Faculty of Biological and Environmental Sciences
Ecosystems and Environment Research Programme
Juha Mikola
Warming up
the Arctic
BETUMICS – what was it all about?
• Birches (Betula) are abundant in many ecosystems in boreal and Subarctic climate zones > let’s focus on their responses to climate warming!
• Growth chamber experiments to reveal “northern Betulatraits” (e.g. Punkaharju 61°N vs. Kittilä 67°N)
• Reciprocal transfer of populations (among Florence 43°N, Punkaharju 61°N and Kolari 67°N) to estimate the ultimate boundaries of Betula acclimation capacity
• A field experiment at the Kevo Subarctic Research Station (Utsjoki 69°N) to study responses of northern Betulapopulations and Subarctic mountain birch forest ecosystem to climate warming
Kevo warming experiment
- twenty field plots, with a2×2 factorial set-up consisting of warming and herbivory treatments (n = 5)
- plots with ambient vs. + 3 °C “leaf” temperature(infrared heaters)
- plots with normal vs. reduced insect herbivory (weekly insecticide sprayings)
- cloned offspring of northern Betula populations planted on each plot
”Leaf”
In field plots, all Betula species had positive responses to warming, with growth ratesincreasing by 20–60%.
Mea
n +
1 S
E
In a growth chamber test, a northern silver birch population had 50% higher photosynthesis rate than a southern population (adaptation to cold climate), but the same optimum temperature of 18 °C
Data by Antti Tenkanen, UEF
Population
67°N
61°N
Growth temperature (°C)
Photo
synth
esis
rate
(µm
ol
CO
2m
-2s-1
)
For most part of the growing season 2017, air temperatures in Kevo were below 18 °C > plant photosynthesis rates were likely raised by warming
0
100
200
300
400
500
600
1.7
.
17
.7.
7.8
.
30
.8.
3.9
.
6.9
.
10
.9.
13
.9.
17
.9.
20
.9.
24
.9.
27
.9.
30
.9.
Leaf
ch
loro
ph
yll c
on
ten
t (m
g/m
2)
In field plots, warming raised late season leaf chlorophyll concentrations (all Betula species included)
Ambient
Heated
Mea
n ±
1 S
E
In field plots, warming increased ecosystem CO2 uptake through the growing season > mitigation for climate change
-0,6
-0,5
-0,4
-0,3
-0,2
-0,1
0
0,1
1Ju
n
14
Jun
25
Jun
28
Jun
2Ju
l
10
Jul
24
Jul
15
Au
g
24
Au
g
6Se
p
28
Sep
22
Oct
NEE
(m
g C
O2
m-2
s-1
)
Mea
n ±
1 S
E
Ambient
Heated
Net
eco
syst
em e
xch
ange
(mg
CO
2m
-2s-1
)
-0,6
-0,5
-0,4
-0,3
-0,2
-0,1
0
0,1
1Ju
n
14
Jun
25
Jun
28
Jun
2Ju
l
10
Jul
24
Jul
15
Au
g
24
Au
g
6Se
p
28
Sep
22
Oct
NEE
(m
g C
O2
m-2
s-1
)Ambient
Heated
Reducedherbivory
Insect herbivory decreased ecosystem CO2 uptake
Mea
n ±
1 S
E
Net
eco
syst
em e
xch
ange
(mg
CO
2m
-2s-1
)
Herbivores reduced Betulagrowth by 15–50%- local mountain and dwarf birch were more resistant than more southern silver and downy birch
0
100
200
300
400
500
600
1.7
.
17
.7.
7.8
.
30
.8.
3.9
.
6.9
.
10
.9.
13
.9.
17
.9.
20
.9.
24
.9.
27
.9.
30
.9.
Leaf
ch
loro
ph
yll c
on
ten
t (m
g/m
2)
Herbivores decreased leaf chlorophyll concentrations(all Betula species included)
Ambient
Heated
Reducedherbivory
Leaf damages by herbivores doubled with 3 °C warming(all Betula species included) M
ean
+ 1
SE
Aboveground growth reduction had belowground consequences: herbivores reduced mineral soil C stocks and microbial biomass by 50–60%
Dat
a b
y K
rist
iina
Kar
hu
an
d N
ele
Mey
er, U
H
Mea
n +
1 S
E
When warming up the Arctic:• Plants are ready for action
- high photosynthesis rates in northern populations- high optimum temperature for photosynthesis- warming increases leaf chlorophyll concentrations>> plant growth and CO2 uptake will increase
• …but watch out for the herbivores- insect herbivores decrease plant growth and belowground C allocation- warming increases herbivore damages>> increasing plant growth, CO2 uptake and soil C storages can be significantly curtailed by increasing herbivory
• Herbivory and trophic interactions need to be involved in climate change models and predictions
Acknowledgements to all BETUMICS participants and collaborators!
Tarja SilfverTuukka Ryynänen
Kristiina KarhuNele Meyer
Mika AurelaLauri Heiskanen
Matti RousiKaisa Nieminen
Elina OksanenAntti TenkanenKristiina Myller
Rajendra GhimireMaija MarushchakJohanna Kerttula
Maya DeepakSari Kontunen-Soppela
Sarita Keski-Saari
Elina VainioOtso SuominenIlkka SyvänperäKEVO Subarctic
Research Station