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1.
Forests are considered key biomes that could contribute to minimising global warming as they sequester carbon (C) and contribute to mitigate emissions of the potent greenhouse gases (GHG) including nitrous oxide (N 2O), methane (CH 4) and carbon dioxide (CO 2). Management practices are prevalent in forestry, particularly in dryland ecosystems, known to be water and nitrogen (N) limited. Irrigation and fertilisation are thus routinely applied to increase the yield of forest products. However, the contribution of forest management practices to current GHG budgets and consequently to soil net global warming potential (GWP) is still largely unaccounted for, particularly in dryland ecosystems. We quantified the long-term effect (six years) of irrigation and fertilisation and the impact of land-use change, from grassland to a Eucalyptus plantation on N 2O, CH 4 and CO 2 emissions and soil net GWP, within a dryland ecosystem. To identify biotic and abiotic drivers of GHG emissions, we explored the relationship of N 2O, CH 4 and CO 2 fluxes with soil abiotic characteristics and abundance of ammonia-oxidizers, N 2O-reducing bacteria, methanotrophs and total soil bacteria. Our results show that GHG emissions, particularly N 2O and CO 2 are constrained by water availability and both N 2O and CH 4 are constrained by N availability in the soil. We also provide evidence of functional microbial groups being key players in driving GHG emissions. Our findings illustrate that GHG emission budgets can be affected by forest management practices and provide a better mechanistic understanding for future mitigation options. 相似文献
2.
In situ field measurements as well as targeted laboratory studies have shown that freeze–thaw cycles (FTCs) affect soil trace gas fluxes. However, most of past laboratory studies adjusted soil moisture before soil freezing, thereby neglecting that snow cover or water from melting snow may modify effects of FTCs on soil trace gas fluxes. In the present laboratory study with a typical semi-arid grassland soil, three different soil moisture levels (32 %, 41 %, and 50 % WFPS) were established (a) prior to soil freezing or (b) by adding fresh snow to the soil surface after freezing to simulate field conditions and the effect of the melting snow on CO 2, CH 4, and N 2O fluxes during FTCs more realistically. Our results showed that adjusting soil moisture by watering before soil freezing resulted in significantly different cumulative fluxes of CH 4, CO 2, and N 2O throughout three FTCs as compared to the snow cover treatment, especially at a relatively high soil moisture level of 50 % WFPS. An increase of N 2O emissions was observed during thawing for both treatments. However, in the watering treatment, this increase was highest in the first thawing cycle and decreased in successive cycles, while in the snow cover treatment, a repetition of the FTCs resulted in a further increase of N 2O emissions. These differences might be partly due to the different soil water dynamics during FTCs in the two treatments. CO 2 emissions were a function of soil moisture, with emissions being largest at 50 % WFPS and smallest at 32 % WFPS. The largest N 2O emissions were observed at WFPS values around 50 %, whereas there were only small or negligible N 2O emissions from soil with relatively low soil water content, which indicates that a threshold value of soil moisture might exist that triggers N 2O peaks during thawing. 相似文献
3.
Agricultural soils are important sources of greenhouse gases (GHGs). Soil properties and environmental factors have complex interactions which influence the dynamics of these GHG fluxes. Four arable and five grassland soils which represent the range of soil textures and climatic conditions of the main agricultural areas in the UK were incubated at two different moisture contents (50 or 80% water holding capacity) and with or without inorganic fertiliser application (70 kg N ha −1 ammonium nitrate) over 22 days. Emissions of N 2O, CO 2 and CH 4 were measured twice per week by headspace gas sampling, and cumulative fluxes were calculated. Multiple regression modelling was carried out to determine which factors (soil mineral N, organic carbon and total nitrogen contents, C:N ratios, clay contents and pH) that best explained the variation in GHG fluxes. Clay, mineral N and soil C contents were found to be the most important explanatory variables controlling GHG fluxes in this study. However, none of the measured variables explained a significant amount of variation in CO 2 fluxes from the arable soils. The results were generally consistent with previously published work. However, N 2O emissions from the two Scottish soils were substantially more sensitive to inorganic N fertiliser application at 80% water holding capacity than the other soils, with the N 2O emissions being up to 107 times higher than the other studied soils. 相似文献
4.
A laboratory investigation was performed to compare the fluxes of dinitrogen (N 2), N 2O and carbon dioxide (CO 2) from no-till (NT) and conventional till (CT) soils under the same water, mineral nitrogen and temperature status. Intact soil cores (0-10 cm) were incubated for 2 weeks at 25 °C at either 75% or 60% water-filled pore space (WFPS) with 15N-labeled fertilizers (100 mg N kg −1 soil). Gas and soil samples were collected at 1-4 day intervals during the incubation period. The N 2O and CO 2 fluxes were measured by a gas chromatography (GC) system while total N 2 and N 2O losses and their 15N mole fractions in the soil mineral N pool were determined by a mass spectrometer. The daily accumulative fluxes of N 2 and N 2O were significantly affected by tillage, N source and soil moisture. We observed higher ( P<0.05) fluxes of N 2+N 2O, N 2O and CO 2 from the NT soils than from the CT soils. Compared with the addition of nitrate (NO 3−), the addition of ammonium (NH 4+) enhanced the emissions of these N and C gases in the CT and NT soils, but the effect of NH 4+ on the N 2 and/or N 2O fluxes was evident only at 60% WFPS, indicating that nitrification and subsequent denitrification contributed largely to the gaseous N losses and N 2O emission under the lower moisture condition. Total and fertilizer-induced emissions of N 2 and/or N 2O were higher ( P<0.05) at 75% WFPS than with 60% WFPS, while CO 2 fluxes were not influenced by the two moisture levels. These laboratory results indicate that there is greater potential for N 2O loss from NT soils than CT soils. Avoiding wet soil conditions (>60% WFPS) and applying a NO 3− form of N fertilizer would reduce potential N 2O emissions from arable soils. 相似文献
5.
We conducted laboratory incubation experiments to elucidate the influence of forest type and topographic position on emission and/or consumption potentials of nitrous oxide (N 2O) and methane (CH 4) from soils of three forest types in Eastern Canada. Soil samples collected from deciduous, black spruce and white pine forests were incubated under a control, an NH 4NO 3 amendment and an elevated headspace CH 4 concentration at 70% water-filled pore space (WFPS), except the poorly drained wetland soils which were incubated at 100% WFPS. Deciduous and boreal forest soils exhibited greater potential of N 2O and CH 4 fluxes than did white pine forest soils. Mineral N addition resulted in significant increases in N 2O emissions from wetland forest soils compared to the unamended soils, whereas well-drained soils exhibited no significant increase in N 2O emissions in-response to mineral N additions. Soils in deciduous, boreal and white pine forests consumed CH 4 when incubated under an elevated headspace CH 4 concentration, except the poorly drained soils in the deciduous forest, which emitted CH 4. CH 4 consumption rates in deciduous and boreal forest soils were twice the amount consumed by the white pine forest soils. The results suggest that an episodic increase in reactive N input in these forests is not likely to increase N 2O emissions, except from the poorly drained wetland soils; however, long-term in situ N fertilization studies are required to validate the observed results. Moreover, wetland soils in the deciduous forest are net sources of CH 4 unlike the well-drained soils, which are net sinks of atmospheric CH 4. Because wetland soils can produce a substantial amount of CH 4 and N 2O, the contribution of these wetlands to the total trace gas fluxes need to be accounted for when modeling fluxes from forest soils in Eastern Canada. 相似文献
6.
We studied the effects of soil management and changes of land use on soils of three adjacent plots of cropland, pasture and oak ( Quercus robur) forest. The pasture and the forest were established in part of the cropland, respectively, 20 and 40 yr before the study began. Soil organic matter (SOM) dynamics, water-filled pore space (WFPS), soil temperature, inorganic N and microbial C, as well as fluxes of CO 2, CH 4 and N 2O were measured in the plots over 25 months. The transformation of the cropland to mowed pasture slightly increased the soil organic and microbial C contents, whereas afforestation significantly increased these variables. The cropland and pasture soils showed low CH 4 uptake rates (<1 kg C ha −1 yr −1) and, coinciding with WFPS values >70%, episodes of CH 4 emission, which could be favoured by soil compaction. In the forest site, possibly because of the changes in soil structure and microbial activity, the soil always acted as a sink for CH 4 (4.7 kg C ha −1 yr −1). The N 2O releases at the cropland and pasture sites (2.7 and 4.8 kg N 2O-N ha −1 yr −1) were, respectively, 3 and 6 times higher than at the forest site (0.8 kg N 2O-N ha −1 yr −1). The highest N 2O emissions in the cultivated soils were related to fertilisation and slurry application, and always occurred when the WFPS >60%. These results show that the changes in soil properties as a consequence of the transformation of cropfield to intensive grassland do not imply substantial changes in SOM or in the dynamics of CH 4 and N 2O. On the contrary, afforestation resulted in increases in SOM content and CH 4 uptake, as well as decreases in N 2O emissions. 相似文献
7.
It has been well documented that restored wetlands in the Prairie Pothole Region of North America do store carbon. However, the net benefit of carbon sequestration in wetlands in terms of a reduction in global warming forcing has often been questioned because of potentially greater emissions of greenhouse gases (GHGs) such as nitrous oxide (N 2O) and methane (CH 4). We compared gas emissions (N 2O, CH 4, carbon dioxide [CO 2]) and soil moisture and temperature from eight cropland and eight restored grassland wetlands in the Prairie Pothole Region from May to October, 2003, to better understand the atmospheric carbon mitigation potential of restored wetlands. Results show that carbon dioxide contributed the most (90%) to net-GHG flux, followed by CH 4 (9%) and N 2O (1%). Fluxes of N 2O, CH 4, CO 2, and their combined global warming potential (CO 2 equivalents) did not significantly differ between cropland and grassland wetlands. The seasonal pattern in flux was similar in cropland and grassland wetlands with peak emissions of N 2O and CH 4 occurring when soil water-filled pore space (WFPS) was 40-60% and >60%, respectively; negative CH 4 fluxes were observed when WFPS approached 40%. Negative CH 4 fluxes from grassland wetlands occurred earlier in the season and were more pronounced than those from cropland sites because WFPS declined more rapidly in grassland wetlands; this decline was likely due to higher infiltration and evapotranspiration rates associated with grasslands. Our results suggest that restoring cropland wetlands does not result in greater emissions of N 2O and CH 4, and therefore would not offset potential soil carbon sequestration. These findings, however, are limited to a small sample of seasonal wetlands with relatively short hydroperiods. A more comprehensive assessment of the GHG mitigation potential of restored wetlands should include a diversity of wetland types and land-use practices and consider the impact of variable climatic cycles that affect wetland hydrology. 相似文献
8.
Forest soils can be sources or sinks of greenhouse gases (GHGs) depending on soil attributes that affect biomass and activity of soil micro-organisms involved in GHGs fluxes. In this work, we tested the hypothesis that soil physical, chemical and microbiological attributes, under different forests ecosystems, affect the soil GHGs [nitrous oxide (N 2O), carbon dioxide (CO 2) and methane (CH 4)] fluxes. The study was carried out in two locations in southern Brazil in 2019, with three experimental plots of 900 m 2 in native forests of the Atlantic Forest biome and in loblolly pine ( Pinus taeda) plantations. Air samples released from the soil surface were analysed for concentration and flux of CO 2, N 2O and CH 4. Soil samples were analysed for chemical attributes, density (Ds), soil microporosity (MiPs), soil macroporosity (MaPs), total porosity (TP), water-filled pore space (WFPS), microbial biomass carbon (MB-C), basal respiration (BR), microbial (qMic) and metabolic (qCO 2) quotient and activities of soil urease and β-glucosidase enzymes. The seasons influenced the CO 2 and N 2O emissions, probably because of the changes in seasonal conditions. However, native forests consumed more CH 4 than pine plantations. Meanwhile, the native forests presented soils with lower Ds (average 21.5% lower), more TP (average 12.5% higher) and more moisture (average 33% higher), which improved the microbiological attributes of the soil (20% to 60% more MB-C, 67% higher urease activity and 30% higher β-glucosidase activity) compared with pine plantations. Native forests contributed more intensely to CH 4 consumption than pine plantations because they present better physical, chemical and microbiological soil conditions. Therefore, it is possible that forestry practices that improve soil physical attributes are likely to contribute to increase CH 4 consumption, and to reduce GHGs emissions in forest ecosystems. 相似文献
9.
Agriculture significantly contributes to global greenhouse gas (GHG) emissions and there is a need to develop effective mitigation strategies. The efficacy of methods to reduce GHG fluxes from agricultural soils can be affected by a range of interacting management and environmental factors. Uniquely, we used the Taguchi experimental design methodology to rank the relative importance of six factors known to affect the emission of GHG from soil: nitrate (NO 3?) addition, carbon quality (labile and non‐labile C), soil temperature, water‐filled pore space (WFPS) and extent of soil compaction. Grassland soil was incubated in jars where selected factors, considered at two or three amounts within the experimental range, were combined in an orthogonal array to determine the importance and interactions between factors with a L 16 design, comprising 16 experimental units. Within this L 16 design, 216 combinations of the full factorial experimental design were represented. Headspace nitrous oxide (N 2O), methane (CH 4) and carbon dioxide (CO 2) concentrations were measured and used to calculate fluxes. Results found for the relative influence of factors (WFPS and NO 3? addition were the main factors affecting N 2O fluxes, whilst glucose, NO 3? and soil temperature were the main factors affecting CO 2 and CH 4 fluxes) were consistent with those already well documented. Interactions between factors were also studied and results showed that factors with little individual influence became more influential in combination. The proposed methodology offers new possibilities for GHG researchers to study interactions between influential factors and address the optimized sets of conditions to reduce GHG emissions in agro‐ecosystems, while reducing the number of experimental units required compared with conventional experimental procedures that adjust one variable at a time. 相似文献
10.
PurposeForests play a critical role in terrestrial ecosystem carbon cycling and the mitigation of global climate change. Intensive forest management and global climate change have had negative impacts on the quality of forest soils via soil acidification, reduction of soil organic carbon content, deterioration of soil biological properties, and reduction of soil biodiversity. The role of biochar in improving soil properties and the mitigation of greenhouse gas (GHG) emissions has been extensively documented in agricultural soils, while the effect of biochar application on forest soils remains poorly understood. Here, we review and summarize the available literature on the effects of biochar on soil properties and GHG emissions in forest soils. Materials and methodsThis review focuses on (1) the effect of biochar application on soil physical, chemical, and microbial properties in forest ecosystems; (2) the effect of biochar application on soil GHG emissions in forest ecosystems; and (3) knowledge gaps concerning the effect of biochar application on biogeochemical and ecological processes in forest soils. Results and discussionBiochar application to forests generally increases soil porosity, soil moisture retention, and aggregate stability while reducing soil bulk density. In addition, it typically enhances soil chemical properties including pH, organic carbon stock, cation exchange capacity, and the concentration of available phosphorous and potassium. Further, biochar application alters microbial community structure in forest soils, while the increase of soil microbial biomass is only a short-term effect of biochar application. Biochar effects on GHG emissions have been shown to be variable as reflected in significantly decreasing soil N2O emissions, increasing soil CH4 uptake, and complex (negative, positive, or negligible) changes of soil CO2 emissions. Moreover, all of the aforementioned effects are biochar-, soil-, and plant-specific. ConclusionsThe application of biochars to forest soils generally results in the improvement of soil physical, chemical, and microbial properties while also mitigating soil GHG emissions. Therefore, we propose that the application of biochar in forest soils has considerable advantages, and this is especially true for plantation soils with low fertility. 相似文献
11.
Purpose Land use type is an important factor influencing greenhouse gas emissions from soils, but the mechanisms involved in affecting
potential greenhouse gas (GHG) emissions in different land use systems are poorly understood. Since the northern regions of
Canada and China are characterized by cool growing seasons, GHG emissions under low temperatures are important for our understanding
of how soil temperature affects soil C and N turnover processes and associated greenhouse gas emissions in cool temperate
regions. Therefore, we investigated the effects of temperature on the emission of N 2O, CO 2, and CH 4 from typical forest and grassland soils from China and Canada. 相似文献
12.
Soil moisture and nitrogen (N) are two important factors influencing N 2O emissions and the growth of microorganisms. Here, we carried out a microcosm experiment to evaluate effects of soil moisture level and N fertilizer type on N 2O emissions and abundances and composition of associated microbial communities in the two typical arable soils. The abundances and community composition of functional microbes involved in nitrification and denitrification were determined via quantitative PCR (qPCR) and terminal restriction length fragment polymorphism (T-RFLP), respectively. Results showed that N 2O production was higher at 90% water-filled pore (WFPS) than at 50% WFPS. The N 2O emissions in the two soils amended with ammonium were higher than those amended with nitrate, especially at relatively high moisture level. In both soils, increased soil moisture stimulated the growth of ammonia-oxidizing bacteria (AOB) and nitrite reducer ( nirK). Ammonium fertilizer treatment increased the population size of AOB and nirK genes in the alluvial soil, while reduced the abundances of ammonia-oxidizing archaea (AOA) and denitrifiers ( nirK and nosZ) in the red soil. Nitrate addition had a negative effect on AOA abundance in the red soil. Total N 2O emissions were positively correlated to AOB abundance, but not to other functional genes in the two soils. Changed soil moisture significantly affected AOA rather than AOB community composition in both soils. The way and extent of N fertilizers impacted on nitrifier and denitrifier community composition varied with N form and soil type. These results indicate that N 2O emissions and the succession of nitrifying and denitrifying communities are selectively affected by soil moisture and N fertilizer form in the two contrasting types of soil. 相似文献
13.
Soil structure affects microbial activity and thus influences greenhouse gas production and exchange in soil. Structure is variable and increasingly vulnerable to compaction and erosion damage as agriculture intensifies and climate changes. Few studies have specifically related the impact of structure and its variability to greenhouse gas (GHG) emissions over a wide range of soils and management treatments. The objective of this study was to draw from research in Scotland, Japan and New Zealand, which examined how soil structures affected by wheel compaction, animal trampling, tillage and land‐use change influence GHG emissions in order to help identify key controlling properties. Nitrous oxide (N 2O) is the main focus, though carbon dioxide (CO 2), methane (CH 4) and nitric oxide (NO) are included. Gas emissions were measured by using static chambers in the field or incubated intact cores. Poor structure, measured as small relative gas diffusivities and air permeabilities, restricted aeration, resulting in N 2O emission or consumption dependent on mineral nitrogen contents. Structural damage (identifiable using the Visual Evaluation of Soil Structure) was especially important near the soil surface where microsites of microbial activity were exposed and aeration was impaired. Moist, well‐aerated soils favoured CH 4 oxidation and CO 2 exchange. N 2O emissions were not necessarily increased in anaerobic soils because of possible N 2O consumption and microbial adaptation. Soil matric potential, volumetric water content, relative diffusivity, air permeability and water‐filled pore space are relevant indicators for N 2O and CH 4 flux and aeration status. As pore continuity and size are so relevant, pore‐scale models are likely to have an increasing role in understanding mechanisms of GHG production, transport and release. 相似文献
14.
The application of nitrogen (N) fertilizers and liming (CaCO 3) to improve soil quality and crop productivity are regarded as effective and important agricultural practices. However, they may increase greenhouse gas (GHG) emissions. There is limited information on the GHG emissions of tropical soils, specifically when liming is combined with N fertilization. We therefore conducted a full factorial laboratory incubation experiment to investigate how N fertilizer (0 kg N ha −1, 12.5 kg N ha −1 and 50 kg N ha −1) and liming (target pH = 6.5) affect GHG emissions and soil N availability. We focussed on three common acidic soils (two ferralsols and one vertisol) from Lake Victoria (Kenya). After 8 weeks, the most significant increase in cumulative carbon dioxide (CO 2) and nitrous oxide (N 2O) fluxes compared with the unfertilized control was found for the two ferralsols in the N + lime treatment, with five to six times higher CO 2 fluxes than the control. The δ 13C signature of soil-emitted CO 2 revealed that for the ferralsols, liming (i.e. the addition of CaCO 3) was the dominant source of CO 2, followed by urea (N fertilization), whereas no significant effect of liming or of N fertilization on CO 2 flux was found for the vertisol. In addition, the N 2O fluxes were most significantly increased by the high N + lime treatment in the two ferralsols, with four times and 13 times greater N 2O flux than that of the control. No treatment effects on N 2O fluxes were observed for the vertisol. Liming in combination with N fertilization significantly increased the final nitrate content by 14.5%–39% compared with N fertilization alone in all treatment combinations and soils. We conclude that consideration should be given to the GHG budgets of agricultural ferralsols since liming is associated with high liming-induced CO 2 and N 2O emissions. Therefore, nature-based and sustainable sources should be explored as an alternative to liming in order to manage the pH and the associated fertility of acidic tropical soils. 相似文献
15.
Mine‐land reclamation for biomass production is often achieved by means of large applications of N and organic C with amendments that could create soil conditions favorable for N 2O production and emissions. To investigate this possibility, we conducted a laboratory experiment using mine soil collected from an active surface coal mine site near Philipsburg, Pennsylvania. During a 37‐d incubation period, we measured N 2O and CO 2 fluxes from non‐amended soil and from soil amended with ammonium nitrate (L + F), composted poultry manure (Comp), poultry manure alone (Man) and mixed with 3 rates of paper mill sludge (PMS) to obtain carbon to nitrogen ratios of 14, 20 and 27 (Man + PMS14, 20 and 27), each at 60% and 80% water filled pore space (WFPS). Results showed that manure alone leads to a greater emission of N 2O under laboratory conditions than with L + F. However, composting manure effectively reduced the emissions compared to that of L + F despite a large addition of organic C and N. Composted manure‐treated soil emitted less than all other manure‐based treatments at both 60% and 80% WFPS. The emissions were greater from soil amended with the Man + PMS treatments compared to non‐amended and L + F‐amended soil, and it increased during periods of intense microbial activity created by the application of manure and PMS. Higher water content increased emissions particularly during periods of intense microbial activity coupled with inorganic N availability. Cumulative N 2O emissions from manure‐treated soils represented less than 0·1% loss of total applied N. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
16.
Greenhouse gases are known to play an important role in global warming. In this study, we determined the effects of selected soil and climate variables on nitrous oxide (N 2O), methane (CH 4), and carbon dioxide (CO 2) emissions from a tropical grassland fertilized with chicken slurry, swine slurry, cattle slurry, and cattle compost. Cumulative N 2O emissions did not differ between treatments and varied from 29.26 to 32.85 mg N m -2. Similarly, cumulative CH 4 emissions were not significantly different among the treatments and ranged from 6.34 to 57.73 mg CH 4 m -2. Slurry and compost application induced CO 2 emissions that were significantly different from those in the control treatment. The CH 4 conversion factors measured were 0.21%, 1.39%, 4.39%, and 5.07% for cattle compost, chicken slurry, swine slurry, and cattle slurry, respectively, differing from the recommendations of the Intergovernmental Panel on Climate Change (IPCC). The fraction of added N emitted as N 2O was 0.39%, which was lower than the IPCC default value of 2%. Our findings suggest that N 2O emissions could be mitigated by replacing synthetic fertilizer sources with either biofertilizer or compost. Our results indicate the following:N 2O emission was mainly controlled by soil temperature, followed by soil moisture and then soil NH 4+ content; CH 4 fluxes were mainly controlled by soil moisture and chamber headspace temperature; and CO 2 fluxes were mainly controlled by chamber headspace temperature and soil moisture. 相似文献
17.
Soil moisture changes, arising from seasonal variation or from global climate changes, could influence soil nitrogen (N) transformation rates and N availability in unfertilized subtropical forests. A 15?N dilution study was carried out to investigate the effects of soil moisture change (30–90 % water-holding capacity (WHC)) on potential gross N transformation rates and N 2O and NO emissions in two contrasting (broad-leaved vs. coniferous) subtropical forest soils. Gross N mineralization rates were more sensitive to soil moisture change than gross NH 4 + immobilization rates for both forest soils. Gross nitrification rates gradually increased with increasing soil moisture in both forest soils. Thus, enhanced N availability at higher soil moisture values was attributed to increasing gross N mineralization and nitrification rates over the immobilization rate. The natural N enrichment in humid subtropical forest soils may partially be due to fast N mineralization and nitrification under relatively higher soil moisture. In broad-leaved forest soil, the high N 2O and NO emissions occurred at 30 % WHC, while the reverse was true in coniferous forest soil. Therefore, we propose that there are different mechanisms regulating N 2O and NO emissions between broad-leaved and coniferous forest soils. In coniferous forest soil, nitrification may be the primary process responsible for N 2O and NO emissions, while in broad-leaved forest soil, N 2O and NO emissions may originate from the denitrification process. 相似文献
18.
Freezing and thawing influence many physical, chemical and biological processes in soils, including the production of trace gases. We studied the effects of freezing and thawing on three soils, one sandy, one silty and one loamy, on the emissions of N 2O and CO 2. We also studied the effect of varying the water content, expressed as the percentage of the water‐filled pore space (WFPS). Emissions of N 2O during thawing decreased in the order 64% > 55% > 42% WFPS, which suggests that the retardation of the denitrification was more pronounced than the acceleration of the nitrification with increasing oxygen concentration in the soil. However, emissions of N 2O at 76% WFPS were less than at 55% WFPS, which might be caused by an increased ratio of N 2/N 2O in the very moist conditions. The emission of CO 2 was related to the soil water, with the smallest emissions at 76% WFPS and largest at 42% WFPS. The emissions of CO 2 during thawing exceeded the initial CO 2 emissions before the soils were frozen, which suggests that the supply of nutrients was increased by freezing. Differences in soil texture had no marked effect on the N 2O emissions during thawing. The duration of freezing, however, did affect the emissions from all three soils. Freezing the soil for less than 1 day had negligible effects, but freezing for longer caused concomitant increases in emissions. Evidently the duration of freezing and soil water content have important effects on the emission of N 2O, whereas the effects of texture in the range we studied were small. 相似文献
19.
Knowledge is scarce on mineralization of soil organic carbon (SOC) in and N 2O emissions from tundra soils in periods of alternate freezing and thawing. Our objectives were to study the CO 2 and N 2O emissions from two silty gleyic soils formed in different climate zones (a gleyic Cryosol located in the Russian tundra, and a stagnic Gleysol located in an oak stand in central Germany) during freeze-thaw events. Soils were adjusted to a matric potential of −0.2 kPa and emissions were measured in 3-h intervals during an incubation period of 50 days including three freeze-thaw cycles. CO 2 emissions from the German oak forest soil were twofold higher than those of the tundra soil. The ratios of the mean CO 2 production rate before the freezing to the mean CO 2 production rate after thawing ranged from 0.63 to 0.73 for the forest soil and from 0.85 to 0.89 for the tundra soil. The specific CO 2-C production rate (CO 2-C/SOC) was 0.16 for the tundra soil and 0.57 for the forest soil. The results indicate that bioavailability of SOC was markedly smaller in the tundra soil than in the forest soil. Large N 2O emissions were found for the German forest soil, but no N 2O emissions were observed for the tundra soil. The main reason for the absence of N 2O emissions was most likely the negligible availability of nitrate for denitrification. There was some indication that the initial increase in mineralization of SOC induced by freezing and thawing differs between soils from various climatic regions, probably mainly due to a differing bioavailability of the SOC and differing releases of nutrients after thawing. 相似文献
20.
Wood ash has been used to alleviate nutrient deficiencies and acidification in boreal forest soils. However, ash and nitrogen (N) fertilization may affect microbial processes producing or consuming greenhouse gases: methane (CH 4), nitrous oxide (N 2O) and carbon dioxide (CO 2). Ash and N fertilization can stimulate nitrification and denitrification and, therefore, increase N 2O emission and suppress CH 4 uptake rate. Ash may also stimulate microbial respiration thereby enhancing CO 2 emission. The fluxes of CH 4, N 2O and CO 2 were measured in a boreal spruce forest soil treated with wood ash and/or N (ammonium nitrate) during three growing seasons. In addition to in situ measurements, CH 4 oxidation potential, CO 2 production, net nitrification and N 2O production were studied in laboratory incubations. The mean in situ N 2O emissions and in situ CO 2 production from the untreated, N, ash and ash + N treatments were not significantly different, ranging from 11 to 17 μg N 2O m ?2 h ?1 and from 533 to 611 mg CO 2 m ?2 h ?1. However, ash increased the CH 4 oxidation in a forest soil profile which could be seen both in the laboratory experiments and in the CH 4 uptake rates in situ. The mean in situ CH 4 uptake rate in the untreated, N, ash and ash + N plots were 153 ± 5, 123 ± 8, 188 ± 10 and 178 ± 18 μg m ?2 h ?1, respectively. 相似文献
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