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1.
In-field management practices of corn cob and residue mix (CRM) as a feedstock source for ethanol production can have potential effects on soil greenhouse gas (GHG) emissions. The objective of this study was to investigate the effects of CRM piles, storage in-field, and subsequent removal on soil CO2 and N2O emissions. The study was conducted in 2010–2012 at the Iowa State University, Agronomy Research Farm located near Ames, Iowa (42.0°′N; 93.8°′W). The soil type at the site is Canisteo silty clay loam (fine-loamy, mixed, superactive, calcareous, mesic Typic Endoaquolls). The treatments for CRM consisted of control (no CRM applied and no residue removed after harvest), early spring complete removal (CR) of CRM after application of 7.5 cm depth of CRM in the fall, 2.5 cm, and 7.5 cm depth of CRM over two tillage systems of no-till (NT) and conventional tillage (CT) and three N rates (0, 180, and 270 kg N ha−1) of 32% liquid UAN (NH4NO3) in a randomized complete block design with split–split arrangements. The findings of the study suggest that soil CO2 and N2O emissions were affected by tillage, CRM treatments, and N rates. Most N2O and CO2 emissions peaks occurred as soil moisture or temperature increased with increase precipitation or air temperature. However, soil CO2 emissions were increased as the CRM amount increased. On the other hand, soil N2O emissions increased with high level of CRM as N rate increased. Also, it was observed that NT with 7.5 cm CRM produced higher CO2 emissions in drought condition as compared to CT. Additionally, no differences in N2O emissions were observed due to tillage system. In general, dry soil conditions caused a reduction in both CO2 and N2O emissions across all tillage, CRM treatments, and N rates. 相似文献
2.
Quantitative information is critical in policy making related to the roles of agriculture in greenhouse gas (GHG) emissions. A Unit Response (UR) curve method was developed in this study for modeling GHG emissions from soil after liquid manure applications. The emission sources (soils and liquid manures) are conceptualized as a set of linear cascaded chambers with equal storage-release coefficients, or two sets of cascaded chambers in parallel, each set having equal storage-release coefficients. The model is based on a two-parameter gamma distribution. Three parameters in this model denote the number of cascaded chambers, the storage-release coefficient, and the multiplier (referring to the total net emissions) added to the gamma distribution function. These parameters can be expressed as functions of site-specific background fluxes without applications of manure/fertilizer. The method was assessed with emissions data from five fields in Washington State. The results showed that at the WSU and Lynden sites, the average excess CH4 emissions due to manure applications were 0.39 and 0.17 kg CH4–C ha? 1, respectively; the average excess CO2 emissions were 216.50 and 25.20 kg CO2–C ha? 1, respectively; and the average excess N2O were 0.37 and 0.03 kg N2O–N ha? 1, respectively. The UR method may fill the gaps between field measurements, simple emission factor (EF) method, and complex process-oriented models. This method has the potential to be used for estimating additional GHG emissions due to manure/fertilizer applications. 相似文献
3.
Fertilization with animal residues together with no-tillage is being widely used in dryland Mediterranean agriculture. The aim of this work is to assess the potential impacts of these combined management practices on oribatid mite species, and to evaluate their potential use as bioindicators of soil disturbances. From an experiment established ten years ago, eight fertilization treatments (including minerals or pig slurries), all combined with minimum tillage (MT) and no-tillage (NT), were studied. Four of these combinations were sampled three times during the winter cereal cropping season. The rest, and a neighbouring oak forest, were only sampled close to the end of the season (May). In total, 34 oribatid species and 4140 individuals were recovered. Oribatid abundance responded positively (p < 0.05) to the reduction of tillage intensity (NT) and marginally (p < 0.1) to slurry fertilization at sowing (close to maximum legislation allowed rate: <210 kg N ha−1 yr−1). At this slurry rate, Shannon index of diversity varied through the season, and was higher in May in MT than in NT plots. The Berger–Parker index of abundance signals plots without slurries as the most disturbed (compared with the forest). Nitrogen slurry over-fertilization reduced abundance of Oribatula (Zygoribatula) connexa connexa , but the impact on the most relevant species depended on the tillage system: Epilohmannia cylindrica cylindrica dominated in MT plots; under NT it was balanced by Tectocepheus velatus sarekensis and Passalozetes (Passalozetes) africanus. Scutovertex sculptus is also very negatively affected by tillage. Oribatida are a good target for the biological indication of soil disturbances associated to agricultural management. 相似文献
4.
Relationships between CH4, CO2, and N2O emissions were studied in soil that had been freshly amended with large deposits of cattle wastes. Dynamics of CH4, CO2, and N2O emissions were investigated with flux chambers from early April to late June 2011, during the 3 months following cattle overwintering at the site. This 81-day field study was supplemented with soil analyses of available C and N content and measurement of denitrification activity. In a more detailed field investigation, the daily time course of emissions was determined. The field research was complemented with a laboratory experiment that focused on the short-term time course of N2O and CH4 production in artificially created anoxic soil microsites. The following hypotheses were tested: (i) a large input of C (and N and other nutrients) in cattle manure creates conditions suitable for methanogenesis, and therefore overwintering areas can produce large amounts of CH4; (ii) N2O is produced and emitted until the level of mineral N decreases, while the level of CH4 production is low; and (iii) production of CH4 is greater when N immobilization decreases the level of NO3− in soil. N2O emissions were relatively large during the first 3 weeks, then peaked (at ca. 4000 μg N2ON m−2 h−1) and soon decreased to almost zero; the changes were related to the mineral and soluble organic N content in soil. CH4 fluxes were large, though variable, in the first 2 months (600–3000 μg CH4C m−2 h−1) and were independent of C and N availability. Although time courses differed for CH4 and N2O, a negative relationship between N2O and CH4 emissions was not detected. Contrary to CH4 and N2O fluxes, CO2 emissions progressively increased to ca. 300 mg CO2C m−2 h−1 at the end of the field study and were closely related to air and soil temperatures. Diurnal measurements revealed significant correlations between temperature and emissions of CH4, N2O, and CO2. Addition of C to soil during anaerobic incubation increased the production and consumption of N2O and supported the emission of CH4. The results suggest that rapid denitrification significantly contributes to the exhaustion of oxidizing agents and helps create microsites supporting methanogenesis in otherwise N2O-producing upland soil. The results also indicate that accurate estimate of gas fluxes in animal-impacted grassland areas requires assessment of both diurnal and long-term changes in CH4, CO2, and N2O emissions. 相似文献
5.
Marine ecosystems are a known net source of greenhouse gases emissions but the atmospheric gas fluxes, particularly from the mangrove swamps occupying inter-tidal zones, are characterized poorly. Spatial and seasonal fluxes of nitrous oxide (N2O) and carbon dioxide (CO2) from soil in Mai Po mangrove swamp in Hong Kong, South China and their relationships with soil characteristics were investigated. The N2O fluxes averaged from 32.1 to 533.7 μg m−2 h−1 and the CO2 fluxes were between 10.6 and 1374.1 mg m−2 h−1. Both N2O and CO2 fluxes in this swamp showed large spatial and seasonal variations. The fluxes were higher at the landward site than the foreshore bare mudflat, and higher fluxes were recorded in warm, rather than cold, seasons. The landward site had the highest content of soil organic carbon (OC), total Kjeldahl nitrogen (TKN), nitrate (NO3−–N) and total phosphorus (TP), while the bare mudflat had the highest ammonium nitrogen (NH4+–N) concentration and soil denitrification potential activity. The N2O flux was related, positively, to CO2 flux. Soil NO3−–N and TP increased N2O flux, while soil OC and TP concentrations contributed to the CO2 flux. The results indicated that the Mai Po mangrove swamp emitted significant amounts of greenhouse gases, and the N2O emission was probably due to soil denitrifcation. 相似文献
6.
《Applied soil ecology》2005,28(3):247-257
Carbon dioxide emissions from soils beneath canopies of two Mediterranean plants, Artemisia absinthium L. and Festuca pratensis Huds. cv. Demeter, were monitored over a 7-day period that included an artificial precipitation event of 4 cm. The experiments were conducted using 0.2 m3 soil microcosms inside greenhouses with CO2 concentrations of either 360 or 500 μmol mol−1. Carbon dioxide flux from the soil surface, as calculated using a diffusive transport model agreed well with CO2 flux measurements made using a dynamic flow system. Soil CO2 emissions did not differ significantly between the 360 and 500 μmol mol−1 CO2 treatments when soils were dry (volumetric soil moisture content ≤9%). A simulated precipitation event caused an immediate exhalation of CO2 from soil, after which CO2 emissions declined slightly and remained constant for approximately 36 h. CO2 emissions from soil microcosms with F. pratensis plants growing in 500 μmol mol−1 CO2 then rose to levels that were significantly greater than CO2 emissions from soils in the microcosms exposed to 360 μmol mol−1 CO2. For A. absinthium growing in 500 μmol mol−1 CO2, the rise in soil CO2 emissions following the wetting event was not significantly greater than emissions from soils with A. absinthium growing under 360 μmol mol−1 CO2. A. absinthium above ground biomass increased by 46.1 ± 17.9% (mean ± S.E., n = 4, P ≤ 0.05). Above ground biomass did not significantly increase for F. pratensis (14.4 ± 6.5%, P ≥ 0.10). Root biomass, on the other hand, increased for both species; by 50.6 ± 17.9% (P ≤ 0.05) for A. absinthium and by 55.9 ± 12.7% (P ≤ 0.05) for F. pratensis. Our results demonstrate two events following precipitation onto dry soils, an immediate release of CO2 followed by a gradual increase from enhanced biological activity The gradual increase was greater for the herbaceous ruderal perennial F. pratensis under elevated CO2. 相似文献
7.
《Applied soil ecology》2011,48(3):221-225
The impact of tillage practices on microbial N transformations in Vertisols is poorly understood and data from long-term field experiments are scarce, particularly in semiarid regions. We evaluated the effects of traditional tillage (TT) vs no-tillage (NT) on denitrification in a long-term field experiment under a rainfed crop rotation system (cereal-sunflower-legumes) on a Vertisol (SW Spain). In general, the abundance of denitrifiers and the respective potential denitrification rates was higher under NT compared to TT during the vegetation period, but not after harvesting. However differences in denitrifier numbers were within the same order of magnitude (0.5–3 × 107 copies g soil dw). The abundance of nitrite reducers and N2O reducers was relatively similar. In addition, N2O/N2 ratios between 1 and 2 were found for both treatments. These results emphasize that NT has a limited impact on denitrification in Vertisols under fertilizer regime and legume-crop rotation and thus losses of N2O are expected to be comparable to those of traditional tillage systems. 相似文献
8.
Silvia M. Contreras-Ramos Dioselina Álvarez-Bernal Joaquín A. Montes-Molina Oswald Van Cleemput Luc Dendooven 《Applied soil ecology》2009,41(1):69-76
Soils in Mexico are often contaminated with hydrocarbons and addition of waste water sludge and earthworms accelerates their removal. However, little is known how contamination and subsequent bioremediation affects emissions of N2O and CO2. A laboratory study was done to investigate the effect of waste water sludge and the earthworm Eisenia fetida on emission of N2O and CO2 in a sandy loam soil contaminated with the polycyclic aromatic hydrocarbons (PAHs): phenanthrene, anthracene and benzo(a)pyrene. Emissions of N2O and CO2, and concentrations of inorganic N (ammonium (NH4+), nitrite (NO2?) nitrate (NO3?)) were monitored after 0, 5, 24, 72 and 168 h. Adding E. fetida to the PAHs contaminated soil increased CO2 production rate significantly 2.0 times independent of the addition of sludge. The N2O emission rate from unamended soil expressed on a daily base was 5 μg N kg?1 d?1 for the first 2 h and increased to a maximum of 325 μg N kg?1 d?1 after 48 h and then decreased to 10 μg N kg?1 d?1 after 168 h. Addition of PAHs, E. fetida or PAHs + E. fetida had no significant effect on the N2O emission rate. Adding sludge to the soil sharply increased the N2O emission rate to >400 μg N kg?1 d?1 for the entire incubation with a maximum of 1134 μg N kg?1 d?1 after 48 h. Addition of E. fetida, PAHs or PAHs + E. fetida to the sludge-amended soil reduced the N2O emission rate significantly compared to soil amended with sludge after 24 h. It was found that contaminating soil with PAHs and adding earthworms had no effect on emissions of N2O. Emission of N2O, however, increased in sludge-amended soil, but addition of earthworms to this soil and contamination reduced it. 相似文献
9.
Benedikt J. Fest Stephen J. Livesley Matthias Drösler Eva van Gorsel Stefan K. Arndt 《Agricultural and Forest Meteorology》2009,149(3-4):393-406
Forests are the largest C sink (vegetation and soil) in the terrestrial biosphere and may additionally provide an important soil methane (CH4) sink, whilst producing little nitrous oxide (N2O) when nutrients are tightly cycled. In this study, we determine the magnitude and spatial variation of soil–atmosphere N2O, CH4 and CO2 exchange in a Eucalyptus delegatensis forest in New South Wales, Australia, and investigate how the magnitude of the fluxes depends on the presence of N2-fixing tree species (Acacia dealbata), the proximity of creeks, and changing environmental conditions. Soil trace gas exchange was measured along replicated transects and in forest plots with and without presence of A. dealbata using static manual chambers and an automated trace gas measurement system for 2 weeks next to an eddy covariance tower measuring net ecosystem CO2 exchange. CH4 was taken up by the forest soil (?51.8 μg CH4-C m?2 h?1) and was significantly correlated with relative saturation (Sr) of the soil. The soil within creek lines was a net CH4 source (up to 33.5 μg CH4-C m?2 h?1), whereas the wider forest soil was a CH4 sink regardless of distance from the creek line. Soil N2O emissions were small (<3.3 μg N2O-N m?2 h?1) throughout the 2-week period, despite major rain and snowfall. Soil N2O emissions only correlated with soil and air temperature. The presence of A. dealbata in the understorey had no influence on the magnitude of CH4 uptake, N2O emission or soil N parameters. N2O production increased with increasing soil moisture (up to 50% Sr) in laboratory incubations and gross nitrification was negative or negligible as measured through 15N isotope pool dilution.The small N2O emissions are probably due to the limited capacity for nitrification in this late successional forest soil with C:N ratios >20. Soil–atmosphere exchange of CO2 was several orders of magnitude greater (88.8 mg CO2-C m?2 h?1) than CH4 and N2O, and represented 43% of total ecosystem respiration. The forest was a net greenhouse gas sink (126.22 kg CO2-equivalents ha?1 d?1) during the 2-week measurement period, of which soil CH4 uptake contributed only 0.3% and N2O emissions offset only 0.3%. 相似文献
10.
The increasing frequency of periodic droughts followed by heavy rainfalls is expected for this current century, but little is known about the effects of wetting intensity on the in situ biogenic greenhouse gas (GHG) fluxes of forest soils and soil microbial biomass. To gain new insights into the underlying mechanisms responsible for wetting-induced GHG fluxes in situ, rain simulation field experiments during a natural prolonged drought period were done under a temperate forest in northeast China. The intensity of rainfall-induced CO2 pulses increased from 0.84 to 2.08 g CO2–C m? 2 d? 1 with the intensity of wetting up to ca. 80% water-filled pore space, which coincided with an increase in soil microbial biomass and with a decrease in soil labile organic C following wetting. Methane uptake rates decreased from 1.76 to 0.87 mg CH4–C m? 2 d? 1 with the intensity of wetting. Wetting dry forest floor increased N2O fluxes from 6.2 to 25.9 μg N2O–N m? 2 d? 1, but there was no significant difference between all experimental wetted plots. The rainfall-induced N2O pulses with increasing wetting intensity were opposite to that of the CO2 pulses, showing a maximum response at the lowest wetting intensity. An analysis of the temperature sensitivity of GHG fluxes indicated that temperature had an increased effect on the in situ CO2 flux and CH4 uptake, respectively, under wetted and dry conditions. The global warming potential of GHG fluxes and Q10 value of the temperature response of CO2 fluxes increased linearly with wetting intensity. The results indicate that the rainfall-induced soil CO2 pulse is mainly due to enhanced microbial consumption on substrates and highlight the complex nature of belowground C-cycling responses to climate change in northeast China forests that normally experience periodic droughts followed by heavy rainfalls over the year. 相似文献
11.
《Applied soil ecology》2007,35(2-3):219-229
Rising atmospheric CO2 concentrations are expected to have marked impacts on the carbon (C) turnover in agro-ecosystems through increased plant photosynthetic rates, leading to an enhanced biomass, and wider plant C/N ratios. Through increased carbon allocation below-ground, as well as through changed litter quality, CO2 enrichment will indirectly affect soil faunal communities. In the present study we investigated how elevated atmospheric CO2 and two different levels of N fertilization may affect abundance and diversity of collembolans, as important catalysts in decomposition processes, within an agro-ecosystem under winter wheat cultivation. The investigations were carried out in 2002 within a field experiment using the “Free Air CO2 Enrichment” technique (FACE) at the Federal Agricultural Research Centre (Braunschweig, Germany). Stable C-isotopic analysis of collembolans, soil, and crops gave insight into C translocation. During our investigations δ13C values of all components analysed were significantly more negative under FACE compared to ambient air conditions. Stable C-isotopic signatures of collembolans were similar to those of soil under ambient air, but in between those of soil and roots under elevated CO2 conditions. Our results revealed significant effects of both treatments (CO2 enrichment and N fertilization) on density and species diversity of collembolans. Overall, collembolans were stimulated under elevated CO2 conditions, showing an increased abundance of more than 50% (11 240 ind m−2) as well as a higher biodiversity (Shannon Weaver index = 2.5; evenness = 0.75) compared to ambient air conditions (7520 ind m−2; Shannon Weaver index = 2.2; evenness = 0.72). With regard to N supply, a decrease of about 20–30% under CO2 enrichment and 45–55% under ambient air conditions in collembolan abundance with no alteration in diversity was recorded under reduced N fertilization. The observed impacts were species-specific. 相似文献
12.
Laura Sánchez-Martín Antonio Vallejo Jan Dick Ute M Skiba 《Soil biology & biochemistry》2008,40(1):142-151
Contradictory effects of simultaneous available organic C and N sources on nitrous oxide (N2O), carbon dioxide (CO2) and nitric oxide (NO) fluxes are reported in the literature. In order to clarify this controversy, laboratory experiments were conduced on two different soils, a semiarid arable soil from Spain (soil I, pH=7.5, 0.8%C) and a grassland soil from Scotland (soil II, pH=5.5, 4.1%C). Soils were incubated at two different moisture contents, at a water filled pore space (WFPS) of 90% and 40%. Ammonium sulphate, added at rates equivalent to 200 and 50 kg N ha?1, stimulated N2O and NO emissions in both soils. Under wet conditions (90% WFPS), at high and low rates of N additions, cumulative N2O emissions increased by 250.7 and 8.1 ng N2O–N g?1 in comparison to the control, respectively, in soil I and by 472.2 and 2.1 ng N2O–N g?1, respectively, in soil II. NO emissions only significantly increased in soil I at the high N application rate with and without glucose addition and at both 40% and 90% WFPS. In both soils additions of glucose together with the high N application rate (200 kg N ha?1) reduced cumulative N2O and NO emissions by 94% and 55% in soil I, and by 46% and 66% in soil II, respectively. These differences can be explained by differences in soil properties, including pH, soil mineral N and total and dissolved organic carbon content. It is speculated that nitrifier denitrification was the main source of NO and N2O in the C-poor Spanish soil, and coupled nitrification–denitrification in the C-rich Scottish soil. 相似文献
13.
Carolina Castro Silva Marco Luna Guido Juan Manuel Ceballos Rodolfo Marsch Luc Dendooven 《Soil biology & biochemistry》2008,40(7):1813-1822
Soil of the former lake Texcoco is alkaline saline with pH often >10 and electrolytic conductivity (EC) >70 dS m?1 with rapidly changing water contents. Little is known how fertilizing this area with urea to vegetate the soil would affect emissions of carbon dioxide (CO2) and dynamics of N. Texcoco soil with electrolytic conductivity (EC) 2.3 dS m?1 and pH 8.5 (TEXCOCO A soil), EC 2.0 dS m?1 and pH 9.0 (TEXCOCO B soil) and 200 dS m?1 and pH 11.2 (TEXCOCO C soil) was amended with or without urea and incubated at 40% of water holding capacity (WHC), 60% WHC, 80% WHC and 100% WHC, while emissions of nitrous oxide (N2O) and CO2 and dynamics of ammonium (NH4+), nitrite (NO2?) and nitrate (NO3?) were monitored for 7 days. An agricultural soil served as control (ACOLMAN soil). The emission of CO2 increased in the urea amended soil 1.5 times compared to the unamended soil, it was inhibited in TEXCOCO C soil and was >1.2 larger in soil incubated at 40%, 60% and 80% WHC compared to soil incubated at 100% WHC. The emission of N2O increased in soil added with urea compared to the unamended soil, was similar in TEXCOCO A and B soils, but was <0.2 mg N kg?1 soil day?1 in TEXCOCO C soil and generally larger in soil incubated at 60% and 80% WHC compared to soil incubated at 40% and 100% WHC. The water content of the soil had no significant effect on the mean concentration of NH4+, but addition of urea increased it in all soils. The concentration of NO2? was not affected by the water content and the addition of urea except in TEXCOCO A soil where it increased to values ranging between 20 and 40 mg N kg?1. The concentration of NO3? increased in the ACOLMAN, TEXCOCO A and TEXCOCO B soil amended with urea compared to the unamended soil, but not in the TEXCOCO C soil. It decreased with increased water content, but not in TEXCOCO C soil. It was found that the differences in soil characteristics, i.e. soil organic matter content, pH and EC between the soils had a profound effect on soil processes, but even small changes affected the dynamics of C and N in soil amended with urea. 相似文献
14.
Soil N2O emissions can affect global environments because N2O is a potent greenhouse gas and ozone depletion substance. In the context of global warming, there is increasing concern over the emissions of N2O from turfgrass systems. It is possible that management practices could be tailored to reduce emissions, but this would require a better understanding of factors controlling N2O production. In the present study we evaluated the spatial variability of soil N2O production and its correlation with soil physical, chemical and microbial properties. The impacts of grass clipping addition on soil N2O production were also examined. Soil samples were collected from a chronosequence of three golf courses (10, 30, and 100-year-old) and incubated for 60 days at either 60% or 90% water filled-pore space (WFPS) with or without the addition of grass clippings or wheat straw. Both soil N2O flux and soil inorganic N were measured periodically throughout the incubation. For unamended soils, cumulative soil N2O production during the incubation ranged from 75 to 972 ng N g−1 soil at 60% WFPS and from 76 to 8842 ng N g−1 soil at 90% WFPS. Among all the soil physical, chemical and microbial properties examined, soil N2O production showed the largest spatial variability with the coefficient of variation ~110% and 207% for 60% and 90% WFPS, respectively. At 60% WFPS, soil N2O production was positively correlated with soil clay fraction (Pearson's r = 0.91, P < 0.01) and soil NH4+–N (Pearson's r = 0.82, P < 0.01). At 90% WFPS, however, soil N2O production appeared to be positively related to total soil C and N, but negatively related to soil pH. Addition of grass clippings and wheat straw did not consistently affect soil N2O production across moisture treatments. Soil N2O production at 60% WFPS was enhanced by the addition of grass clippings and unaffected by wheat straw (P < 0.05). In contrast, soil N2O production at 90% WFPS was inhibited by the addition of wheat straw and little influenced by glass clippings (P < 0.05), except for soil samples with >2.5% organic C. Net N mineralization in soil samples with >2.5% organic C was similar between the two moisture regimes, suggesting that O2 availability was greater than expected from 90% WFPS. Nonetheless, small and moderate changes in the percentage of clay fraction, soil organic matter content, and soil pH were found to be associated with large variations in soil N2O production. Our study suggested that managing soil acidity via liming could substantially control soil N2O production in turfgrass systems. 相似文献
15.
《Soil biology & biochemistry》2001,33(7-8):1077-1093
We studied soil moisture dynamics and nitrous oxide (N2O) fluxes from agricultural soils in the humid tropics of Costa Rica. Using a split-plot design on two soils (clay, loam) we compared two crop types (annual, perennial) each unfertilized and fertilized. Both soils are of andic origin. Their properties include relatively low bulk density and high organic matter content, water retention capacity, and hydraulic conductivity. The top 2–3 cm of the soils consists of distinct small aggregates (dia. <0.5 cm). We measured a strong gradient of bulk density and moisture within the top 7 cm of the clay soil. Using automated sampling and analysis systems we measured N2O emissions at 4.6 h intervals, meteorological variables, soil moisture, and temperature at 0.5 h intervals. Mean daily soil moisture content at 5 cm depth ranged from 46% water filled pore space (WFPS) on clay in April 1995 to near saturation on loam during a wet period in February 1996. On both soils the aggregated surface layer always remained unsaturated. Soils emitted N2O throughout the year. Mean N2O fluxes were 1.04±0.72 ng N2O-N cm−2 h−1 (mean±standard deviation) from unfertilized loam under annual crops compared to 3.54±4.31 ng N2O-N cm−2 h−1 from the fertilized plot (351 days measurement). Fertilization dominated the temporal variation of N2O emissions. Generally fluxes peaked shortly after fertilization and were increased for up to 6 weeks (‘post fertilization flux’). Emissions continued at a lower rate (‘background flux’) after fertilization effects faded. Mean post-fertilization fluxes were 6.3±6.5 ng N2O-N cm−2 h−1 while the background flux rate was 2.2±1.8 ng N2O-N cm−2 h−1. Soil moisture dynamics affected N2O emissions. Post fertilization fluxes were highest from wet soils; fluxes from relatively dry soils increased only after rain events. N2O emissions were weakly affected by soil moisture during phases of low N availability. Statistical modeling confirmed N availability and soil moisture as the major controls on N2O flux. Our data suggest that small-scale differences in soil structure and moisture content cause very different biogeochemical environments within the top 7 cm of soils, which is important for net N2O fluxes from soils. 相似文献
16.
《Pedobiologia》2014,57(4-6):263-269
Nitrogen (N) availability is an important factor that determines ecosystem productivity and respiration, especially in N-limited alpine ecosystems. However, the magnitude of this response depends on the timing and amounts of N input. Moreover, we have only a limited understanding of the potential effects of the timing of N fertilization on ecosystem carbon (C) and N processes, and activities of the soil microbes. A nitrogen fertilization experiment was conducted in an alpine meadow on the Tibetan Plateau to determine how plant productivity and ecosystem respiration (RE) respond to the timing and amount of N application. In this study, half of the N was added either in the early spring (ES), before the growing season, or in the late fall (LF), after the growing season. All treatments received the other half of the N in mid-July. Three N levels (10, 20, 40 kg N hm−2 yr−1) were used for each of two N treatments, with no N addition used as a control. Plant aboveground biomass, ecosystem respiration (RE) and soil respiration (RS) were measured for the 2011 and 2012 growing seasons. The LF treatment enhanced ecosystem CO2 efflux compared with the ES treatment at high N addition levels, resulting from an increase of soil dissolved organic C (DOC) and soil microbial activity. The ES treatment resulted in increased plant aboveground biomass when compared with LF during both growing seasons, although this increase accounted for little variation in ecosystem and soil respiration. Overall, the ES treatment is likely to increase the ecosystem C pool, while the LF treatment could accelerate ecosystem C cycling, especially for the high N treatment. Our results suggest that supplying N during the early stage of the growing season benefits both forage production and soil C sequestration in this alpine ecosystem. 相似文献
17.
Northern peatlands contain substantial reservoirs of carbon (C). Forestry activities endanger the C storages in some of these areas. While the initial impacts of forestry drainage on peatland greenhouse gas (GHG) balance have been studied, the impacts of other silvicultural practices, e.g. logging residue (LR) retention or removal, are not known. We measured the CH4, N2O and CO2 fluxes between peat soil and atmosphere with and without decomposing LR over three (2002–2004) seasons (May–Oct) following clearfelling in a drained peatland forest, along with the mass loss of LR. Seasonal average CO2 efflux from plots with LR (3070 g CO2 m−2 season−1) was twice as high as that from plots without LR (1447 g CO2 m−2 season−1). Less than 40% of this difference was accounted for by the decay of logging residues (530 g CO2 m−2 season−1), so the majority of the increased CO2 efflux was caused by increased soil organic matter decomposition under the LR. Furthermore LR increased soil N2O fluxes over 3-fold (0.70 g N2O m−2 season−1), compared to plots without LR (0.19 g N2O m−2 season−1), while no change in CH4 emissions was observed. Our results indicate that LR retention in clearfelled peatland sites may significantly increase GHG emissions and C release from the soil organic matter C storage. This would make the harvesting of LR for biofuel more beneficial, in the form of avoided emissions. Further investigations of the sources of CO2 under logging residues are, however, needed to confirm this finding. 相似文献
18.
Hermann F. Jungkunst Heiner Flessa Christoph Scherber Sabine Fiedler 《Soil biology & biochemistry》2008,40(8):2047-2054
Hydromorphic soils should exhibit higher climate change feedback potentials than well aerated soils since soil organic matter (SOM) losses in them are predicted to be much larger than those of well aerated soils. To evaluate a combined feedback relationship between groundwater level (GWL) and total greenhouse gas (GHG) emission, a greenhouse microcosm experiment was performed by exposing three hydromorphic forest soil types that differed in carbon content to three water levels (?40, ?20 and ?5 cm) while plants were excluded. Net GHG fluxes were measured continuously. GHG concentrations plus oxygen were measured in soil air and soil water at different depths. In this study, soil type hardly affected GHG emissions but GWL did. CO2 emissions peaked at GWL of ?40 cm and declined on average to 65 and 33% during GWL at ?20 and ?5 cm, respectively. CH4 emissions showed the opposite pattern having the highest emission rates at GWL of ?5 cm and compared to that on average only ?3 and ?8% during GWL at ?20 and ?40 cm, respectively. The highest mean N2O emissions were detected at the intermediate GWL of ?20 cm, whereas it is reduced on average to 18% for GWL at ?40 cm and at ?5 cm. The highest greenhouse gas emissions (in CO2 equivalents) were calculated for GWL at ?20 cm. During GWL at ?40 cm, CO2 equivalent fluxes were only insignificantly lower. CO2 equivalent fluxes reduced explicitly in mean to 35% with GWL at ?5 cm. The outcome emphasizes that anaerobic SOM decomposition apparently produces a lower warming potential than aerobic SOM decomposition. Undoubtedly, hydromorphic soils have to be considered for climate–carbon feedback scenarios. 相似文献
19.
Anaerobic digestion of organic materials generates residues of differing chemical composition compared to undigested animal manures, which may affect the soil microbial ecosystem differently when used as fertilizers. This study investigated the effects of two biogas residues (BR-A and BR-B) and cattle slurry (CS) applied at rates corresponding to 70 kg NH4+-N ha−1 on bacterial community structure and microbial activity in three soils of different texture (a sandy, a clay and an organic clay soil). 16S rRNA genes were targeted in PCR reactions and bacterial community profiles visualized using terminal restriction fragment length polymorphism. General microbial activity was measured as basal respiration (B-resp), substrate-induced respiration (SIR), specific growth rate (μSIR), metabolic quotient (qCO2) and nitrogen mineralization capacity (NMC). Non-metric multidimensional scaling analysis visualized shifts in bacterial community structure related to microbial functions. There were significant differences in bacterial community structure after 120 days of incubation (+20 °C at 70% of WHC) between non-amended (control) and amended soils, especially in the sandy soil, where CS caused a more pronounced shift than biogas residues. Terminal-restriction fragment (TRF) 307, the predominant peak in CS-amended sandy soil, was identified as possibly Bacillus or Streptococcus. TRF 226, the dominant peak in organic soil amended with BR-B, was classified as Rhodopseudomonas. B-resp significantly increased and SIR decreased in all amendments to organic soil compared with the control, potentially indicating decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass. This was also reflected in an elevated qCO2 in the organic soil. The μSIR level was higher in the sandy soil amended with BR-A than with BR-B or CS, indicating a shift toward species capable of rapidly utilizing glucose. NMC was significantly elevated in the clay and organic soils amended with BR-A and BR-B and in the sandy soil amended with BR-B and CS. Thus, biogas residues and cattle slurry had different effects on the bacterial community structure and microbial activity in the three soils. However, the effects of biogas residues on microbial activities were comparable in magnitude to those of cattle slurry and the bacterial community structure was less affected. Therefore, we do not see any reason not to recommend using biogas residues as fertilizers based on the results presented. 相似文献
20.
《Pedobiologia》2014,57(4-6):277-284
Assimilating atmospheric carbon (C) into terrestrial ecosystems is recognized as a primary measure to mitigate global warming. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) is the dominant enzyme by which terrestrial autotrophic bacteria and plants fix CO2. To investigate the possibility of using RubisCO activity as an indicator of microbial CO2 fixation potential, a valid and efficient method for extracting soil proteins is needed. We examined three methods commonly used for total soil protein extraction. A simple sonication method for extracting soil protein was more efficient than bead beating or freeze–thaw methods. Total soil protein, RubisCO activity, and microbial fixation of CO2 in different agricultural soils were quantified in an incubation experiment using 14C-CO2 as a tracer. The soil samples showed significant differences in protein content and RubisCO activity, defined as nmol CO2 fixed g−1 soil min−1. RubisCO activities ranged from 10.68 to 68.07 nmol CO2 kg−1 soil min−1, which were closely related to the abundance of cbbL genes (r = 0.900, P = 0.0140) and the rates of microbial CO2 assimilation (r = 0.949, P = 0.0038). This suggests that RubisCO activity can be used as an indicator of soil microbial assimilation of atmospheric CO2. 相似文献