A presentation by Dr. Peter Okoth

1. The solution to global warming could be in the soil
Peter Okoth , Jeroen Huising , Joyce Jefwa , Sheila Okoth , Fredrick Ayuke , & Joseph Mung’atu
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*, 1)
Tropical Soil Biology and Fertility Institute of the International centre for Tropical Agriculture (TSBF-CIAT), UN Avenue ICRAF Complex, P.O. Box 30677-00100, Nairobi, Kenya: Email: p.okoth@cgiar.org
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University of Nairobi, Chiromo Campus, School of Biological Sciences, P.O Box 30197-00100 , Nairobi, Kenya
Keywords: Carbon sequestration, fungi, bacteria, humification, soil fauna, global warming, climate change
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Introduction and Concepts References
Global warming is the increase in the average temperature of the Earth’s near-surface air and oceans since the mid-20th century and its projected continuation. Global Ayuke, F.O., (2010). Soil macro-fauna functional groups and their effects on soil
Earth’s-near surface temperature increased 0.74 °C and 1.33 °F between the start and the end of the 20th century. Most of the observed temperature increase was caused structure, as related to agricultural management practices across agro-ecological
by increasing concentrations of greenhouse gases resulting from human activity such as fossil fuel burning and deforestation. The effects of global warming are already zones of sub-Saharan Africa. PhD thesis, Wageningen University, The Netherlands
Bardgett, R.D. (2005). The Biology of Soil: A Community and Ecosystem Approach.
being felt in terms of drought, floods and emergence of diseases. The available options in response to these undesirable effects are mitigation to reduce further emissions;
New York: Oxford University Press. ISBN 0198525036.
adaptation to reduce the damage caused by warming; and, more speculatively, geoengineering to reverse global warming. Most often, mitigations involve reductions in the Carrera, N., Barreal, M. E., Gallego, P.P., and Briones, M.J.I., (2009). Soil invertebrates
concentrations of greenhouse gases, either by reducing their sources or by increasing their sinks. The main natural sinks known are the oceans, soil organic matter (SOM) control peatland C fluxes in response to warming. Functional Ecology 23, 637-648.
and photosynthetic plants and algae. Hoeksema, J.D., Lussenhop J. And Teeri, J.A. (2000). Soil nematodes indicate food
web responses to elevated atmospheric CO2. Pedobiologia 44: 725-735.
However the activities of soil organisms and their possible role in carbon sequestration are largely ignored. Soil carbon is the generic name for carbon held within the soil, Holden, J., (2005). Peatland hydrology and carbon release: why small scale process
primarily in association with its organic content. Over 2700 Gt of carbon is stored in soils worldwide, which is well above the combined total of atmosphere (780 Gt) or matters. Philosophical Transactions of the Royal Society. A Mathematical, Physical
biomass (575 Gt), most of which is wood. Carbon is taken out of the atmosphere by plant photosynthesis. About 60 Gt annually becomes various types of soil organic matter and Engineering Science, 363, 2891-2913.
including surface litter while about 60 Gt annually is respired or oxidized from soil (Lal, 2008). Kibblewhite, M.G., Ritz, K. and Swift, M.J. (2008). Soil health in agricultural systems.
Philosophical Transactions of the Royal Society series B, 363, 685-701.
Soil carbon which is a major sink of CO2 is generated through a series of processes. First, plant litter and other biomass accumulate as organic matter in soils, and are Lal, R., (2008). Sequestration of atmospheric CO2 in global carbon pools. Energy and
decomposed by chemical weathering and biological degradation. Usually, decomposition involves a succession of different organisms. One set of organisms takes over Environmental Science 1: 86-100.
after the last one has eaten what it can, and in doing so, changed the physical and chemical composition of its environment. Thus, ecological succession takes place in Marshall, V.G., (2000). Impacts of Forest Harvesting on Biological Processes in Northern
the microenvironment created by any decomposing log or animal corpse. For example lignin and cellulose are the major structural components of plant material, and these forest Soils. Forest Ecology and Management 133, 43-60.
compounds are very difficult to break down. Only certain organisms can produce the enzymes needed to break the chemical bonds in lignin and cellulose and thus return Muya E.M., N. Karanja, P.F. Z. Okoth, H. Roimen, J. Munga’tu, B. Mutsotso and
them to the ecosystem. Fungi and bacteria are by far the most active decomposers. They are remarkably efficient, and the smaller the pieces to be decomposed, the faster G.Thuranira, 2009. Comparative description of land use and characteristics
these microorganisms are able to do their job. Organic waste, such as leaf matter and the droppings of herbivores, first feeds a host of small animals including insects, of belowground biodiversity Benchmark sites in Kenya. Journal of Tropical and
earthworms and other small invertebrates living in the plant litter). Subtropical Agroecosystems, 11 (2009): 263 - 275
Snyder, B.A., Baas B. And Hendrix, F.P., (2009). Competition between invasive
earthworms (Amynthas corticis, Megascolecidae) and native North American
Successive decomposition of dead material and modified millipedes (Pseudopolydesmus erasus, Polydesmidae): Effects on carbon cycling
organic matter results in the formation of a more complex organic and soil structure. Soil Biology and Biochemistry, 41, 1442-1440.
matter called humus. This process is called humification. Humus Young, A., Young, R. (2001). Soils in the Australian Landsacpe Melbourne: Oxford
affects soil properties. As it slowly decomposes, it colours the University Press. ISBN 9780195515503.
soil darker; increases soil aggregation and aggregate stability;
increases the CEC (the ability to attract and retain nutrients);
and contributes N, P and other nutrients. On the other hand, soil
macro-fauna affects SOM dynamics through tearing and cutting
of fresh vegetation, organic matter incorporation, decomposition
and the formation of stable aggregates. The waste products
produced by micro-organisms are also soil organic matter. This
waste material is less decomposable than the original plant
and animal material, but it can be used by a large number of
organisms. By breaking down carbon structures and rebuilding
new ones or storing the C into their own biomass, soil biota plays
the most important role in nutrient cycling processes and, thus,
in the ability of a soil to provide the crop with sufficient nutrients
to harvest a healthy product. The organic matter content,
especially the more stable humus, increases the capacity to
store water and store (sequester) C from the atmosphere.
Figure 2a and 2b: Multivariate analysis of soil organisms’ occurrence in different
The objective of this paper was to demonstrate that soil land use kinds.
organisms participate in processes and by which elevated
atmospheric CO2 can be sequestered in to the soil to increase
the soil carbon reserve and thereby mitigate climate change
and global warming.
Figure 1 shows our conceptual thinking on the role of soil
organisms in carbon sequestration. From the figure, soil organisms
Figure 1 shows our conceptual thinking on the role of soil organisms in carbon sequestration. From the contribute to tearing and cutting of fresh litter, decomposition,
figure, soil organisms contribute to tearing and cutting of fresh litter, decomposition, humification, chelation, humification, chelation, aggregation, soil particles bonding,
aggregation, soil particles bonding, including symbiosis and plant root system extension. including symbiosis and plant root system extension.
Methodology Conclusion and Take away Message
The methodology used in this work was a combination of literature review and inventory Soil organisms (microbes and fauna) are important drivers of carbon sequestration. Figure 3a and 3b: Multivariate analysis of land use classes and soil chemical
results of a global project on the conservation and sustainable management of below Important in this prospect are the possibilities of increasing soil microbes and properties showing relationships between the land use classes and the soil
ground biodiversity being implemented in seven tropical countries including: Brazil, macro-fauna abundance enhance vegetative decomposition, humufication, soil chemical properties in Taita –Kenya (Muya et al, 2009).
Cote d’Ivoire, India, Indonesia, Kenya, Mexico and Uganda. The project inventoried aggregation and increased biomass accumulation. Increasing microbial abundance
the occurrence of soil organisms in diverse land use kinds ranging from forests to will accelerate biological Nitrogen fixation, decomposition, chelation, and mycelial
cultivated land. Soil samples were collected to determine the abundance, diversity growth in the soil and root hairs including controlling diseases in crops. Increased
and composition of the soil organisms while at the same time analyzing to determine soil carbon will certainly increase the soil and crop productivity and hence elevate
the soil physical and chemical properties based on several methods. The organisms soil and crop productivity and thereby promote an increase in food production.
ranged from microbes (bacteria and fungi) to meso-fauna (collembolans, mites, etc) More financial and research resources should be availed to shed more light in this
and macro-fauna (Earthworms, Ants, Termites, etc). important subject matter and to finds means of out-scaling processes that use soil
organisms to sequester carbon into the soil. Planted and natural forests, fallows
and agro-forestry systems are the best options to manage above ground carbon
Results and Discussions sequestration while inoculation should be used to increase the abundance of soil
organisms above and beneath the soil. Ultimately, the two cornerstone processes of
The results show that soil carbon is mostly well correlated with indigenous forests, every ecosystem are photosynthesis and decomposition.
with planted forests and with fallow systems which also coincide with the occurrence
of the majority of the soil organisms (Figures 2a, 2b, 3a 3b,). The shift in high
abundance and diversity of organisms from these forests to a low abundance and Acknowledgements
diversity in grasslands and cultivated lands is explained by disturbance and land
cover type which dictates substrate (SOM) availability. These findings agree with The authors would like to acknowledge the support provided by the Global Environment
observations of Marshall (2000) that simple communities of soil organisms present facility and the United National Environmental Programme to the project Conservation
from the earliest stages of forest soil genesis become more complex and grow to and sustainable management of below ground biodiversity. The presented data are
astronomical numbers in mature forest soils. Figure 4 from Fatima et al., (2008) shows obtained within the framework of this project. The project is coordinated by the
the part played by soil fauna in the provision and regulation of ecosystem services. Tropical Soil Biology and Fertility Institute of CIAT (TSBF-CIAT) with co-financing from
Several studies (Snyder et al., 2009; Ayuke, 2010), show that earthworm abundance, the Global Environmental Facility (GEF), and implementation support from the United
biomass and diversity are more important drivers of management-induced changes Nations Environment Programme (UNEP). The views expressed in this Poster are
in aggregate stability and soil C and N pools than other macro-fauna. Carrera et al., those of their authors and do not necessary reflect those of the authors’ organizations,
2009 concluded that temperature change alone does not explain all the observed The United Nations Environment Programme or the Global Environment Facility. Figure 4: The relationship between the activities of the soil biological community
increases in soil respiration and dissolved organic carbon (DOC) produced in peatland and a range of ecosystem goods and services that society might expect
soils but rather soil invertebrate responses to warming are crucial in controlling C from agricultural soils (Source Kibblewhite et al., 2008)
fluxes in peatland soils.