The development of roots and root systems in white spruce (Picea glauca ((Moench) Voss) seedlings and the influence of cultural treatments on root morphology, anatomy, and the capacity to conduct water

Root development in Picea glauca seedlings was studied anatomically during the first year after germination. With progressing development, root hairs gradually diminished and colonization of roots by mycorrhizal fungi increased. The development of primary tissues in long roots, relative to the distance from the root tip, appeared to be related to their rate of root elongation. In elongating short roots, endodermal cells attained their primary state only 2–4 cells away from the proximal part of the apical meristem. In non-elongating roots, the secondary-state endodermis was connected to the metacutis just above the apical meristem. The endodermis did not develop past the secondary state. Through the presence of passage cells, it remained functional until its disruption by secondary growth. Low frequency of plasmodesmata in the endodermis indicated that the plasma membrane - cell wall - plasma membrane type of transport was the main means of molecule exchange between the cortex and the stele in white spruce roots. Undifferentiated tissues of the root near the apical meristem were almost impermeable to fluorescent dye tracers Sulforhodamine G and fluorescein diacetate. The metacutis and the endodermis at the primary and secondary state were impermeable to the apoplastic tracer Sulforhodamine G.; Roots and root systems were structurally and physiologically affected by cultural treatments such as pruning and fertilizer application. Roots of seedlings grown at low nitrogen (N) supply were thin and their tracheids were narrow. Excess N did not significantly increase root diameter and tracheid dimensions, compared to the optimum supply. Dimensions of bordered pits were not significantly affected by the N level. Seedlings with different root systems modified by nursery culture exhibited different patterns of root growth after planting. Root elongation and root surface area increases immediately after planting were greater in container-grown than in mechanically box-pruned seedlings but this was unrelated to the longer-term performance of these seedlings. Root pressure, comparable to that reported for angiosperm seedlings, was found in white spruce seedlings during the first few weeks after planting. This is contrary to the general notion that conifers do not develop notable root pressure. The initiation and elongation of roots in unfertilized organic compartments was poor compared to root growth in unfertilized mineral compartments, especially in mechanically pruned seedlings whose roots proliferated in the latter compartments. Root development in different types of planting stock was differently affected by the soil substrate type and the addition of the slow release fertilizer. (Abstract shortened by UMI.)...