Detecting changes in soil C pools and Detecting changes in soil C pools and dynamics by means of stable isotopes dynamics by means of stable isotopes

and SOM fractionationand SOM fractionation

M.Francesca CotrufoM.Francesca Cotrufo

Dip. Scienze Ambientali

Seconda Università di Napoli

3rd CARBOEUROPE Meeting, Finland 2005

Motivation:

“Looking for small changes in large pools and fluxes”

Organic Matter

Stabilized soil organic carbon

turnover

Fresh soil carbon input

turnover

Soil respirationLitter fall

Wood & Litter decomposition

Root respiration & decomposition

Litter and soil C fluxes

Joint workshop“Partitioning soil CO2 efflux”

 Villa Orlandi, Capri, Italy Oct 2nd - 4th 2004

CARBOEUROPE/COST Action 627

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 500 1000 1500 2000 2500

RS (g C m -2 y-1)

RH /

RS

Heterotrophic contribution to soil respiration

Results of a meta-analytical review

RH/RS = -0.149 ln(RS) +1.569

Subke, Inglima & Cotrufo, GCB Annual Review, 2006

Plant and fungal debris

Clay microstructures

Fungal or microbial metabolites

Biochemically recalcitrant organic matterSilt-sized aggregates with microbially derived organomineral associations

Microaggregates ~ 50-250 m

Particulate organic matter colonized by saprophytic fungi

Decomposing roots and detritus become encrusted with mineral particles forming microaggregates

Decomposition continues at a slow rate in stable aggregates, due to formation of organomineral associations

Eventually, organic binding agents decompose sufficiently for aggregate to be destabilized, accelerating decomposition until new aggregate is formed

The SOM aggregation conceptThe SOM aggregation concept

Fractionation by size and density

scheme

Density flotation

Light fraction(< 1.85 g cm-3)

Intra-microaggregatePOM (iPOM)

Density flotation

Light fraction(< 1.85 g cm-3)

Intra-microaggregatePOM (iPOM)

>250 m fraction<53 m fraction

53-250 m fraction (m)

Wet sieving

Micro-aggregate isolator

Silt + clayCoarse POM

Micro’s (mM)

8 mm sieved soil

HYPOTHESES:

•Afforestation increases aggregate stability and soil C sequestration

• Elevated [CO2] increases aggregation and SOC pools through higher C input

Short-term effects on SOM dynamics after change in land use and exposure to increased [CO2]

The EUROFACE project

EUROFACE

Location: Tuscania, Central Italy (42° 22’ N 11° 48’ E 150 m asl) .

Climate: Annual rainfall 676 mm, annual mean temperature 15 °C.

Project PopFACE (EKV 4-CT96_0657)/ EUROFACE: from 1999 – Establisment of a poplar plantation (P.x euroamericana) on an agricultural region.

6 exsperimental plots, whitin the plantation, each with three poplar species (Populus alba, (clone A), P. nigra, (clone B), e P.x euroamericana, (clone C));

3 plots are exposed to ambient and 3 to elevated (+200 ppm) concentration of CO2 with a FACE (Free Air Carbon dioxide Enrichment) operating system

Experimental design & methods

4 Vegetation types: Agricultural field (T. aestivum) (A); Poplar plantation (P); clones B (P. nigra) and C (P. x euroamericana) for the FACE system.

6 Replicated samplings along two 50m transects, for A and P @ 0-10 cm depth.

10 Soil cores per sampling plot – Pooled.

4 soil cores, pooled, for clones B and C for each ring of the FACE.

Fractionation for size and density.

Analyses of C content for the total and for all the fractions isolated.

ln(RRPA)

-0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4

Total

M

CP

mM

IPOM_mM

SC_mM

SC_M

m

IPOM_m

SC_m

SC

Carbon changes in SOM fractions:

1. LAND USE CHANGE EEFFECT

A

P

C

CRR ln)ln(

CP = C content of soil fractions under poplar

plantation

CA = C content of respective fractions in the agriculture soils

Del Galdo et al. GCB, submitted

ln(RRFC)

-0.8 -0.6 -0.4 -0.2 0 0.2 0.4

Total

M

CP

mM

IPOM_mM

SC_mM

SC_M

m

IPOM_m

SC_m

SC

P. nigra

P. euroamericana

2. ELEVATED [CO2] EFFECT

CF = C content in FACE soil fractions

CC = C content of controls

C

F

C

CRR ln)ln(

Del Galdo et al. GCB, submitted

Past present and future atmospheric [CO2] effects on SOM dynamics

Sky Oaks CO2-enrichment field station

HYPOTHESIS:

• From pre-industrial level to 750 ppm, the increase in atmospheric [CO2] increases aggregation and SOC pools due to higher plant C input, thus the soil “close” to plants is the most affected.

Sky Oaks CO2-enrichment field station (Warner Springs, CA, USA)

12 closed chambers within an Adenostoma fasciculatum-dominated chaparral ecosystem, fumigated for 6 years with labelled CO2 ranging from 250 to 750 ppm in 100 ppm step increments, with a total of two replicate chambers for each of the six treatments.

Three non-fumigated open chambers were selected as control (ambient).

Sky Oaks CO2-enrichment field station

Soil sampling (0-10 cm)• 2 soil cores sampled close to the A. fasciculatum

(pooled); • 2 soil cores collected far from the plant.

Soil fractionation for size and density;

Analyses of C and 13C for the totals and for all the fractions isolated

)(

)(

aveg

ae

e f

Experimental design & methods

SOM C distribution:

0

1000

2000

3000

4000

control 250 350 450 550 650 750

CO2 (ppm)

C (

g m

-2)

SC

m

M

0

500

1000

1500

2000

2500

3000

3500

4000

control 250 350 450 550 650 750

CO2 (ppm)

C (

g m

-2) SC

m

M

Close to plant

Far from plant

Del Galdo et al. SBB, submitted

Total microaggregates C

R2 = 0.7188

0

500

1000

1500

2000

150 250 350 450 550 650 750 850

CO2 (ppm)

C (

g m

-2)

close

P<0.005

Change in old-new C

-2000

-1500

-1000

-500

0

500

1000

1500M m SC M m SC M m SC M m SC M m SC M m SC

250 350 450 550 650 750

CO2 (ppm)

C (

g m

-2)

Change in old C

New C

Effects of land use change on soil C

0

1000

2000

3000

4000

5000

6000

Grassland Maize crop Afforested

Soil

C (

g m

-2)

0-10 cm

10-30 cm

100 years 20 years

Partitioning of soil C into:Partitioning of soil C into:“new” - C derived from vegetation “new” - C derived from vegetation “old” – native SOC“old” – native SOC

10-30 cm

0

50

100

150

200

250

C A G C A G C A G C A G C A G C A G C A G M coarse POM mM iPOM_mM Silt&clayM m iPOM_m

0-10 cm

0

50

100

150

200

250

C A G C A G C A G C A G C A G C A G C A G M coarse POM mM iPOM_mM silt&clayM m iPOM_m

g C

kg-1

sandfr

ee a

ggre

gate

C= CropA=AfforestedG=Grassland

New C

Old C

Del Galdo et al., GCB, 2003

Identify SOC dynamics

-1500

-1000

-500

0

500

10000-10 cm 10-30 cm

M m silt&clay M m silt&clay

C g

m-2

C nuovo

C nativo

Del Galdo et al., GCB, 2003

Decomposition rate (y-1) calculated for the old carbon of all measured physical fractions of afforested soil assuming an eponential decay {k=-ln(Cold/Ctotal)/t}. Default values decomposition rates of Roth C model are reported for comparison. Standard errors in parenthesis.n.d.= not detectable.

Measured decomposition rate factors (y-1)

M

> 250 m

m

53-250 m

Silt&clay

< 53 m

Total

Fraction

Coarse

POM

mM

IPOM

mM

silt&clayM Total

Fraction

IPOM

m

Total

Fraction

0.039

(>0.3)

0.108

(>0.3)

0.042

(>0.3)

0.024

(>0.3)

0.008

(>0.3)

n.d.

n.d.

n.d.

RothC decomposition rate factors (y-1)

Decomposable

Plant Material

DPM

Resistant Plant

Material

RPM

Humified Organic

Matter

HUM

Microbial

Biomass

BIO

Inert Organic

Matter

IOM

10 0.3 0.02 0.66 0.00

Del Galdo et al., GCB, 2003

“Modelling the measurable” “Measuring the modellable”

Fr(t)

r(t)

s(t)

Conventional approach

Fr(t)

r(t)

s(t)

The soil is a dynamic system!

Rubino et al., in progress

Litter respiration measurements in lab-experiment

0,000

0,009

0 100 200time (d)

C-C

O2

(g/d

)

Soil & P. Soil & P. taedataedaSoil & C. canadensisSoil & C. canadensis

Soil & L. styracifluaSoil & L. styraciflua

Rubino et al., in progress

Dynamics of 13C-CO2

-17,7 -17,9

-43,9

-43,0-43,4-43,3

-43,7

-47,0

-15,0

0 100 200time (d)

13

C-C

O2

(‰)

Soil & P. Soil & P. taedataedaSoil & C. canadensisSoil & C. canadensis

Soil & L. styracifluaSoil & L. styraciflua

Bulk soil

Bulk litters

Discrimination during heterotrophic respiration ???

Soil substrate

1:1

J. phaenicia

P. lentiscus

C. mospeliensisLeaf litter

substrate

-17,7 -17,9

-25,0

0 100 200days

13C

-CO

2 (‰

)

-50

-45

-40

-35

-30

-25

-50 -45 -40 -35 -30 -25Litter 13C

13C

-CO

2

Ambient

Mixture

Elevated

Partitioning of C loss from decomposing litter into soil C input and respired CO2

Input in soil vs C-CO2 loss

-20%

0%

20%

40%

60%

80%

100%

120%

Cereis Styra Pinus

C (

%)

Cinput (g) C-CO2 (g)

MUFA & PUFA

-44

-6

n-C

13C

vs

PD

B(‰

)

Control soil Soil incubated with C. canadensis

Soil incubated with L. styraciflua Soil incubated with P . taeda

SATFA

-44

-6

n-C

13C

vsP

DB

(‰)

Control soil Soil incubated with C. canadensis

Soil incubated with L. styraciflua Soil incubated with P . taeda

Rubino et al., in progress

Identification of SOM chemical

compounds where litter derived C is

allocated

Soil only

0

50

100

Are

a (%

)

-50

-25

13C

(p

er m

il)

Soil with litter-derived C

0

50

100

Are

a (%

)

-50,0

-25,0

13 C

(p

er

mil

)

CONCLUSIONS

Coupling of SOM fractionation by size and density and stable C isotope “labelling” proved to be a useful approach to quantify changes in soil organic C pools

Elevated atmospheric CO2 appears to increase soil C losses proportionally more than inputs, resulting in a net decrease of soil C. Is it a true effect or rather due to the “step change” of manipulation “step change” of manipulation studies??studies??

After 20 years, afforestation increased the total amount of soil C by 23% and 6% in the 0–10 and in the 10–30cm depth layer, respectively. Forest-derived carbon contributed 43% and 31% to the total soil C storage in the afforested systems in the 0–10 and 10–30cm depths, respectively. Furthermore, afforestation resulted in significant sequestration of new C and stabilization of old C in physically protected SOM fractions, associated with microaggregates (53–250 m) and silt&clay (<53 m).

II.. Del Galdo, Del Galdo, G. Battipaglia, T. Bertolini,G. Battipaglia, T. Bertolini, I I.. Inglima, M Inglima, M.. Rubino, Rubino, F. Marzaioli, D. Piermatteo, C. LubrittoF. Marzaioli, D. Piermatteo, C. Lubritto

APPENDIX

Cs(t) = Csv(t) + Cs

n(t)

s(t)Cs(t) = vCsv(t) + n(t)Cs

n(t)

f’ Csv(t)/Cs(t) = [s(t) - n(t)]/[v - n(t)]

f Csv(t)/Cs(t) = [s(t) - s(0)]/[v - s(0)]

Fr(t) =Frv(t) +Fr

n(t)

rFr(t) = rvFr

v(t) + rnFr

n(t)

Fr(t) [r(t) - s(0)] = Frv(t) [v - n(t)]

Frn(t) = ksCs

n(t) Frv(t) = Fvkv + ksCs

v(t)

ks = [Fr(t)/Cs(t)] * [δr(t)- δv]/[δs(t)- δv]

Cs(t) - Cs(0) = Csv(t) - Fr

s(t) dt

Cs(t) - Cs(0) = Cs(t) [δs(t) - δs(0)]/[ δv - δs(0)] - Fr(t) [δr(t) - δv]/[δs(0) - δv] dt

Cs(t) - Cs(0) = f · Cs(t) – Fr(t) · Rs/Rt dt

SOM DECAY and TURNOVER SOM DECAY and TURNOVER

Six et al. 1998