CLIMATE CHANGE EFFECTS ON SOIL COCLIMATE CHANGE EFFECTS ON SOIL CO22 AND CH AND CH44 FLUXES IN FOUR FLUXES IN FOUR ECOSYSTEMS ALONG AN ELEVATIONAL GRADIENT IN NORTHERN ECOSYSTEMS ALONG AN ELEVATIONAL GRADIENT IN NORTHERN ARIZONA ARIZONA Joseph C. Blankinship1, James R. Brown1, Paul Dijkstra1,2, Bruce A. Hungate1,2

Significance

Methods

Results Implications

1 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011; 2 Merriam-Powell Center for Environmental Research, Flagstaff, AZ, 86011 E-mail of corresponding author: joseph.blankinship@nau.edu

Carbon dioxide (CO2) and methane (CH4) are important greenhouse gases that contribute to global warming, but little is known about how predicted interactive changes in temperature and precipitation will affect soil fluxes in different ecosystems. Globally, heterotrophic soil organisms and plant root respiration release about 85 Pg (1015 g) of CO2-C into the atmosphere annually, and high-affinity methane-oxidizing bacteria consume about 30 Tg (1012 g) of CH4-C from the atmosphere annually (IPCC 2001).

1.Will predicted magnitudes of warming and altered precipitation affect soil CO2 production and CH4 consumption?

2.Will responses depend on interactions between warming and altered precipitation?

3.Will responses depend on ecosystem type?

Merriam Climatic Change ExperimentMerriam Climatic Change Experiment

Aboveground Biomass

(no grazing allowed)

Soil (organic & mineral)

Roots

Microorganisms

Macrofauna

Leachate Collector

mixed conifer forestmixed conifer forest precip.= 790 mm y-1 mean annual T = 4.0°C

ponderosa pine forestponderosa pine forest 660 mm y-1

piñon-juniper woodlandpiñon-juniper woodland 380 mm y-1

high desert grasslandhigh desert grassland 230 mm y-1

Great Basin desertGreat Basin desert 180 mm y-1 mean annual T = 10.0°C

+1.5°C

+1.5°C

+1.5°C

+1.5°C

Flagstaff, AZ (est. 2002)3-way complete factorial design 3-way complete factorial design (n=6 or 7(n=6 or 7))::

44 ecosystems

22 temperatures (ambient and elevated) through elevational transplantation

33 precipitations (-30%, ambient, and +50%)

through rainout shelters and funnels

30 cm diameter

30

cm

de

ep

el. 2615 m

el. 1540 m

All cores were taken from grassy interspaces to standardize vegetation type and shading effects

soil type = loam

sandy loam

loam

clay

PV

C ly

sim

ete

rP

VC

lysi

me

ter

160 total lysimeters

Soils were sampled in Sept 2005, Soils were sampled in Sept 2005, 3 years after treatments began 3 years after treatments began

Harvest Harvest SoilsSoils

Hour 0 Hour 48sieve, weigh into bottles (adjust water content)

HEADSPACE SAMPLE #1

Start Start IncubationsIncubations

HEADSPACE SAMPLE #3

Finish Finish Incubations Incubations

Hour 96

Co

nce

ntr

ati

on

Time

Laboratory MeasurementsLaboratory Measurements

net CH4 consumption

Incubation conditions:

Warm (25°C), Dark, Unshaken

Standardized moisture (35% WHC)

Elevated [CH4] (10x ambient, 18 ppm)

Hour 60

HEADSPACE SAMPLE #2

gas chromatograph

0-20 cm deep cores

12 ml gas storage vials

250 ml bottles

CO2 production

Flagstaff, Arizona, USAFlagstaff, Arizona, USA

-50

0

50

100

150

200

Mixed ConiferForest

PonderosaPine Forest

Piñon-JuniperWoodland

High DesertGrassland

Eff

ect

size

of

fiel

d w

arm

ing

on

la

bo

rato

ry s

oil

CO

2 p

rod

uct

ion

((

Ele

v -

Am

b)

/ Am

b *

10

0%

)

Reduced Precip

Ambient Precip

Elevated Precip

*

*

*

*

3-way ANOVA interactionEcosystem x Temp x Precip p=0.01

-100

0

100

200

300

400

500

Mixed ConiferForest

PonderosaPine Forest

Piñon-JuniperWoodland

High DesertGrassland

Eff

ect

size

of

fiel

d w

arm

ing

on

p

ote

nti

al s

oil

CH

4 co

nsu

mp

tio

n

((E

lev

- A

mb

) / A

mb

* 1

00

%)

*

*

*

*

2-way ANOVA interactionEcosystem x Temp p<0.0001

-80

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

Mixed ConiferForest

PonderosaPine Forest

Piñon-JuniperWoodland

High DesertGrassland

Eff

ect

size

of

elev

ated

pre

cip

itat

ion

on

po

ten

tial

so

il C

H4

con

sum

pti

on

((

Ele

v -

Am

b)

/ Am

b *

10

0%

)

*

2-way ANOVA interactionEcosystem x Precip p=0.02

Actual CO2 and CH4 fluxes measured monthly between Aug – Oct 2005, three years after treatments began

Laboratory CO2 and potential CH4 fluxes measured in Sept 2005, three years after treatments began

Ecosystem differences

Actual CO2 production Lab CO2 production Actual CH4 consumption Potential CH4 consumption(g C m-2 d-1) (μg CO2 g

-1 soil h-1) (mg C m-2 d-1) (ng CH4 g-1 soil h-1)

Mixed Conifer Forest 27.1 ± 3.3 (A) 2.9 ± 0.5 (A) 5.7 ± 0.8 (BC) 0.8 ± 0.3 (C)

Ponderosa Pine Forest 21.6 ± 1.8 (AB) 3.3 ± 0.4 (A) 4.6 ± 0.5 (C) 0.5 ± 0.1 (C)

Piñon-Juniper Woodland 18.8 ± 3.7 (B) 1.8 ± 0.2 (B) 6.9 ± 0.9 (AB) 1.8 ± 0.4 (B)

High Desert Grassland 10.3 ± 3.4 (C) 1.8 ± 0.2 (B) 7.6 ± 1.2 (A) 2.4 ± 0.4 (A)

0

5

10

15

20

25

30

Reduced Precip Ambient Precip Elevated Precip

Ac

tua

l C

O2 P

rod

uc

tio

n

(g

C m

-2 d

-1)

1-way ANOVA effectPrecipp=0.01

aa

a

0

1

2

3

4

5

6

7

8

9

Reduced Precip Ambient Precip Elevated Precip

Act

ual

CH

4 C

on

sum

pti

on

(mg

C

m-2 d

-1)

1-way ANOVA effectPrecipp=0.006a

ab

b

-100

-80

-60

-40

-20

0

20

40

60

80

100

Mixed ConiferForest

PonderosaPine Forest

Piñon-JuniperWoodland

High DesertGrassland

Eff

ect

size

of

fiel

d w

arm

ing

on

ac

tual

CO

2 p

rod

uct

ion

((

Ele

v -

Am

b)

/ Am

b *

10

0%

)

*

*

*

2-way ANOVA interactionEcosystem x Temp p<0.0001

-20

-15

-10

-5

0

5

10

15

20

25

30

35

Mixed ConiferForest

PonderosaPine Forest

Piñon-JuniperWoodland

High DesertGrassland

Eff

ect

size

of

fiel

d w

arm

ing

on

ac

tual

CH

4 co

nsu

mp

tio

n

((E

lev

- A

mb

) / A

mb

* 1

00

%)

2-way ANOVA interactionEcosystem x Temp p=0.05

CO2

CH4

Actual rates of CO2 production were precipitation-limited, regardless of ecosystem type.

Actual rates of CH4 consumption were negatively affected by precipitation, regardless of ecosystem type, suggesting that all ecosystems were vulnerable to diffusional limitation.

Potential rates of CH4 consumption suggest that the wettest mixed conifer forest was especially vulnerable to diffusional limitation by elevated precipitation, or that methanogenesis increased. (* indicates significant effect)

The effect of temperature on actual rates of CO2 production depended on ecosystem type. (* indicates significant effect)

Laboratory rates of CO2 production suggest that the positive effect of warming in the coldest ecosystem is mediated by water availability. (* indicates significant effect)

The effect of temperature on actual rates of CH4 consumption depended on ecosystem type. The mixed conifer forest and high desert grassland tended to be positively affected by warming, and the piñon-juniper woodland tended to be negatively affected.

The effect of temperature on potential rates of CH4 consumption also depended on ecosystem type. The mixed conifer forest and high desert grassland were positively affected by warming, and the piñon-juniper woodland and ponderosa pine forest were negatively affected. (* indicates significant effect)

1.In a wetter world, these soils become a larger source of CO2 and a smaller sink of CH4 (positive feedbacks to global warming).

CH4 consumption was most sensitive to elevated precipitation in the wettest ecosystem, probably because of lower rates of atmospheric CH4 diffusion or higher rates of O2 consumption through respiration

2.Interactions between climate change factors and between ecosystems can mediate changes in soil CO2 and CH4 fluxes.

A 3-way interactive effect (ecosystem x temp x precip) suggests that soil respiration is only temperature-limited in colder ecosystems when supplied with enough precipitation

3.Ecosystem type is most important for predicting temperature effects.

Probably mediated by relative water availability

Positive effects of warming were most consistent in the coldest ecosystem

Time

net CH4 consumption CO2 production

Co

nce

ntr

ati

on

0 min 20 min

40 min