Skógræktarritið - 15.05.2001, Page 159

the same time, a possible role of
this mechanism as a way of pre-
venting undesired growth
(Lambers 1980) raises question
as to the relationship between
growth and plant survival in cold
environments.
As a case study to examine cli-
matic adaptations and acclima-
tion potential (BiIIings 1974),
mountain birch ecótypes could
give valuable information about
growth/respiration relationships.
As an old immigrant, Beiuía pubes-
cens is assumed to have evolved
close adaptations to the climate
at its provenance. in addition to
respiration, measurements of
growth and photosynthesis in
birch are necessary to obtain
information about climatic adap-
tations and the acclimation
potential in birch ecotypes.
Because arctic ecotypes of
plants seem to be more adapted
to a low-growth strategy for sur-
vival than southern and lowland
ecotypes (Chapin 1979, Skre
1991 a) one wou ld expect a lower
proportion of ATP-linked growth
respiration in northern ecotypes
than in their southern relatives. To
investigate possible differences in
response to nitrogen application
between birch ecotypes and to
what extent slow-growing birch
seedlings have evolved alternative
respiration as a growth-regulating
mechanism, a series of experi-
ments was initiated, where normal
and cyanide-resistant dark respira-
tion was measured in various
birch tissue types at different tem-
perature and nutrient levels.
Measurements of growth parame-
ters and chemical analysis of plant
tissue were performed on parallel
subsamples, to investigate the
source-sink relationships in plants
of different origin.
Material and methods
Seeds from three Betula pubescens
populations were sown in moist-
Table 1. Monthly means and extreme temperatures (oC|
at Fana and Kvamskogen 1987.
Mean Monthly
temp. maximum minimum
Fana
July 14.6 25.8 5.2
August 12.8 21.6 3.4
Septembcr 10.0 18.5 1.4
October 9.4 18.0 2.6
Kvainskogen
July 12.3 24.3 2.0
August 10.9 18.3 1.5
September 7.4 14.7 -1.5
October 6.8 15.3 -1.5
ened and fertilized peat in May
1987. The seed populations were:
• BA = Löten southeastern Nor-
way (60°51’N) 200 m altitude
• BS = Fana southwestern
Norway (60°16'N) 50 m altitude
• B) = Kevo, northern Finland
(69°44'N) 200 m altitude
When the plants had developed
four leaves, they were transferred
to 0.6 1 plastic pots filled with a
mixture of peat and pearlite in
the ratio 2:1. The plants were
allowed to recover for 2 days at
low temperature and then dis-
tributed at two field sites at dif-
ferent altitudes:
• Fana (60° 16'N) 50 m altitude
• Kvamskogen (60°24'N) 450 m
altitude
Each pot received 100 ml of
nutrient solution per week during
the remainder of the season with
the following composition:
• +N Complete nutrient solu-
tion equivalent to about 10 g N
m‘2yr_l
• -N Complete nutrient solu-
tion but without nitrogen.
• -P Complete nutrient solu-
tion but without phosphorus
Due to peat decomposition,
some nitrogen and phosphorus
were available even in the pots
where no such nutrients were
added. Soil samples were there-
fore taken from different treat-
ments and sites at the end of
season for control.
Temperatures were recorded at
nearby meteorological stations,
mean monthly, daily mean and
extreme temperatures are given
in Table 1.
On September 14th, while the
leaves were still green, five
plants per population and treat-
ment were harvested and sepa-
rated into leaf, stem and root tis-
sue. This was repeated on
October 28th after leaf abscission.
Dried plant tissue was then
analysed for total nitrogen and
total non-structural carbohydrate
content. Total nitrogen was mea-
sured by the Kjeldahl method
after digestion in sulphuric acid
and for total non-structural car-
bohydrates the anthrone method
was used (Dreywood 1946).
Duplicate samples were homo-
genised and digested in 10 ml
20% HCI04 for 10 min at 20 °C
(Hansen & Moller 1975) after
which the anthrone reagent was
added. After subsequent heating
the absorbancy at 490 nm was
recorded against digested starch,
measured as glucose equiva-
lents. Cellulose is not digested
by perchloric acid and therefore
not included in the test(Clegg
1956). This was confirmed in the
present experiment (Skre
unpubl.). The C/N ratio is there-
fore defined as the ratio between
the total non-structural carbohy-
drate content and the total nitro-
gen content, as measured by the
Kjeldahl method.
Measurements of alternative
and normal dark respiration
The experiment was repeated the
SKÓGRÆKTARRITIÐ 2001 l.tbl.
157