Skógræktarritið - 15.05.2001, Síða 160

Table 2. Variance ratios (F) and significance levels forchemical components in dif-
ferent tissue types of birch seedlings, grown at varying temperatures and nutrient
levels , harvested before and after leaf fall 1987, The following symbols are used:
NST and NRT = nitrogen content (mg/plant) in stem and root tissue, CST and CRT =
non-structural carbohydrates (mg/plant) in stem and root tissue, and S, R and T =
C/N ratios in stem, root and total plant tissue respectively. Significance levels are:
*P<0.05, **P<0.0l. DF = degrees of freedom. R2 = square multiple correlation coef-
ficient, SS = sum of squares.The nitrogen and carbohydrate content has been sub-
jected to iogarithmic transformation. Interactions that are not significant in any vari-
able, are not included in the table.
Source DF NST N„T CST CrT s R T
Population 2 10.6* 9.0* 85.9* 73.6* 140.8* 126.5* 251.0*
Temperature 1 9.9+ 8.5+ 10.5+ 15.2* 12.4* 18.2* 30.9*
Nutrient level 1 20.9* 19.2* 14.2* 11.7+ 6.8° 13.8* 24.4*
Time 1 2.3 2.1 1.8 0.3 34.2* 6.5+ 21.2*
Pop x temp 2 3.0 0.8 15.7* 3.2 14.5* 9.8* 17.3*
Pop x nut 2 0.7 0.5 1.6 1.2 3.5° 5.1 + 10.0*
Temp x nut 1 10.5* 0.6 11.8* 3.0 0.1 0.0 0.3
Nut x time 1 0.5 0.0 1.5 0.9 1.2 10.0+ 12.0+
Temp x nut x time 1 1.8 6.2° 0.0 2.4 5.4° 9.6+ 13.0*
Pop x nut x time 2 0.6 2.6 0.7 0.4 3.1 15.0* 17.4*
Temp x pop x nut x time 2 0.5 0.3 0.4 0.2 1.4 10.6* 12.0*
error ss 23 3.0 4.5 3.3 4.3 299 839 315
total ss 47 14.1 19.4 41.0 42.5 5556 16100 1079.2
0.79 Q.7Z— 0.92 0.90 m 0.97
next spring (1988) for extended
respiration studies. Because of
lack of germination the western
coastal BS seed source was
replaced by the subalpine BH
seed source.
The dark respiration was mea-
sured by the Warburg manometric
technique on growing leaf, stem
and root tissue by the method
described by Skre (1992a). The
cyanide-resistant (alternative)
respiration was measured by
means of a modification of the
method of Bahr & Bonner (1973)
and Lambers et al. (1983).
During the sample period the
plants reached the stage of 12
visible leaves, and measure-
ments of cyanide-resistant respi-
ration were performed on leaf
discs from leaf number 7 and 8
from the stem base. These leaves
were assumed to be in a stage of
maintenance with stable respira-
tion rates. Similar measurements
were carried out on 4 mm stem
and root segments, grown at dif-
ferent elevations (temperature)
with or without added nitrogen.
All measurements were carried
out at 20°C in darkness. Each
sample contained six leaf discs
and 10-12 stem or root seg-
ments, and four parallel repli-
cates were run per treatment.
Statistical treatment of data
All variables were tested by GLM
variance analysis (Goodnight
1976). The analysis included
growth measurements and
results from chemical analysis.
Results and discussion
Effects of fertilization on growth
There was a strong temperature
effect on the growth of plants in
the field experiment (Fig. 1) with
2-3 times higher plant biomass
at harvesting in plants from the
low elevation site than in plants
from the high elevation site (see
also Skre 1992b). In addition to
the direct temperature effect on
shoot growth, there was also an
indirect effect because of raised
soil temperature and more rapid
uptake rates of nutrients (cf.
Karlsson & Nordell 1987). The
destructive samplings (Fig. 1)
confirmed the results of Karlsson
& Nordell (1987) and showed
that the effect of added nutrients
was strongly temperature-depen-
dent. At the lowland site, growth
was roughly doubled by adding
nitrogen and phosphorus to
seedlings of the lowland popula-
tion (BA) as compared with
plants without these two ele-
ments, with most of the growth
increase taking place in the
shoot. As a result the shoot/root
ratios were higher in fertilized
than in unfertilized plants of this
population. The biomass
increased in all three popula-
tions after nitrogen addition, rel-
ative to non-fertilized plants. At
the high elevation site, the effect
of added nutrients was much
weaker and hardly significant,
but the unfertilized plants pro-
duce.d fewer and smaller leaves
(Skre 1992b).
There was a strong accumula-
tion of nitrogen in leaves of fer-
tilized plants at the high temper-
atures (=low elevation) and a
correspondingly strong accumu-
lation of carbohydrates in roots
of unfertilized plants at lower
temperatures (Fig. 2). The experi-
ment confirmed earlier results
and showed that the leaves are
the main sink for nitrogen and
the roots and stems are the main
sink for carbon. Leaf proteins
account for 60-70% of the nitro-
gen in Betula papyrifera, while 8-
11% is found in nucleic acids
(Chapin & Kedrowski 1983).
When grown at low temperatures
and deprived of nutrients, moun-
tain birch tended to keep a high
nitrogen concentration in its tis-
sue by reducing its growth. This
is similar to Thornley's (1972)
and Chapin's (1979) conclusions
about arctic plants. Only in the
two southern populations was
there a reduction in nitrogen
content a a result of low nutrient
strength. At the low elevation
site, a substantial part of the
nitrogen in roots of fertilized
plants from the southern coastal
population (BS) was translocated
158
SKÓGRÆKTARRITIÐ 2001 l.tbl.