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

• Benefits 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 deep-rooting 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 over 2.5 tonnes of litter per hectare is left on site after harvest. How much C does this add to the soil?

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

2.54

2.88

2.04

1.92

1.60

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

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

Ann

ual C

O2 e

mis

sion

s (t

CO

2-C

∙ ha-1

)

Treatment

Annual CO2 effluxed from belowground respiration

a, b a b, c c c

How much CO2 is lost through the influence of roots or litter annually? Removing Miscanthus roots has a statistically significant impact on annual CO2 emissions

CO2 emissions over time

0

10

20

30

40

50

60

70

80

Resp

irat

ion

rate

(mg

CO2-

C ∙ m

-2 ∙

hr-1

) Single Litter

No Roots or Litter

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

Seasonal CO2 emissions

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

Resp

irat

ion

rate

(mg

CO2-

C m

-2 h

r-1)

Double Litter No Litter No Roots No Roots or Litter

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

*

*

* *

CO2 emissions by source

How much of the C emissions are from Miscanthus sources? Each year the presence of roots alone creates more C emissions than the presence of litter alone

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

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

Ann

ual C

O2 e

mis

sion

s (t

CO

2-C

∙ ha-1

)

Treatment

Pre-experiment C4 influence C4 - Miscanthus Carbon C3 - Original 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

• Estimate the longevity of Miscanthus-derived soil C by use of physio-chemical fractionation

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 Mike Whitfield Simon Oakley Harriet Richardson Photo credits to Emily Bottoms and www.SimplyNetworking.com