The

effect

of

temperature

on

growth

and

competition

between

Sphagnum

species

Peat

bogs

play

a

large

role

in

the

global

sequestration

of

C

and

are

often

dominated

by

different

Sphagnum

species

Therefore

it

is

crucial

to

understand

how

Sphagnum

vegetation

in

peat

bogs

will

respond

to

global

warming

We

performed

a

greenhouse

experiment

to

study

the

effect

of

four

temperature

treatments

-LRB-

and

°C

-RRB-

on

the

growth

of

four

Sphagnum

species

S.

fuscum

and

S.

balticum

from

a

site

in

northern

Sweden

and

S.

magellanicum

and

S.

cuspidatum

from

a

site

in

southern

Sweden

In

addition

three

combinations

of

these

species

were

made

to

study

the

effect

of

temperature

on

competition

We

found

that

all

species

increased

their

height

increment

and

biomass

production

with

an

increase

in

temperature

while

bulk

densities

were

lower

at

higher

temperatures

The

hollow

species

S.

cuspidatum

was

the

least

responsive

species

whereas

the

hummock

species

S.

fuscum

increased

biomass

production

from

the

lowest

to

the

highest

temperature

treatment

in

monocultures

Nutrient

concentrations

were

higher

at

higher

temperatures

especially

N

concentrations

of

S.

fuscum

and

S.

balticum

increased

compared

to

field

values

Competition

between

S.

cuspidatum

and

S.

magellanicum

was

not

influenced

by

temperature

The

mixtures

of

S.

balticum

with

S.

fuscum

and

S.

balticum

with

S.

magellanicum

showed

that

S.

balticum

was

the

stronger

competitor

but

it

lost

competitive

advantage

in

the

highest

temperature

treatment

These

findings

suggest

that

species

abundances

will

shift

in

response

to

global

warming

particularly

at

northern

sites

where

hollow

species

will

lose

competitive

strength

relative

to

hummock

species

and

southern

species

Introduction

Peat

bogs

play

a

large

role

in

the

global

sequestration

of

C.

Although

northern

peatlands

cover

only

of

the

total

land

surface

they

store

about

one-third

of

the

world

soil

C

in

the

form

of

peat

-LRB-

Gorham

-RRB-

It

is

therefore

important

to

know

how

ombrotrophic

bog

ecosystems

which

form

a

large

part

of

northern

peatlands

will

respond

to

predicted

climate

changes

especially

since

the

rise

in

temperature

is

expected

to

be

above

the

global

average

at

high

latitudes

-LRB-

Christensen

et

al.

-RRB-

where

the

majority

of

peat

bogs

occur

-LRB-

Kivinen

and

Pakarinen

Gunnarsson

-RRB-

Vegetation

in

ombrotrophic

bogs

is

often

dominated

by

different

Sphagnum

species

The

Sphagnum

species

account

for

the

bulk

of

the

C

sequestration

in

peat

because

of

their

recalcitrant

litter

-LRB-

Coulson

and

Butterfield

Clymo

and

Hayward

Limpens

et

al.

-RRB-

Therefore

it

is

crucial

to

understand

how

Sphagnum

vegetation

in

bogs

will

respond

to

global

warming

in

order

to

predict

the

role

of

bogs

as

C

sinks

in

the

future

Several

studies

have

revealed

differences

in

production

-LRB-

Lindholm

and

Vasander

Gerdol

Asada

et

al.

Gunnarsson

-RRB-

and

in

decomposition

rate

-LRB-

Rochefort

et

al.

Johnson

and

Damman

Belyea

Limpens

and

Berendse

-RRB-

between

different

Sphagnum

species

These

differences

between

species

are

often

related

to

differences

in

microhabitat

preference

-LRB-

Gunnarsson

-RRB-

Within

a

bog

different

Sphagnum

species

occur

at

different

heights

above

the

water

table

and

at

different

positions

along

pH

and

nutrient

gradients

-LRB-

Andrus

Sjörs

and

Gunnarsson

Limpens

et

al.

-RRB-

The

most

obvious

division

in

microhabitat

preference

is

between

hollow

species

which

grow

in

pools

and

at

shallow

water

levels

and

hummock

species

which

grow

at

deeper

water

levels

Hummock

species

can

also

grow

at

higher

water

levels

but

they

are

then

usually

outgrown

by

hollow

species

-LRB-

Rydin

-RRB-

However

the

competitive

ability

of

species

may

differ

between

years

seasons

and

locations

and

as

such

competitive

replacement

occurs

very

slowly

if

at

all

This

results

in

a

relatively

stable

competitive

balance

between

species

-LRB-

Rydin

-RRB-

Several

studies

found

a

positive

relation

between

Sphagnum

productivity

and

temperature

-LRB-

Moore

Sonesson

et

al.

Gunnarsson

-RRB-

The

positive

effect

that

increased

temperature

might

have

on

C

sequestration

in

bogs

is

however

often

diminished

by

the

positive

effect

of

temperature

on

decomposition

rates

-LRB-

Hobbie

-RRB-

Increased

decomposition

rates

also

lead

to

increased

rates

of

nutrient

release

from

the

peat

layer

enhancing

production

rates

even

further

A

change

in

temperature

influences

not

only

the

production

and

decomposition

of

individual

Sphagnum

species

but

also

the

competitive

balance

that

exists

between

species

An

important

challenge

facing

ecologists

is

to

predict

how

climate

change

will

alter

species

distributions

in

ecosystems

-LRB-

Mooney

-RRB-

Robroek

et

al.

-LRB-

-RRB-

already

found

different

responses

in

biomass

production

among

species

when

temperature

was

increased

It

can

be

imagined

that

when

a

species

with

high

production

and/or

a

low

decomposition

rate

increases

its

relative

abundance

in

a

bog

this

will

increase

the

C

storage

capacity

of

the

system

Not

only

are

there

different

competing

species

within

a

bog

but

there

are

also

differences

in

dominant

species

between

bogs

when

different

climatic

regions

are

compared

In

this

study

we

used

species

from

two

different

sites

At

the

site

in

northern

Sweden

Sphagnum

balticum

and

Sphagnum

fuscum

are

the

dominant

species

while

at

the

site

in

southern

Sweden

these

species

also

occur

but

Sphagnum

magellanicum

and

Sphagnum

cuspidatum

are

the

most

abundant

species

This

corresponds

with

the

general

distribution

of

these

species

in

Europe

since

both

S.

magellanicum

and

S.

cuspidatum

occur

further

south

than

S.

fuscum

and

S.

balticum

-LRB-

Daniels

and

Eddy

-RRB-

To

examine

the

effect

of

temperature

on

the

competition

between

species

we

performed

a

greenhouse

experiment

in

which

we

studied

the

effect

of

four

temperature

treatments

on

the

growth

of

the

four

species

S.

fuscum

and

S.

balticum

from

a

northern

Swedish

site

and

S.

magellanicum

and

S.

cuspidatum

from

a

southern

Swedish

site

Three

combinations

of

species

were

made

to

study

the

effects

of

temperature

on

interspecific

competition

In

our

experiment

we

tried

to

answer

the

following

questions

What

is

the

effect

of

increased

temperature

on

the

growth

of

different

Sphagnum

species

We

expect

all

species

to

show

an

increase

in

both

height

increment

and

biomass

production

as

a

direct

result

of

increased

temperature

and

indirectly

through

increased

nutrient

availability.What

is

the

effect

of

temperature

on

competition

between

species

Since

S.

fuscum

and

S.

magellanicum

grow

in

drier

and

therefore

also

warmer

microhabitats

than

S.

balticum

and

S.

cuspidatum

respectively

we

expect

these

species

to

be

better

adapted

to

higher

temperatures

S.

magellanicum

grows

at

more

southern

sites

than

S.

balticum

so

we

expect

this

species

to

be

better

adapted

to

higher

temperatures

Consequently

we

hypothesize

that

increased

temperature

will

have

a

positive

effect

on

competitive

abilities

of

the

hummock

and

southern

species

leading

to

a

relatively

larger

increase

in

height

increment

and

biomass

production

with

temperature

than

for

hollow

and

northern

species

Materials

and

methods

Plant

material

In

August

Sphagnum

cores

-LRB-

diameter

cm

height

cm

-RRB-

were

collected

at

two

different

sites

in

Sweden

From

the

northern

site

Lappmyran

-LRB-

N

E

-RRB-

Sphagnum

fuscum

-LRB-

Schimp

-RRB-

H.

Klinggr

cores

and

Sphagnum

balticum

-LRB-

Russ

-RRB-

C.

Jens

cores

were

collected

This

site

is

a

string

flark

mire

or

mixed

mire

with

ridges

of

hummocks

and

hollows

where

S.

fuscum

is

dominant

on

the

hummocks

and

S.

balticum

in

the

dryer

parts

of

the

hollows

When

identifying

the

species

from

this

site

in

the

lab

we

found

specimens

of

both

S.

balticum

and

Sphagnum

angustifolium

-LRB-

Russ

-RRB-

C.

Jens

These

species

are

difficult

to

distinguish

which

both

Russow

-LRB-

Smith

-RRB-

and

Klinggraff

-LRB-

Daniels

and

Eddy

-RRB-

recognized

when

they

identified

both

species

as

varietas

of

Sphagnum

recurvum

In

our

samples

we

were

unable

to

quantify

the

exact

percentages

of

S.

balticum

and

S.

angustifolium

As

result

whenever

we

mention

S.

balticum

we

are

referring

to

a

mixture

of

S

balticum

and

S.

angustifolium

From

the

southern

site

Saxnäs

Mosse

-LRB-

N

E

-RRB-

Sphagnum

magellanicum

-LRB-

Brid

-RRB-

cores

and

Sphagnum

cuspidatum

-LRB-

Hoffm

-RRB-

cores

were

collected

At

this

site

S.

magellanicum

occurs

on

the

lawns

and

low

hummocks

and

S.

cuspidatum

in

the

hollows

and

pools

Cores

were

taken

from

monospecific

stands

of

each

Sphagnum

species

-LRB-

-RRB-

with

sparse

vascular

plant

cover

-LRB-

-RRB-

The

cores

were

placed

in

plastic

containers

-LRB-

diameter

cm

height

cm

-RRB-

Vascular

plants

were

clipped

flush

with

the

Sphagnum

and

other

Sphagnum

species

were

removed

with

tweezers

The

containers

were

brought

to

Wageningen

and

stored

outside

for

weeks

before

the

greenhouse

was

available

As

a

result

containers

from

both

sites

could

acclimate

to

the

same

climate

to

some

extent

Experimental

design

At

the

start

of

the

experiment

the

containers

were

brought

into

the

greenhouse

and

randomly

divided

over

the

treatments

and

five

replicate

blocks

with

seven

species

combinations

-LRB-

four

monocultures

and

three

mixtures

-RRB-

and

four

temperature

treatments

per

block

All

four

species

were

kept

in

monoculture

and

the

following

three

species

combinations

were

made

to

study

interspecific

competition

two

northern

species

S.

fuscum

with

S.

balticum

two

southern

species

S.

magellanicum

with

S.

cuspidatum

and

a

northern

with

a

southern

species

S.

balticum

with

S.

magellanicum

To

study

competition

between

a

northern

and

a

southern

species

we

chose

the

combination

of

S.

balticum

and

S.

magellanicum

because

they

occur

at

similar

water

levels

To

make

the

combinations

the

cores

were

cut

into

four

equal

quarters

and

two

quarters

of

both

species

were

placed

alternately

in

an

empty

container

In

potting

the

species

combinations

we

made

certain

that

the

surface

of

the

mixture

was

uniform

We

did

not

cut

monocultures

in

four

quarters

but

another

experiment

showed

no

difference

in

water

content

between

cut

and

uncut

monocultures

-LRB-

Robroek

et

al.

-RRB-

The

experiment

was

conducted

in

four

adjacent

climate

controlled

greenhouse

compartments

from

November

till

April

for

a

total

of

days

Each

compartment

was

assigned

one

of

four

temperature

treatments

Treatments

and

containers

were

switched

between

compartments

every

weeks

to

minimize

any

effect

of

the

different

compartments

The

position

of

the

blocks

and

the

position

of

containers

within

the

blocks

were

also

switched

every

weeks

The

average

day

temperatures

in

the

four

temperature

treatments

were

and

°C

respectively

-LRB-

Table

-RRB-

During

the

dark

period

of

h

the

day

temperature

was

lowered

by

approximately

and

°C

resulting

in

mean

temperatures

of

and

°C

in

temperature

treatments

and

respectively

In

the

region

of

the

northern

site

the

mean

temperature

in

July

is

°C

-LRB-

Alexandersson

et

al.

-RRB-

and

in

the

southern

site

the

mean

temperature

in

July

is

°C

-LRB-

Malmer

et

al.

-RRB-

A

light

period

of

h

was

applied

If

light

intensity

was

low

during

this

period

SON-T

AGRO

-LRB-

Philips

Powertone

-RRB-

lamps

were

used

Table

and

night

mean

values

of

temperature

-LRB-

°C

-RRB-

relative

humidity

-LRB-

-RRB-

and

vapour

pressure

deficit

-LRB-

VPD

-RRB-

-LRB-

kPa

-RRB-

of

the

four

treatments

SE

n

Relative

humidity

during

the

day

was

set

at

In

the

greenhouse

it

was

not

possible

to

keep

the

relative

humidity

exactly

the

same

with

all

temperatures

The

rise

in

temperature

between

treatments

corresponded

with

a

decrease

in

relative

humidity

which

caused

an

additional

increase

in

vapour

pressure

deficit

-LRB-

VPD

-RRB-

with

temperature

-LRB-

Table

-RRB-

The

difference

in

relative

humidity

only

explained

of

the

increase

in

VPD

with

the

highest

temperature

If

relative

humidity

would

have

been

equal

in

all

compartments

VPD

would

still

have

been

twice

as

high

at

temperature

as

at

temperature

Our

highest

VPD

of

kPa

with

a

temperature

of

°C

is

actually

still

quite

low

compared

to

field

conditions

Although

not

many

data

on

VPD

are

published

for

similar

ecosystems

Hobbie

and

Chapin

-LRB-

-RRB-

did

find

the

following

values

for

VPD

in

Toolik

Lake

Alaska

in

June

and

July

in

open

field

sites

kPa

with

temperatures

ranging

from

to

°C

and

under

small

plastic

greenhouses

kPa

with

temperatures

ranging

from

to

°C

Dorrepaal

et

al.

-LRB-

-RRB-

measured

a

VPD

of

under

normal

conditions

and

in

open-top

chambers

with

an

average

temperature

of

°C

in

June

and

July

in

Abisko

Sweden

The

water

level

was

set

to

cm

below

capitula

at

the

start

of

the

experiment

All

species

were

subjected

to

the

same

water

level

so

that

temperature

was

the

only

changing

environmental

variable

This

relatively

high

water

level

was

used

for

all

species

because

hollow

species

can

not

grow

at

low

water

levels

while

hummock

species

can

survive

the

environmental

conditions

of

hollows

quite

well

nonetheless

they

are

absent

from

these

areas

because

of

biotic

factors

-LRB-

Rydin

and

McDonald

-RRB-

Grosvernier

et

al.

-LRB-

-RRB-

found

that

growth

in

height

and

dry

weight

is

equal

for

S.

fuscum

grown

at

water

levels

of

cm

and

cm

below

moss

surface

while

for

S.

magellanicum

and

especially

for

Sphagnum

fallax

growth

in

height

and

dry

weight

is

much

greater

with

the

high

water

level

During

the

experiment

an

artificial

rainwater

solution

an

dilution

of

a

sea

water

solution

-LRB-

Garrels

and

Christ

-RRB-

was

added

twice

a

week

to

bring

the

water

level

back

to

cm

below

capitula

The

amount

of

water

added

was

used

as

a

measure

of

evaporation

The

drop

in

the

water

table

was

highest

in

the

highest

temperature

treatment

but

water

level

never

dropped

more

than

cm

below

moss

surface

between

two

water

additions

In

a

number

of

containers

Sphagnum

grew

higher

than

cm

above

the

container

To

keep

the

water

level

at

cm

below

the

moss

surface

a

plastic

ridge

was

glued

onto

the

containers

and

the

crack

was

filled

with

silicone

kit

Water

content

was

measured

using

a

theta

probe

-LRB-

Delta-T

Devices

Cambridge

UK

-RRB-

before

the

final

harvest

of

the

experiment

This

was

done

days

after

watering

the

containers

for

the

last

time

so

the

water

content

would

reflect

possible

differences

between

treatments

Measurements

Height

increment

of

the

Sphagnum

carpet

was

measured

non-destructively

every

month

using

a

variation

of

the

cranked

wire

method

-LRB-

Clymo

-RRB-

We

used

plastic

rods

that

were

inserted

to

a

depth

of

approximately

cm

and

anchored

by

plastic

broom

bristles

this

method

kept

the

cranked

wires

firm

at

the

same

place

so

they

did

not

move

with

Sphagnum

growth

Two

plastic

rods

were

inserted

in

the

monocultures

and

one

plastic

rod

was

inserted

in

each

quarter

of

the

mixtures

The

rods

had

a

diameter

of

mm

and

did

not

seem

to

interfere

with

the

growth

of

the

surrounding

Sphagna

At

the

end

of

the

experiment

columns

with

a

diameter

of

cm

were

cut

around

each

cranked

wire

and

cut

off

at

cm

length

Each

column

was

put

in

a

plastic

Ziplock

bag

and

fresh

weight

was

determined

All

bags

were

stored

at

°C

till

further

measurements

could

be

taken

Capitula

were

defined

as

the

top

cm

of

each

individual

plant

and

stem

as

the

cm

part

Capitula

and

stems

were

separated

per

column

and

oven

dried

at

°C

for

at

least

h

and

then

weighed

The

weight

of

the

total

sample

was

used

to

calculate

bulk

density

and

the

biomass

production

per

squared

centimetre

to

account

for

changes

in

capitulum

density

For

nutrient

analyses

samples

of

capitula

were

pooled

per

species

for

each

container

Total

N

P

and

K

concentrations

were

determined

by

digesting

mg

of

homogeneous

milled

material

with

salicylic

acid

Se

and

All

samples

were

analysed

for

total

N

and

P

spectrophotometrically

using

an

auto-analyzer

-LRB-

Skalar

-RRB-

K

concentrations

were

measured

with

an

atomic

absorption

spectrophotometer

-LRB-

Varian

AAS

-RRB-

To

compare

capitulum

bulk

density

and

nutrient

concentrations

with

field

values

we

collected

five

samples

-LRB-

d

cm

-RRB-

from

monocultures

of

the

four

Sphagnum

species

in

the

two

Swedish

sites

in

August

Measurements

on

capitulum

bulk

density

and

nutrient

concentrations

were

executed

as

described

above

To

measure

the

change

in

cover

of

the

species

in

the

mixtures

digital

pictures

were

made

at

the

start

and

at

the

end

of

the

experiment

In

these

pictures

we

measured

the

total

surface

cover

per

species

in

each

pot

with

Image

J

-LRB-

Abramoff

et

al.

-RRB-

The

biomass

production

per

unit

area

-LRB-

g

m

-RRB-

was

calculated

as

follows

Data

analysis

Data

were

tested

for

normality

and

equality

of

variance

When

necessary

data

were

square-root

transformed

to

achieve

homogeneous

variances

Block

effect

was

tested

as

random

factor

When

no

block

effect

was

detected

which

was

usually

the

case

block

was

omitted

from

the

analysis

to

gain

extra

df

All

analyses

were

conducted

using

the

SPSS

statistical

package

for

Windows

-LRB-

-RRB-

One

container

with

a

monoculture

of

S.

balticum

under

temperature

was

heavily

affected

by

a

fungal

infection

probably

Lyophyllum

palustre

After

months

of

the

plant

material

had

died

This

container

was

further

omitted

from

the

analyses

Height

increment

in

monocultures

was

tested

per

species

with

one-way

ANOVA

with

temperature

as

independent

factor

Height

increment

biomass

production

cover

change

bulk

density

water

content

and

nutrient

concentrations

were

tested

per

species

Two-way

ANOVAs

were

performed

with

temperature

and

species

combination

as

independent

factors

The

effect

of

temperature

species

and

competition

on

the

concentrations

of

N

P

and

K

was

tested

using

a

three-way

ANOVA

Differences

between

the

treatments

were

analysed

using

a

Tukey

post

hoc

test

To

test

how

the

environmental

variables

temperature

N

concentration

and

water

content

influenced

biomass

production

we

performed

a

stepwise

regression

analysis

per

species

Results

Height

increment

In

the

monocultures

the

height

increment

increased

with

temperature

in

each

species

-LRB-

Fig.

Table

-RRB-

For

S.

cuspidatum

this

effect

was

least

distinct

with

the

lowest

height

growth

at

temperature

and

no

difference

in

growth

between

temperatures

and

Fig.

increment

of

species

in

monocultures

-LRB-

cm

-RRB-

Data

are

mean

values

SE

n

except

for

Sphagnum

balticum

at

n

Different

letters

indicate

significant

differences

-LRB-

P

-RRB-

between

temperature

treatments

within

each

species

For

temperature

treatments

see

Table

and

P-values

and

direction

of

main

effects

influencing

height

increment

and

biomass

production

per

speciesa

corrected

for

cover

using

a

two-way

ANOVATemperatureCombinationT

combinationFPEffectFPEffectFPHeight

incrementSphagnum

fuscum

-LRB-

Sphagnum

balticum

-RRB-

S.

balticum

-LRB-

S.

fuscum

-RRB-

S.

balticum

-LRB-

Sphagnum

magellanicum

-RRB-

S.

magellanicum

-LRB-

S.

balticum

-RRB-

S.

magellanicum

-LRB-

Sphagnum

cuspidatum

-RRB-

S.

cuspidatum

-LRB-

S.

magellanicum

-RRB-

Biomass

productionS

fuscum

-LRB-

S.

balticum

-RRB-

S.

balticum

-LRB-

S.

fuscum

-RRB-

S.

balticum

-LRB-

S.

magellanicum

-RRB-

S.

magellanicum

-LRB-

S.

balticum

-RRB-

S.

magellanicum

-LRB-

S.

cuspidatum

-RRB-

S.

cuspidatum

-LRB-

S.

magellanicum

-RRB-

aNumber

of

observations

n

except

for

S.

balticumn

Only

S.

fuscum

showed

no

difference

in

height

increment

between

monoculture

and

mixture

All

other

species

showed

a

growth

reduction

in

mixtures

-LRB-

Table

-RRB-

There

were

no

significant

interactions

between

the

effect

of

temperature

and

competition

on

height

increment

except

for

S.

balticum

in

combination

with

S.

magellanicum

-LRB-

Table

-RRB-

Temperature

increased

height

increment

of

S.

balticum

in

monoculture

while

there

was

no

effect

of

temperature

in

mixture

with

S.

magellanicum

-LRB-

Figs.

-RRB-

When

we

compared

height

increment

between

the

two

species

in

each

mixture

the

wet

species

S.

balticum

and

S.

cuspidatum

had

higher

values

than

the

dry

species

S.

fuscum

and

S.

magellanicum

at

temperature

treatments

and

-LRB-

Fig.

-RRB-

When

temperature

increased

the

differences

in

height

increment

between

the

two

species

disappeared

Fig.

increment

of

the

individual

species

at

each

temperature

treatment

-LRB-

see

Table

-RRB-

within

the

three

mixtures

of

species

aSphagnum

fuscum

S.

balticum

bSphagnum

magellanicum

S.

balticum

and

cS

magellanicum

Sphagnum

cuspidatum

Data

are

mean

values

SE

n

Different

letters

indicate

significant

differences

between

treatments

-LRB-

P

-RRB-

Cover

The

hollow

species

S.

balticum

and

S.

cuspidatum

increased

in

area

in

out

of

containers

when

growing

in

the

mixtures

In

the

other

seven

containers

-LRB-

three

with

S.

magellanicum

S.

balticum

two

with

S.

fuscum

S.

balticum

two

with

S.

magellanicum

S.

cuspidatum

-RRB-

cover

changed

less

than

For

S.

balticum

there

were

significant

effects

of

temperature

-LRB-

F

P

-RRB-

and

neighbouring

species

-LRB-

F

P

-RRB-

on

expansion

-LRB-

Fig.

b

-RRB-

Maximum

change

in

cover

was

for

S.

balticum

in

combination

with

S.

fuscum

with

temperature

and

There

was

no

effect

of

temperature

on

expansion

of

S.

cuspidatum

-LRB-

Fig.

F

P

-RRB-

Fig.

change

for

hollow

species

aS

balticum

in

combination

with

S.

fuscum

bS

balticum

in

combination

with

S.

magellanicum

and

cS

cuspidatum

in

combination

with

S.

magellanicum

Data

are

mean

values

SE

n

There

were

no

significant

differences

between

treatments

-LRB-

P

-RRB-

For

temperature

treatments

see

Table

Biomass

production

The

response

of

biomass

production

to

the

temperature

treatments

was

similar

to

the

response

of

height

increment

-LRB-

Table

-RRB-

In

all

species

biomass

production

increased

with

increased

temperature

S.

fuscum

showed

the

strongest

response

this

species

increased

its

biomass

production

from

the

lowest

to

the

highest

temperature

treatment

in

monocultures

-LRB-

Fig.

-RRB-

Only

for

S.

balticum

in

combination

with

S.

magellanicum

was

there

a

significant

interaction

between

temperature

and

species

combination

in

biomass

production

-LRB-

Table

-RRB-

Temperature

increased

biomass

production

of

S.

balticum

in

monoculture

and

in

mixture

with

S.

fuscum

while

there

was

no

effect

of

temperature

in

mixture

with

S.

magellanicum

Fig.

production

corrected

for

change

in

cover

for

species

in

monocultures

-LRB-

mono

-RRB-

and

in

mixtures

-LRB-

mix

-RRB-

for

each

temperature

treatment

-LRB-

see

Table

-RRB-

and

species

combination

aS

fuscum

-LRB-

fus

-RRB-

S.

balticum

-LRB-

bal

-RRB-

bS

magellanicum

-LRB-

mag

-RRB-

S.

balticum

and

cS

magellanicum

S.

cuspidatum

-LRB-

cus

-RRB-

Data

are

mean

values

SE

n

Different

letters

indicate

significant

differences

between

treatments

-LRB-

P

-RRB-

When

differences

in

biomass

production

between

monocultures

and

mixtures

are

compared

per

temperature

treatment

it

shows

that

S.

fuscum

suffered

from

competition

with

S.

balticum

at

temperature

because

production

was

lower

in

mixture

than

in

monoculture

but

it

no

longer

suffered

at

temperature

-LRB-

Fig.

-RRB-

At

temperature

S.

balticum

does

suffer

from

competition

with

S.

fuscum

but

not

at

lower

temperatures

In

the

mixtures

of

S.

magellanicum

and

S.

balticum

S.

magellanicum

suffers

from

competition

at

temperature

and

whereas

S.

balticum

suffers

from

competition

at

temperature

and

-LRB-

Fig.

-RRB-

Biomass

production

of

S.

cuspidatum

did

not

show

any

effect

of

competition

with

S.

magellanicum

while

biomass

production

of

S.

magellanicum

did

suffer

from

competition

at

temperatures

and

-LRB-

Fig.

-RRB-

In

the

stepwise

regression

for

biomass

production

of

S.

balticum

water

content

was

selected

as

the

most

explanatory

variable

-LRB-

P

-RRB-

For

biomass

production

of

S.

fuscum

-LRB-

P

-RRB-

S.

magellanicum

-LRB-

P

-RRB-

and

S.

cuspidatum

-LRB-

P

-RRB-

temperature

was

selected

as

the

most

explanatory

variable

Bulk

density

Bulk

densities

were

lower

at

higher

temperatures

for

all

species

except

for

bulk

density

of

the

capitula

and

stems

of

S.

cuspidatum

-LRB-

Table

-RRB-

Compared

to

field

values

capitulum

bulk

density

of

S.

fuscum

and

S.

balticum

decreased

with

temperature

while

capitulum

bulk

density

of

S.

magellanicum

and

S.

cuspidatum

seemed

to

increase

at

low

temperatures

Table

density

of

capitula

section

stem

section

and

total

sample

Data

are

mean

values

SE

pooled

within

temperature

treatment

-LRB-

see

Table

-RRB-

and

within

competition

treatment

Different

letters

indicate

significant

differences

between

treatments

within

a

species

-LRB-

P

-RRB-

There

were

no

significant

interactions

between

temperature

and

competition

treatments

fus

S.

fuscum

bal

S.

balticum

mag

S.

magellanicum

cus

S.

cuspidatumField

balmag

balmag

cusBulk

density

capitula

-LRB-

mg

cm

-RRB-

S.

S.

S.

density

stems

-LRB-

mg

cm

-RRB-

S.

S.

S.

density

total

sample

-LRB-

mg

cm

-RRB-

S.

S.

S.

for

material

from

the

sites

of

origin

-LRB-

Field

values

n

-RRB-

are

given

for

comparison

Number

of

observations

for

each

species

for

each

temperature

treatment

S.

fuscum

and

S.

cuspidatum

n

S.

balticum

n

S.

magellanicum

n

Number

of

observations

for

each

species

for

each

combination

n

Bulk

densities

of

both

capitula

and

stems

were

lower

in

mixtures

than

in

monocultures

of

S.

fuscum

and

S.

balticum

Similarly

in

S.

cuspidatum

the

bulk

density

of

the

capitula

was

lower

in

mixtures

than

in

monocultures

There

were

no

significant

interactions

between

temperature

and

species

combination

Nutrient

concentrations

The

concentrations

of

all

nutrients

-LRB-

N

P

and

K

-RRB-

differed

between

species

and

rose

with

increasing

temperature

N

concentration

was

also

affected

by

the

interactions

of

temperature

by

species

-LRB-

F

P

-RRB-

and

species

by

combination

-LRB-

F

P

-RRB-

At

temperatures

and

N

concentrations

were

lower

for

S.

fuscum

and

S.

balticum

than

for

S.

magellanicum

and

S.

cuspidatum

as

was

also

the

case

in

field

values

At

temperature

only

the

N

concentration

of

S.

balticum

was

lower

than

that

of

S.

magellanicum

At

temperature

N

concentrations

of

S.

balticum

were

lower

than

those

of

S.

magellanicum

and

S.

fuscum

-LRB-

Table

-RRB-

Compared

to

field

values

all

species

showed

an

increased

N

concentration

with

temperature

Table

P

and

K

concentration

-LRB-

mg

g

-RRB-

of

the

capitula

Data

are

mean

values

SE

pooled

within

temperature

treatment

-LRB-

see

Table

-RRB-

and

within

competition

treatment

Different

letters

indicate

significant

differences

between

treatments

within

a

species

-LRB-

P

-RRB-

There

were

no

significant

interactions

between

temperature

and

competition

treatments

For

abbreviations

see

Table

balmag

balmag

cusN

-LRB-

mg

g

-RRB-

S.

S.

S.

S.

aP

-LRB-

mg

g

-RRB-

S.

S.

S.

S.

K

-LRB-

mg

g

-RRB-

S.

S.

S.

S.

aField

values

-LRB-

n

-RRB-

are

given

for

comparison

Number

of

observations

for

each

species

for

each

temperature

treatment

S.

fuscum

and

S.

cuspidatum

n

S.

balticum

n

S.

magellanicum

n

Number

of

observations

for

each

species

for

each

combination

n

P

and

K

concentrations

were

affected

by

temperature

-LRB-

P

concentration

F

P

K

concentration

F

P

-RRB-

and

species

-LRB-

P

concentration

F

P

K

concentration

F

P

-RRB-

P

and

K

concentrations

were

higher

at

high

temperature

for

all

species

-LRB-

Table

-RRB-

P-values

decreased

compared

to

field

values

while

K

concentration

increased

compared

to

field

values

Evaporation

and

water

content

Water

content

decreased

with

temperature

treatment

-LRB-

Table

-RRB-

Water

content

was

lowest

in

S.

balticum

in

mixture

with

S.

fuscum

Evaporation

increased

with

temperature

and

therefore

with

VPD

for

all

species

-LRB-

Table

-RRB-

Evaporation

in

S.

fuscum

in

both

monoculture

and

mixture

was

lower

than

in

other

species

Table

content

-LRB-

volume

-RRB-

at

cm

depth

and

evaporation

-LRB-

mm

day

-RRB-

per

temperature

treatmenta

-LRB-

see

Table

-RRB-

and

per

species

combinationb

Data

are

mean

values

SE

Different

letters

indicate

significant

differences

between

treatments

-LRB-

P

-RRB-

There

were

no

significant

interactions

between

temperature

and

competition

treatmentsWater

contentEvaporationTemperature

a

b

c

dMonoculturesS

aS

bcS

cS

cMixturesS

fuscum

S.

aS

magellanicum

S.

bS

magellanicum

S.

bcS

of

observations

for

each

temperature

treatment

for

water

content

n

for

evaporation

n

Number

of

observations

for

each

competition

treatment

for

water

content

and

for

evaporation

n

Discussion

Effect

of

temperature

on

growth

As

expected

all

species

in

monoculture

increased

height

increment

with

temperature

-LRB-

Fig.

-RRB-

All

species

also

showed

a

looser

growth

form

with

higher

temperatures

which

resulted

in

lower

densities

-LRB-

Table

-RRB-

Despite

the

lower

bulk

density

at

higher

temperatures

biomass

production

still

increased

with

temperature

for

all

species

-LRB-

Table

Fig.

-RRB-

The

response

of

height

increment

to

temperature

was

about

a

factor

larger

than

the

response

of

biomass

production

Growth

of

Sphagnum

was

probably

increased

by

a

higher

rate

of

photosynthesis

and

a

higher

N

availability

Photosynthesis

in

Sphagnum

has

been

shown

to

increase

with

temperature

up

to

an

optimum

around

°C

-LRB-

Skre

and

Oechel

Harley

et

al.

-RRB-

When

temperature

increased

the

nutrient

concentrations

in

Sphagnum

were

higher

-LRB-

Table

-RRB-

Moreover

N

and

K

concentration

increased

compared

to

field

values

-LRB-

Table

-RRB-

As

biomass

production

also

increased

N

and

K

uptake

must

have

increased

considerably

with

increasing

temperature

No

nutrients

were

added

with

the

rainwater

solution

so

the

higher

availability

of

nutrients

must

have

come

from

Sphagnum

itself

and

the

peat

below

Probably

the

lower

Sphagnum

parts

in

the

containers

decomposed

faster

when

the

temperature

was

higher

making

more

N

and

K

available

for

growth

This

temperature-induced

stimulation

of

nutrient

mineralization

is

probably

larger

than

it

would

be

in

field

conditions

as

the

peat

soil

in

the

containers

is

surrounded

by

warm

air

on

every

side

resulting

in

relatively

high

soil

temperatures

in

our

experiment

However

it

can

be

expected

that

increased

temperature

as

a

result

of

climate

change

will

also

enhance

decomposition

rates

in

field

situations

-LRB-

Hobbie

-RRB-

thereby

increasing

nutrient

availability

for

both

Sphagnum

and

vascular

plants

The

lower

N

concentrations

of

S.

fuscum

and

S.

balticum

compared

with

S.

magellanicum

and

S.

cuspidatum

at

temperatures

and

are

probably

caused

by

the

different

sites

of

origin

In

the

northern

site

the

N

deposition

is

much

lower

-LRB-

approximately

g

N

m

year

-RRB-

than

in

the

southern

site

-LRB-

approximately

g

N

m

year

-RRB-

where

S.

magellanicum

and

S.

cuspidatum

were

collected

In

this

experiment

we

provided

near

optimal

growing

conditions

for

Sphagnum

with

high

water

level

and

high

humidity

which

explains

why

the

Sphagnum

plants

could

grow

with

a

lower

bulk

density

and

still

keep

their

capitula

moist

However

Sphagnum

water

content

still

decreased

with

an

increase

in

temperature

In

field

conditions

it

would

probably

not

have

been

possible

for

the

Sphagnum

plants

to

change

their

density

so

much

since

it

would

have

led

to

problems

in

maintaining

the

water

content

of

the

capitula

The

effect

of

temperature

on

height

increment

might

therefore

also

have

been

less

In

a

few

field

studies

no

positive

or

even

negative

effects

of

temperature

on

production

were

found

However

in

these

experiments

there

were

other

factors

besides

temperature

that

could

have

had

a

negative

effect

on

biomass

production

like

drought

stress

-LRB-

Hobbie

et

al.

Weltzin

et

al.

Gunnarsson

et

al.

-RRB-

and

higher

vascular

plant

cover

which

could

have

resulted

in

etiolation

of

the

Sphagnum

plants

and

reduced

biomass

production

because

of

increased

shading

-LRB-

Gunnarsson

et

al.

-RRB-

In

other

studies

also

positive

effects

of

temperature

on

height

growth

and

production

were

found

for

different

species

in

both

greenhouse

-LRB-

Robroek

et

al.

-RRB-

and

field

experiments

-LRB-

Moore

Gerdol

Sonesson

et

al.

Dorrepaal

et

al.

-RRB-

In

accordance

with

our

hypothesis

Asada

et

al.

-LRB-

-RRB-

suggested

that

Sphagnum

species

respond

positively

to

increased

temperature

and

that

hollow

and

lawn

species

are

more

sensitive

to

temperature

than

hummock

species

This

however

does

not

correspond

with

the

low

response

of

S.

cuspidatum

to

temperature

in

our

experiment

Dorrepaal

et

al.

-LRB-

-RRB-

also

found

a

decrease

in

bulk

density

with

increased

temperature

Since

the

response

of

height

increment

and

bulk

density

to

temperature

were

in

opposite

directions

the

dry

matter

production

of

S.

fuscum

did

not

show

a

significant

increase

with

temperature

Our

relatively

high

height

increment

and

low

density

of

S.

fuscum

compared

to

the

values

of

Dorrepaal

et

al.

-LRB-

-RRB-

can

probably

be

explained

by

the

much

higher

water

levels

in

our

experiment

Dorrepaal

et

al.

-LRB-

-RRB-

used

water

levels

of

to

cm

below

moss

surface

during

their

measurements

However

the

Sphagnum

densities

we

measured

-LRB-

Table

-RRB-

agreed

quite

well

with

densities

from

other

studies

-LRB-

Lindholm

and

Vasander

Moore

et

al.

Asada

et

al.

-RRB-

From

our

results

we

conclude

that

the

height

increment

and

biomass

production

of

all

Sphagnum

species

in

bogs

can

increase

with

an

increase

in

temperature

However

the

literature

shows

us

that

particularly

under

field

conditions

this

potential

response

may

not

be

realized

in

instances

of

competition

from

vascular

plants

drought

stress

or

extreme

temperature

increases

Effect

of

temperature

on

competition

We

hypothesized

that

increased

temperature

will

have

a

positive

effect

on

competitive

abilities

of

S.

fuscum

and

S.

magellanicum

This

hypothesis

was

confirmed

in

the

competition

with

S.

balticum

since

the

height

increment

and

biomass

production

of

S.

balticum

at

the

highest

temperature

treatment

were

no

longer

larger

than

those

of

S.

fuscum

and

S.

magellanicum

-LRB-

Figs.

-RRB-

However

S.

balticum

still

increased

its

cover

at

the

expense

of

S.

fuscum

and

S.

magellanicum

in

all

mixtures

-LRB-

Fig.

b

-RRB-

This

could

be

expected

as

the

water

level

we

used

was

relatively

high

and

in

the

range

of

the

natural

habitat

of

these

species

These

results

correspond

to

the

findings

from

a

field

experiment

of

Rydin

-LRB-

-RRB-

who

found

an

expansion

of

S.

balticum

at

the

expense

of

S.

fuscum

at

a

water

level

of

cm

At

water

levels

of

and

cm

he

found

a

small

expansion

of

S.

balticum

but

at

a

water

level

of

cm

S.

fuscum

showed

large

expansion

In

agreement

with

the

hypothesis

the

difference

in

height

increment

and

biomass

production

between

S.

fuscum

and

S.

balticum

disappeared

as

temperature

increased

-LRB-

Figs.

-RRB-

S.

fuscum

kept

increasing

height

increment

with

temperature

but

S.

balticum

already

reached

maximum

height

growth

at

temperature

which

is

comparable

to

the

summer

temperature

in

the

site

of

origin

of

these

species

Also

the

expansion

in

cover

became

lower

for

S.

balticum

at

temperature

-LRB-

Fig.

-RRB-

As

a

result

the

difference

in

biomass

production

between

S.

fuscum

and

S.

balticum

slowly

decreased

with

an

increase

in

temperature

until

there

was

no

significant

difference

at

the

highest

temperature

Apparently

the

hummock

species

S.

fuscum

is

better

able

to

profit

from

a

high

increase

in

temperature

than

S.

balticum

even

at

relatively

high

water

levels

This

is

confirmed

by

the

stepwise

regression

analysis

which

shows

that

biomass

production

of

S.

fuscum

is

correlated

most

to

temperature

and

biomass

production

of

S.

balticum

to

water

content

As

could

be

expected

S.

fuscum

as

a

hummock

species

has

a

higher

water

content

than

S.

balticum

also

at

higher

temperatures

-LRB-

Table

-RRB-

and

therefore

can

profit

more

from

increased

temperature

because

water

does

not

become

limiting

for

growth

S.

fuscum

also

seems

to

be

the

better

competitor

for

nutrients

The

N

and

P

concentrations

in

S.

fuscum

tended

to

be

higher

in

the

mixtures

than

in

the

monocultures

whereas

in

S.

balticum

the

opposite

was

the

case

-LRB-

Table

-RRB-

Indeed

S.

fuscum

is

known

for

its

high

N

uptake

rate

-LRB-

Jauhiainen

et

al.

-RRB-

Our

results

show

that

S.

balticum

loses

competitive

strength

with

increasing

temperature

With

a

slight

increase

in

temperature

in

northern

bogs

S.

balticum

may

remain

the

stronger

competitor

at

high

water

levels

but

at

higher

temperature

increases

S.

fuscum

will

gain

a

competitive

advantage

over

S.

balticum

also

because

increased

temperature

may

lead

to

lower

water

tables

in

bogs

Recent

climate

change

simulation

models

predict

an

increase

of

°C

in

summer

temperature

in

northern

Europe

with

increasing

precipitation

in

northern

Scandinavia

-LRB-

Christensen

et

al.

-RRB-

This

limited

rise

in

temperature

almost

similar

to

the

increase

from

temperature

to

would

not

affect

competition

between

S.

balticum

and

S.

fuscum

very

strongly

However

the

effect

of

a

predicted

increase

in

winter

temperature

of

°C

-LRB-

Christensen

et

al.

-RRB-

could

shift

the

competitive

balance

between

S.

balticum

and

S.

fuscum

further

because

increased

snow

cover

and

spring

temperature

have

been

shown

to

increase

S.

fuscum

production

-LRB-

Dorrepaal

et

al.

-RRB-

For

S.

magellanicum

and

S.

cuspidatum

temperature

is

comparable

to

the

summer

temperature

in

their

site

of

origin

There

was

no

effect

of

a

temperature

increase

from

temperature

to

on

biomass

production

and

relative

performance

of

the

species

This

implies

that

with

the

predicted

increase

in

temperature

of

°C

-LRB-

Christensen

et

al.

-RRB-

the

competitive

balance

between

S.

magellanicum

and

S.

cuspidatum

will

remain

unchanged

The

mixtures

of

S.

balticum

and

S.

magellanicum

show

the

largest

difference

in

height

increment

and

biomass

production

at

temperature

which

is

comparable

to

the

summer

temperature

in

the

site

of

origin

of

S.

balticum

Also

the

expansion

in

cover

of

S.

balticum

was

highest

at

this

temperature

When

temperature

increases

the

difference

in

height

growth

and

biomass

production

became

smaller

and

then

disappeared

in

mixtures

whereas

in

monocultures

the

difference

in

biomass

production

between

species

remained

This

implies

that

S.

balticum

as

a

northern

species

can

enhance

its

production

with

an

increase

in

temperature

as

long

as

it

grows

in

monocultures

If

S.

magellanicum

expanded

its

distribution

further

to

the

north

as

a

result

of

global

warming

it

would

be

a

strong

competitor

for

S.

balticum

thereby

reducing

S.

balticum

production

Gunnarsson

et

al.

-LRB-

-RRB-

also

showed

that

S.

balticum

performs

less

well

under

competition

with

increased

temperatures

They

performed

a

competition

experiment

in

a

poor

fen

close

to

the

site

of

origin

of

the

S.

balticum

material

They

found

that

when

Sphagnum

papillosum

was

transplanted

to

an

area

with

S.

balticum

S.

papillosum

decreased

in

area

by

However

when

temperature

was

increased

by

°C

S.

papillosum

increased

by

This

treatment

is

comparable

to

the

increase

from

temperature

to

temperature

in

our

experiment

but

with

lower

water

tables

ranging

from

to

cm

under

the

moss

surface

Generally

we

conclude

from

our

experiment

that

an

increase

in

temperature

can

favour

hummock

and

lawn

species

compared

to

hollow

species

This

corresponds

to

the

findings

of

Mauquoy

et

al.

-LRB-

-RRB-

who

showed

from

peat

core

analyses

that

in

periods

with

lower

temperature

due

to

decreased

solar

activity

there

was

a

shift

in

representation

from

lawn

and

hummock

species

to

hollow

species

in

ombrotrophic

mires

in

Denmark

and

the

UK

In

conclusion

our

findings

suggest

that

production

rates

can

increase

and

that

Sphagnum

species

abundances

can

shift

in

response

to

global

warming

particularly

at

northern

sites

There

hollow

species

such

as

S.

balticum

will

lose

competitive

strength

relative

to

hummock

species

such

as

S.

fuscum

and

southern

species

such

as

S.

magellanicum

What

the

consequences

for

the

C

balance

of

bog

ecosystems

will

be

depends

not

only

on

the

production

rates

but

also

on

decomposition

In

general

decomposition

rates

also

increase

with

temperature

and

increased

N

availability

-LRB-

Hobbie

Limpens

and

Berendse

-RRB-

and

hummock

species

decompose

slower

than

hollow

species

-LRB-

Rochefort

et

al.

Johnson

and

Damman

Limpens

and

Berendse

-RRB-

but

virtually

nothing

is

known

about

the

temperature

sensitivity

of

decomposition

of

bog

plant

species

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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