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1.
The impact of intensified drought and rewetting on C cycling in peatlands is debated. We conducted drying/rewetting (DW) experiments with intact monoliths of a temperate fen over a period of 10 months. One treatment with original vegetation (DW-V) and one defoliated treatment (DW-D) were rewetted after an experimental drought of 50 days; another treatment was kept permanently wet (W-V). Soil water content was determined by the TDR technique, C fluxes from chamber measurements and gas profiles in the soils, and respiration from mass balancing CO2 and CH4 fluxes in the peat using hourly to weekly data. Zones of high root associated respiration were determined from a 13C labeling experiment. Autotrophic respiration contributed from 55 to 65% to an average ecosystem respiration (ER) of 92 (DW-D), 211 (DW-V), and 267 mmol m?2 d?1 (W-V). Photosynthesis ranged from 0 (DW-D) to 450 mmol m?2 d?1 (W-V), and strongly declined for about 30 days after rewetting (DW-V), while ER remained constant during the drying and rewetting event. Drying raised air-filled porosity in the soil to 2–13%, temporarily increased respiration to estimated anaerobic and aerobic rates of up to 550 and 1000 nmol cm?3 d?1, and delayed methane production and emission by weeks to months. Root associated respiration was concentrated in the uppermost peat layer. In spite of clear relative changes in respiration during and after drought, the impact on carbon exchange with the atmosphere was small. We attribute this finding to the importance of respiration in the uppermost and soil layer, which remained moist and aerated, and the insensitivity of autotrophic respiration to drought. We expect a similar dynamics to occur in other temperate wetland soils in which soil respiration is concentrated near the peatland surface, such as rich minerotrophic fens.  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.
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   

4.
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   

5.
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   

6.
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   

7.
《Soil biology & biochemistry》2001,33(12-13):1797-1804
Sulphur transformations were monitored in a unique set of arable, grassland and woodland soils from the Broadbalk Classical Experiment, which started in 1843. In an open incubation experiment with periodic leaching, 14–35 mg SO42−-S kg−1 was mineralised in 28 weeks at 25°C, equivalent to 4.4–8.3% soil organic S. Cumulative amounts of S mineralised increased linearly during the 28 weeks, indicating constant rates of mineralisation. The rate of mineralisation was the greatest in the woodland soil (170 μg SO4-S kg−1 day−1), followed by the grassland (120 μg SO4-S kg−1 day−1) and the arable soil from the farmyard manure (FYM) plot (110 μg SO4-S kg−1 day−1). Three soils from arable plots receiving different inorganic fertiliser treatments but no FYM had similar rates of S mineralisation (~70 μg SO4-S kg−1 day−1). In an incubation experiment with 35SO42−, addition of glucose greatly enhanced S immobilisation. In 132 days, the woodland and grassland soils immobilised more S than the arable soils, with or without glucose amendment. Immobilisation and mineralisation of S occurred concurrently, and both were stimulated by glucose addition. The results show that S mineralisation and immobilisation were influenced strongly by the type of land-use and long-term organic manuring, whereas annual application of sulphate-containing fertilisers for over 150 years had few effects on short-term S transformations.  相似文献   

8.
Tussocks formed by Carex stricta are a relatively large carbon (C) pool in sedge meadows, but the stability of organic matter in these ecosystems is not well understood. We initiated year-long incubation experiments (22.5 °C) to evaluate the CO2 and CH4 production potentials of sedge meadow substrates under field moist and inundated treatments from five sites in the Upper Midwest, USA (4 reference, 1 restored). C mineralization potentials decreased with depth (tussocks > underlying soil), and were positively correlated with macro-organic matter content and negatively with lignin. Across sites, C stored in tussocks and soil at the restoration was the least stable, suggesting that the restoration of C-storage function may take decades. Mineralization potentials were similar between field moist and inundated treatments, but inundation resulted in higher methane production, accounting for 24–51% of total carbon mineralized from tussocks. In the field however, C. stricta tussocks emitted less methane (393 ± 76 mg CH4 m−2 d−1) than tussock interspaces (1362 ± 371 mg CH4 m−2 d−1) early in the growing season; we suggest that tussock tops oxidized methane produced from deeper anoxic horizons. Our results highlight the importance of considering how microtopography modulates greenhouse gas flux from wetlands and suggests that the C stored in the older, more decomposed C. stricta tussock sedge meadow substrates (both within and between sites) is relatively stable.  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.
The main aim of this study is to analyze the influence of 4-nonylphenol (NP) on soil water retention and biological activity. Two doses of 4-nonylphenol (25 and 50 mg kg−1) were tested in a loam soil with and without peat amendment. In general, one week after the start of the experiment, the soil water content retained at −0.75 MPa of soil suction was 18% higher in the soil amended and its basal respiration (BR) was 15% higher than soil without peat. In contrast, the microbial activity indices (CM: coefficient of mineralization or BR:total organic carbon (TOC) ratio; Cmic:Corg: microbial biomass carbon (MBC):TOC ratio; qCO2: metabolic quotient or BR:MBC ratio) were higher in the soil without peat, compared to the soil amended with peat. On the other hand, the addition of NP to soil was able to modify soil biological but not physical (water retention, desorption) properties. When soil was amended with peat, MBC was reduced one week after applying NP. In contrast, no effects of NP on MBC were observed in the soil without peat. BR was reduced by 16% one week after applying 50 mg kg−1 of NP to soil with peat, and was increased by 46% one week after applying 25 mg kg−1 of NP to soil without peat. The effects of NP on MBC and BR could be associated more with the adsorption of NP by soil organic matter, while changes in CM or Cmic:Corg ratio were more closely related to changes in soil water retention. The potential toxic effects of NP (high qCO2 values) were only observed in the absence of peat amendments. Peat addition reduced NP toxic effects on microorganisms.  相似文献   

11.
Intermittent irrigation is an important option for mitigating CH4 emissions from paddy fields. In order to better understand its controlling processes in CH4 emission, CH4 fluxes, CH4 production and oxidation potentials in paddy soils, and 13C-isotopic signatures of CH4 were observed in field and incubation experiments. The relative contribution of acetate to total CH4 production (fac) and fraction of CH4 oxidized (fox) in the field was also calculated using the isotopic data. At the beginning of the rice season, the theoretical ratio of acetate fermentation: H2/CO2 reduction = 2:1 was reached, however, in the late season H2/CO2-dependent methanogenesis became dominant. Compared to continuous flooding, intermittent irrigation significantly reduced CH4 production potential and slightly decreased fac-value, indicating methanogens, particularly acetate-utilizing methanogens, were inhibited. CH4 oxidation was very important, especially in paddy fields under intermittent irrigation where 19–83% of the produced CH4 was oxidized. Intermittent irrigation enhanced CH4 oxidation potential slightly and raised fox-value significantly relative to continuous flooding. Intermittent irrigation significantly decreased CH4 flux creating a more positive δ13C-value of emitted CH4 by 12–22‰. A significant negative correlation was found between CH4 fluxes and values of δ13CH4 suggesting that the less the CH4 oxidation, the higher the CH4 emission, and the lower the δ13C-value of emitted CH4. Collectively, the findings show that intermittent irrigation reduced the seasonal CH4 production potential by 45% but increased the fraction of CH4 oxidized by 45–63%, thus decreasing the seasonal CH4 emission from the paddy fields by 71%, relative to continuous flooding.  相似文献   

12.
We used natural gradients in soil and vegetation δ13C signatures in a savannah ecosystem in Texas to partition soil respiration into the autotrophic (Ra) and heterotrophic (Rh) components. We measured soil respiration along short transects from under clusters of C3 trees into the C4 dominated grassland. The site chosen for the study was experiencing a prolonged drought, so an irrigation treatment was applied at two positions of each transect. Soil surface CO2 efflux was measured along transects and CO2 collected for analysis of the δ13C signature in order to: (i) determine how soil respiration rates varied along transects and were affected by localised change in soil moisture and (ii) partition the soil surface CO2 efflux into Ra and Rh, which required measurement of the δ13C signature of root- and soil-derived CO2 for use in a mass balance model.The soil at the site was unusually dry, with mean volumetric soil water content of 8.2%. Soil respiration rates were fastest in the centre of the tree cluster (1.5 ± 0.18 μmol m?2 s?1; mean ± SE) and slowest at the cluster–grassland transition (0.6 ± 0.12 μmol m?2 s?1). Irrigation produced a 7–11 fold increase in the soil respiration rate. There were no significant differences (p > 0.5) between the δ13C signature of root biomass and respired CO2, but differences (p < 0.01) were observed between the respired CO2 and soil when sampled at the edge of the clusters and in the grassland. Therefore, end member values were measured by root and soil incubations, with times kept constant at 30 min for roots and 2 h for soils. The δ13C signature of the soil surface CO2 efflux and the two end member values were used to calculate that, in the irrigated soils, Rh comprised 51 ± 13.5% of the soil surface CO2 efflux at the mid canopy position and 57 ± 7.4% at the drip line. In non-irrigated soil it was not possible to partition soil respiration, because the δ13C signature of the soil surface CO2 efflux was enriched compared to both the end member values. This was probably due to a combination of the very dry porous soils at our study site (which may have been particularly susceptible to ingress of atmospheric CO2) and the very slow respiration rates of the non-irrigated soils.  相似文献   

13.
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   

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.
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   

16.
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   

17.
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   

18.
Meat and bone meal (MBM) utilization for animal production was banned in the European Union since 2000 as a consequence of the appearance of transmissive spongiform encephalopathies. Soil application could represent a lawful and effective strategy for the sustainable recycling of MBM due to its relevant content of nutritive elements and organic matter. The effectiveness of MBM as organic fertilizer needs to be thoroughly investigated since there is a lack of knowledge about the mineralization dynamics of MBM in soil and the impact of such residues, in particular the high content of lipids, on soil biochemical and microbiological properties. For this aim, a defatted (D) and the correspondent non-defatted (ND) MBM were added at two rates (200 and 400 kg N ha?1) to two different moist soils and incubated at 15 and 20 °C for 14 d. MBM mineralization dynamics was studied by measuring CO2 evolution. Water extractable organic C, K2SO4-extractable NO3? and NH4+, microbial biomass ninhydrin-reactive N, enzymatic activities (FDA, urease, protease, alkaline phosphatase) and microbial composition (aerobic and anaerobic bacteria, fungi) were measured 2 and 14 d after MBM addition to the soil. The rate of CO2 evolution showed a maximum 2–3 d after the addition of MBM, followed by a decrease approaching the control. MBM mineralization was fast with, on average, 54% of total CO2 evolved in the first 4 d of incubation at 20 °C. The percentage of added C which was evolved as CO2 at the end of the incubation period ranged between 8% and 16% and was affected by temperature, soil type and MBM treatment (ND > D). Soil amendment with MBM caused a noteworthy increase in both extractable NH4+ and NO3? (about 50% of added N) which was higher for ND. The addition of MBM also enhanced microbial content and activity. Microbial biomass increased as a function of the rate of application and was higher for ND with respect to D. The increase in numbers of aerobic and anaerobic bacteria and fungi caused by MBM addition was, in general, more pronounced with ND. Enzymatic activity in amended soils showed an enhancement in nutrient availability and element cycling. At the rate of application of present work, lipids did not cause adverse effects on soil microorganisms.The potential of MBM as effective organic fertilizer was supported by the large increase in available N and the enhancement of the size and activity of soil microorganisms.  相似文献   

19.
Drying and rewetting to a variable extent influence the C gas exchange between peat soils and the atmosphere. We incubated a decomposed and compacted fen peat and investigated in two experiments 1) the vertical distribution of CO2 and CH4 production rates and their response to drying and 2) the effects of temperature, drying intensity and duration on CO2 production rates and on CH4 production recovery after rewetting. Surface peat down to 5 cm contributed up to 67% (CO2) and above 80% (CH4) of the depth-aggregated (50 cm) production. As CO2 production sharply decreased with depth water table fluctuations in deeper peat layers are thus not expected to cause a substantial increase in soil respiration in this site. Compared to anaerobic water saturated conditions drying increased peat CO2 production by a factor between 1.4 and 2.1. Regarding the effects of the studied factors, warmer conditions increased and prolonged drying duration decreased CO2 production whereas the soil moisture level had little influence. No significant interactions among factors were found. Short dry events under warmer conditions are likely to result in greatest peaks of CO2 production rates. Upon rewetting, CH4 production was monitored over time and the recovery was standardized to pre-drying levels to compare the treatment effects. Methane production increased non-linearly over time and all factors (temperature, drying intensity and duration) influenced the pattern of post-drying CH4 production. Peat undergoing more intense and longer drying events required a longer lag time before substantial CH4 production occurred and warmer conditions appeared to speed up the process.  相似文献   

20.
《Soil biology & biochemistry》2001,33(7-8):965-971
Laboratory experiments were conducted to find out under which conditions the soil from Italian rice fields could change from a source into a sink of atmospheric CH4. Moist (30% H2O=68% of the maximum water holding capacity (whc)) rice field soil oxidized CH4 with biphasic kinetics, exhibiting both a low (145 ppmv CH4) and a high (20,200 ppmv CH4) Km value and Vmax values of 16.8 and 839 nmol gdw−1 h−1, respectively. The activity with the low Km allowed the oxidation of atmospheric CH4. Uptake rates of high CH4 concentrations (16.5% v/v) and of O2 linearly decreased with aggregate size of soil between 2 and 10 mm. Atmospheric CH4 (1.8 ppmv) was consumed in soil aggregates <6 mm, but soil aggregates >6 mm released CH4 into the atmosphere. Similarly, net uptake of atmospheric CH4 turned into net release of CH4 when the soil moisture was decreased below a water content of about 20% whc. The uptake rate of atmospheric CH4 increased threefold when the soil was amended with sterile quartz sand. Flooded microcosms with non-amended and quartz-amended soil emitted CH4 into the atmosphere. The CH4 emission rate increased when the flux was measured under an atmosphere of N2 instead of air, indicating that 30–99% of the produced CH4 was oxidized in the oxic soil surface layer. Removal of the flood water resulted in increase of CH4 emission rates until a water content of about 75–82% whc was reached, and subsequently in a rapid decrease. However, the soil microcosms never showed net uptake of atmospheric CH4. Our results show that the microorganisms consuming atmospheric CH4 were inactivated at an earlier stage of drainage than the microorganisms producing CH4, irrespective of the soil porosity which was adjusted by addition of quartz sand. Hence, it is unlikely that the Italian rice fields can act as a net sink for atmospheric CH4 even when drained.  相似文献   

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