We have created this Blog and the database to provide a place where the scientific community can share and update the fast growing knowledge and data on the study of greenhouse gas CO2, CH4, and N2O fluxes in Africa.

We are grateful for the numerous researchers and technicians who provide invaluable data. It is impossible to cite all the references due to limited space allowed and we apologize for the authors whose work has not been cited.

Tyler et al. 1998. Measurements and interpretation of d13C of methane from termites, rice paddies, and wetlands in Kenya



Tyler SC, Zimmerman PR, Cumberbatch C, Greenberg JP, Westberg C, Darlington JP: Measurements and interpretation of d13C of methane from termites, rice paddies, and wetlands in Kenya. Glob Biogeochem Cy 1988, 2:341-355.

Abstract
Ratios of 13C/12C have been measured in methane from a variety of sources in tropical Kenya. Ranges of δ13C in CH4 for termites (most values range from −56 to −64‰, one is at −44‰ one is at ∼−73‰), rice paddies (range −57 to −63‰), and wetlands (range −45 to − 50‰ for Lake Baringo, ∼−55‰ in the Moloi River, ∼−62‰ and ∼−31‰ in two swamp areas) are presented. The data are interpreted with the help of additional measurements of δ13C of CO2 gas, and organic carbon in plant material, termite bodies, and termite fungus combs. The implications of these findings are related to the problem of studying the atmospheric methane budget.

Macdonald et al. 1998. Methane emission by termites and oxidation by soils, across a forest disturbance gradient in the Mbalmayo Forest Reserve, Cameroon

 Macdonald JA, Eggleton P, Bignell DE, Forzi F, Fowler D: Methane emission by termites and oxidation by soils, across a forest disturbance gradient in the Mbalmayo Forest Reserve, Cameroon. Glob Change Biol 1998, 4:409-418.

Abstract

Methane fluxes were measured, using static chambers, across a disturbance gradient in a West African semi-deciduous humid forest. Soil-feeding termite biomass was simultaneously determined, in an attempt to examine its influence on the net soil-atmosphere exchange of CH4. CH4 emission rates from individual termite species were determined under laboratory conditions, permitting the gross production of CH4 to be compared with net fluxes to the atmosphere. Both net CH4 oxidation(-) and emission were observed, and CH4 fluxes ranged from – 24.6 to 40.7 ng m–2 s–1. A statistically significant relationship between termite biomass and CH4 flux was observed across the forested sites such that: CH4 flux (ng m–2 s–1) = 4.95 × termite biomass (gm–2)–10.9 (P < 0.001). Rates of CH4 oxidation were on average 60% smaller at the clearfelled and Terminalia plantation sites than at the near-primary forest site. Two of the disturbed sites were net CH4 sources during one of the sampling periods. Disturbance of tropical forests, resulting in a decrease in the CH4 sink capacity of the soil, may therefore increase the contribution of termite-derived CH4 to the atmosphere. Measurements from the mounds of the soil-feeding termites Thoracotermes macrothorax and Cubitermes fungifaber from the old plantation site gave a CH4 emission of 636 and 53.4 ng s–1 mound–1, respectively. The forest floor surrounding the mounds was sampled in three concentric bands. Around the mound of T. macrothorax the soil was a net source of CH4 estimated to contribute a further 148 ng s–1. Soil surrounding the mound of C. fungifaber was mostly a net sink. The mounds of soil-feeding termites are point sources of CH4, which at the landscape scale may exceed the general sink capacity of the soil, to an extent dependent on seasonal variations in soil moisture and level of disturbance.



Baggs et al. 2006. A short-term investigation of trace gas emissions following tillage and no-tillage of agroforestry residues in western Kenya.



Baggs EM, Chebii J, Ndufa JK (2006) A short-term investigation of trace gas emissions following tillage and no-tillage of agroforestry residues in western Kenya. Soil and Tillage Research 90: 69-76.
 

Abstract

Improved-fallow agroforestry systems are increasingly being adopted in the humid tropics for soil fertility management. However, there is little information on trace gas emissions after residue application in these systems, or on the effect of tillage practice on emissions from tropical agricultural systems. Here, we report a short-term experiment in which the effects of tillage practice (no-tillage versus tillage to 15 cm depth) and residue quality on emissions of N2O, CO2 and CH4 were determined in an improved-fallow agroforestry system in western Kenya. Emissions were increased following tillage of Tephrosia candida (2.1 g N2O-N ha−1 kg N applied−1; 759 kg CO2-C ha−1 t C applied−1; 30 g CH4-C ha−1 t C applied−1) and Crotalaria paulina residues (2.8 g N2O-N ha−1 kg N applied−1; 967 kg CO2-C ha−1 t C applied−1; 146 g CH4-C ha−1 t C applied−1) and were higher than from tillage of natural-fallow residues (1.0 g N2O-N ha−1 kg N applied−1; 432 kg CO2-C ha−1 t C applied−1; 14.7 g CH4-C ha−1 t C applied−1) or from continuous maize cropping systems. Emissions from these fallow treatments were positively correlated with residue N content (r = 0.62–0.97; P < 0.05) and negatively correlated with residue lignin content (r = −0.56, N2O; r = −0.92, CH4; P < 0.05). No-tillage of surface applied Tephrosia residues lowered the total N2O and CO2 emitted over 99 days by 0.33 g N2O-N ha−1 kg N applied−1 and 124 kg CO2-C ha−1 t C applied−1, respectively; estimated to provide a reduction in global warming potential of 41 g CO2 equivalents. However, emissions were increased from this treatment over the first 2 weeks. The responses to tillage practice and residue quality reported here need to be verified in longer term experiments before they can be used to suggest mitigation strategies appropriate for all three greenhouse gases.

Michelsen et al. 2004. Carbon stocks, soil respiration and microbial biomass in fire-prone tropical grassland, woodland and forest ecosystems

Michelsen, A., Andersson, M., Jensen, M., Kjøller, A., Gashew, M., 2004. Carbon stocks, soil respiration and microbial biomass in fire-prone tropical grassland, woodland and forest ecosystems. Soil Biol. Biochem. 36, 1707-1717.

Abstract

A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO2 emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios (δ13C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in δ13C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation–extraction method (Cmic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in Cmic and substrate-induced respiration (SIR) were large. In woodland and woodland–wooded grassland Cmic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands Cmic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor Cmic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.

Andersson et al. 2004. Tropical savannah woodland: effects of experimental fire on soil microorganisms and soil emissions of carbon dioxide

Andersson, M., Michelsen, A., Jensen, M., Kjøller, A., 2004. Tropical savannah woodland: effects of experimental fire on soil microorganisms and soil emissions of carbon dioxide. Soil Biol. Biochem. 36, 849-858.

Abstract

Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (Cmic) was 52% (fumigation–extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of Cmic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24–85%) and nitrate (47–76%) in the soil until 90 d after burning, while soil NH4+–N was not affected to the same extent. The increase in soil NO3–N but not NH4+–N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH4+–N to NO3–N. In the subsequent rainy season, NO3–N and, consequently, PDA were reduced by ash deposition. Further, Cmic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.

Gerschlauer et al. 2014. Greenhouse gas exchange in tropical mountain ecosystems in Tanzania

Gerschlauer et al. 2014. Greenhouse gas exchange in tropical mountain ecosystems in Tanzania. EGU General Assembly 2014, held 27 April - 2 May, 2014 in Vienna, Austria

Abstract
Tropical mountain ecosystems with their mostly immense biodiversity are important regions for natural resources but also for agricultural production. Their supportive ecosystem processes are particularly vulnerable to the combined impacts of global warming and the conversion of natural to human-modified landscapes. Data of impacts of climate and land use change on soil-atmosphere interactions due to GHG (CO2, CH4, and N2O) exchange from these ecosystems are still scarce, in particular for Africa. Tropical forest soils are underestimated as sinks for atmospheric CH4 with regard to worldwide GHG budgets (Werner et al. 2007, J GEOPHYS RES Vol. 112). Even though these soils are an important source for the atmospheric N2O budget, N2O emissions from tropical forest ecosystems are still poorly characterized (Castaldi et al. 2013, Biogeosciences 10). To obtain an insight of GHG balances of selected ecosystems soil-atmosphere exchange of N2O, CH4 and CO2 was investigated along the southern slope of Mt. Kilimanjaro, Tanzania. We will present results for tropical forests in three different altitudes (lower montane, Ocotea, and Podocarpus forest), home garden (extensive agro-forestry), and coffee plantation (intensive agro-forestry). Therefore we used a combined approach consisting of a laboratory parameterization experiment (3 temperature and 2 moisture levels) and in situ static chamber measurements for GHG exchange. Field measurements were conducted during different hygric seasons throughout two years. Seasonal variation of temperature and especially of soil moisture across the different ecosystems resulted in distinct differences in GHG exchange. In addition environmental parameters like soil bulk density and substrate availability varying in space strongly influenced the GHG fluxes within sites. The results from parameterization experiments and in situ measurements show that natural forest ecosystems and extensive land use had higher uptakes of CH4. For the investigated forest ecosystems we found considerable differences in soil sink strength for CH4. N2O emissions were highest in natural forest ecosystems even though N input in the intensively managed system was considerably higher. Highest N2O efflux rates were identified in the region of highest mean annual precipitation. CO2 emissions reduced from managed to natural ecosystems. In general an increase in temperature as well as in soil moisture caused higher GHG fluxes throughout all investigated natural and managed ecosystems. With increasing altitude of the investigated forests GHG emissions reduced overall. 

http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10821.pdf

Rabenarivo et al. 2014. Emissions of CO2 and N2O from a pasture soil from Madagascar—Simulating conversion to direct-seeding mulch-based cropping in incubations with organic and inorganic inputs. J. Plant Nutr. Soil Sci.

Rabenarivo, M., Wrage-Moennig, N., Chotte, J.-L., Rabeharisoa, L., Razafimbelo, T.M., Chapuis-Lardy, L., Emissions of CO2 and N2O from a pasture soil from Madagascar—Simulating conversion to direct-seeding mulch-based cropping in incubations with organic and inorganic inputs. J. Plant Nutr. Soil Sci. DOI: 10.1002/jpln.201300032

 

Abstract

In the highlands of Madagascar, agricultural expansion gained on grasslands, and cropping systems based on direct seeding with permanent vegetation cover are emerging as a means to sustain upland crop production. The objective of this study was to examine how such agricultural practices affect greenhouse-gas emissions from a loamy Ferralsol previously used as a pasture. We conducted an experiment under controlled laboratory conditions combining cattle manure, crop residues (rice straw), and mineral fertilizers (urea plus NPK or di-NH4-phosphate) to mimic on-field inputs and examined soil CO2 and N2O emissions during a 28-d incubation at low and high water-filled pore space (40% and 90% WFPS). Emissions of N2O from the control soil, i.e., soil receiving no input, were extremely small (< 5 ng N2O-N (g soil)–1 h–1) even under anaerobic conditions. Soil moisture did not affect the order of magnitude of CO2 emissions while N2O fluxes were up to 46 times larger at high soil WFPS, indicating the potential influence of denitrification under these conditions. Both CO2 and N2O emissions were affected by treatments, incubation time, and their interactions. Crop-residue application resulted in larger fluxes of CO2 but reduced N2O emissions probably due to N immobilization. The use of di-NH4-phosphate was a better option than NPK to reduce N2O emissions without increasing CO2 fluxes when soil received mineral fertilizers. Further studies are needed to translate the findings to field conditions and relate greenhouse-gas budgets to crop production.

Thomas and Hoon, 2010. Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting.

Thomas, A.D., Hoon, S.R.,2010. Carbon dioxide fluxes from biologically-crusted Kalahari Sands after simulated wetting. J. Arid Environ. 74, 131-139.

Abstract

We report surface CO2 efflux and subsoil CO2 concentrations in biologically-crusted soils from the Kalahari. Fluxes were determined in-situ using a closed chamber coupled to a portable gas chromatograph on dry soils and on soils subject to simulated light and heavy rainfall. Surface efflux was measured in an artificially darkened environment in order to determine by difference, whether photosynthesis was occurring. Dry soil efflux rates were 2.8–14.8 mg C m2 h−1 throughout a diurnal cycle. Light rainfall led to an immediate increase in efflux to a peak of 65.6 mg C m2 h−1. Heavy rainfall resulted in a large pulse of CO2 with efflux rates of 339.2 mg C m2 h−1 over the first hour after wetting. Peak rates remained high over the following 2 days (87.8 and 87.0 mg C m2 h−1). Given sufficient moisture, fluxes increased with temperature. We believe hydration of the subsoil stimulates microorganisms which repsire available C either from extracellular polysaccharide sheaths (EPS) or released into the soil through lysis of microbial cells. Higher fluxes from the soil kept in the dark suggests photosynthesis occurs in wetted crusts during the daytime but net C uptake is masked by respiration from other microorganisms.

Thomas et al. 2008. Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari.

Thomas, A.D., Hoon, S.R., Linton, P.E., 2008. Carbon dioxide fluxes from cyanobacteria crusted soils in the Kalahari. Applied Soil Ecology 39, 254-263.

Abstract

The surface of dryland soils is frequently characterised by a biological crust comprising of various combinations of cyanobacteria, algae, moss and lichens. In the Kalahari of Botswana, soil crusts are predominantly made up of cyanobacteria, which when moist, are capable of fixing N and C. Many cyanobacteria also produce extracellular polymeric substances (EPS) which bind soil particles together and decrease erodibility. The physical integrity and metabolic activity of soil crusts is thus critical to ecological productivity, erodibility and CO2 fluxes in dryland regions. There are, however, few studies of the magnitude and controlling factors of soil CO2 flux within these systems.
Our aim was to quantify in situ soil CO2 flux during contrasting antecedent moisture conditions in the south west Kalahari of Botswana. We have designed a gas exchange chamber for field deployment coupled to a portable gas chromatograph, control and data logging instrumentation. The optical and active thermal control specifications of the chamber have been designed to permit photosynthesis and cope with the temperature extremes of the Kalahari whilst minimizing disturbance to the cyanobacteria soil crust. This approach has enabled CO2 fluxes to be monitored in situ with a high degree of precision for extended periods.
In August 2005, when the surface and subsoils were dry, the ambient CO2 efflux was negative and low during the daytime (−6.15 mg C m2 h−1). When 8 mm rainfall equivalent of water was added to the surface there was an immediate uptake of CO2 during the daytime at rates up to 75 mg C m2 h−1 demonstrating that rates of net photosynthesis are greatly enhanced by available moisture. In contrast, in May 2006 following a prolonged wet period when the subsoil was moist, there was a net positive efflux of CO2 from the soil at rates of up to 60 mg C m2 h−1 irrespective of whether the surface soil was moist or not. This is consistent with subsoil heterotrophic bacterial respiration becoming an important contributor to soil efflux.

Thomas et al., 2012. Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana.

 Thomas, A.D., 2012. Impact of grazing intensity on seasonal variations in soil organic carbon and soil CO2 efflux in two semiarid grasslands in southern Botswana. Philosophical Transactions of the Royal Society B: Biological Sciences 367, 3076-3086.

Abstract

Biological soil crusts (BSCs) are an important source of organic carbon, and affect a range of ecosystem functions in arid and semiarid environments. Yet the impact of grazing disturbance on crust properties and soil CO2 efflux remain poorly studied, particularly in African ecosystems. The effects of burial under wind-blown sand, disaggregation and removal of BSCs on seasonal variations in soil CO2 efflux, soil organic carbon, chlorophyll a and scytonemin were investigated at two sites in the Kalahari of southern Botswana. Field experiments were employed to isolate CO2 efflux originating from BSCs in order to estimate the C exchange within the crust. Organic carbon was not evenly distributed through the soil profile but concentrated in the BSC. Soil CO2 efflux was higher in Kalahari Sand than in calcrete soils, but rates varied significantly with seasonal changes in moisture and temperature. BSCs at both sites were a small net sink of C to the soil. Soil CO2 efflux was significantly higher in sand soils where the BSC was removed, and on calcrete where the BSC was buried under sand. The BSC removal and burial under sand also significantly reduced chlorophyll a, organic carbon and scytonemin. Disaggregation of the soil crust, however, led to increases in chlorophyll a and organic carbon. The data confirm the importance of BSCs for C cycling in drylands and indicate intensive grazing, which destroys BSCs through trampling and burial, will adversely affect C sequestration and storage. Managed grazing, where soil surfaces are only lightly disturbed, would help maintain a positive carbon balance in African drylands.

Thomas et al. 2011. Soil respiration at five sites along the Kalahari Transect: Effects of temperature, precipitation pulses and biological soil crust cover.

Thomas, A.D., Hoon, S.R., Dougill, A.J., 2011. Soil respiration at five sites along the Kalahari Transect: Effects of temperature, precipitation pulses and biological soil crust cover. Geoderma 167-168, . 284-294.

Abstract

There are increasing concerns that climatic and land use changes will enhance soil respiration rates and soil organic carbon loss, compromising agricultural productivity and further elevating atmospheric CO2. Current understanding of dryland respiration is, however, insufficient to enable prediction of the consequences of these changes for dryland soils and CO2 fluxes. The objectives of this paper are to present in-situ respiration data from five remote sites along a climatic gradient in the Kalahari of Botswana and to determine the effects of temperature, moisture and biological crust cover on soil CO2 fluxes. Moisture was the primary limiting factor to efflux which increased with amount of simulated rainfall. On dry soils, mean CO2 efflux was between 1.5 and 5.9 mg C m− 2 h− 1. After 2 mm and 50 mm simulated wetting, mean rates increased to 4.0 to 21.8 and 8.6 to 41.5 mg C m− 2 h− 1 respectively. Once wet, soil CO2 efflux increases with temperature, and sites at the hotter northern end of the transect lost more CO2 than cooler southerly sites. Net respiration rates are, however, muted by autotrophic organisms in biological soil crusts which photosynthesise and take up CO2. The temperature sensitivity of soil CO2 efflux increased with moisture. Dry, 2 mm and 50 mm treated soils had a Q10 of 1.1, 1.5 and 1.95 respectively. Our findings indicate that higher temperatures and a loss of biological crust cover will lead to greater soil C loss through respiration.

Thongo M'Bou et al., 2010. Growth and maintenance respiration of roots of clonal Eucalyptus cuttings: scaling to stand-level

Thongo M'Bou, A., Saint-Andre, L., Grandcourt, A.s., Nouvellon, Y., Jourdan, C., Mialoundama, F.l., Epron, D., 2010. Growth and maintenance respiration of roots of clonal Eucalyptus cuttings: scaling to stand-level. Plant Soil 332, 41-53.

Abstract

Root respiration consumes an important part of the daily assimilated carbon but the magnitude of this component of forest net ecosystem exchange and its partitioning among the different energy demanding processes in roots are still poorly documented. 5-month old Eucalyptus cuttings were grown in a greenhouse in pot filled with coarse sand. They were fertilized with three different amounts of a slow-release fertilizer with the doses of 8, 24 and 48 g of nitrogen per plant. Root respiration was measured using an infrared gas analyser by perfusing air through the pot on 9 plants per treatment on three dates 14 days apart. Measure of root respiration of the three treatments over time was made in order to obtain a large range of growth and nutrient uptake. Root respiration normalized at 22°C ranged from 0.09 to 0.23 gC d−1 for the three treatments during all the experiment. It was well predicted with a model that includes root growth rate and root nitrogen content.The nitrogen related maintenance coefficient was negatively correlated to the root nitrogen concentration suggesting a decrease in protein turnover with increasing fertility. Growth rate of fine root in a virtual stand was simulated using age-related allometric equations and further used to estimate root respiration in the field. Simulated root respiration increased over time from 0.39 to 3.14 gC m−2 d−1 between 6 and 126 months assuming a turnover of 2 yr−1 for fine roots. The major fraction of simulated root respiration in the field (78–92%) was used for the maintenance of the existing biomass.