Electrolyte leakage
test in assessing
of cold hardiness
in roots
Relative electrolyte leakage
1.0
0.8
Results and discussion
0.6
0.4
LT50 in September
0.2
LT50 in November
LT50 in December
0.0
-50
-40
-30
-20
-10
0
10
Exposure temperature (oC)
Fig. 1. Regression curves for calculation of
LT50-value.
1) [email protected],
[email protected], University of Joensuu,
Faculty of Forestry, P.O. Box 111, FI-80101
Joensuu, Finland
2) [email protected], The Finnish Forest
Research Institute, Joensuu Research Unit,
P.O. Box 68, FI-80101 Joensuu, Finland
10
Temperature (oC)
Mikko Räisänen1, Tapani Repo2
Tarja Lehto1
In the field experiment, assessed cold
hardiness of roots was, however, rather low
compared to minimum soil temperatures
during winter (Fig. 2).
0
-10
We examined root cold hardiness in
Norway spruce trees in a field experiment
by electrolyte leakage test after controlled
freezing exposures. Roots were separated
from soil by washing them prior to freezing
tests.
When roots were exposed to frost, relative
electrolyte leakage of samples increased
enabling the assessment of cold hardiness of
roots (Fig. 1).
5 cm depth (thick snow)
0cm depth (thick snow)
0cm depth (shallow snow)
5cm depth (shallow snow)
-20
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Despite that, there was no more root mortality
in surface layer of soil which was exposed to
more severe freezing during winter (Fig. 3)
and not under the trees where isolating snow
cover was shallow (Fig. 4).
Fig. 2. Soil temperature in the experimental site
(lines) and LT50 of roots (plot with S.E. bars).
Material and Methods
Depth (cm)
0-1
Fine roots for cold hardiness tests were sampled
during autumn and prepared for electrolyte leakage
tests prior to freezing tests. Samples were frozen at
seven different freezing temperatures.
For studying the mortality of fine roots in the field
during winter, root samples were collected in the
spring and the viability of roots was estimated
visually under stereomicroscope.
On the basis of results we are
concerned that:
2-3
3-4
4-5
0
20
40
60
80
100
Proportion of dead roots (%)
Fig. 3. Proportion of dead roots on DW basis at
different depths of humus layer in May 2003.
Proportion of dead roots (%)
Relative electrolyte leakage was calculated as
percentage of ions in solution of test tubes after frost
exposure (EL1) and after heat killing of samples
(EL2). Freezing tolerance (LT50-value) was
calculated by non-linear regression of EL1/EL2
against exposure temperature (Fig. 1).
1-2
-either freezing tolerance decreased in
roots during sample preparation,
75
0-1cm
-or the calculated freezing tolerance
(LT50-value) is not the lethal
temperature for roots.
4-5 cm
50
25
0
0
5
10
Snow cover (cm)
15
Fig. 4. Proportion of dead roots on DW basis at two
depths of soil in May in relation to snow cover
under sampled trees in December 2002.