Partitioning belowground CO2 emissions for a Miscanthus plantation in Lincolnshire, UK

Andy Robertson (PhD candidate at CEH Lancaster)

Supervised by Dr. N. McNamara, Dr. C. Davies and Prof. P. Smith with help from Dr. E. Bottoms, Dr. A. Stott and H. Grant

Problems and solutions

• The UK government aims to reduce CO2 emissions by 80% by 2050

• But energy demands are not projected to fall enough to offset the CO2 emissions from fossil fuel derived energy

• Renewable sources of energy are likely to be part of the solution

• Bioenergy has great potential but uncertain just how beneficial it can be - data is lacking!

Viability of bioenergy

• Sustainability criteria required before implementation • Ecosystem services, carbon budgets, biodiversity...

• This research focuses on C budgets and C cycling

• Changes are very location dependent but measuring everywhere is impossible – therefore, modelling is required

• Several components of C cycling models are poorly quantified and this research aims to ‘fill the gaps’

Miscanthus as a bioenergy crop

• Very different to other crops grown in the UK but trials show it is undemanding and productive

• Miscanthus is a C4 crop species that can grow up to 4 meters tall and produce >10 t · ha-1 · yr-1 aboveground

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

• Measuring 13CO2 emitted and changes in soil 13C makes Miscanthus ideal to study short term C cycling

Miscanthus life cycle

April

June August

March December

October

February

Carbon inputs to soil – litter vs roots

• Each year >2.5 tonnes litter per hectare is still on site after harvest

• Belowground biomass can be >15 tonnes per hectare

How much C do these add to the soil individually?

Root and litter manipulation experiment

• Roots extend down up to 4m

• Litter accumulates over time

• Plots set up in March 2009

• Sampled monthly at noon for 13CO2 from all treatments

25.74

28.47

20.92

18.02

15.91

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

Single Litter Double Litter No Litter No Roots No Roots or Litter

Resp

irat

ion

rate

(mg

CO2-

C ∙ m

-2 ∙

hr-1

) CO2 effluxed from belowground

respiration

a a b b,c c

How much CO2 is lost through the influence of roots or litter? Removing Miscanthus roots and/or litter significantly reduces average CO2 emissions

CO2 emissions over time

How do belowground CO2 emissions vary throughout the year? CO2 emissions peak during summer months when the crop is growing and the soil is warmer

0

10

20

30

40

50

60

Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

Resp

irat

ion

rate

(mg

CO2-

C ∙ m

-2 ∙

hr-1

) Single Litter

Difference in CO2 emissions from control

How do the treatments affect respiration throughout the year? CO2 is decreased considerably when roots and/or litter are removed, particularly from May-Nov

-25

-20

-15

-10

-5

0

5

10

Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb

Diff

eren

ce in

resp

irat

ion

rate

from

Sin

gle

Litt

er t

reat

men

t (m

g CO

2-C

m-2

hr-1

)

Double Litter No Litter No Roots No Roots or Litter

Seasonal CO2 emissions – difference from control

1.11

4.88 4.94

-7.41 -6.58

-5.48

-6.38

-13.85

-1.53

-6.88

-19.26

-7.60

-25

-20

-15

-10

-5

0

5

10

Mar-Jun Jul-Oct Nov-Feb

Diff

eren

ce in

resp

irat

ion

rate

from

Sin

gle

Litt

er t

reat

men

t (m

g CO

2-C

m-2

hr-1

)

Double Litter No Litter No Roots No Roots or Litter

How do CO2 emissions vary seasonally? Does the influence of litter or roots vary? The presence of roots is statistically significant during summer and litter during winter

*

*

* *

Average respiration by source C3 vs C4

How much of the CO2 emissions can be attributed to new Miscanthus inputs? More CO2 comes from C3 and pre-experiment C4 sources than from new root and litter inputs

5.10 4.83 6.61 5.99

7.19

11.92 14.93

5.60

3.31

0

5

10

15

20

25

30

Single Litter Double Litter No Litter No Roots No Roots or Litter

Resp

irat

ion

rate

(mg

CO2-

C ∙ m

-2 ∙

hr-1

)

Pre-experiment C4 influence

C4 - Miscanthus carbon

C3 - Original soil carbon

Future research

• Further statistical analysis on gas fluxes and remove treatment effects on abiotic factors

• Study the amount of Miscanthus C in soil from different treatments

• Working with modellers in Aberdeen and Colorado to apply the data to C cycling models

• Determine where changes in soil C are lost from or added to by use of physio-chemical fractionation

Conclusions

• Roots account for 30% of CO2 and aboveground plant litter accounts for 19%

• Between year 4 and year 8 less than 50% of CO2 emitted came from fresh C inputs

• No roots only significantly decreases CO2 emissions from Jul-Oct and no plant litter only significantly decreases emissions Nov-Feb

• With information regarding the destination of new soil C sequestered the longevity of any increased soil C can be attained

Acknowledgements

Supervisors Niall McNamara (CEH Lancaster)

Pete Smith (University of Aberdeen)

Christian Davies (Shell Global Solutions)

Other acknowledgements Emily Bottoms Andy Stott Helen Grant Sean Case Jon Finch Johnathan Wright Colleagues at CEH Lancaster Photo credits to Emily Bottoms and www.SimplyNetworking.com