Post on 01-Feb-2016
description
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
Total heterotrophic respiration ~10
(4-7 yr)
Total autotrophic respiration ~20
(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)
RootRootrespirationrespiration
Fluxes from Chambers et al.
Units are MgC ha-1 yr-1
Dead wood excludes trees <10cm DBH
Bias removes wood component
3.3 dead wood (50-100) yr
Total heterotrophic respiration ~10
(20-37 yr)
Total autotrophic respiration ~20
(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)
RootRootrespirationrespiration
Fluxes from Chambers et al.
Units are MgC ha-1 yr-1
Dead wood excludes trees <10cm DBH
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