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

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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

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17

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7.8

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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

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p

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(m

g C

O2

m-2

s-1

)

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Ambient

Heated

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eco

syst

em e

xch

ange

(mg

CO

2m

-2s-1

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g C

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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

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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%

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a b

y K

rist

iina

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d N

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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