The age of C respired from ecosystems

The age of C respired from ecosystems

Susan Trumbore, Jim Randerson, Claudia Czimczik, Nicole Nowinski

(UC Irvine)

Jeff Chambers (Tulane)

Eric Davidson (Woods Hole Research Center)

Ted Schuur (Univ. Florida)

Simone Vieira, Plínio Camargo

(Centro de Energía Nuclear na Agricultura, USP, Brazil)

The age of C respired from ecosystems

Photosynthesis

leaf

stem

root

Allocation

storage

Microbial community

Stabilized SOM

Soil respiration

Litter and SOMdecomposition

Ecosystem respiration

RootRespiration

Fire

Loss by leaching, erosion

-1.5-1

-0.50

0.51

1.5

0 100 200 300 400 500

time

Production

Ecosystem Respiration

Heterotrophic decomposition

Why this might be interesting

• Measure of the capacity for storage of C and interannual variability in C balance

• Isodisequilibrium; improve 13C deconvolutions• Potential for direct comparison of data with models

Time

C stored C lost C stored

Dev

iati

on f

rom

mea

n

Radiocarbon of soil-respired CO2 provides a direct measure of isodisequilibrium “mean age” of several years up to a decade

14 C

14 C

50

150

250

350

450

550

650

1960 1970 1980 1990 2000

50

100

150

200

1998 2000 2002 2004

Harvard Forest MAatmosphere

Howland Forest, METapajos Forest, BrazilBonanza Creek, Alaska

Manitoba, Canada

Atmosphere- north hemisphere from Levin

and Hessheimer 2000

50

100

150

200

1998 2000 2002 2004

1

4C

(p

er m

il)

Local atmosphere(Autotrophic respiration)

CASA

Empirical

Soil respired CO2 is a mix of heterotrophic and autotrophic sources

Data from Harvard Forest, MA

Heterotrophic values – from models

Heterotrophic Respiration can be measured by putting litter and 0-5 cm soil cores in sealed jars, then measuring the rate of CO2 evolution and the isotopic signature of evolved CO2.

50

100

150

200

1998 2000 2002 2004

14

C (

per

mil

)

Local atmosphere(Autotrophic respiration)

Soil respired CO2 is a mix of heterotrophic and autotrophic sources

O horizon

A horizon

CO2 evolved in incubation

Data from Harvard Forest, MA

Flux weighted mean

14C = 14C of CO2 evolved in

incubation - 14C of CO2 in atmosphere

020406080

100120140

-10 0 10 20 30 40 50 60

14C

(p

er

mil)

organic

soil

litter

Latitude of site

Tropical forest

Desert shrub

Temperate forest

Boreal forest

Manaus,Santarem

Joshua Tree*

Harvard,Bear Brook

3 age standsManitoba*

*see posters by Czimczik, Nowinski

020406080

100120140

-10 0 10 20 30 40 50 60

14C

(p

er

mil

)Flux-weighted total heterotrophic

respiration for comparison with model

Tropical forest

Desert shrub

Temperate forest

Boreal forest

Manaus,Santarem

Joshua Tree*

Harvard,Bear Brook 3 age

standsManitoba*

Latitude

0

25

50

75

100

125

0 5 10 15 20 25

Manaus, Brazil

Santarem, Brazil

Joshua Tree, CA

Harvard Forest, MA

Bear Brook, ME

NOBS, Manitoba

Determine age of respired CO2 using pulse-response function for CASA

Years since pulse

CO

2 r

espi

red

Tropical forest

Desert shrub

Temperate forest

Boreal forest

Thompson,and Randerson, Global ChangeBiol., 1999.

0

10

20

30

40

0 0.25 0.5 0.75 1

Age

of

resp

ired

C (

yr)

Fraction of total respiration

Tropical forest

Desert shrub

Temperate forest

Boreal forest

Mean age of heterotrophically respired C from CASA range from 10- 40 years

0

50

100

150

0 0.25 0.5 0.75 1

Tropical forest

Desert shrub

Temp. forest

Boreal forest

Fraction of total respiration

14

CX

14C from CASA

0

25

50

75

100

125

0 5 10 15 20 25-200

0

200

400

600

800

1000

1950197019902010

1

4C

(p

er m

il)

X

020406080

100120140

-10 0 10 20 30 40 50 60

14C

(p

er

mil

)Model-data comparison initially disappointing at low latitudes

CASA Prediction

20 years ~ 4 years

Latitude

020406080

100120140

-10 0 10 20 30 40 50 60

14C

(p

er

mil

)Agreement improves if the oldest

25-50% of respired CO2 is removed

100%

75%

50%25%

Latitude

Problems with incubations

• Overemphasis of ‘young’ part of the respiration distribution– Exclusion of woody debris from soil

sampling will bias against the longer ‘tail’

- Artifacts with incubation in general - Inclusion of roots in incubations

emphasizes ‘young’ pools (variation with time)

Potential issues with CASA

Too long of a ‘tail’ - treats wood as a single pool with

homogeneous turnover (do we need multiple pools to reflect different life strategies in tropical forest? Vieira et al. in revision PNAS)

- model may allocate too much NPP to stem growth in tropical forests (stem allocation <1/3 of NPP)

2.0 dead wood (50-100) yr

Total heterotrophic respiration ~10

(11-24 yr)

Total autotrophic respiration ~20

(0.01-1 yr)

Total ecosystem respiration ~30(3 – 8 yr)

3.3 leaf litter

(2-3 yr)

4.7 Root/SOM

(5-10 yr)

Photosynthesis(~30)

RootRootrespirationrespiration

Fluxes from Chambers et al.

Units are MgC ha-1 yr-1

Dead wood excludes trees <10cm DBH

ObservationsManaus ZF2

0 dead wood (50-100) yr


(4-7 yr)


(0.01-1 yr)

Total ecosystem respiration ~30(0.9-1.6 yr)

3.3 leaf litter

(2-3 yr)

6.7 Root/SOM +wood

(5-10 yr)

Photosynthesis(~30)





Bias removes wood component

3.3 dead wood (50-100) yr


(20-37 yr)


(0.1-1 yr)

Total ecosystem respiration ~30(7-24 yr)

3.3 leaf litter

(2-3 yr)

3.3 Root/SOM

(5-10 yr)

Photosynthesis(~30)





CASA

Conclusions

• Radiocarbon provides a measure of time elapsed between photosynthesis and respiration

• The mean age of C respired from soils ranges from <1 – 20 years

• Heterotrophically respired C has ages from 3-40 years

• Comparisons of model with data show that either data are skewed ‘young’ or models are skewed ‘old’; largest problem in low latitude forests

Biomass C MgC/ha 180 141 Growth MgC/ha/yr 1.6-2.1 2.2 -3.0 MRT of C (yr) 86-112 47-64(stock/growth)**Mean age of C (yr)* 260 220

Manaus Santarém

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The age of C respired from ecosystems