Skógræktarritið - 15.05.2001, Síða 158

SKÓGRÆKT HANDAN SKÓGARMARKA / NSSE
ODDVARSKRE
Temperature adaptations in
growth and carbon balance
in relation to nutrient level
in seedlings of Betula pubescens
from different populations
in Scandinavia
SAMANTEKT
Sagt er frá tilraun þar sem mældir voru vaxtarþættir, köfnunarefnis- og
kolvetnainnihald í mismunandi plöntuhlutum og öndun í mismunandi
plöntuhlutum á birkiplöntum af þremur mismunandi kvæmum rækt-
aðar við mismunandi áburðargjöf og í mismunandi hæð yfir sjávarmáli.
í ljós kom að plöntur sem ræktaðar voru við lágt hitastig (meiri hæð)
og Iágt N drógu einkum úr vexti sprota og Iaufblaða. Engu að síður var
N-innihald í laufblöðum þessara plantna tiltölulega hátt, sérstaklega
hjá norðlægasta kvæminu. Við þessar aðstæður eykst sérstök tegund
öndunar í laufblöðum sem ekki tengist vexti en við hana sparast N.
í rótum er hins vegar venjuleg öndun og þær vaxa. Norðlæg kvæmi
virðast vera sérstaklega aðlöguð þessum kringumstæðum enda er
mikill vöxtur ofanjarðar ekki heppilegur þegar skortur er á næringu.
Abstract
Seedlings of three different pop-
ulations of white birch {Betula
pubescens) were grown in fertil-
ized peat at two different nutri-
ent levels equivalent to 1 and 10
g N m'2 yr '■ at 50 m and 450 m
elevation in southern Norway.
The experiment showed a
strong accumulation of carbohy-
drates in roots of high altitude
plants relative to low altitude
replicates. In these field-grown
plants normal and alternative
(cyanide-resistant) respiration
was measured on stem and root
segments and on excised leaf
discs from three Betula pubescens
populations. The total respira-
tion rates decreased with tem-
perature in leaf discs and stem
segments, while there was an
increase in roots. At low nutrient
level there seemed to be a
depression of respiration rates in
shoots at high temperature, and
most of it was cyanide-resistant,
i.e. not related to growth.
The ecological significance of
these findings is that at low tem-
peratures increased respiration
rates in leaf and stem tissue may
lead to reduced growth. At high
temperatures, however, in-
creased respiration in roots may
indicate increased root growth
rates that may increase nitrogen
absorption rates and lead to
increased photosynthetic capaci-
ty, compensating partly for car-
bohydrate exhaustion. The
increased alternative respiration
at low nutrient Ievel may be a
mechanism to prevent growth at
unfavorable growth conditions.
Introduction
In areas with a summer and a
winter season, plants have
evolved different methods to sur-
vive the unfavourable season,
and the selection pressure is
determined by abiotic factors
rather than by competition
(Kallio 1984). Nitrogen availabili-
ty is the most important limiting
factor for plant growth at high
latitudes (Ágren 1985). On cold
soils decomposition of organic
matter is slow and the concentra-
tion of inorganic nitrogen and
phosphorus is low. Uptake rates
of nitrogen and phosphorus have
been shown to be strongly tem-
perature-dependent as a result
of active uptake in roots (Chapin
1980, Karlsson & Nordell 1987).
The energy required for this
active uptake is usually supplied
through dark respiration or growtfi
respiration, which is therefore an
important limiting factor for
growth at low temperatures. The
existence of an alternative respira-
tion as an overflow mechanism
which is not linked with ATP-pro-
duction (Beevers 1970) is further
evidence forthis relationship. At
156
SKÓGRÆKTARRITIÐ 2001 I. tbl