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1.
《Applied soil ecology》2009,42(3):269-276
Earthworms can be used to remove polycyclic aromatic hydrocarbons (PAHs) from soil, but this might affect their survival and they might accumulate the contaminants. Sterilized and unsterilized soil was contaminated with phenanthrene (Phen), anthracene (Anth) and benzo(a)pyrene (BaP), added with or without Eisenia fetida, sewage sludge or vermicompost. Survival, growth, cocoon formation and concentrations of PAHs in the earthworms were monitored for 70 days. Addition of sewage sludge to sterilized or unsterilized soil maintained the number of earthworms and their survival was 94%. The addition of sludge significantly increased the weight of earthworms 1.3 times compared to those kept in the unamended soil or in soil amended with vermicompost. The weight of earthworms was significantly lower in sterilized than in unsterilized soil. Cocoons were only detected when sewage sludge was added to unsterilized soil. A maximum concentration of 62.3 μg Phen kg−1 was found in the earthworms kept in sterilized soil amended with vermicompost after 7 days and 22.3 μg Phen kg−1 when kept in the unamended unsterilized soil after 14 days. Concentrations of Phen in the earthworms decreased thereafter and ≤2 μg kg−1 after 28 days. A maximum Anth concentration of 82.5 μg kg−1 was found in the earthworms kept in sterilized soil amended with vermicompost and 45.8 μg Anth kg−1 when kept in the unamended unsterilized soil after 14 days. A maximum concentration of 316 μg BaP kg−1 was found in the earthworms kept in sterilized soil amended with vermicompost after 56 days and 311 μg BaP kg−1 when kept in the unsterilized soil amended with vermicompost after 28 days. The amount of BaP in the earthworm was generally largest after 28 days, but after 70 days still 60 μg kg−1 was found in E. fetida when kept in the sterilized soil amended with sewage sludge. It was found that E. fetida survived in PAHs contaminated soil and accumulated only small amounts of the contaminants, but sewage sludge was required as food for its survival and cocoon production.  相似文献   

2.
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   

3.
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   

4.
Earlier research with endogeic and epigeic earthworm species in loamy arable soil has shown that both earthworm groups can increase nitrous oxide (N2O) emissions, provided that crop residue placement matches the feeding strategy of the earthworm ecological group(s). However, it is not yet clear whether these effects also occur in sandy soils which typically contain less soil organic matter and have low soil aggregation levels. Here, we aimed to quantify N2O emissions as affected by endogeic and/or epigeic earthworm species, and to relate changes in N2O emissions to earthworm-induced changes in soil properties in a sandy soil. A 90 day mesocosm study was conducted with sandy soil and 15N-labeled radish (Raphanus sativus cv. Adagio L.) residue applied on top. Treatments included: (i) no earthworm addition, (ii) addition of the endogeic species Aporrectodea caliginosa (Savigny), (iii) addition of the epigeic species Lumbricus rubellus (Hoffmeister), and (iv) both species combined. An additional treatment was included without earthworms and with residue manually incorporated into the soil. L. rubellus significantly increased cumulative N2O emissions from 228 to 859 μg N2O–N kg?1 (F1,12 = 83.12, P < 0.001), whereas A. caliginosa did not affect N2O emissions. In contrast to earlier studies in loamy soil, no positive interaction between both species with regard to N2O emissions was found. This was probably related to high competition for organic resources in the relatively poor soil and a low potential for stable soil aggregate formation (and associated anaerobic microsites) by endogeic worms in sandy soil. 15N isotope analysis revealed that the activity of L. rubellus significantly increased (F1,12 = 6.20, P = 0.028) the recovery of 15N in the 250–8000 μm size fraction, indicating incorporation of crop residues into the mineral soil. When residues were manually incorporated, N2O emissions were significantly (P < 0.008) lower (509 μg N2O–N kg?1) than when incorporated by L. rubellus. The high N2O emissions in the presence of L. rubellus, when compared to manual mixing, suggest a stimulation of microbial activity and/or changes in the microbial community composition. Insights on the earthworm effects on N2O emission from such soils are discussed.  相似文献   

5.
Nitrous oxide emissions were monitored at three sites over a 2-year period in irrigated cotton fields in Khorezm, Uzbekistan, a region located in the arid deserts of the Aral Sea Basin. The fields were managed using different fertilizer management strategies and irrigation water regimes. N2O emissions varied widely between years, within 1 year throughout the vegetation season, and between the sites. The amount of irrigation water applied, the amount and type of N fertilizer used, and topsoil temperature had the greatest effect on these emissions.Very high N2O emissions of up to 3000 μg N2O-N m?2 h?1 were measured in periods following N-fertilizer application in combination with irrigation events. These “emission pulses” accounted for 80–95% of the total N2O emissions between April and September and varied from 0.9 to 6.5 kg N2O-N ha?1.. Emission factors (EF), uncorrected for background emission, ranged from 0.4% to 2.6% of total N applied, corresponding to an average EF of 1.48% of applied N fertilizer lost as N2O-N. This is in line with the default global average value of 1.25% of applied N used in calculations of N2O emissions by the Intergovernmental Panel on Climate Change.During the emission pulses, which were triggered by high soil moisture and high availability of mineral N, a clear diurnal pattern of N2O emissions was observed, driven by daily changes in topsoil temperature. For these periods, air sampling from 8:00 to 10:00 and from 18:00 to 20:00 was found to best represent the mean daily N2O flux rates. The wet topsoil conditions caused by irrigation favored the production of N2O from NO3? fertilizers, but not from NH4+ fertilizers, thus indicating that denitrification was the main process causing N2O emissions. It is therefore argued that there is scope for reducing N2O emission from irrigated cotton production; i.e. through the exclusive use of NH4+ fertilizers. Advanced application and irrigation techniques such as subsurface fertilizer application, drip irrigation and fertigation may also minimize N2O emission from this regionally dominant agro-ecosystem.  相似文献   

6.
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   

7.
The treatment of manures may improve their agricultural value and environmental quality, for instance with regards to greenhouse gases mitigation and enhancement of carbon (C) sequestration. The present study verified whether different pig slurry treatments (i.e. solid/liquid separation and anaerobic digestion) changed slurry composition. The effect of the slurry composition on N2O and CO2 emissions, denitrification and soil mineral nitrogen (N), after soil incorporation, was also examined during a 58-day mesocosm study. The treatments included a non-treated pig slurry (NT), the solid fraction (SF), and the liquid fraction (LF) of a pig slurry and the anaerobically digested liquid fraction (DG). Finally, a non-fertilized (N0) and a treatment with urea (UR) were also present.The N2O emissions measured represented 4.8%, 2.6%, 1.8%, 1.0% and 0.9% of N supplied with slurry/fertilizer for NT, LF, DG, SF and UR, respectively. Cumulative CO2 emissions ranged from 0.40 g CO2-C kg?1 soil (0.38 Mg CO2-C ha?1) to 0.80 g CO2-C kg?1 soil (0.75 Mg CO2-C ha?1). They were highest for SF (56% of C applied), followed by NT (189% of C applied), LF (337% of C applied) and DG (321% of C applied). Ammonium was detected in the soil for all treatments only at day one, while nitrate concentration increased linearly from day 15 to day 58, at a rate independent of the type of slurry/fertilizer applied. The nitrate recovery at day 58 was 39% of the N applied for NT, 19% for SF, 52% for LF, 67% for DG, and 41% for UR. The solid fraction generally produced higher potential denitrification fluxes (75.3 for SF, 56.7 for NT, 53.6 for LF, 47.7 for DG and 39.7 mg N2O + N2-N kg?1 soil for UR). The high variability of actual denitrification results obfuscated any treatment effect.We conclude that treatment strongly affects slurry composition (mainly its C, fibre and NH4+ content), and hence N2O and CO2 emission patterns as well as denitrification processes and nitrate availability. In particular, the solid fraction obtained after mechanical separation produced the most pronounced difference, while the liquid fraction and the anaerobically digested liquid fraction did not show significant difference with respect to the original slurry for any of the measured parameters. Combining data from the different fractions we showed that separation of slurry leads to reduced N2O emissions, irrespective of whether the liquid fraction is digested or not. Furthermore, our results suggested that the default emission factor for N2O emissions inventory is too low for both the non-treated pig slurry and its liquid fraction (digested or not), and too high for the separated solid fraction and urea.  相似文献   

8.
A phylogenetic analysis of the archaeal community in the soil of the former Lake Texcoco showed that some of the clones identified were affiliated to Archeae that reduce nitrate (NO3?) to nitrite (NO2?) and NO2? to unknown products under aerobic conditions. Previous research suggested that this indeed might occur when an easily decomposable C-substrate is available, but little is known about the factors that control the possible processes involved. The sandy clay loam soil with pH 10 and electrolytic conductivity 56 dS m?1 was spiked with 1000 mg glucose-C kg?1 soil (GLUCOSE pre-treatment), 200 mg NO3?-N kg?1 soil (NITRATE pre-treatment), or left unamended (CONTROL pre-treatment) and conditioned for eight days. Pre-treated soil was then added with 1000 mg glucose-C kg?1 soil and 200 mg NO3?-N kg?1 soil and amended with ammonium (NH4+) (AMM treatment) and l-glutamine (GLUT treatment), acetylene (C2H2) (ACE treatment), oxygen (O2) (OXI treatment), left untreated (CON treatment) or sterilized. No abiotic factors affected concentrations of NH4+, NO2? or NO3?. In the CONTROL pre-treatment, concentration of NO3? decreased 170 mg N kg?1 soil within 72 h, in the GLUCOSE pre-treatment with 182 mg N kg?1 soil within 2 h and in the NITRATE pre-treatment with 272 mg N kg?1 soil within 168 h. Mean concentration of NO2? was 3.2 mg N kg?1 soil in unamended soil, 5.7 mg N kg?1 soil in the CONTROL pre-treatment, but >20 mg kg?1 soil in the GLUCOSE pre-treatment and ≥40 mg kg?1 in the NITRATE pre-treatment. The application of NO3? and glucose increased the mean concentration of NH4+ compared to the unamended soil independently of pre-treatment. It was found that microorganisms in the alkaline saline soil of the former Lake Texcoco can reduce concentrations of NO3? while releasing NO2? under aerobic conditions when an easy decomposable substrate is available without it being directly related to microbial activity and this being more outspoken when glucose or nitrate were previously added.  相似文献   

9.
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   

10.
A 67-day incubation experiment was carried out with a soil initially devoid of any organic matter due to heating, which was amended with sugarcane sucrose (C4-sucrose with a δ13C value of ?10.5‰), inorganic N and an inoculum for recolonisation and subsequently at day 33 with C3-cellulose (δ13C value of ?23.4‰). In this soil, all organic matter is in the microbial biomass or in freshly formed residues, which makes it possible to analyse more clearly the role of microbial residues for decomposition of N-poor substrates. The average δ13C value over the whole incubation period was ?10.7‰ in soil total C in the treatments without C3-cellulose addition. In the CO2 evolved, the δ13C values decreased from ?13.4‰ to ?15.4‰ during incubation. In the microbial biomass, the δ13C values increased from ?11.5‰ to ?10.1‰ at days 33 and 38. At day 67, 36% of the C4-sucrose was left in the treatment without a second amendment. The addition of C3-cellulose resulted in a further 7% decrease, but 4% of the C3-cellulose was lost during the second incubation period. Total microbial biomass C declined from 200 μg g?1 soil at day 5 to 70 μg g?1 soil at day 67. Fungal ergosterol increased to 1.5 μg g?1 soil at day 12 and declined more or less linearly to 0.4 μg g?1 soil at day 67. Bacterial muramic acid declined from a maximum of 35 μg g?1 soil at day 5 to a constant level of around 16 μg g?1 soil. Glucosamine showed a peak value at day 12. Galactosamine remained constant throughout the incubation. The fungal C/bacterial C ratio increased more or less linearly from 0.38 at day 5 to 1.1 at day 67 indicating a shift in the microbial community from bacteria to fungi during the incubation. The addition of C3-cellulose led to a small increase in C3-derived microbial biomass C, but to a strong increase in C4-derived microbial biomass C. At days 45 and 67, the addition of N-free C3-cellulose significantly decreased the C/N ratio of the microbial residues, suggesting that this fraction did not serve as an N-source, but as an energy source.  相似文献   

11.
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   

12.
The substrate availability for microbial biomass (MB) in soil is crucial for microbial biomass activity. Due to the fast microbial decomposition and the permanent production of easily available substrates in the rooted top soil mainly by plants during photosynthesis, easily available substrates make a very important contribution to many soil processes including soil organic matter turnover, microbial growth and maintenance, aggregate stabilization, CO2 efflux, etc. Naturally occurring concentrations of easily available substances are low, ranging from 0.1 μM in soils free of roots and plant residues to 80 mM in root cells. We investigated the effect of adding 14C-labelled glucose at concentrations spanning the 6 orders of magnitude naturally occurring concentrations on glucose uptake and mineralization by microbial biomass. A positive correlation between the amount of added glucose and its portion mineralized to CO2 was observed: After 22 days, from 26% to 44% of the added 0.0009 to 257 μg glucose C g?1 soil was mineralized. The dependence of glucose mineralization on its amount can be described with two functions. Up to 2.6 μg glucose C g?1 soil (corresponds to 0.78% of initial microbial biomass C), glucose mineralization increased with the slope of 1.8% more mineralized glucose C per 1 μg C added, accompanied by an increasing incorporation of glucose C into MB. An increased spatial contact between micro-organisms and glucose molecules with increasing concentration may be responsible for this fast increase in mineralization rates (at glucose additions <2.6 μg C g?1). At glucose additions higher than 2.6 μg C g?1 soil, however, the increase of the glucose mineralization per 1 μg added glucose was much smaller as at additions below 2.6 μg C g?1 soil and was accompanied by decreasing portions of glucose 14C incorporated into microbial biomass. This supports the hypothesis of decreasing efficiency of glucose utilization by MB in response to increased substrate availability in the range 2.6–257 μg C g?1 (=0.78–78% of microbial biomass C). At low glucose amounts, it was mainly stored in a chloroform-labile microbial pool, but not readily mineralized to CO2. The addition of 257 μg glucose C g?1 soil (0.78 μg C glucose μg?1 C micro-organisms) caused a lag phase in mineralization of 19 h, indicating that glucose mineralization was not limited by the substrate availability but by the amount of MB which is typical for 2nd order kinetics.  相似文献   

13.
Dicyandiamide (DCD, C2H4N4) is a nitrification inhibitor that has been studied for more than 80 years. However, there are few papers that have examined the use of DCD on dairy farms where cattle graze pasture and where urine is the primary form of nitrogen (N) deposited onto soils. After DCD was applied (10 kg DCD ha?1) with bovine urine (700–1200 kg N ha?1) to five soils throughout New Zealand, the reduction in direct nitrous oxide (N2O) emissions was significant and remarkably consistent (71 ± 8%, average ± standard error). The application of DCD to these soils occurred in autumn and winter; daily average soil temperature (T) was reported but these data were not further analysed. Perusal of the literature suggested no consensus on the temperature dependence of DCD degradation in soils. Based on published data from controlled-environment studies of soils sampled in four countries, we quantified the relation between T and the time for DCD concentration in soils to decline to half its application value (t½) as t½ (T) = 168e?0.084T with parameter standard errors of ±16 d and ±0.011 d?1, respectively (n = 16). For example, at 5 °C a 1 °C increase in T reduced t½ from 110 to 101 d whereas at 25 °C the reduction was 20–19 d. Analysing T data from the New Zealand trials using our t½ (T) function, over 43–89 d when direct N2O emissions from treated plots became indistinguishable from the controls, the estimated percentage of applied DCD remaining in the soil averaged 43 ± 10%. These calculations suggested the apparently remaining DCD was ineffective with respect to direct N2O emissions. In the absence of measurements, explanations for this interpretation included vertical displacement of the DCD and sorption onto organic matter in soils. The consistent DCD efficacy from these trials corresponded with T generally <10 °C, so it is suggested as an application criteria for the reduction of direct N2O emissions from pastoral soils subjected to urine excretion by grazing cattle.  相似文献   

14.
V.O. Polyakov  R. Lal 《Geoderma》2008,143(1-2):216-222
Soil organic carbon (SOC) is an important component of the global carbon cycle. Its dynamics depends upon various natural and anthropogenic factors including soil erosion. A study on Miamian silty clay loam soil in central Ohio was conducted to investigate the effect of soil erosion on SOC transport and mineralization. Runoff plots 10, 20 and 30 m long on a 7% slope under natural rainfall were used. Total soil loss, evolution of CO2 from the displaced aggregates of various fractions, and total SOC concentrations were determined. It was shown that the primary ways of SOC loss resulted from two processes: 1) mechanical preferential removal of SOC by overland flow and 2) erosion-induced mineralization. Significant amounts of SOC mobilized by erosion at the upper part of the slope during the season (358 kg ha? 1) could be lost to the atmosphere within 100 days (15%) and transported off site (44%). Breakup of initial soil aggregates by erosive forces was responsible for increased CO2 emission. During the initial 20 days of incubation the amount of CO2 released from coarse size sediment fractions (0.282 g C kg? 1 soil d? 1) was 9 times greater than that in fine fractions (0.032 g C kg? 1 soil d? 1) due to the greater initial amount of SOC and its exposure to the environment. Sediment size distribution as well as its residence time on the site was the primary controllers of CO2 loss from eroded soil.  相似文献   

15.
《Soil biology & biochemistry》2001,33(7-8):1103-1111
Biologically active fractions of soil organic matter are important in understanding decomposition potential of organic materials, nutrient cycling dynamics, and biophysical manipulation of soil structure. We evaluated the quantitative relationships among potential C and net N mineralization, soil microbial biomass C (SMBC), and soil organic C (SOC) under four contrasting climatic conditions. Mean SOC values were 28±11 mg g−1 (n=24) in a frigid–dry region (Alberta/British Columbia), 25±5 mg g−1 (n=12) in a frigid–wet region (Maine), 11±4 mg g−1 (n=117) in a thermic–dry region (Texas), and 12±5 mg g−1 (n=131) in a thermic–wet region (Georgia). Higher mean annual temperature resulted in consistently greater basal soil respiration (1.7 vs 0.8 mg CO2–C g−1 SOC d−1 in the thermic compared with the frigid regions, P<0.001), greater net N mineralization (2.8 vs 1.3 mg inorganic N g−1 SOC 24 d−1, P<0.001), and greater SMBC (53 vs 21 mg SMBC g−1 SOC, P<0.001). Specific respiratory activity of SMBC was, however, consistently lower in the thermic than in the frigid regions (29 vs 34 mg CO2–C g−1 SMBC d−1, P<0.01). Higher mean annual precipitation resulted in consistently lower basal soil respiration (1.1 vs 1.3 mg CO2–C g−1 SOC d−1 in the wet compared with the dry regions, P<0.01) and lower SMBC (31 vs 43 mg SMBC g−1 SOC, P<0.001), but had inconsistent effects on net N mineralization that depended upon temperature regime. Specific respiratory activity of SMBC was consistently greater in the wet than the dry regions (≈33 vs 29 mg CO2–C g−1 SMBC d−1, P<0.01). Although the thermic regions were not able to retain as high a level of SOC as the frigid regions, due likely to high annual decomposition rates, biologically active soil fractions were as high per mass of soil and even 2–3-times greater per unit of SOC in the thermic compared with the frigid regions. These results suggest that macroclimate has a large impact on the portion of soil organic matter that is potentially active, but a relatively small impact on the specific respiratory activity of SMBC.  相似文献   

16.
In recent years alternative farming practices have received considerable attention from Canadian producers as a means to improve their net return from grain and oilseed production. Enhancing the efficiency of nitrogen fertilizer use, including a pulse crop in the rotation, reducing tillage and pesticide use are seen as viable options to reduce reliance on fossil fuel, lower input costs and decrease the risk of soil, air and water degradation. The objective of this study was to determine the effects of 16 alternative management practices for a 2-year spring wheat (Triticum aestivum L.)–field pea (Pisum sativum L.) rotation on economic returns, non-renewable energy use efficiency, and greenhouse gas emissions. The alternative management methods for wheat consisted of a factorial combination of high vs. low soil disturbance one pass seeding, four nitrogen (N) fertilizer rates (20 kg N ha?1, 40 kg N ha?1, 60 kg N ha?1 and 80 kg N ha?1), and recommended vs. reduced rates of in-crop herbicide application. Alternative management practices for field pea were high vs. low soil disturbance one pass seeding. The resulting 16 cropping systems were evaluated at the whole farm level based on 4 years (two rotation cycles) of data from field experiments conducted on two Orthic Black Chernozem soils (clay loam and loam textures) in Manitoba, Canada. The highest net returns on the clay loam soil were for the high disturbance system with 60 kg N ha?1 applied to wheat and the recommended rates of in-crop herbicides. The lowest application rate of N, together with low disturbance seeding, provided the highest economic returns on the loam soil. Energy use efficiency was highest for the lowest rate of N application for both tillage systems. The highest rate of N fertilizer and recommended rates of in-crop herbicide produced little additional yield response, lower net returns, and higher GHG emissions. An increase in N fertilizer application from 20 kg ha?1 to 80 kg ha?1 increased whole farm energy requirements by about 40%, while reducing herbicide rates had negligible effects on grain yields and total energy input. Overall, as N fertilizer rate increased, the associated GHG emissions were not offset by an increase in carbon retained in the above-ground crop biomass. Moderate to high soil test NO3-N levels at experimental sites reduced the potential for positive yield responses to N fertilizer in this study, thus minimizing the economic benefits derived from N fertilizer application.  相似文献   

17.
We used the eddy-covariance technique to measure evapotranspiration (E) and gross primary production (GPP) in a chronosequence of three coastal Douglas-fir (Pseudotsuga menziesii) stands (7, 19 and 58 years old in 2007, hereafter referred to as HDF00, HDF88 and DF49, respectively) since 1998. Here, we focus on the controls on canopy conductance (gc), E, GPP and water use efficiency (WUE) and the effect of interannual climate variability at the intermediate-aged stand (DF49) and then analyze the effects of stand age following clearcut harvesting on these characteristics. Daytime dry-foliage Priestley–Taylor α and gc at DF49 were 0.4–0.8 and 2–6 mm s?1, respectively, and were linearly correlated (R2 = 0.65). Low values of α and gc at DF49 as well at the other two stands suggested stomatal limitation to transpiration. Monthly E, however, showed strong positive linear correlations to monthly net radiation (R2 = 0.94), air temperature (R2 = 0.77), and daytime vapour pressure deficit (R2 = 0.76). During July–September, monthly E (mm) was linearly correlated to monthly mean soil water content (θ, m3 m?3) in the 0–60 cm layer (E = 453θ ? 21, R2 = 0.69), and GPP was similarly affected. Annual E and GPP of DF49 for the period 1998–2007 varied from 370 to 430 mm and from 1950 to 2390 g C m?2, respectively. After clearcut harvesting, E dropped to about 70% of that for DF49 while ecosystem evapotranspiration was fully recovered when stand age was ～12 years. This contrasted to GPP, which varied hyperbolically with stand age. Monthly GPP showed a strong positive linear relationship with E irrespective of the stand age. While annual WUE of HDF00 and HDF88 varied with age from 0.5 to 4.1 g C m?2 kg?1 and from 2.8 to 4.4 g C m?2 kg?1, respectively, it was quite conservative at ～5.3 g C m?2 kg?1 for DF49. N-fertilization had little first-year response on E and WUE. This study not only provides important results for a more detailed validation of process-based models but also helps in predicting the influences of climate change and forest management on water vapour and CO2 fluxes in Douglas-fir forests.  相似文献   

18.
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   

19.
Documented approaches for measuring soil microbial activities and their controlling factors under field conditions are needed to advance understanding of soil microbial processes for numerous applications. We manipulated field plots with carbon (C) and nitrogen (N) additions to test the capability of a respiratory assay to: (1) measure respiration of endogenous soil C in comparison to field-measured CO2 fluxes; (2) determine substrate-induced respiratory (SIR) activities that are consistent with substrate availability in the field; and, (3) report N availability in the field based on assay responses with and without added N. The respiratory assay utilizes a microplate containing an oxygen-sensitive fluorescent ruthenium dye. Respiratory activities measured with this approach have previously been shown to occur within short (6–8 h) incubation periods using low substrate concentrations that minimize enrichment during the assay. Field treatments were conducted in a randomized full-factorial design with C substrate (casamino acids, glucose, or none) and inorganic N (±) as the treatment factors. With one exception, we found that respiration of endogenous soil C in the assay responded to the field treatments in a similar manner to CO2 fluxes measured in the field. Patterns of SIR with low concentrations of added amino acid or carbohydrate substrate (200 μg C g−1 soil) were consistent with field treatments. The ratio (Nratio) of carbohydrate respiration with added N (25 μg N g−1 soil) to the same without N in the assay was significantly (P < 0.05) decreased by field N amendment. The carbohydrate Nratio exhibited a logarithmic relationship (r = 0.64, P < 0.05) with extractable inorganic soil nitrate and ammonium concentrations. These data significantly extend and support the capability of this oxygen-based respiratory assay to evaluate in situ soil activities and examine factors that limit these activities.  相似文献   

20.
We studied a semi-natural forest in Northern Italy that was set aside more than 50 years ago, in order to better understand the soil carbon cycle and in particular the partitioning of soil respiration between autotrophic and heterotrophic respiration. Here we report on soil organic carbon, root density, and estimates of annual fluxes of soil CO2 as measured with a mobile chamber system at 16 permanent collars about monthly during the course of a year. We partitioned between autotrophic and heterotrophic respiration by the indirect regression method, which enabled us to obtain the seasonal pattern of single components.The soil pool of organic carbon, with 15.8 (±4.5) kg m?2, was very high over the entire depth of 45 cm. The annual respiration rates ranged from 0.6 to 6.9 μmol CO2 m?2 s?1 with an average value of 3.4 (±2.3) μmol CO2 m?2 s?1, and a cumulative flux of 1.1 kg C m?2 yr?1. The heterotrophic component accounted for 66% of annual CO2 efflux. Soil temperature largely controlled the heterotrophic respiration (R2 = 0.93), while the autotrophic component followed irradiation, pointing to the role of photosynthesis in modulating the annual course of soil respiration.Most studies on soil respiration partitioning indicate autotrophic root respiration as a first control of the spatial variability of the overall respiration, which originates mainly from the uppermost soil layers. Instead, in our forest the spatial variability of soil respiration was mainly linked to soil carbon, and deeper layers seemed to provide a significant contribution to soil respiration, a feature that may be typical for an undisturbed, naturally maturing ecosystem with well developed pedobiological processes and high carbon stocks.  相似文献   

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