首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
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   

2.
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   

3.
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   

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.
Underestimation of nocturnal CO2 respiration using the eddy covariance method under calm conditions remains an unsolved problem at many flux observation sites in forests. To evaluate nocturnal CO2 exchange in a Japanese cypress forest, we observed CO2 flux above the canopy (Fc), changes in CO2 storage in the canopy (St) and soil, and trunk and foliar respiration for 2 years (2003–2004). We scaled these chamber data to the soil, trunk, and foliar respiration per unit of ground area (Fs, Ft, Ff, respectively) and used the relationships of Fs, Ft, and Ff with air or soil temperature for comparison with canopy-scale CO2 exchange measurements (=Fc + St). The annual average Fs, Ft, and Ff were 714 g C m−2 year−1, 170 g C m−2 year−1, and 575 g C m−2 year−1, respectively. At small friction velocity (u*), nocturnal Fc + St was smaller than Fs + Ft + Ff estimated using the chamber method, whereas the two values were almost the same at large u*. We replaced Fc + St measured during calm nocturnal periods with a value simulated using a temperature response function derived during well-mixed nocturnal periods. With this correction, the estimated net ecosystem exchange (NEE) from Fc + St data ranged from −713 g C m−2 year−1 to −412 g C m−2 year−1 in 2003 and from −883 g C m−2 year−1 to −603 g C m−2 year−1 in 2004, depending on the u* threshold. When we replaced all nocturnal Fc + St data with Fs + Ft + Ff estimated using the chamber method, NEE was −506 g C m−2 year−1 and −682 g C m−2 year−1 for 2003 and 2004, respectively.  相似文献   

6.
We explore the impact of agriculture, forest and cloud feedback on the surface energy budget using data obtained using a research aircraft, mesonet towers and model data. The forest has an order of magnitude larger roughness length, a lower albedo, a much smaller seasonal cycle in surface Bowen ratio (BR) and a weak mid-summer maximum of CO2 uptake compared to agricultural areas, which have much smaller BR and much higher mid-summer CO2 uptake, but a net CO2 release and much reduced evaporation in spring and fall. Higher surface temperatures and the higher albedo over agricultural land reduce Rnet near local noon in the warm season by about 50 W m−2 in comparison with the adjacent boreal forest. The annual averaged Rnet, derived from 2 years of tower data, is 14 W m−2 less over grass sites than over forest sites. A reanalysis time-series for the BOREAS southern study area shows the coupling on daily timescales between the surface energy partition, the mean boundary layer depth, the cloud field and the long-wave and short-wave radiation fields. The albedo of the cloud field, the cloud short-wave forcing at the surface, varies over the range 0.1–0.8 with decreasing surface BR, and plays a major role in the surface energy budget. We estimate that this cloud feedback may increase albedo by 0.13 and reduce Rnet by 25 W m−2 in summer over agricultural land.  相似文献   

7.
Net ecosystem exchange of carbon (FNEE) was estimated for a temperate broadleaf, evergreen eucalypt forest ecosystem at Tumbarumba in south-eastern Australia to investigate the processes controlling forest carbon sinks and their response to climate. Measurements at a range of temporal and spatial scales were used to make three different estimates of FNEE based on: (1) the difference between fluxes of carbon input by photosynthesis and output by autotrophic plus heterotrophic respiration, (2) changes over time in the carbon pools in the above- and below-ground biomass, soil and litter, and (3) micrometeorological flux measurements that provide a continuous estimate of the net exchange. A rigorous comparison of aggregated component fluxes and the net eddy fluxes within a flux tower source area was achieved based on an inventory of the site and a detailed sampling strategy. Measurements replicated in space and time provided mean values, confidence limits and patterns of variation of carbon pools and fluxes that allowed comparisons within known limits of uncertainty. As a result of comparisons between nighttime eddy flux and chamber measurements of respiration, a revised micrometeorological method was developed for estimating nighttime carbon flux using flux tower measurements. Uncertainty in the final estimate of FNEE was reduced through mutual constraints of each of these measurement approaches. FNEE for the period October 2001–September 2002, with average rainfall, was an uptake of 6.7 (5.1–8.3) tC ha?1 yr?1 estimated from component fluxes, and 5.4 (3.0–7.5) tC ha?1 yr?1 estimated from the revised eddy flux method. Biomass increment was 4.5 (3.7–5.4) tC ha?1 yr?1 and the remaining 0.9–2.2 tC ha?1 yr?1 could represent a carbon sink in the soil and litter pools or lie within the confidence limits of the measured fluxes. FNEE was reduced to ?0.1 to 2.4 tC ha?1 yr?1 during a period of drought and insect disturbance in October 2002–September 2003, with biomass increment being the main component reduced. The forest is a large carbon sink compared with other forest ecosystems, but this is subject to high-annual variability in response to climate variability and disturbance.  相似文献   

8.
A dual-beam surface layer scintillometer (SLS), for the estimation of sensible heat flux density H for a path length of 101 m, was used in a mixed grassland community in the eastern seaboard of South Africa for 30 months. Measurements also included Bowen ratio (BR) and eddy covariance (EC) estimates of H. Acceptable SLS data between 0600 h and 1800 h, judged by the percent of error-free 1 kHz data exceeding 25% and an inner scale of turbulence exceeding 2 mm, showed little seasonal variation and was consistently high—between 86.7% and 94.8%. An analysis of the various Monin–Obukhov similarity theory (MOST) empirical dimensionless stability functions used for estimating H from the SLS measurements showed percent differences in H that varied from ?30% to 28% for neutral to unstable conditions, respectively and for stable continuous conditions the differences in H were within 60 W m?2 with much larger differences for stable sporadic conditions. The good agreement in measurements of H over an extended period for the SLS, BR and EC methods demonstrates the applicability and robustness of the SLS method and the associated MOST empirical functions used for estimating H for a range of canopy heights, stability conditions and diurnal and seasonal weather conditions. Furthermore, there was no evidence for an underestimation in EC sensible heat compared to SLS and BR measurements, which implies that any lack of energy balance closure points to possible latent energy EC underestimation or due to energy fluxes not included in the shortened energy balance if the net irradiance and soil heat flux components are correct. A sensitivity analysis was used to determine the relative importance of the SLS data inputs of air temperature, atmospheric pressure, beam path length and beam height on H estimates. Worst-case errors in air temperature, atmospheric pressure, beam path length and beam height resulted in errors in H within 1.0%, 1.3%, 3.0% and 4.0%, respectively. Overall, the worst-case total percent error in SLS-estimated H is within 5.3% and the typical percent error is within 3.9%. Accounting for the error in net irradiance and soil heat flux measurements, the seasonal variation in the error in daily evaporation estimated as a residual of the energy balance is generally less than 0.2 mm (0.49 MJ m?2) in winter when the daily evaporation was about 1 mm (2.45 MJ m?2) and typically less than 0.4 mm (0.98 MJ m?2) when the evaporation exceeded 4 mm (9.8 MJ m?2). Soil heat flux density measurements can contribute significantly to the overall error.  相似文献   

9.
It is reported a simple approach to transform daily values of grass net (all-wave) radiation (Rn, MJ m−2 day−1), as measured over standard grass surface at meteorological stations, into whole tree canopy net radiation (A, MJ tree−1 day−1). The revolving Whirligig device [McNaughton, K.G., Green, S.R., Black, T.A., Tynam, B.R., Edwards, W.R.N., 1992. Direct measurement of net radiation and photosynthetically active radiation absorbed by a single tree. Agric. For. Meteorol. 62, 87–107] describing a sphere about the tree measured A in five trees of different species (walnut, dwarf apple, normal apple, olives and citrus), with leaf area LA varying from 8.65 to 40 m2. For each tree, A and Rn were linearly related (A = bRn), as previously reported elsewhere, but it was found that the slope of such regression was also a linear function of LA or, b = 0.303 (±0.032) LA. Consequently, the hypothesis that total daily tree canopy net radiation per unit leaf area is linearly related to grass net radiation could not be rejected after 86 days of measurements in five locations, and the empirical relationship is A = 0.303 (±0.032) RnLA (R2 = 0.9306).  相似文献   

10.
An investigation of the detection of water stress in non-homogeneous crop canopies such as orchards using high-spatial resolution remote sensing thermal imagery is presented. An airborne campaign was conducted with the Airborne Hyperspectral Scanner (AHS) acquiring imagery in 38 spectral bands in the 0.43–12.5 μm spectral range at 2.5 m spatial resolution. The AHS sensor was flown at 7:30, 9:30 and 12:30 GMT in 25 July 2004 over an olive orchard with three different water-deficit irrigation treatments to study the spatial and diurnal variability of temperature as a function of water stress. A total of 10 AHS bands located within the thermal-infrared region were assessed for the retrieval of the land surface temperature using the split-window algorithm, separating pure crowns from shadows and sunlit soil pixels using the reflectance bands. Ground truth validation was conducted with infrared thermal sensors placed on top of the trees for continuous thermal data acquisition. Crown temperature (Tc), crown minus air temperature (Tc − Ta), and relative temperature difference to well-irrigated trees (Tc − TR, where TR is the mean temperature of the well-irrigated trees) were calculated from the ground sensors and from the AHS imagery at the crown spatial resolution. Correlation coefficients for Tc − TR between ground IRT sensors and airborne image-based AHS estimations were R2 = 0.50 (7:30 GMT), R2 = 0.45 (9:30 GMT) and R2 = 0.57 (12:30 GMT). Relationships between leaf water potential and crown Tc − Ta measured with the airborne sensor obtained determination coefficients of R2 = 0.62 (7:30 GMT), R2 = 0.35 (9:30 GMT) and R2 = 0.25 (12:30 GMT). Images of Tc − Ta and Tc − TR for the entire field were obtained at the three times during the day of the overflight, showing the spatial and temporal distribution of the thermal variability as a function of the water deficit irrigation schemes.  相似文献   

11.
The great areal extent of boreal forests confers these ecosystems potential to impact on the global surface-atmosphere energy exchange. A modelling approach, based on a simplified two-source energy balance model, was proposed to estimate energy balance fluxes above boreal forests using thermal infrared measurements. Half-hourly data from the Solar-Induced Fluorescence Experiment, carried out in a Finnish boreal forest, was used to evaluate the performance of the model. Energy balance closure, determined by linear regression, found all fluxes to underestimate available energy by 9% (r2 = 0.94). Significance in the energy balance of the heat storage in the air and in the soil terms was also analyzed. Canopy temperatures, measured by a CIMEL Electronique CE 312 radiometer, together with ancillary meteorological variables and vegetation characteristics, were used to run the model. Comparison with ground measurements showed errors lower than ±15 W m?2 for the retrieval of net radiation, soil heat flux and storage heat flux, and about ±50 W m?2 for the sensible and latent heat fluxes. A sensitivity analysis of the approach to typical operational uncertainties in the required inputs was conducted showing the necessity of accurate measurements of the target radiometric surface temperature.  相似文献   

12.
The purpose of this study was to investigate the effects of high cadmium and nickel soil concentrations on selected physiological parameters of Arundo donax L. A 2-year pot experiment was held in the field and the pots were irrigated with aqueous solutions of Cd and Ni in concentrations of 5, 50 and 100 ppm, against the control (tap water). At the end of the cultivation periods the pots soil was divided into three equal zones and total and NH4OAc extractable Cd and Ni concentrations were determined. The top zone exhibited the highest metal content. Cadmium and nickel total concentrations at the end of the experiment were up to 973.8 mg kg−1 and 2543.3 mg kg−1 respectively, while NH4OAc extractable Cd was up to 291.7 mg kg−1 and Ni up to 510.3 mg kg−1. Stomatal conductance ranged between 0.3 and 0.8 mol CO2 m−2 s−1, intercellular CO2 concentration ranged between 212.9 and 243.0 ppm CO2, stomatal resistance between 0.6 and 1.3 s cm−1, chlorophyll content (SPAD values) between 46.3 and 57.0 and chlorophyll fluorescence (Fv/Fm) ranged between 0.8 and 0.9. All studied physiological parameters did not show statistically significant differences among control and heavy metal treated plants for both years; therefore, high soil cadmium and nickel concentration did not inhibit stomatal opening and did not affect the function of the photosynthetic machine of A. donax plants.  相似文献   

13.
Polar ecosystems are currently experiencing some of the fastest rates of climate warming. An increase in soil temperature in High Arctic regions may stimulate soil permafrost melting and microbial activity, thereby accelerating losses of greenhouse gases. It is therefore important to understand the factors regulating the rates of C turnover in polar soils. Consequently, our aims were to: (1) assess the concentration of low molecular weight (MW) dissolved organic carbon (DOC) in soil, (2) to investigate the temperature-dependent turnover of specific low MW compounds, and (3) to analyse the influence of substrate concentration on C cycling. Microbial mineralisation of labile low MW DOC in two High Arctic tundra soils was investigated using soil solutions spiked with either 14C-labelled glucose or amino acids. Spiked solutions were added to the top- and sub-soil from two ecosystem types (lichen and Carex dominated tundra), maintained at three temperatures (4–20 °C), and their microbial mineralisation kinetics monitored. 14CO2 evolution from the tundra soils in response to 14C-glucose and -amino acid addition could best be described by a double first order exponential kinetic equation with rate constants k1 and k2. Both forms of DOC had a short half-life (t1/2) in the pool of microbial respiratory substrate (t1/2 = 1.07 ± 0.10 h for glucose and 1.63 ± 0.14 h for amino acids; exponential coefficient k1 = 0.93 ± 0.07 and 0.64 ± 0.06 h?1 respectively) whilst the second phase of mineralisation, assumed to be C that had entered the microbial biomass, was much slower (average k2 = 1.30 × 10?3 ± 0.49 × 10?4 h?1). Temperature had little effect on the rate of mineralisation of 14C used directly as respiratory substrate. In contrast, the turnover rate of the 14C immobilized in the microbial biomass prior to mineralisation was temperature sensitive (k2 values of 0.99 × 10?3 h?1 and 1.66 × 10?3 h?1 at 4 and 20 °C respectively). Concentration-dependent glucose and amino acid mineralisation kinetics of glucose and amino acids (0–10 mM) were best described using Michaelis–Menten kinetics; there was a low affinity for both C substrates by the microbial community (Km = 4.07 ± 0.41 mM, Vmax = 0.027 ± 0.005 mmol kg?1 h?1). In conclusion, our results suggest that in these C limiting environments the flux of labile, low MW DOC through the soil solution is extremely rapid and relatively insensitive to temperature. In contrast, the turnover of C incorporated into higher molecular weight microbial C pools appears to show greater temperature sensitivity.  相似文献   

14.
The relationship between the two radiant fluxes is studied from almost a 3-year data archive of hourly photosynthetically active photon flux (QP) and global solar irradiance (RS) performed at Athalassa, Cyprus. These data are used to determine temporal variability of the ratio (QP/RS) and its dependence on sky conditions. The seasonal variation of the ratio obtained from daily data ranges from 1.942 E MJ−1 (summer) to 1.892 E MJ−1 (winter) with an annual mean value of 1.919 E MJ−1. The ratio increased from 1.865 to 2.01 E MJ−1 (daily values) or from 1.878 to 2.197 μE J−1 (hourly values), as sky conditions changed from clear to overcast. Effective atmospheric parameters such as sky clearness, brightness and path length were found to cause substantial changes to the PAR fraction.  相似文献   

15.
《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   

16.
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   

17.
Nitrogen (N) from urine excreted by grazing animals can be transformed into N compounds that have detrimental effects on the environment. These include nitrate, which can cause eutrophication of waterways, and nitrous oxide, which is a greenhouse gas. Soil microbes mediate all of these N transformations, but the impact of urine on microbes and how initial soil conditions and urine chemical composition alter their responses to urine are not well understood. This study aimed to determine how soil inorganic N pools, nitrous oxide fluxes, soil microbial activity, biomass, and the community structure of bacteria containing amoA (nitrifiers), nirK, and nirS (denitrifiers) genes responded to the addition of urine over time. Bovine urine containing either a high (15.0 g K+ l?1) or low salt content (10.4 g K+ l?1) was added to soil cores at either low or high moisture content (hereafter termed dry and wet soil respectively; 35% or 70% water-filled pore space after the addition of urine). Changes in soil conditions, inorganic N pools, nitrous oxide fluxes, and the soil microbial community were then measured 1, 3, 8, 15, 29 and 44 days after urine addition. Urine addition increased soil ammonium concentrations by up to 2 mg g d.w.?1, soil pH by up to 2.7 units, and electrical conductivity (EC) by 1.0 and 1.6 dS m?1 in the low and high salt urine treatments respectively. In response, nitrate accumulation and nitrous oxide fluxes were lower in dry compared to wet urine-amended soils and slightly lower in high compared to low salt urine-amended soils. Nitrite concentrations were elevated (>3 μg g d.w.?1) for at least 15 days after urine addition in wet urine-amended soils, but were only this high in the dry urine-amended soils for 1 day after the addition of urine. Microbial biomass was reduced by up to half in the wet urine-amended soils, but was largely unaffected in the dry urine-amended soils. Urine addition affected the community structure of ammonia-oxidising and nitrite-reducing bacteria; this response was also stronger and more persistent in wet than in dry urine-amended soils. Overall, the changes in soil conditions caused by the addition of urine interacted to influence microbial responses, indicating that the effect of urine on soil microbes is likely to be context-dependent.  相似文献   

18.
Endogeic and juvenile anecic earthworm abundance was measured in soil samples and anecic populations were studied by counting midden numbers at the sites of two long-term cropping systems trials in South-central Wisconsin. The three grain and three forage systems at each site were designed to reflect a range of Midwestern USA production strategies. The primary objectives of this work were to determine if the abundance of endogeic or anecic earthworms varied among cropping systems or crop phases within a cropping system and were there specific management practices that impacted endogeic or anecic earthworm numbers. The earthworms present in the surface soil were: Aporrectodea tuberculata (Eisen), A. caliginosa (Savigny), A. trapezoides (Dugés); and juvenile Lumbricus terrestris (L.). True endogeic abundance was greatest in rotationally grazed pasture [188 m?2 at Arlington (ARL) and 299 m?2 at Elkhorn (ELK)], and smallest in conventional continuous corn (27 m?2 at ARL and 32 m?2 at ELK). The only type of anecic earthworm found was L. terrestris L. There was an average of 1.2 middens per adult anecic earthworm and the population of anecics was greatest in the no-till cash grain system (28 middens m?2 at ARL, 18 m?2 at ELK) and smallest in the conventional continuous corn system (3 middens m?2 at ARL, 1 m?2 at ELK). Earthworm numbers in individual crop phases within a cropping system were too variable from year-to-year to recommend using a single phase to characterize a whole cropping system. Indices for five management factors (tillage, manure inputs, solid stand, pesticide use, and crop diversity) were examined, and manure use and tillage were the most important impacting earthworm numbers across the range of cropping systems. Manure use was the most important management factor affecting endogeic earthworm numbers; but no-tillage was the most important for the juvenile and adult anecic groups and had a significantly positive influence on endogeic earthworm counts as well. The pesticides used, which were among the most commonly applied pesticides in the Midwestern USA, and increasing crop diversity did not have a significant effect on either the endogeic or anecic earthworm groups in this study. Consequently, designing cropping systems that reduce tillage and include manure with less regard to omitting pesticides or increasing crop diversity should enhance earthworm populations and probably improve sustainability.  相似文献   

19.
We investigated the fate of root and litter derived carbon in soil organic matter and dissolved organic matter in soil profiles, in order to explain mechanisms of short-term soil carbon storage. A time series of soil and soil solution samples was investigated at the field site of The Jena Experiment between 2002 and 2004. In addition to the main experiment with C3 plants, a C4 species (Amaranthus retroflexus L.) naturally labeled with 13C was grown on an extra plot. Changes in organic carbon concentration in soil and soil solution were combined with stable isotope measurements to follow the fate of plant carbon into the soil and soil solution. A split plot design with plant litter removal versus double litter input simulated differences in biomass input. After 2 years, the no litter and double litter treatment, respectively, showed an increase of 381 g C m?2 and 263 g C m?2 to 20 cm depth, while 71 g C m?2 and 393 g C m?2 were lost between 20 and 30 cm depth. The isotopic label in the top 5 cm indicated that 115 g C m?2 and 156 g C m?2 of soil organic carbon were derived from C4 plant material on the no litter and the double litter treatment, respectively. Without litter, this equals the total amount of 97 g C m?2 that was newly stored in the same soil depth, whereas with double litter this clearly exceeded the stored amount of 75 g C m?2. Our results indicate that litter input resulted in lower carbon storage and larger carbon losses and consequently accelerated turnover of soil organic carbon. Isotopic evidence showed that inherited soil organic carbon was replaced by fresh plant carbon near the soil surface. Our results suggest that primarily carbon released from soil organic matter, not newly introduced plant organic matter, was transported in the soil solution. However, the total flow of dissolved organic carbon was not sufficient to explain the observed carbon storage in deeper soil layers, and the existence of additional carbon uptake mechanisms is discussed.  相似文献   

20.
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号