10
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Soils as carbon sinks or sources:
from mid-Wales to the Arctic
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
> Alan Jones,
John Scullion and
Dylan Gwynn-Jones
With so much attention currently paid to rising levels of
atmospheric CO2, we would be forgiven in thinking that
this was the greatest part of the climate change story.
However, soil carbon represents the ‘hidden half’ of the
global carbon (C) balance and this is often overlooked by
popular imagination. Soil represents a major global store
of carbon, holding approximately twice the quantity of
carbon than is present in the atmosphere and three times
that of terrestrial vegetation. The potential for soil to
either store or emit carbon depending on the prevailing
conditions, and its immense relative size, means that soil
management for carbon worldwide is a pressing concern
in our response to global climate change.
When land management is changed markedly or
environmental conditions are perturbed, soil carbon stocks
can respond relatively rapidly as the soil-atmosphere
system equilibrates to the new circumstances. A recent
example of this is the rapid erosion of peat-rich moorland
and associated release of dissolved organic carbon
observed in some upland areas of the UK (Freeman et
al., 2004). Determining exactly how soils respond to such
external changes is imperative if we are to optimally
manage carbon stocks in the future. Environmental
factors such as soil temperature and biological activity are
also important for carbon stability (Hartley and Ineson,
2008). In parts of the UK where the climate is cooler
and wetter, soil carbon accumulates naturally. This is
especially true for soils with impeded drainage, and some
mire ecosystems in Wales represent very large long-term
carbon stores. However, such areas are also subject to
short-term climatic variability and so the medium-term
impacts of climate change are very uncertain. In these and
many other ecological communities, the future stability
of carbon stocks is very much open to question.
Rising atmospheric CO2 concentrations will in the future
have indirect effects on the carbon dynamics and stability
of soils via impacts on vegetation and litter (Freeman
et al., 2004). There is significant international interest
on how this will impact soils that have successfully
accumulated carbon in the past and whether they will
have the capacity to continue to sequester carbon under
elevated concentrations of CO2. The Arctic biome holds
enormous carbon stocks in its soil, representing one third
of the global soil C store. With a rapidly warming climate
in this region and future elevated concentrations of CO2,
will this stock in the future represent a net sink or emitter
of CO2?
To address these issues, IBERS scientists are now
synthesising work on soil carbon from a series of
experiments, ranging in location from Wales to Arctic
Sweden. Project teams led by Drs John Scullion and Dylan
Gwynn-Jones have received funding from the Welsh
European Funding Office (WEFO) under the Convergence
Programme and from the Natural Environment Research
Council (NERC), respectively, to investigate the dynamics
of carbon cycling and sequestration in soils.
1. Carbon soil sequestration: land changes
and amendments (SEREN Project)
> John Scullion, Gareth Griffth,
Dylan Gwynn-Jones, Mike Humphreys,
Iain Donnison and Kerrie Farrar
The SEREN project started in spring 2011 and involves
collaboration between Aberystwyth, Bangor and Cardiff
universities. Aberystwyth and Bangor research in SEREN
focuses on the potential for soil carbon sequestration and
retention under a range of land use scenarios. The IBERS
team will investigate the soil carbon impacts of different
restoration strategies on land degraded by mining or
industry, the effects of novel cropping and soil amendments,
and the opportunities for plant breeding to improve carbon
sequestration.
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13
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
Bioenergy crops as carbon sequesters
A key focus of research in Wales has been to investigate ways
to optimise levels of soil carbon sequestration. Bioenergy
crops have received much media attention of late due
to their perceived negative impacts on food security but
such crops can provide an excellent potential strategy for
combating rising atmospheric CO2 levels.
Figure 1. Reclaimed soils on opencast mining land: a potential future
target area for enhanced soil carbon accumulation.
Carbon sequestration in restored soils
Degraded soils in Wales on land disturbed by activities
such as mining (Fig. 1) have depleted organic carbon levels
(Scullion and Malik, 2001) and offer significant opportunities
for carbon sequestration through their rehabilitation and
re-vegetation. The value of this approach in terms of carbon
gain will be governed by the initial condition of the soils,
the efficacy of the techniques used and the range of plant
species employed (see Fig. 2). The purpose of the SEREN
carbon soil sequestration project is to test a variety of
rehabilitation approaches for carbon sequestration and
evaluate their wider applicability in real world conditions.
15
IBERS scientists have already developed a range of
biomass crops at the Plas Gogerddan campus. The SEREN
project makes use of existing replicated field experiments
investigating Miscanthus, willow, switchgrass and reed
canary grass for their bioenergy cropping potential. It also
makes the assumption that biofuel crops of the future will
often be grown on more marginal or reclaimed land, hence
experimental sites are located on several different soil types.
This provides a unique opportunity to investigate how many
soil factors, including fertility, texture and moisture levels,
affect below-ground carbon allocation in such systems.
Carbon sequestration using Biochar
SEREN is also considering the potential role of biochar, a
fine grained, organic charcoal produced by pyrolysis of
agricultural plant biomass, including that derived from
biofuel production. When used as a soil amendment, biochar
has the potential to make a direct contribution to stable soil
carbon stores, thereby enhancing carbon sequestration
(Laird, 2008). There are further benefits to be gained
that may lead to this technology being even more widely
accepted, since biochar can also have positive effects on
crop performance. Descriptions of the field and glasshouse
experiments underway at IBERS to investigate these benefits
can be found in the paper by Hodgson, Bevan and Farrar in
this issue (see p17).
Novel grass hybrids
There is much interest in the prospect of genetically
engineering crops to obtain favourable yields and benefits
for the environment. Many of these effects may also be
obtained by conventional breeding of novel hybrids which
combine the favourable traits of two species. One such IBERS
breeding programme has developed a ryegrass x fescue
hybrid, known as Festulolium (see Humphreys paper in
this issue.). With a greater efficiency of resource use than
conventional cultivars, Festulolium is potentially resilient
to climate change, and has added advantages of enhancing
soil stabilisation and reducing the soil’s greenhouse gas
emissions.
to reduce the carbon footprint of grassland agriculture.
SEREN research will evaluate existing Festulolium cultivars
by comparing root growth and turnover during three
consecutive growing seasons, in conjunction with a second
trial to compare the relative productivity of these grasses as
forage. The carbon sequestration potential of each cultivar
will be quantified, together with appraisals of their suitability
as a practical component of grassland agriculture in Wales.
If a successful hybrid is developed and grown widely, it
would therefore not only benefit productivity but, most
importantly, would also allow grassland agriculture to play
a part in offsetting greenhouse gas emissions.
2. Securing Arctic soil carbon stocks in an
elevated CO2 world
> Dylan Gwynn-Jones, Alan Jones,
John Scullion
The Arctic project also started in the spring of 2011 but
builds on nearly two decades of research investment in
this area. Sub-Arctic heath communities in Northern
Sweden (68oN)were first exposed to elevated CO2 levels in
1993, with the aim of investigating how plants, ecological
communities and carbon stocks would respond in the year
2050. The experiment continues to the present day (Fig. 4)
and represents one of the longest running experiments of
its kind in the world. Experiments are based at the Abisko
Scientific Research station which is an international hub for
climate change research.
By generating cultivars of fescue-ryegrass hybrids (Fig. 3)
that also maximise below-ground carbon storage, scientists
at IBERS will determine the potential of plant breeding
Anaerobic digestion aids carbon sequestration
Given the heavy reliance on livestock production in Wales,
inroads can be made locally in the sustainable management
of livestock waste products and their potential utility in
aiding carbon sequestration through soil application.
5
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10
Fast growing bioenergy crops such as Miscanthus, willow,
switchgrass and reed canary grass not only substitute for
non-renewable fossil fuel sources, thereby lowering carbon
emissions, but have the added benefit that some of their
carbon content can also be sequestered to the soil as root
biomass. In the case of Miscanthus, between 0.5 and 1.5
tonnes of carbon may be sequestered below-ground per
hectare annually (Hansen et al., 2003). Until recently, the focus
of research on biomass fuel crops has been on enhancing their
above-ground productivity and structural characteristics as
fuels. There is now increasing interest in their wider impacts
(Fernando et al., 2010), including their below-ground
characteristics and the impacts of their cropping techniques
on soil carbon stores (Garten and Wullschleger, 1999).
receiving mineral fertilisers or conventionally managed slurries/
manures to those treated with anaerobic digestates.
Figure 2. Percentage soil organic matter (as loss on ignition (LOI))
data (Scullion and Malik, 2001), comparing undisturbed land and
restored opencast mine soils. Restored soils were subject to high
and low intensity fertilisation treatments over 9 and 21 years.
In a 2010 report, Defra highlighted the important contribution
that anaerobic digestion (AD) can make to mitigating climate
change, firstly by reducing greenhouse gas emissions from
manure and secondly as a source of renewable energy. In
addition to this, however, anaerobic digestates may also be
useful as alternative land amendments to mineral fertilisers.
Using the extensive glasshouse and field trials facilities at IBERS,
SEREN will compare soil organic carbon allocation in grasslands
Figure 3. Lolium multiflorum and Lolium perenne x Festuca.mairei
and Festuca glaucescens –Festulolium hybrids produced by IBERS.
Figure 4. Elevated CO2 fumigation experiment in Abisko (Sweden)
based on a Vaccinium empetrum forest heath.
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15
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
Soils as carbon sinks or sources:
from mid-Wales to the Arctic
The vast majority of experiments that have exposed plant
communities to elevated CO2 levels have seen a stimulation
of above-ground growth during the first seasons of exposure.
However, following this early stimulation, such growth
benefits are not maintained and communities are believed
to acclimatise to the new CO2 conditions. A major limitation
with such research has been the limited longevity of previous
experiments, with most typically maintained for just 3-5
years. With already nearly two decades of observations
at Abisko, however, we are able to look beyond the initial
acclimation and investigate the relative dynamics of aboveground growth to below-ground processes, studying how
elevated CO2 has affected the long-term carbon dynamics
and stocks in the system (Fig. 5).
Elevated
CO 2
Respired
CO 2
some insight into how these wider communities might
respond to predicted atmospheric composition in the year
2050 and allow us to interrogate their carbon stability and
dynamics thoroughly.
During summer 2011, the research team will investigate
above-ground photosynthetic activity at both species and
community level. We will also look at CO2 fluxes from the
soil and at plant respiration levels.
despite it often being overlooked. Research carried out over
the next few years will inform future policies and practice,
with potentially global implications. By developing these
methods, IBERS scientists are clearly leading the way towards
progressive new approaches to address the problems raised
by climate change.
During 2012, the work will focus on quantifying biomass
production and harvesting carbon from all components
of the community, including more detailed studies of the
important soil microbial ecosystem. The soil’s organic matter
will be separated into its constituent fractions, enabling, for
the first time in this habitat, assessments of the relative rates
of organic matter breakdown under elevated CO2 conditions,
and also allowing the relative size of the organic pool to be
quantified. This last aspect will be especially important as
soil organic matter forms the main store of soil carbon. Data
SEREN is part funded by the European Regional Development
Fund and undertaken in conjunction with Cardiff University,
the British Geological Survey, Bangor University and WDS
Environmental.
Litter C
Root C store
Root exudades
& root material
Acknowledgement
The Arctic research is supported by NERC grant 10334 and
is undertaken in collaboration with Dr Nick Ostle at CEH
Lancaster, Prof. Terry Callaghan of Abisko Scientific Research
Station and Prof. John Lee of Sheffield University.
References
DEFRA (2010). Accelerating the Uptake of Anaerobic Digestion in
England: an Implementation Plan.
http://archive.defra.gov.uk/environment/waste/ad/documents/
implementation-plan2010.pdf
Freeman, C., Fenner, N., Ostle, N.J., Kang, H., Dowrick, D.J., Reynolds,
B., Lock, M. A., Sleep, D., Hughes, S. and Hudson, J. (2004). Export of
dissolved organic carbon from peatlands under elevated carbon dioxide
levels. Nature 430, 195-197.
Hartley, I. P. and Ineson, P. (2008). Substrate quality and the temperature
sensitivity of soil organic matter decomposition. Soil Biology and
Biochemistry 40, 1567-1574.
Scullion, J. and Malik, A. (2001). The influence of land use and
earthworm activity on organic matter dynamics in soils restored after
opencast coal mining. In: Rees, R. M., Ball, B. C., Campbell, C. D. and
Watson, C. A. (Eds). Sustainable management of soil organic matter.
Wallingford, UK, CABI Publishing, pp. 377-385.
Hansen, E.M., Christensen, B.T., Jensen, L.S. and Kristensen, K. (2003).
Carbon sequestration in soil beneath long-term Miscanthus plantations
as determined by 13C abundance. Biomass and Bioenergy 26, 97-105.
Fernando, A.L., Duarte, M.P., Almeida, J., Boleo, S. and Mendes, B.
(2010). Environmental impact assessment of energy crops cultivation in
Europe. Biofuels Bioproducts & Biorefining 4, 594-604.
Recalcitrant
Organic Matter
Garten, C.T. and Wullschleger, S.D. (1999). Soil carbon inventories under
a bioenergy crop (switchgrass): measurement limitations. Journal of
Environmental Quality 28, 1359–1365.
Microbial
biomass C
Laird, D.A. (2008). The charcoal vision: a win–win–win scenario for
simultaneously producing bioenergy, permanently sequestering carbon,
while improving soil and water quality. Agronomy Journal 100, 178-181.
Soil Organic
Matter Fractions
Dissolved organic
carbon
Figure 5. A simplified conceptual model of elevated carbon flows
in Arctic heath.
A very important question for the future will be whether
plants in natural communities photosynthesise more
carbon at elevated CO2. If they do, is the additional carbon
metabolised expressed as increased above-ground growth,
or is the extra carbon stored below-ground, or is it released
back into the atmosphere via the soil? The fact that the
additional CO2 added at Abisko over the past 20 years
has a specific δ13C carbon isotope signal will be of great
assistance in tracing where the elevated CO2 has gone, as
it will remain detectable in leaves, roots, soil, microbes and
the surrounding atmosphere. The heath community being
studied is found as part of a typical sub-arctic birch forest (Fig.
6), a type of ecosystem which covers vast areas of Northern
Europe. The findings from this research will therefore allow
Figure 6. Sub-Arctic birch forest – a characteristic plant community
of large areas of northern Europe.
from these analyses will then be accessible for modelling
land-based changes in sub-Arctic carbon dynamics in the
future. Given the large land areas covered by the type of
plant communities being studied at Abisko, the importance
of this biome for carbon sequestration and its relative
sensitivity to a wide range of environmental changes, this
information will be of global significance.
Conclusion
These combined IBERS research programmes demonstrate
how management of soil carbon can become a versatile tool
in our strategies to adapt to rising atmospheric CO2 levels,