Land use change to Miscanthus: measured and modelled changes in soil carbon fractions

Andy Robertson (PhD candidate at CEH Lancaster)

Supervised by Dr. N. McNamara, Dr. C. Davies and Prof. P. Smith

April

June

October

December

March

Problems and solutions Ba

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ound

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Con

text

• Climate change policy means governments are committed to offsetting greenhouse gas emissions

• Bioenergy has the potential to displace some demand for fossil fuels and it’s renewable

• Before we implement - sustainability criteria • Carbon budgets, ecosystem services, biodiversity...

• Effects are location dependent but measuring everywhere is impossible – therefore, we model

Why Miscanthus? Ba

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ound

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Con

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• C4 species growing up to 4 meters tall that can produce >15 dry t aboveground and >20 dry t belowground per ha per yr

• High sequestration potential through large C inputs

• Miscanthus C has a different isotopic signature to soil C in the UK allowing changes to be quantified

• Ideal annual life cycle for studying these C cycles

Miscanthus life cycle Ba

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ound

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Con

text

April

June August

March December

October

February

Miscanthus C inputs Ba

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ound

and

Con

text

• When harvested, lots of plant litter left on site

Project aim #1 Ai

m #

1 –

Part

ition

ing

soil

C st

ocks

Quantify and partition soil C stocks to assess the source of new additions

• Five plots sampled quarterly for 13C (0-15cm and 15-30cm)

• Bulk density measurements used to determine C3 and C4 stocks

Photo credit: Kim Parmar

Partitioning soil C stocks (0-15cm)

Do soil C stocks change over the 7 years? Does new C4 soil C displace old C3 soil C? Despite noteworthy variation, after 7 years of growth soil C stocks are unchanged.

Aim

#1

– Pa

rtiti

onin

g so

il C

stoc

ks

0

5

10

15

20

25

30

35

40

45

Soil

Carb

on S

tock

(t ·

ha-1

)

0

5

10

15

20

25

30

35

40

45

Soil

Carb

on S

tock

(t ·

ha-1

)

C4 Soil C

C3 Soil C

Partitioning soil C stocks (0-15cm)

Do soil C stocks change over the 7 years? Does new C4 soil C displace old C3 soil C? Miscanthus-derived soil C stocks increase from 1.76 to 4.23 t ha-1 and C3 soil C falls by 1.01 t ha-1

Aim

#1

– Pa

rtiti

onin

g so

il C

stoc

ks

Project aim #2 Ai

m #

2 –

Frac

tiona

ting

soil

C

Fractionate the soil C stock to determine where the Miscanthus-derived C is stored

• Five plots sampled annually (0-15cm and 15-30cm)

• Physiochemical fractionation of soils below Miscanthus and adjacent reference site using a physiochemical method

• Each of these 5 resulting fractions can be analysed for C and N content and the 13C value used to establish Miscanthus C

Physiochemical soil fractionation

s + c silt and clay

DOC Dissolved Organic

Carbon

S+A Sand and Aggregates

POM Particulate Organic

Matter

rSOC Resisitant Soil Organic

Carbon

Aim

#2

– Fr

actio

natin

g so

il C

Figure adapted from Zimmermann et al (2007)

Soil C fractions by source (0-15cm)

How much C is stored in more stable pools? Where is Miscanthus-derived C allocated? ≈85% of all soil C is in C3 pools and the majority in s+c (≈65% of total) and rSOC,(≈18% of total)

0

5

10

15

20

25

30

35

40

45

Mar-09 Mar-10 Mar-11 Mar-12 Mar-13

Soil

Carb

on S

tock

(t ·

ha-1

)

C4 rSOC C4 DOC C4 POM C4 S+A C4 s+c C3 rSOC C3 DOC C3 POM C3 S+A C3 s+c

Aim

#2

– Fr

actio

natin

g so

il C

POM fraction (0-15cm)

How much C is stored in more stable pools? Where is Miscanthus-derived C allocated? POM represents the pool with the fastest turnover time: >50% is Miscanthus-derived after 7 years

0

5

10

15

20

25

30

35

40

45

Mar-09 Mar-10 Mar-11 Mar-12 Mar-13

Soil

Carb

on S

tock

(t ·

ha-1

)

C4 rSOC C4 DOC C4 POM C4 S+A C4 s+c C3 rSOC C3 DOC C3 POM C3 S+A C3 s+c

Aim

#2

– Fr

actio

natin

g so

il C

rSOC fraction (0-15cm)

How much C is stored in more stable pools? Where is Miscanthus-derived C allocated? rSOC is deemed to be the most stable pool but after 7 years ≈8.5% was Miscanthus-derived

0

5

10

15

20

25

30

35

40

45

Mar-09 Mar-10 Mar-11 Mar-12 Mar-13

Soil

Carb

on S

tock

(t ·

ha-1

)

C4 rSOC C4 DOC C4 POM C4 S+A C4 s+c C3 rSOC C3 DOC C3 POM C3 S+A C3 s+c

Aim

#2

– Fr

actio

natin

g so

il C

Miscanthus-C fractions (0-15cm)

How much C is stored in more stable pools? Where is Miscanthus-derived C allocated? Miscanthus-derived s+c (incl. rSOC) and POM are increasing at 0.44 and 0.26 t ha-1 yr-1, respectively

2.46

0.27

1.83

0.11 0.59

0

1

2

3

4

5

6

Mar-09 Mar-10 Mar-11 Mar-12 Mar-13

Soil

Carb

on S

tock

(t ·

ha-1

)

C4 rSOC C4 DOC C4 POM C4 S+A C4 s+c

Aim

#2

– Fr

actio

natin

g so

il C

Project aim #3 Ai

m #

3 –

Mea

sure

d fra

ctio

ns to

mod

el p

ools

Assign turnover times to the soil C fractions measured

Figure adapted from Zimmermann et al. (2007)

DPM Decomposable Plant Matter

(Fast turnover - decay rate 10yr-1) RPM

Resistant Plant Matter (Medium turnover - decay rate 0.3yr-1)

BIO Biomass

(Medium turnover - decay rate 0.66yr-1) HUM

Humified Organic Matter (Slow turnover - decay rate 0.02yr-1)

IOM Inert Organic Matter

(Very slow turnover ~50,000 yrs)

Soil C turnover times (March 2013)

0

5

10

15

20

25

30

0-15 15-30

Single Litter

Carb

on st

ored

in m

odel

soil

pool

s (t ·

ha-1

) Litter C (0-1yrs)

Litter C (1-100yrs)

Soil C (0-1yrs)

Soil C (1-100yrs)

Soil C (100+ yrs)

How quickly will the soil C turnover throughout the soil profile? Most carbon below the Miscanthus plantation is in soil pools that turn over slowly or very slowly Ai

m #

3 –

Mea

sure

d fra

ctio

ns to

mod

el p

ools

DPM (Very fast turnover) RPM (Medium turnover) BIO (Medium turnover) HUM (Slow turnover) IOM (Very slow turnover)

Future aims Ai

ms #

......

......

• Use this data to parameterise and validate mechanistic models (ECOSSE and DayCent)

• Use model simulations to predict changes in soil C stocks as influenced by environmental factors

• Will Miscanthus sequester enough C over the lifetime of the plantation to offset emissions from use as bioenergy fuel

• Twin this work with an input manipulation experiment carried out to exclude roots/plant litter

• Come and see my poster after this session Green Posters G35 from 15:30 until 17:00

Thank you! Th

ank

You!

Supervisors Niall McNamara (CEH Lancaster)

Pete Smith (University of Aberdeen)

Christian Davies (Shell)

Other acknowledgements Emily Bottoms Andy Stott Helen Grant Sean Case Mike Whitfield Simon Oakley Harriet Richardson Tom Walker Everyone else at CEH Lancaster!

AND THANK YOU FOR LISTENING! If you have any questions please ask

Project aim #X Ai

m #

X –

Part

ition

ing

soil

resp

iratio

n

Quantify and partition CO2 efflux into old and new sources

• Commercial Miscanthus plantation established in 2006

• Five plots sampled monthly for 13CO2 since March 2009 using static chambers

Photo credit: Emily Clark

Partitioning CO2 efflux

Are most CO2 emissions from old (C3) or new (C4) sources? Does this change seasonally? Annually, ≈75% of emissions are from Miscanthus sources and most when the crop is growing

0 20 40 60 80

100 120 140 160 180 200

Resp

iratio

n ra

te (m

g CO

2-C

· m-2

· hr

-1)

C4 Emissions

C3 Emissions

78%

22%

March to June

82%

18%

July to October

73%

27%

November to February

Aim

#1

– Pa

rtiti

onin

g so

il re

spira

tion