Page 35 - Volume 1, Issue 2, July 2008

Effects of Mg supply on “Colt” cuttings 87
with increasing Mg supply (Table 4). At 0
μmol Mg l -1 the UAR of K, Ca, N and P ap-
proached zero from 71 DAP and thereafter.
At the other external Mg supplies the UAR
of K, Ca, N and P decreased over time.
Discussion
The symptoms of Mg deficiency (Figure
3) were first appeared on the basal mature
leaves of the “Colt”. This re-distribution of
Mg was expected since it is generally re-
garded as an easily redistributed nutri-
ent (20), although there is some conflict-
ing evidence (1). The results of the current
experiment showed that when the [Mg] in
leaves were less than 2mg g-1 DW the plants
showed Mg deficiency symptoms.
Mg-deficient “Colt” plants had a de-
creased stem diameter. Similar results were
found by Ford (7) in Mg-deficient MM-102
apple rootstock. The LA was also reduced by
decreasing the external Mg supply (Table
2). This reduction probably caused a reduc-
tion in the assimilate production from the
leaves that could have affected the growth
of the stem since Harper (10) showed that
the increase in the diameter of a stem, es-
pecially at its base, depended upon assimi-
lates from active leaves and Proebsting (19)
found a cessation of the radial increase of
wood in defoliated apple trees.
In the current experiment the length
of new shoots of cherry increased with in-
creasing external supply of Mg. However,
in apple the extension growth of the new
shoots and leaf production, as well as in-
ternode length, were unaffected by Mg
deficiency (8).
The severe Mg deficiency (0 μmol Mg
l-1) probably altered the distribution of the
assimilates between the shoot and root
of “Colt”. The root ÷ shoot ratio decreased
with a decreasing external supply of Mg im-
plying a relatively greater shoot growth in
respect to root growth in the Mg-deficient
plants. This greater shoot than root growth
of the Mg-deficient plants was not found
by Troyanos et al (22) in cherries grown in a
flowing solution culture system, Hermans
and Overburden (12) in Arabidopsis thal-
iana and Hermans et al. (11) in spinach.
However, Cakmak et al. (3, 4) found a similar
increase in the growth of shoots of Mg-defi-
cient plants of Phaseolus vulgaris L. and Eric-
sson and Kahr (5) in birch.
The concentrations of K (22-26 mg g-1
DW), Ca (12-15 mg g-1 DW), N (31 -33 mg
g-1 DW) and P (3-4 mg g-1 DW) were with-
in the range considered to be optimum for
the growth of cherries (16). The unit ab-
sorption rates of K, Ca, N and P increased
with increasing the external supply of Mg
whereas their concentrations were not af-
fected significantly by the Mg external
supply. This probably suggests that the
growth made in response to an increased
external supply of Mg determined the up-
take of K, Ca, N and P.
Literature Cited
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1960. Absorption and mobility of 28Mg in the
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Cacmak, I., Hengeler, C. and Marschner, H. 1994a. 3.
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Cacmak, I., Hengeler, C. and Marschner, H. 4.
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