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Conversion of humid tropical forest to agriculture significantly alters trace gas emissions from soils. We report nitrous oxide (N(2)O), nitric oxide (NO), and methane (CH(4)) fluxes from secondary forest soils prior to and during deforestation, and throughout the first agricultural cropping. Annual average nitrogen oxide emissions from forest soil...
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... sites were on a fertile, loamy soil developed on low river terraces (fluventic Eutropept), and two were on less fertile clay soils developed on high river terraces (andic Dystropept). Physical and chemical soil characteristics are given in Table 1. Large parts of the original forest in the areas were cleared for agriculture about 1953. ...
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... was converted to NO 2 on a CrO3 catalyst; then NO 2 was quantified by luminol chemiluminescence detection (Scintrex Reiners , 1994]. The gravimetric soil water content 0g (g g-i) was derived after oven drying of soil to constant weight within 48 hours at 105øC and was convened to proportion of water-filled pore space (% wfps) using the formula given by Linn and Doran [1984] % wfps = (0g x bd x 100%) / ( 1 -(bd / 2.65)) with bulk density (bd (Mg m-3)) data measured from forest soils (Table 1), and particle density estimated as 2.65 Mg m '3. For soil carbon and total nitrogen analyses bulk soil samples were taken from one soil pit per site at 0.05-, 0.15-, 0.3-, 0.5-, 0.7-, and 0.9-m depth, air dried, passed through a 2-mm sieve, and shipped to the laboratory. ...
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... densities were low in both soil types (Table 1), with higher densities measured in the Dystropept (clay) profile compared to the Eutropept (loam). In both soils the topsoil structure is dominated by well developed, loosely packed crumb aggregates. ...
Citations
... Soil water content controls microbial access to oxygen, which determines whether nitrification (aerobic) or denitrification (anaerobic) dominates and often predicts NO:N 2 O emission ratios (Davidson et al. 2000). Fires can reduce shade from aboveground vegetation and combust soil organic matter, changing soil texture and forming hydrophobic layers in some surface soils (DeBano 2000) which can alter water infiltration and promote dry/aerobic conditions Pinto 2002;Weitz et al. 1998). Aerobic soil may initially promote nitrification which is associated with high NO flux (Firestone & Davidson 1989); however, as hydrophobic layers degrade, soils could become saturated for longer periods of time following rain due to lack of plant transpiration (Graham et al. 2016). ...
... Nitric oxide Weitz et al. (1998) and Neff et al. (1995) both noted statistically significant short-lived bursts of NO from Costa Rican tropical secondary forests up to 3 months post-fire which they attributed to increased nitrification rates. Verchot et al. (1999) also observed NO fluxes up to 6 times higher than unburned fluxes within 6 months after fire in a Brazilian primary forest but observed no corresponding increase in nitrification potential or net mineralization to explain this. ...
... Despite this diversity, six out of nine studies in tropical forests reported significantly increased N 2 O emissions after fires. Of these six, half associated increased nitrification rates with increased N 2 O emissions (Ishizuka et al. 2002;Melillo et al. 2001;Weitz et al. 1998) while the other half did not measure any explanatory variables (Arai et al. 2014;Luizao et al. 1989;Takakai et al. 2006). Verchot et al. (1999) found no change in nitrification or net mineralization rates following fire and Zhao et al. (2015) found no difference in N 2 O emissions between burned and unburned plots, despite measuring an increase in NH 4 + . ...
Wildfires may increase soil emissions of trace nitrogen (N) gases like nitric oxide (NO) and nitrous oxide (N 2 O) by changing soil physicochemical conditions and altering microbial processes like nitrification and denitrification. When 34 studies were synthesized, we found a significant increase in both NO and N 2 O emissions up to 1 year post-fire across studies spanning ecosystems globally. However, when fluxes were separated by ecosystem type, we found that individual ecosystem types responded uniquely to fire. Forest soils tended to emit more N 2 O after fire, but there was no significant effect on NO. Shrubland soils showed significant increases in both NO and N 2 O emissions after fires; often with extremely large but short-lived NO pulses occurring immediately after fire. Grassland NO emissions increased after fire, but the size of this effect was small relative to shrublands. N 2 O emissions from burned grasslands were highly variable with no significant effect. To better understand the variation in responses to fire across global ecosystems, more consistent measurements of variables recognized as important controls on soil fluxes of NO and N 2 O (e.g., N cycling rates, soil water content, pH, and substrate availability) are needed across studies. We also suggest that fire-specific elements like burn severity, microbial community succession, and the presence of char be considered by future studies. Our synthesis suggests that fires can exacerbate ecosystem N loss long after they burn, increasing soil emissions of NO and N 2 O with implications for ecosystem N loss, climate, and regional air quality as wildfires increase globally.
... Cette combustion entraine aussi la restitution au sol d'une partie de l'azote stockée par la plante (Ojima et al., 1994) dont une partie peut devenir disponible pour les micro-organismes produisant du N2O. Weitz et al. (1998) ont par exemple évalué que la destruction d'une parcelle de forêt secondaire tropicale par brûlis entraîne une augmentation des émissions de N2O du sol par rapport à la forêt voisine restée intacte avec en moyenne des émissions deux fois supérieures à la moyenne annuelle et un pic d'émission de 91 gN ha -1 j -1 peu de temps après le brûlis. Chalco Vera et al. ...
Le protoxyde d'azote (N2O) est un gaz à effet de serre très puissant qui participe à la destruction de l'ozone stratosphérique et dont la concentration atmosphérique augmente avec l'utilisation d'engrais azotés en agriculture. De nombreux facteurs influencent les processus de production et d'émission de N2O par les sols comme le climat et sa variabilité, le type de sol et son occupation, les activités d'élevage ou agricole et leur intensité. Dans le but d'atténuer l'emballement climatique en réduisant les émissions de N2O, il est nécessaire d'évaluer et de quantifier les effets de ces facteurs à différentes échelles (parcelle/territoire/région). Dans cette optique, mon projet de thèse a pour but d'analyser et de modéliser les émissions de N2O sous différents degrés de pression anthropique et climatique. J'ai poursuivi ce double objectif à travers l'étude de plusieurs sites aux fonctionnements contrastés en termes de climat et de niveau d'anthropisation : deux sites dans le Sud-Ouest de la France, un site en savane Sénégalaise et un site agricole proche du Lac Victoria au Kenya. En m'appuyant sur les données issues des deux sites Sud-Ouest, j'ai mis en place une nouvelle méthodologie pour reconstruire les données manquantes de séries temporelles d'émission journalières de N2O issues de ces sites. Celle-ci combine à la fois la traditionnelle méthode de l'interpolation linéaire avec la méthode des réseaux de neurones. Le niveau des résultats obtenus montre que cette méthodologie pourrait servir de référence à l'avenir. L'analyse des séries complètes montre que les cultures de maïs irrigué possèdent un potentiel élevé d'émissions de N2O et que le travail du sol, la minéralisation de printemps et la fertilisation azotée, lorsqu'ils sont combinés à de la pluie et à de l'irrigation ont un fort potentiel d'émission de N2O dont l'intensité varie en fonction de la couverture végétale. La quantification de l'impact de ces différents facteurs a permis de proposer une méthode d'estimation d'émissions de N2O plus performante que la méthode Tier 1 du GIEC. En région africaine, j'ai étudié les émissions de N2O du site de savane sénégalaise et des sites agricoles au Kenya en m'appuyant sur des mesures et sur le modèle STEP-GENDEC-N2O pour le site de savane. Le contenu en eau du sol s'est révélé être le facteur d'influence le plus important des émissions de N2O à l'échelle de la saison. J'ai mis en place une simulation régionale avec le modèle RegCM-CLM sur un domaine comprenant l'ensemble des sites. Ce travail a mis en avant la complexité de la modélisation des processus biogéochimiques du sol et la difficulté d'utiliser une paramétrisation universelle pour des climats tempérés et tropicaux. Ce travail de thèse a montré l'existence d'interactions complexes entre les principaux facteurs d'influence des émissions de N2O sur les régions étudiées.[...]
... Biomass burning is frequently used as land clearing method for livestock and agricultural activities; however, it causes negative impacts by increasing GHG emissions (i.e. N 2 O), among other gases (including nitrogen oxides -NO x ), which affect both nitrogen and carbon dioxide cycles (Castellanos et al., 2014;Crutzen et al., 2016;Weitz et al., 1998). Biomass burning has been associated with deforestation in many LA countries, and it is undoubtedly an important source of global N 2 O emissions (Chuvieco et al., 2008;Keller et al., 1993). ...
Reactive nitrogen has both positive and negative effects on environment and human health. The use of nitrogen fertilization enabled raising crops and livestock to feed an increasing world population, but at the same time resulted in a succession of unwanted impacts occurring through air, soil, and water, with detrimental consequences for all mankind. Nitrogen pollution is one of Latin America's most widespread and challenging environmental problems and is caused due to excess of nitrogen emissions from productive activities, especially agriculture, to attend a growing demand for food and energy. Here, we develop a conceptual framework of nitrogen emissions in Latin America to better understand the complexity of nitrogen dynamics in the region, the diverse drivers, and potential harms to environment and human health, as well as to support the formulation of adequate mechanisms to deal with the adverse impacts while increasing the benefits. Thus, our objective was to generate a functional tool not just for nitrogen scientists, but also for decision and policy makers. Using Brazil as an example, our main finding was that the increase in N emissions is due to demand drivers (demand for food, energy, and housing, connected with socioeconomic factors), while preparing and implementing a successful response to solve the N pollution problem depends entirely on the structural drivers (political and institutional factors, as governance issues). We highlighted the crucial role of political decision and institutional forcefulness in designing and implementing suitable policy instruments to handle the duality of nitrogen use. This finding prompts us to rethink about the (often non-existent) policy responses and the challenge for Latin American countries to deal with the nitrogen dilemma, “too much or too little of a very important nutrient”.
... Clearing and burning of tropical forests for use as cropland can lead to transitory increases of mineral N, available C and N 2 O emissions that last for several days, followed by elevated N 2 O emissions that can last for weeks until crops start competing with N 2 O-producing microorganisms for available N (reF. 107 ). The progressive declines in SOC and available N during the first years following deforestation 70,84 eventually lead to lower soil N 2 O fluxes, especially in unfertilized agricultural systems, relative to the original forest 125 . ...
Soils under natural, tropical forests provide essential ecosystem services that have been shaped by long-term soil–vegetation feedbacks. However, deforestation of tropical forest, with a net rate of 5.5 million hectares annually in 2010–2015, profoundly impacts soil properties and functions. Reforestation is also prominent in the tropics, again altering the state and functioning of the underlying soils. In this Review, we discuss the substantial changes in dynamic soil properties following deforestation and during reforestation. Changes associated with deforestation continue for decades after forest clearing eventually extend to deep subsoils and strongly affect soil functions, including nutrient storage and recycling, carbon storage and greenhouse gas emissions, erosion resistance and water storage, drainage and filtration. Reforestation reverses many of the effects of deforestation, mainly in the topsoil, but such restoration can take decades and the resulting soil properties still deviate from those under natural forests. Improved management of soil organic matter in converted land uses can moderate or reduce the ecologically deleterious effects of deforestation on soils. We emphasize the importance of soil knowledge not only in cross-disciplinary research on deforestation and reforestation but also in developing effective incentives and policies to reduce deforestation.
... Although Livesley et al. (2011) did not detect a difference between burnt and unburnt treatments, they observed a large short-term CH 4 pulse immediately after burning from smoldering ashes. In contrast, other studies found that burning inhibited CH 4 oxidation (Priemé and Christensen, 1999;Weitz et al., 1998), and attributed it to decreases in methanotrophic bacteria populations at the surface soil due to hot fires and increased amounts of NH 4 + , salts and nitrite (NO 2 − ) in the ash. The lack of a fire effect on soil CH 4 fluxes at our sites is not surprising, considering that fire intensities were very low, that most termites live belowground, which would have left them untouched by the fire (Doamba et al., 2014), and that there were no changes in NH 4 + concentrations ( Fig. 1i and j). ...
In this study, we report the impacts woodland savanna burning has on the soil trace gas fluxes in seasonally dry woodland savannas in Burkina Faso. We measured nitrous oxide (N 2 O), nitric oxide (NO), carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes at two ongoing long-term experimental sites (Tiogo and Dindéresso), each included three fire-exclusion plots and four annually burnt plots (0.24–0.25 ha plot size). We measured soil trace gas fluxes using chamber methods before and after fire during the dry season and at the start of and during the wet season. There was considerable volatilization of aboveground biomass C and N during fire, but soil N 2 O, NO, CO 2 and CH 4 fluxes were not significantly influenced following fire events. Instead, soil moisture dynamics were more important in regulating soil CO 2 and N 2 O emissions. The onset of the wet season induced a short-term pulse of N 2 O emissions, when water-filled pore space exceeded 60%. We also detected a short-term pulse of NO emissions, lasting only four hours, following fire. The low soil N-oxide fluxes reflected the sites’ extremely low inorganic N levels in the soil.
... If the grassland receives N fertiliser N 2 O emissions will increase [18,[64][65][66]. Any previous land use change to croplands, generally resulted in high N 2 O emissions (2.8-9.4 kg/ha/year; Table 2; [18,67,68]). However, N 2 O emissions measurements are too few for the tropical mineral soils, especially for oil palm and rubber plantations, to draw firm conclusions at this stage. ...
The increasing global demand for vegetable oils has resulted in a significant increase in the area under oil palm in the tropics during the last couple of decades, and this is projected to increase further. The Roundtable on Sustainable Palm Oil discourages the conversion of peatlands to oil palm and rubber plantations. However, our understanding of the effects on soil organic carbon (SOC) stocks and associated greenhouse gas (GHG) emissions of land use conversion is incomplete, especially for mineral soils under primary forests, secondary forests, rubber and other perennial plantations in the tropics. In this review we synthesised information on SOC stocks and GHG emissions from tropical mineral soils under forest, oil palm and rubber plantations and other agroecosystems across the tropical regions. We found that the largest SOC losses occurred after land use conversion from primary forest to oil palm and rubber plantations. Secondary forest and pasture lands showed lower SOC losses as well as total GHG (CO2, N2O and CH4) emissions when converted to oil palm and rubber plantations. However, due to the limited data available on all three GHG emissions, there remains high uncertainty in GHG emissions estimates, and regional GHG accounting is more reliable. We recommend long-term monitoring of oil palm and other perennial plantations established on tropical mineral soils on different soil types and regions on SOC stock changes and total GHG emissions and evaluate appropriate management practices to optimise production and sustainable economic returns, and minimise environmental impact.
... In this study, we focussed on savanna deforestation and land preparation for agricultural use. These phases result in a series of events that may lead to pulsed GHG emissions that would otherwise be missed or greatly underestimated by episodic measurements taken at a weekly or monthly frequency after an initial treefelling event (Neill et al., 2006;Weitz et al., 1998). We used the eddy covariance methodology as it provides a direct and non-destructive measurement of the net exchange of CO 2 and other GHG gases at high temporal resolution, ranging from 30 min intervals to daily, monthly, seasonal and annual estimates. ...
The clearing and burning of tropical savanna leads to globally significant emissions of greenhouse gases (GHGs); however there is large uncertainty relating to the magnitude of this flux. Australia's tropical savannas occupy the northern quarter of the continent, a region of increasing interest for further exploitation of land and water resources. Land use decisions across this vast biome have the potential to influence the national greenhouse gas budget. To better quantify emissions from savanna deforestation and investigate the impact of deforestation on national GHG emissions, we undertook a paired site measurement campaign where emissions were quantified from two tropical savanna woodland sites; one that was deforested and prepared for agricultural land use and a second analogue site that remained uncleared for the duration of a 22-month campaign. At both sites, net ecosystem exchange of CO2 was measured using the eddy covariance method. Observations at the deforested site were continuous before, during and after the clearing event, providing high-resolution data that tracked CO2 emissions through nine phases of land use change. At the deforested site, post-clearing debris was allowed to cure for 6 months and was subsequently burnt, followed by extensive soil preparation for cropping.
During the debris burning, fluxes of CO2 as measured by the eddy covariance tower were excluded. For this phase, emissions were estimated by quantifying on-site biomass prior to deforestation and applying savanna-specific emission factors to estimate a fire-derived GHG emission that included both CO2 and non-CO2 gases. The total fuel mass that was consumed during the debris burning was 40.9 Mg C ha⁻¹ and included above- and below-ground woody biomass, course woody debris, twigs, leaf litter and C4 grass fuels. Emissions from the burning were added to the net CO2 fluxes as measured by the eddy covariance tower for other post-deforestation phases to provide a total GHG emission from this land use change.
The total emission from this savanna woodland was 148.3 Mg CO2-e ha⁻¹ with the debris burning responsible for 121.9 Mg CO2-e ha⁻¹ or 82 % of the total emission. The remaining emission was attributed to CO2 efflux from soil disturbance during site preparation for agriculture (10 % of the total emission) and decay of debris during the curing period prior to burning (8 %). Over the same period, fluxes at the uncleared savanna woodland site were measured using a second flux tower and over the 22-month observation period, cumulative net ecosystem exchange (NEE) was a net carbon sink of −2.1 Mg C ha⁻¹, or −7.7 Mg CO2-e ha⁻¹.
Estimated emissions for this savanna type were then extrapolated to a regional-scale to (1) provide estimates of the magnitude of GHG emissions from any future deforestation and (2) compare them with GHG emissions from prescribed savanna burning that occurs across the northern Australian savanna every year. Emissions from current rate of annual savanna deforestation across northern Australia was double that of reported (non-CO2 only) savanna burning. However, if the total GHG emission, CO2 plus non-CO2 emissions, is accounted for, burning emissions are an order of magnitude larger than that arising from savanna deforestation. We examined a scenario of expanded land use that required additional deforestation of savanna woodlands over and above current rates. This analysis suggested that significant expansion of deforestation area across the northern savanna woodlands could add an additional 3 % to Australia's national GHG account for the duration of the land use change. This bottom-up study provides data that can reduce uncertainty associated with land use change for this extensive tropical ecosystem and provide an assessment of the relative magnitude of GHG emissions from savanna burning and deforestation. Such knowledge can contribute to informing land use decision making processes associated with land and water resource development.
... 是大气主要的温室气体。人类活动引起的CO 2 、CH 4 和N 2 O等温室气体的排放对全球增温的贡献率达 80%并有不断增加的趋势, 是近50年来驱动气候变 暖的主要原因 (Christiansen et al., 2015)。 土地利用与 土地覆盖变化(LULCC)是影响陆地生态系统碳循环 的一个关键因素 (Willcock et al., 2016)。土地利用与 土地覆盖变化的改变将改变土壤微环境及土壤物理 化学过程和微生物活动, 进而影响土壤温室气体的 产生与排放(Ball et al., 2002;Flechard et al., 2007; 刘慧峰等, 2014)。 森林砍伐是人为引起的一种土地利用变化, 是 影响大气温室气体浓度变化的最重要的驱动因子 (Houghton, 2003)。森林砍伐后, 热带森林土壤有机 质减少7%-54%, 温带森林土壤减少20%-50% (张 金屯, 1998)。对寒带森林和热带雨林的研究发现, 森 林 转 化 为 耕 地 后 , 其 土 壤 CO 2 排 放 通 量 增 加 (Grünzweig et al., 2003;盛浩等, 2010)。而对福建亚 热带季风常绿林、纽约温带季风林和加利福尼亚州 温带森林的研究发现, 森林转变成农田后, 其土壤 CO 2 排放通量显著减少 (Ishizuka et al., 2002;Carlisle et al., 2006;褚金翔和张小全, 2006) (Weitz et al., 1998)。 还有研究发现, 原始林转化成次 生林后, 其土壤N 2 O排放通量下降 (Verchot et al., 1999; ...
Aims It is important to study the effects of land use change and reduced precipitation on greenhouse gas fluxes (CO2, CH4 and N2O) of forest soils.
Methods The fluxes of CO2, CH4 and N2O and their responses to environmental factors of primary forest soil, secondary forest soil and artificial forest soil under a reduced precipitation regime were explored using the static chamber and gas chromatography methods during the period from January to December in 2014.
Important findings Results indicate that CH4 uptake of primary forest soil ((-44.43 ± 8.73) μg C•m-2•h-1) was significantly higher than that of the secondary forest soil ((-21.64 ± 4.86) μg C•m-2•h-1) and the artificial forest soil ((-10.52 ± 2.11) μg C•m-2•h-1). CH4 uptake of the secondary forest soil ((-21.64 ± 4.86) μg C•m-2•h-1) was significantly higher than that of the artificial forest ((-10.52 ± 2.11) μg C•m-2•h-1). CO2 emissions of the artificial forest soil ((106.53 ± 19.33) μg C•m-2•h-1) were significantly higher than that of the primary forest soil ((49.50 ± 8.16) μg C•m-2•h-1) and the secondary forest soil ((63.50 ± 5.35) μg C•m-2•h-1) ( p < 0.01). N2O emissions of the secondary forest soil ((1.91 ± 1.22) μg N•m-2•h-1) were higher than that of the primary forest soil ((1.40 ± 0.28) μg N•m-2•h-1) and the artificial forest soil ((1.01 ± 0.86) μg N•m-2•h-1). Reduced precipitation (-50%) had a significant inhibitory effect on CH4 uptake of the artificial forest soil, while it enhanced CO2 emissions of the primary forest soil and the secondary forest soil. Reduced precipitation had a significant inhibitory effect on CO2 emissions of the artificial forest soil and N2O emissions of the secondary forest ( p < 0.01). Reduced precipitation promotes N2O emissions of the primary forest soil and the artificial forest soil. CH4 uptake of the primary forest and the secondary forest soil increased significantly with the increase of soil temperature under natural and reduced precipitation. CO2 and N2O emission fluxes of the primary forest soil, secondary forest soil and artificial forest soil were positively correlated with soil temperature (p < 0.05). Soil moisture inhibited CH4 uptake of the secondary forest soil and the artificial forest soil (p < 0.05). CO2 emissions of the primary forest soil were significantly positively correlated with soil moisture (p < 0.05). N2O emissions of primary forest soil and secondary forest soil were significantly correlated with the nitrate nitrogen content (p < 0.05). It was implied that reduced precipitation and land use change would have significant effects on greenhouse gas emissions of subtropical forest soils.
... Most likely the low NO and undetectable N2O emissions are related with the low levels of NO3-and nitrification in Cerrado soils, as well as with the high NH4 + -N:NO3 -N ratio found. Nonetheless, the N gases emissions are expected to increase after land use change (Weitz et al., 1998). N conservation in a Namibian savanna soil was also correlated with the low availability of N for nitrification and denitrification; and the use of low amounts of fertilizers did not increase significantly the N2O emissions when compared to the native savanna (Braker et al., 2015). ...
Interactions between soil characteristics and microbiota influence the processes in soil ecosystem, as the terrestrial N is primarily cycled by the microbiota. In the N cycle, nitrification enables plants’ access to nitrate, although N can be lost through nitrate leaching, or N trace gas emission. These N dynamics are being disturbed by climate change, land use modification and the employment of nitrogenous fertilizers. A special interest goes to the largest savanna in South America, the seasonally dry Cerrado biome, where agriculture is changing the biome landscape. Shotgun metagenomics was used to compare the functional attributes of N cycling from the soil microbiota present in two conservation parks of the Cerrado biome, 500 km distant from each other, with varying soil texture and water content. Types of vegetation sampled within each park masked the altitude and distance effects, but all samples showed higher abundance of genes for assimilation of ammonia and ammonification. This corroborates Cerrado literature of ammonia as the main soil N form. In addition, a flooded grassland presented the highest abundance of N fixation genes. Despite the detection of denitrification genes, only two hits for the nitrification process were described. Subsequently, we assessed the impact of soil management on the abundance of Archaea (AOA) and Bacteria (AOB) ammonia oxidizers by quantification of the marker gene (amoA) during different stages of soybean cultivation within the Cerrado. Molecular analysis and classic and isotope techniques exhibited higher content of organic C and NH4+-N during fallow than in the adjacent undisturbed field, and an increase in ammonia oxidizers abundance and nitrification rates in the agricultural soil than in the undisturbed site, with the lowest ammonium/nitrate ratio in tilled soil. AOB abundance was correlated with the increase in pH during soybean cultivation. Further experiments tested the effect of moisture and pH in microcosms containing Cerrado soil, and the possible nitrification inhibition in slurries assembled with a mixture of Cerrado and agricultural soil known for actively oxidizing ammonia (Craibstone soil). Nevertheless, very little NO3- accumulation was observed in Cerrado microcosms with either increasing moisture or pH, despite high ammonia concentration. Nitrification was not inhibited in the mixed soil slurries, and after 21 days it was possible to detect the activity of AOA with the quantification of amoA transcripts. Moreover, DGGE profiles showed a higher number of AOA amoA gene in the Craibstone-only slurries and similar to the mixed slurries, but lower in the Cerrado-only slurries. This was the first assessment of the N metabolism with metagenomic data and qPCR for ammonia oxidation in the Cerrado. However, the little accumulation of NO3- in the field soils or in the treated microcosms or slurries advocates that some other mechanism occurs in this ecosystem to preserve inorganic N preferentially in the NH3 form. Taken these findings together, it is likely that not only the presence of ammonia oxidizers is fundamental for nitrification to occur, but that the microbial community composition and diversity affects the direction in which N process occur in soil. Most possibly there is a correlation between abiotic and biotic conditions that limits the abundance of autotrophic ammonia oxidizers, as for example the competition for NH4+ by plants or heterotrophic microbes or through dissimilatory reduction of NO3- to NH4+.
... The Gaussian patterns of N 2 O emissions against that of CO 2 emissions during the process of fine root decomposition are indirectly supported by a similar pattern of NH 4 þ release and oxidation rate found during the early stages of plant leaf decomposition (Hesselsøe et al., 2001). Our results contribute to the understanding of high N 2 O emissions observed in forests for 1e7 months following disturbances such as hurricanes and deforestation (Steudler et al., 1991;Weitz et al., 1998), or after the installation of bases for N 2 O emission measurements (Keller et al., 2000), which result in the mortality and decomposition of numerous fine roots. ...
