the translocation of minerals in trees - Canadian Forest Service

Calcium45 injected into the white pine trunk had a localized distribution
similar to that of the rubidium86 in yellow birch. In the white pine trunk the
isotope moved upwards from the point of infection, along a relatively narrow
channel. Only two branches, both within six feet of the ground, were found to
contain appreciable activity. Monitoring records on August 22, six weeks
after injection, indicated an accumulation of calcium in the main trunk at a
point where the upper active branch had its origin. From this position in the
trunk, most of the calcium was carried out into the branch. The isotope was
not evenly distributed throughout the branch, as in any given whorl of twigs
some were much more active than others.
The internal distribution of the calcium was investigated by autoradiographs.
In this technique (Belanger and Leblond, 1946) sections of tissue are coated with
a photographic emulsion and left for different periods of exposure ranging from
a few hours to several weeks depending on the degree of localization of the
radioisotope and consequent inten ity of radiation to which the photographic
emulsion in contact with the section is exposed. The autoradiographs of ections
of the stem (Figure 2) showed activity in the sieve cells of the phloem in the
white pine.
During September some of the calcium45 concentrations had materialized
into visible crystals. Figure 3 shows a cross section of crystals in the phloem
cells. By focusing up on the photographic emulsion covering the section of
these cells, the dark dots (Figure 4) represent exposure of the photographic
emulsion indicating that these cells contain calcium45•
Presence of calcium45 was also noted in the buds of yellow birch. Figure 5a
presents photographs of the buds, whereas Figure 5b show autoradiographs of
the same buds indicating the presence of calcium45 in the peripheral parts of
these buds.
Moreland (1950) introduced roots of loblolly pine into jars containing
phosphorus32 solution and noted a maximum translocation rate of more than
four feet per hour.
Yli-Vaakuri (1954) in Finland showed that movement of phosphorus32
would take place from tree to tree and also between trees and stumps through
natural root grafts.
Kuntz and Riker (1955) in Wisconsin studied more extensively the use of
radioisotopes for ascertaining the role of root grafts in the translocation of
minerals between trees. Their experiments with iodine131 and rubidium86
included the insertion of cut branches or roots into a bottle containing a radioactive
solution, or injection of a solution from a cone or trough similar to the
technique used by Fraser and Mawson (1953).
The usual rate of upward movement of the isotope in the translocation
stream of oaks in full sunlight and with low relative humidity was between It
and 3 feet per minute. A limited downward movement into the roots was
noticed. Greater movement occurred in roots naturally grafted onto those of
other trees. Radioactivity was detected within 20 minutes in most branches,
twigs, and leaves of pin oak (Quercus ellipsoidalis E. J. Hill) 35 feet high. Radioactivity
appeared only in narrow vertical streaks which originated at the chisel
cuts, and in certain branches of the bur oak (Quercus macro carp a Michx.).
The diffuse movement of the isotopes throughout trunks and the crown of the
northern pin oak was quite different from the limited linear flow in the trunk and
certain branches of the bur oak. In this respect the bur oak behaved like the
yellow birch and white pine in the experiments by Fraser and Mawson (1953).
Movement of the isotopes was reduced by very low light intensities, free moisture
on the leaves, and absence of functional leaves. Little movement occurred
during the dormant period. When dominant and suppressed trees were connected
by root grafts, isotopes moved both ways but most commonly from the
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