The age of C respired from ecosystems
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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, Pl í nio Camargo

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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
The age of C respired from ecosystems

Photosynthesis

Ecosystem respiration

leaf

Soil respiration

Allocation

Fire

stem

Root

Respiration

Litter and SOM

decomposition

storage

root

Microbial

community

Stabilized SOM

Loss by leaching, erosion


Why this might be interesting
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

Deviation from mean

C lost

C stored

C stored

Time


Radiocarbon of soil-respired CO2 provides a direct measure of isodisequilibrium

“mean age” of several years up to a decade

D14C

D14C

Atmosphere- north hemisphere from Levin and Hessheimer2000


Soil respired CO2 is a mix of heterotrophic and autotrophic sources

Heterotrophic values – from models

CASA

Empirical

Local atmosphere

(Autotrophic respiration)

Data from Harvard Forest, MA


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.


Soil respired CO2 is a mix of heterotrophic and autotrophic sources

CO2 evolved in incubation

O horizon

Flux weighted mean

A horizon

Local atmosphere

(Autotrophic respiration)

Data from Harvard Forest, MA


Dd 14 c d 14 c of co 2 evolved in incubation d 14 c of co 2 in atmosphere
DD14C = D14C of CO2 evolved in incubation - D14C of CO2 in atmosphere

Boreal forest

Temperate

forest

3 age stands

Manitoba*

Harvard,

Bear Brook

Tropical

forest

Joshua Tree*

Desert

shrub

Manaus,

Santarem

Latitude of site

*see posters by Czimczik, Nowinski


Flux weighted total heterotrophic respiration for comparison with model
Flux-weighted total heterotrophic respiration for comparison with model

Temperate

forest

Boreal forest

Harvard,

Bear Brook

3 age stands

Manitoba*

Tropical

forest

Joshua Tree*

Desert

shrub

Manaus,

Santarem

Latitude


Determine age of respired co 2 using pulse response function for casa
Determine age of respired CO with model2 using pulse-response function for CASA

Tropical forest

Desert shrub

Temperate

forest

CO2 respired

Boreal forest

Thompson,and Randerson, Global ChangeBiol., 1999.

Years since pulse


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

Boreal

forest

Temperate

forest

Age of respired C (yr)

Tropical

forest

Desert

shrub

Fraction of total respiration


14 from 10- 40 yearsC from CASA

X

X

Boreal forest

DD14C

Temp.

forest

Tropical

forest

Desert shrub

Fraction of total respiration


Model data comparison initially disappointing at low latitudes
Model-data comparison initially disappointing at low latitudes

~ 4 years

20 years

CASA Prediction

Latitude


Agreement improves if the oldest 25 50 of respired co 2 is removed
Agreement improves if the oldest 25-50% of respired CO latitudes2 is removed

100%

75%

50%

25%

Latitude


Problems with incubations
Problems with incubations latitudes

  • 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
Potential issues with CASA latitudes

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)


Observations latitudes

Manaus ZF2

Total ecosystem respiration ~30

(3 – 8 yr)

Total autotrophic respiration ~20

(0.01-1 yr)

Total heterotrophic respiration ~10

(11-24 yr)

Photosynthesis

(~30)

3.3leaf litter

(2-3 yr)

2.0 dead wood

(50-100) yr

Fluxes from Chambers et al. Units are

MgC ha-1 yr-1

4.7Root/SOM

(5-10 yr)

Root

respiration

Dead wood excludes trees <10cm DBH


Bias removes latitudes

wood component

Total ecosystem respiration ~30

(0.9-1.6 yr)

Total autotrophic respiration ~20

(0.01-1 yr)

Total heterotrophic respiration ~10

(4-7 yr)

Photosynthesis

(~30)

3.3leaf litter

(2-3 yr)

0 dead wood

(50-100) yr

Fluxes from Chambers et al. Units are

MgC ha-1 yr-1

6.7Root/SOM +wood

(5-10 yr)

Root

respiration

Dead wood excludes trees <10cm DBH


CASA latitudes

Total ecosystem respiration ~30

(7-24 yr)

Total autotrophic respiration ~20

(0.1-1 yr)

Total heterotrophic respiration ~10

(20-37 yr)

Photosynthesis

(~30)

3.3leaf litter

(2-3 yr)

3.3 dead wood

(50-100) yr

Fluxes from Chambers et al. Units are

MgC ha-1 yr-1

3.3Root/SOM

(5-10 yr)

Root

respiration

Dead wood excludes trees <10cm DBH


Conclusions
Conclusions latitudes

  • 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


Santar latitudesém

Manaus

  • Biomass C MgC/ha 180 141

  • Growth MgC/ha/yr 1.6-2.1 2.2 -3.0

  • MRT of C (yr)86-11247-64

  • (stock/growth)**

  • Mean age of C (yr)* 260 220


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