This presentation was given at EGU 2013 in Vienna on the 7th April 2013. It was part of the session "HS8.3.3/SSS2.13 entitles 'Trace gases emissions from soils: Sources, mechanisms and process rates'". In this presentation I show the results from an experiment that excludes roots and/or plant litter from soil beneath a Miscanthus plantation in the UK.

1. 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

2. 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!

3. 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’

4. 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

5. Miscanthus life cycle
April
June August
March
December
October
February

6. 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?

7. 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

8. 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
Respirationrate(mgCO2-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

9. 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
Respirationrate(mgCO2-C∙m-2∙hr-1)
Single Litter

10. 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
DifferenceinrespirationratefromSingle
Littertreatment(mgCO2-Cm-2hr-1)
Double Litter
No Litter
No Roots
No Roots or Litter

11. 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
DifferenceinrespirationratefromSingle
Littertreatment(mgCO2-Cm-2hr-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
*
*
*
*

12. 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
Respirationrate(mgCO2-C∙m-2∙hr-1)
Pre-experiment C4 influence
C4 - Miscanthus carbon
C3 - Original soil carbon

13. 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

14. 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

15. 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
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