Yohannes, Y., Shibistova, O., Abate, A., Fetene, M., Guggenberger, G., 2011. Soil CO2 efflux in an Afromontane forest of Ethiopia as driven by seasonality and tree species. Forest Ecology and Management 261, 1090-1098.
Abstract
Variability of soil CO2 efflux strongly depends on soil temperature, soil moisture and plant phenology. Separating the effects of these factors is critical to understand the belowground carbon dynamics of forest ecosystem. In Ethiopia with its unreliable seasonal rainfall, variability of soil CO2 efflux may be particularly associated with seasonal variation. In this study, soil respiration was measured in nine plots under the canopies of three indigenous trees (Croton macrostachys, Podocarpus falcatus and Prunus africana) growing in an Afromontane forest of south-eastern Ethiopia. Our objectives were to investigate seasonal and diurnal variation in soil CO2 flux rate as a function of soil temperature and soil moisture, and to investigate the impact of tree species composition on soil respiration. Results showed that soil respiration displayed strong seasonal patterns, being lower during dry periods and higher during wet periods. The dependence of soil respiration on soil moisture under the three tree species explained about 50% of the seasonal variability. The relation followed a Gaussian function, and indicated a decrease in soil respiration at soil volumetric water contents exceeding a threshold of about 30%. Under more moist conditions soil respiration is tentatively limited by low oxygen supply. On a diurnal basis temperature dependency was observed, but not during dry periods when plant and soil microbial activities were restrained by moisture deficiency. Tree species influenced soil respiration, and there was a significant interaction effect of tree species and soil moisture on soil CO2 efflux variability. During wet (and cloudy) period, when shade tolerant late successional P. falcatus is having a physiological advantage, soil respiration under this tree species exceeded that under the other two species. In contrast, soil CO2 efflux rates under light demanding pioneer C. macrostachys appeared to be least sensitive to dry (but sunny) conditions. This is probably related to the relatively higher carbon assimilation rates and associated root respiration. We conclude that besides the anticipated changes in precipitation pattern in Ethiopia any anthropogenic disturbance fostering the pioneer species may alter the future ecosystem carbon balance by its impact on soil respiration.
Seiler et al. 1984. Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils
Seiler, W., Conrad, R., Scharffe, D., 1984. Field studies of methane emission from termite nests into the atmosphere and measurements of methane uptake by tropical soils. Journal of Atmospheric Chemistry 1, 171-186. doi:10.1007/bf00053839.
Abstract
The flux of CH4 and CO2 from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH4 relative to the flux rate of CO2 in terms of carbon obtained for the individual species showed ratios of 2.9×10-3, 7.0×10-4, 6.7×10-5, 8.7×10-3, 2.0×10-3 and 4.2×10-3, respectively. Using data published on the assimulation efficiencies of termites, the flux of carbon as CH4 accounts for 6.0×10-5 to 2.6×10-3 of the carbon ingested which results in a global CH4 emission by termites of 2 to 5×1012 g/yr. Methane is decomposed in the soil with average decomposition rates of 52
g/m2/h. The annual CH4 consumption in the tropics and subtropics is estimated to be 21×1012 g which exceeds the CH4 emission rate by termites.
Abstract
The flux of CH4 and CO2 from termite nests into the atmosphere has been measured in a broad-leafed-type savannah in South Africa. Measurements were carried out on nests of species of six genera, i.e., Hodotermes, Macrotermes, Odontotermes, Trinervitermes, Cubitermes, and Amitermes. The flux rates of CH4 relative to the flux rate of CO2 in terms of carbon obtained for the individual species showed ratios of 2.9×10-3, 7.0×10-4, 6.7×10-5, 8.7×10-3, 2.0×10-3 and 4.2×10-3, respectively. Using data published on the assimulation efficiencies of termites, the flux of carbon as CH4 accounts for 6.0×10-5 to 2.6×10-3 of the carbon ingested which results in a global CH4 emission by termites of 2 to 5×1012 g/yr. Methane is decomposed in the soil with average decomposition rates of 52
g/m2/h. The annual CH4 consumption in the tropics and subtropics is estimated to be 21×1012 g which exceeds the CH4 emission rate by termites.
Delmas et al. 1991. Sources and sinks of methane in African Savanna. CH4 emissions from biomass burning
Delmas, R.A., Marenco, A., Tathy, J.P., Cros, B., Baudet, J.G.R., 1991. Sources and sinks of methane in African Savanna. CH4 emissions from biomass burning. J. Geophys. Res. 96, 7287-7299. doi:10.1029/90jd02496.
Abstract
Sources and sinks of atmospheric methane are studied in savanna regions of west and central Africa. Flux measured over dry savanna soils, using static chambers, is always negative the average uptake rate being 2 × 1010 molecules/cm2/s. In these regions, sources are linked to biomass burning. Methane and CO2 emission from combustion of savanna plants and wood is studied by both field experiments and laboratory experiments using a combustion chamber. For savanna plants most of the carbon (85%) contained in the biomaterial is volatilized as CO2 and 0.1 to 0.25% as methane. For graminaceous plants like loudetia simplex the ratio C-CH4/C-CO2 is 0.11%; it is 0.28% for hyparrhenia the other main type of savanna plants and it attains 1.4% for the combustion of wood. In natural fire plumes this ratio is around 0.26% for savanna fires and 0.56 to 2.22% for forest fires. These results show that methane release is highly dependent on the type of combustion. Methane to CO2 ratios are also studied in vertical profiles in the troposphere taken during the TROPOZ I campaign, an aerial research expedition carried out over west Africa during the bushfire period. Within polluted layers, the average ratio of CH4 to CO2 excess over ambient air concentration is 0.34%. These results show that biomass burning in tropical Africa constitutes an important source of atmospheric methane estimated to about 9.2 × 106 T(CH4)/yr.
Abstract
Sources and sinks of atmospheric methane are studied in savanna regions of west and central Africa. Flux measured over dry savanna soils, using static chambers, is always negative the average uptake rate being 2 × 1010 molecules/cm2/s. In these regions, sources are linked to biomass burning. Methane and CO2 emission from combustion of savanna plants and wood is studied by both field experiments and laboratory experiments using a combustion chamber. For savanna plants most of the carbon (85%) contained in the biomaterial is volatilized as CO2 and 0.1 to 0.25% as methane. For graminaceous plants like loudetia simplex the ratio C-CH4/C-CO2 is 0.11%; it is 0.28% for hyparrhenia the other main type of savanna plants and it attains 1.4% for the combustion of wood. In natural fire plumes this ratio is around 0.26% for savanna fires and 0.56 to 2.22% for forest fires. These results show that methane release is highly dependent on the type of combustion. Methane to CO2 ratios are also studied in vertical profiles in the troposphere taken during the TROPOZ I campaign, an aerial research expedition carried out over west Africa during the bushfire period. Within polluted layers, the average ratio of CH4 to CO2 excess over ambient air concentration is 0.34%. These results show that biomass burning in tropical Africa constitutes an important source of atmospheric methane estimated to about 9.2 × 106 T(CH4)/yr.
Dick et al. 2006. Effect of N-fixing and non N-fixing trees and crops on NO and N2O emissions from Senegalese soils
Dick, J., Skiba, U., Munro, R., Deans, D., 2006. Effect of N-fixing and non N-fixing trees and crops on NO and N2O emissions from Senegalese soils. Journal of Biogeography 33, 416-423. doi:10.1111/j.1365-2699.2005.01421.x.
Aim Agroforestry systems incorporating N-fixing trees have been shown to be socially beneficial and are thought to be environmentally friendly, both enriching and stabilizing soil. However, the effect of such systems on the emissions of the important greenhouse gas nitrous oxide (N2O) and the tropospheric ozone precursor nitric oxide (NO) is largely unknown.
Location Soil was collected from the research plots of Institut Sénégalais de Recherches Agricoles at Bandia and Bambey, Senegal, West Africa, and from neighbouring farmers’ fields. Trace gas flux measurements and chemical analysis of the soil were carried out at the Centre for Ecology and Hydrology (CEH), Edinburgh, UK.
Methods Nitric oxide (NO) and nitrous oxide (N2O) emissions were measured following simulated rainfall events (10 and 20 mm equivalents) from repacked soil cores collected under two tree species (Acacia raddiana) and Eucalyptus camaldulensis) in each of two provenance trails. In addition, soil samples were collected in local fields growing peanut (Arachis hypogaea) and Sorghum (Sorghum vulgare), close to the species trials in Bambey. NO was measured using a flow through system and was analysed by chemiluminescence. Nitrous oxide was measured from the repacked soil core headspace and was analysed by electron capture gas chromatography. Soil mineral N was extracted with KCl and analysed by colorimetric methods on separate soil columns.
Results Light rainfall, which increased the gravimetric soil moisture content to 20%, stimulated an increase in NO emission but there was no detectable N2O emission. A heavy rainfall event, which increased the gravimetric soil moisture to 30%, stimulated N2O emission with a subsequent peak in NO emissions when the soils became drier. Soil collected under the N-fixing tree species emitted significantly more N2O than soil collected under the N-fixing crop species (P < 0.01). NO and N2O emissions significantly correlated with soil available N (NH4 and NO3) (P < 0.05).
Main conclusions Rainfall intensity, supply of mineral N from organic matter and N fixation were the prime drivers of NO and N2O emissions from seasonally dry tropical soils. The improved soil fertility underneath the trees provided a larger pool of mineral N and yielded larger rates of NO and N2O emissions.
Dick et al. 2008. The contribution of agricultural practices to nitrous oxide emissions in semi-arid Mali
Dick, J., Kaya, B., Soutoura, M., Skiba, U., Smith, R., Niang, A., Tabo, R., 2008. The contribution of agricultural practices to nitrous oxide emissions in semi-arid Mali. Soil Use and Management 24, 292-301. doi:10.1111/j.1475-2743.2008.00163.x.
Abstract
The yield and flux of nitrous oxide (N2O) emitted from continuous cereals (with and without urea), legumes/cereal in rotation and cereal/legume in rotation all with or without organic manure was monitored from January 2004 to February 2005. All treatments except continuous cereals had phosphate added. The cereal grown July–October in 2003 and 2004 was pearl millet (Pennisetum glaucum) and the legume was a bean (Phaseolus vulgaris). The 10 m × 10 m plots were established in a semi-arid climate in Mali. The addition of organic manure and both inorganic fertilizers increased yield and N2O emissions. Continuous cereals treated with both organic manure and urea emitted significantly less N2O (882 g N/ha per year) than plots receiving no organic manure(1535 g N/ha per year). Growing N-fixing crops in rotation did not significantly increase N2O emissions. This study supports the new practice of growing cereal and legumes in rotation as an environmentally sustainable system in semi-arid Mali.
Abstract
The yield and flux of nitrous oxide (N2O) emitted from continuous cereals (with and without urea), legumes/cereal in rotation and cereal/legume in rotation all with or without organic manure was monitored from January 2004 to February 2005. All treatments except continuous cereals had phosphate added. The cereal grown July–October in 2003 and 2004 was pearl millet (Pennisetum glaucum) and the legume was a bean (Phaseolus vulgaris). The 10 m × 10 m plots were established in a semi-arid climate in Mali. The addition of organic manure and both inorganic fertilizers increased yield and N2O emissions. Continuous cereals treated with both organic manure and urea emitted significantly less N2O (882 g N/ha per year) than plots receiving no organic manure(1535 g N/ha per year). Growing N-fixing crops in rotation did not significantly increase N2O emissions. This study supports the new practice of growing cereal and legumes in rotation as an environmentally sustainable system in semi-arid Mali.
Rees et al. 2006. Nitrous oxide fluxes from savanna (miombo) woodlands in Zimbabwe
Rees, R.M., Wuta, M., Furley, P.A., Li, C., 2006. Nitrous oxide fluxes from savanna (miombo) woodlands in Zimbabwe. Journal of Biogeography 33, 424-437. doi:10.1111/j.1365-2699.2005.01423.x.
Aim We test the hypothesis that land use and climate are important controls of nitrous oxide (N2O) emissions from savanna ecosystems, and that these emissions can be represented by a mechanistic model of carbon (C) and nitrogen (N) transformations.
Location Miombo woodlands in Zimbabwe are part of widespread woody savanna formations in southern and central Africa that cover more than 2.7 million km2. The rainfall in this region is around 800 mm and is concentrated in the period between November and March.
Methods Losses of N2O were measured along transects in two field areas using static chambers over a period of 1 year. The vegetation in both areas was dominated by Julbernardia globiflora and Brachystegia spiciformis, but had differing management systems (burned and unburned), soil properties and site characteristics (slope and drainage). The effects of simulated rainfall and fertilizer additions were studied in laboratory incubations.
Results Patterns of N2O emissions were strongly linked to rainfall. The highest fluxes at both sites were measured within 18 days of the onset of the first rains in November, with fluxes of up to 42 μg N m−2 h−1. During the dry season, fluxes were lower, but a large proportion (R2 values between 0.8 and 0.95, P < 0.001) of the N2O flux could be predicted by variations in soil moisture. Soil columns were set up in the laboratory to which simulated rainwater was added, and the amounts and timing of rainwater addition were varied. Losses of N2O were highest within the first week of the laboratory study. Altering the amount of rainwater addition did not significantly affect N2O loss; however, a continuous addition of water resulted in higher losses of N2O (up to 79 μg N m−2 h−1) than periodic addition of the same amount. A model (denitrification–decomposition) was used to simulate N2O release over a 12 month period, using meteorological data recorded in the vicinity of the field site. The simulations and field data suggest that nitrification was the main process responsible for N2O release during the dry season but that denitrification was more important during the wet season.
Main conclusions The release of N2O from dryland savannas was shown to constitute an important nutrient flux, and emissions were strongly linked to patterns of rainfall; however, there was evidence to suggest that the magnitude of fluxes is also influenced locally by differences in soil organic matter concentration and drainage.
Scholes et al. 1997. NO and N2O emissions from savanna soils following the first simulated rains of the season
Scholes, M.C., Martin, R., Scholes, R.J., Parsons, D., Winstead, E., 1997. NO and N2O emissions from savanna soils following the first simulated rains of the season. Nutrient Cycling in Agroecosystems 48, 115-122. doi:10.1023/a:1009781420199.
Abstract
Data on the emissions of oxides of nitrogen from the soil during the early part of the wet season are reported for nutrient-rich and nutrient-poor sandy soils at Nylsvley, South Africa. The emissions of NOx and N2O following the first wetting event of the season are elevated relative to subsequent events. The observed high emission rates (76 ng N-NO m-2 s-1) are partially attributed to the sandiness of the soil, which permits NO to diffuse out of the soil rapidly. The pulse of high emissions following wetting is maintained for approximately 72 hours, thereafter continuing at around 20 ng NO m-2 s-1 while the soil remains moist. The initial pulse is suggested to be due to the accumulation of a substrate pool during the dry period, coupled with an inability of plants and microbes to use it effectively during the first few days after wetting. There were no significant differences in the peak or subsequent emission rates for either NO or N2O between two sites of differing nitrogen mineralisation potentials. N2O emissions averaged 8% of NOx emissions. The enhanced emissions of NOx which follow the first wetting after a prolonged dry period do not make a very large contribution to the annual gaseous N emission budget, but could be a significant contributor to the high tropospheric ozone levels observed over southern Africa in springtime.
Abstract
Data on the emissions of oxides of nitrogen from the soil during the early part of the wet season are reported for nutrient-rich and nutrient-poor sandy soils at Nylsvley, South Africa. The emissions of NOx and N2O following the first wetting event of the season are elevated relative to subsequent events. The observed high emission rates (76 ng N-NO m-2 s-1) are partially attributed to the sandiness of the soil, which permits NO to diffuse out of the soil rapidly. The pulse of high emissions following wetting is maintained for approximately 72 hours, thereafter continuing at around 20 ng NO m-2 s-1 while the soil remains moist. The initial pulse is suggested to be due to the accumulation of a substrate pool during the dry period, coupled with an inability of plants and microbes to use it effectively during the first few days after wetting. There were no significant differences in the peak or subsequent emission rates for either NO or N2O between two sites of differing nitrogen mineralisation potentials. N2O emissions averaged 8% of NOx emissions. The enhanced emissions of NOx which follow the first wetting after a prolonged dry period do not make a very large contribution to the annual gaseous N emission budget, but could be a significant contributor to the high tropospheric ozone levels observed over southern Africa in springtime.
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