Root development in Picea glauca seedlings was studied anatomically during the first year after
germination. The cyclic pattern of elongation of individual roots was established about three
months 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 these roots, the development of Casparian bands in the endodermis often occurred
several millimeters away from the root tip. 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 development of Casparian bands was always prior to the maturation of the
first xylem elements. 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. The secondary development in roots advanced basipetally
but exceptions were found indicating that cambial growth of roots could vary along the root
regardless of the position relative to the root tip. Seedlings with different root systems modified
by nursery culture exhibited different pattems 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. The initially low hydraulic conductance of root systems in box-pruned seedlings increased significantly 6-8 weeks after planting while it remained unchanged or declined in
container-grown 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. The growth of roots in the organic substrates was
enhanced by the addition of slow-release fertilizer to that substrate. The growth response of roots
to slow-release fertilizer added to the mineral substrate was restricted to that compartment but
root growth in both soil compartments was affected by the addition of slow-release fertilizer to
the organic substrate. Root development in different types of planting stock was differently
affected by the soil substrate type and the addition of the slow release fertilizer. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/8770 |
| Date | 02 November 2017 |
| Creators | Krasowski, Marek J. |
| Contributors | Owens, John N. |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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