How combined changes in air humidity and temperature of leaves
affect xylem flux and growth of fast-growing deciduous trees?
Anu Sõber*, Jaak Sõber, Priit Kupper, Arne Sellin, Arvo Tullus
University of Tartu, Institute of Ecology and Earth Sciences
Backround: Regional differences in water regime can occur
simultaneously with global climate warming.
More rain and higher air humidity is predicted for Nothern Europe,
including Baltic region. Temperature is increasing mainly in late autumn and winter, but not
in cloudy and rainy summer, when tree leaves can stay wet for a long time.
How these conditions affect tree growth?
Free air experiment: Relative air humidity of
three experimental plots (with about 100
Hybrid aspen and 100 Silver birch trees)
was rised by misting teqnique.
Three plots served as controls.
Wind direction
Silver birch
Hybrid aspen
Relative humidity and temperature of air
(monthly average values during misting)
RH was ca 10 % higher during misting, but no difference found in air
temperature.
Sap flow measurements to estimate water flux
Vertical bars denote 0.95 confidence intervals
Control
Misting
2,0
-2
-1
Sap flux density (mmol m s )
2,5
Heat balanse method:
4 Kuchera (or Dynamax) sensors per
species in one plot
1,5
1,0
0,5
0,0
Estimation of leaf area
3
4
5
10 11 13 16 17 24 27 28 29 30
31
Day of August
Vertical bars denote 0.95 confidence intervals
-1
Control
Misting
2,0
-2
Sap flow density was ca 30% less
during misting
Sap flux density (mmol m s )
2,5
1,5
1,0
0,5
0,0
1
2
6
7
8
9
12
14
Day of August
15
19
21
22
23
Daily average values of stem sap flux density (mmol m-2 s-1) of
sample trees in control and misting plots during mist fumigation
and on misting-free days in the summers of 2008 and 2009
Year Tree species During mist fumigation
•
C plots H plots P value
2008 silver birch
1.41
1.06
< 0.05
2009 silver birch
1.03
0.75
< 0.01
2009 hybrid aspen 1.26
0.49
< 0.001
Without mist fumigation
C plots H plots P value
1.04
0.98
ns
0.96
1.01
ns
1.03
0.63 < 0.001
Humidity was only 10 % higher, but water
flux was 30% lower in misted plots – why?
*Measurement of leaf temperature:
Average leaf
temperature, 0 C
(with thermocamera and with sensors, attached to leaves)
* Temperature of leaves was lower in misted plots up to 5
degrees. (depends on % of wet leaves and on meteorological
conditions).
C
Temperature of leaves and air
(Silver birch, 18.07.2009)
30,00
25,00
20,00
9:36
H
14:24
19:12
Effect of misting on tree growth
Growth rate decreased in misted trees.
This effect was more pronounced in Silver birch.
Tree hight, autumn 2009
Increment in stem volume
( groving-season 2009)
300
200
100
0
C
H
Hybrid aspen
C
H
Silver birch
Relative stem
volum e increm ent,
%
Tree hight, cm
400
400
300
200
100
0
C
H
Hybrid aspen
C
H
Silver birch
What affects growth?
* 1. Lower temperature of leaves (lower rate of photosynthesis etc)
* 2. Decrease in water flux (less nutrients)
* 3. Damage of young, developing leaves (less leaf area)
As nitrogen and chlorophyll contents of leaves were less in
misted plots, and the negative impact of misting decreased
with increasing plot fertility, we belive, that reduced water
flux was most important factor of stress for fast-growing
trees in this experiment.
Photosynthetic parameters (Silver birch), 2009
The effect of misting on tree growth is a sum previous
and current year effects.
Bud size (buds formed in summer 2008)
Bud length
10
Bud width
4
mm
8
6
2
4
2
0
C
•
•
aspen
birch
H
ring
C
H
Difference in bud length 20% and 30% (accordingly aspen and
birch, p=0.01).
Difference in width 7% and 30% (p=0.01)
Leaf area 2009
3
leaf area dm
2
aspen
birch
2
1
0
C
H
ring
• For birch, there was
nearly 4 times more
leaf area per annual
shoot in control.
• Aspen had ~50%
more leaf area in
control.
Conclusion:
More rain and higher air humidity can reduces water flux through the
canopy and growth rate of deciduous trees in Northern Europe.
This effect will be probably more pronounced at nitrogen-deficient
sites.
Temperature of leaves
Hybrid aspen, Aug, 20, 2009
C1
H1
air
Time
Canopy
conductance,
mmol m -2 s-1
Canopy conductance
(created by stomata and boundary layer)
300
200
100
0
7:12
H
C
12:00
16:48
Time
21:36