can enhance water holding properties, possibly benefiting trees grown in air-pruning trays. However, water availability characteristics are influenced by particle size. In this experiment, coir dust was added into a sphagnum peat-perlite substrate mix at rates of 10, 15 and 20%. An industry standard peat-perlite mix was tested as a fourth substrate type. Red oak (Quercus rubra L.), red maple (Acer rubrum L.), quaking aspen (Populus tremuloides Michx.) and eastern white cedar (Thuja occidentalis L.) were grown from seed in these four substrate types. Physical and chemical properties of all substrate types were analyzed pre-experiment. The particle size distribution was finer and more even in the peat-perlite mix compared to the three coir mixes. The higher proportion of coarse particles in the 20% coir mix may have reduced water availability. Seedlings grown in the 15 and 20% coir mixes had lower above and below-ground growth compared to the 10% coir and peat-perlite mixes in all species except red oak. Index words: soilless media, water holding capacity, air space, particle size distribution, chlorophyll content, tree growth. Species used in the study: red oak (Quercus rubra L.); red maple (Acer rubrum L.); quaking aspen (Populus tremuloides Michx.); eastern white cedar (Thuja occidentalis L.).

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