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1.
During 1999–2001 the chemical composition and fluxes were measured in rainfall, throughfall, soil solution and stream water
in a remote forested site in the Italian Alps. The analysis of temporal patterns revealed the differential behaviour of nitrogen
and sulphur and suggested that different mechanisms controlled their flux. No important changes in sulphate concentration
and fluxes emerged as the solution passed through the various components of the forest ecosystem, and temporal variations
of SO4 in the soil solution and stream were likely driven by the physical process of dilution. The availability of nitrate and ammonia,
by contrast, was drastically reduced as throughfall water entered the soil and passed through the mineral layers, irrespective
of season. The calculated hydrochemical budget based on throughfall and soil solution N fluxes revealed that ~80% N retention
in the forest soil, corresponding to 12 kg ha−1 yr−1, despite a relatively high N deposition loading (15 kg ha−1 yr−1). Most of the leached nitrogen (90%) was in the organic form. Indicators of the N status of this ecosystem, such as C/N ratio
in solid and solution phase of the soil and N foliage content as well as land use history were examined. Despite the strong
N retention in the forested part of the catchment, the stream water N–NO3 levels were consistently above 10 μg l−1 suggesting that the Val Masino catchment as a whole was less efficient in processing atmospheric N inputs. This contrasting
N behaviour illustrates the role of landscape features, such as the soil cover and vegetation type, that is characteristic
of an alpine catchment. 相似文献
2.
Seasonal Variations of Dissolved Nitrogen and DOC:DON Ratios in an Intermittent Mediterranean Stream
Seasonal variations of dissolved inorganic nitrogen (DIN) (NO3–N and NH4–N) and dissolved organic nitrogen (DON) were determined in Fuirosos, an intermittent stream draining an unpolluted Mediterranean
forested catchment (10.5 km2) in Catalonia (Spain). The influence of flow on streamwater concentrations and seasonal differences in quality and origin
of dissolved organic matter, inferred from dissolved organic carbon to nitrogen ratios (DOC:DON ratios), were examined. During
baseflow conditions, nitrate and ammonium had opposite behaviour, probably controlled by biological processes such as vegetation
uptake and mineralization activity. DON concentrations did not have a seasonal trend. During storms, nitrate and DON increased
by several times but discharge was not a good predictor of nutrient concentrations. DOC:DON ratios in streamwater were around
26, except during the months following drought when DOC:DON ratios ranged between 42 and 20 during baseflow and stormflow
conditions, respectively. Annual N export during 2000–2001 was 70 kg km−1 year−1, of which 75% was delivered during stormflow. The relative contribution of nitrogen forms to the total annual export was
57, 35 and 8% as NO3–N, DON and NH4–N, respectively. 相似文献
3.
The Role of Dissolved Organic Carbon, Dissolved Organic Nitrogen, and Dissolved Inorganic Nitrogen in a Tropical Wet Forest Ecosystem 总被引:3,自引:0,他引:3
Although tropical wet forests play an important role in the global carbon (C) and nitrogen (N) cycles, little is known about the origin, composition, and fate of dissolved organic C (DOC) and N (DON) in these ecosystems. We quantified and characterized fluxes of DOC, DON, and dissolved inorganic N (DIN) in throughfall, litter leachate, and soil solution of an old-growth tropical wet forest to assess their contribution to C stabilization (DOC) and to N export (DON and DIN) from this ecosystem. We found that the forest canopy was a major source of DOC (232 kg C ha–1 y–1). Dissolved organic C fluxes decreased with soil depth from 277 kg C ha–1 y–1 below the litter layer to around 50 kg C kg C ha–1 y–1 between 0.75 and 3.5m depth. Laboratory experiments to quantify biodegradable DOC and DON and to estimate the DOC sorption capacity of the soil, combined with chemical analyses of DOC, revealed that sorption was the dominant process controlling the observed DOC profiles in the soil. This sorption of DOC by the soil matrix has probably led to large soil organic C stores, especially below the rooting zone. Dissolved N fluxes in all strata were dominated by mineral N (mainly NO3−). The dominance of NO3– relative to the total amount nitrate of N leaching from the soil shows that NO3– is dominant not only in forest ecosystems receiving large anthropogenic nitrogen inputs but also in this old-growth forest ecosystem, which is not N-limited. 相似文献
4.
Large Loss of Dissolved Organic Nitrogen from Nitrogen-Saturated Forests in Subtropical China 总被引:5,自引:0,他引:5
Yunting Fang Weixing Zhu Per Gundersen Jiangming Mo Guoyi Zhou Muneoki Yoh 《Ecosystems》2009,12(1):33-45
Dissolved organic nitrogen (DON) has recently been recognized as an important component of terrestrial N cycling, especially
under N-limited conditions; however, the effect of increased atmospheric N deposition on DON production and loss from forest
soils remains controversial. Here we report DON and dissolved organic carbon (DOC) losses from forest soils receiving very
high long-term ambient atmospheric N deposition with or without additional experimental N inputs, to investigate DON biogeochemistry
under N-saturated conditions. We studied an old-growth forest, a young pine forest, and a young mixed pine/broadleaf forest
in subtropical southern China. All three forests have previously been shown to have high nitrate (NO3−) leaching losses, with the highest loss found in the old-growth forest. We hypothesized that DON leaching loss would be forest
specific and that the strongest response to experimental N input would be in the N-saturated old-growth forest. Our results
showed that under ambient deposition (35–50 kg N ha−1 y−1 as throughfall input), DON leaching below the major rooting zone in all three forests was high (6.5–16.9 kg N ha−1 y−1). DON leaching increased 35–162% following 2.5 years of experimental input of 50–150 kg N ha−1 y−1. The fertilizer-driven increase of DON leaching comprised 4–17% of the added N. A concurrent increase in DOC loss was observed
only in the pine forest, even though DOC:DON ratios declined in all three forests. Our data showed that DON accounted for
23–38% of total dissolved N in leaching, highlighting that DON could be a significant pathway of N loss from forests moving
toward N saturation. The most pronounced N treatment effect on DON fluxes was not found in the old-growth forest that had
the highest DON loss under ambient conditions. DON leaching was highly correlated with NO3− leaching in all three forests. We hypothesize that abiotic incorporation of excess NO3− (through chemically reactive NO2−) into soil organic matter and the consequent production of N-enriched dissolved organic matter is a major mechanism for the
consistent and large DON loss in the N-saturated subtropical forests of southern China.
Dr. YT Fang performed research, analyzed data, and wrote the paper; Prof. WX Zhu participated in the initial experimental
design, analyzed data, and took part in writing the paper; Prof. P Gundersen conceived the study and took part in writing;
Prof. JM Mo and Prof. GY Zhou conceived study; Prof. M Yoh analyzed part of the data and contributed to the development of
DON model. 相似文献
5.
A. Bryce Cooper 《Plant and Soil》1986,93(3):383-394
Summary Nitrate-N losses to stream waters and soil inorganic N pools, nitrifying potentials and NO3-N production rates were measured in 2 adjacent watersheds, one used as pasture and the other planted in exotic conifer forest
(Pinus radiata D. Don). Estimated NO3-N loss to stream waters draining the pine and pasture watersheds were 0.6kg ha−1 y−1 and 7.6 kg ha−1 y−1 respectively. Ammonium-N pool sizes were not significantly different between soils in the two watersheds but NO3−N pools and nitrifying potentials were always lower in the pine watershed soil samples. Laboratory incubation experiments
indicated that suppression of NO3−N formation in pine watershed soils required the presence of live tree roots and was not due to the direct action of allelopathic
chemicals on nitrifiers. 相似文献
6.
Effects of forest clear-cutting on the carbon and nitrogen fluxes through podzolic soil horizons 总被引:8,自引:0,他引:8
Effects of clear-cutting on the dissolved fluxes of organic C (DOC), organic N (DON), NO3
– and NH4
+ through surface soil horizons were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall and soil water from below the organic (including understorey vegetation and, after clear-cutting, also logging residues), eluvial and illuvial horizons were sampled weekly from 1993 to 1999. Clear-cutting was carried out in September 1996. The removal of the tree canopy decreased the deposition of DOC and DON to the forest floor and increased that of NH4
+ and NO3
– but did not affect the deposition of total N (DTN, <3 kg ha–1 a–1). The leaching of DOC and DON from the organic horizon increased over twofold after clear-cutting (fluxes were on an average 168 kg C and 3.3 kg N ha–1 a–1), but the increased outputs were effectively retained in the surface mineral soil horizons. Inorganic N deposition was mainly retained by the logging residues and organic horizon indicating microbial immobilization. Increased NO3
– formation reflected as elevated concentrations in the percolate from below the mineral soil horizons were observed especially in the third year after clear-cutting. However, the changes were small and the increased leaching of DTN from below the illuvial horizon remained small (<0.4 kg ha–1 a–1) and mainly DON. Effects of clear-cutting on the transport of C and N to surface waters will probably be negligible. 相似文献
7.
Dissolved Nitrogen, Phosphorus, and Sulfur forms in the Ecosystem Fluxes of a Montane Forest in Ecuador 总被引:1,自引:0,他引:1
Rainer Goller Wolfgang Wilcke Katrin Fleischbein Carlos Valarezo Wolfgang Zech 《Biogeochemistry》2006,77(1):57-89
The N, P, and S cycles in pristine forests are assumed to differ from those of anthropogenically impacted areas, but there
are only a few studies to support this. Our objective was therefore to assess the controls of N, P, and S release, immobilization,
and transport in a remote tropical montane forest. The study forest is located on steep slopes of the northern Andes in Ecuador.
We determined the concentrations of NO3-N, NH4-N, dissolved organic N (DON), PO4-P, dissolved organic P (DOP), SO4-S, dissolved organic S (DOS), and dissolved organic C (DOC) in rainfall, throughfall, stemflow, lateral flow (in the organic
layer), litter leachate, mineral soil solution, and stream water of three 8–13 ha catchments (1900–2200 m a.s.l.). The organic
forms of N, P, and S contributed, on average, 55, 66, and 63% to the total N, P, and S concentrations in all ecosystem fluxes,
respectively. The organic layer was the largest source of all N, P, and S species except for inorganic P and S. Most PO4 was released in the canopy by leaching and most SO4 in the mineral soil by weathering. The mineral soil was a sink for all studied compounds except for SO4. Consequently, concentrations of dissolved inorganic and organic N and P were as low in stream water (TDN: 0.34–0.39 mg N l−1, P not detectable) as in rainfall (TDN: 0.39–0.48 mg N l−1, P not detectable), whereas total S concentrations were elevated (stream water: 0.04–0.15, rainfall: 0.01–0.07 mg S l−1). Dissolved N, P, and S forms were positively correlated with pH at the scale of soil peda except inorganic S. Soil drying
and rewetting promoted the release of dissolved inorganic N. High discharge levels following heavy rainstorms were associated
with increased DOC, DON, NO3-N and partly also NH4-N concentrations in stream water. Nitrate-N concentrations in the stream water were positively correlated with stream discharge
during the wetter period of the year. Our results demonstrate that the sources and sinks of N, P, and S were element-specific.
More than half of the cycling N, P, and S was organic. Soil pH and moisture were important controls of N, P, and S solubility
at the scale of individual soil peda whereas the flow regime influenced the export with stream water. 相似文献
8.
John L. Campbell James W. Hornbeck William H. McDowell Donald C. Buso James B. Shanley Gene E. Likens 《Biogeochemistry》2000,49(2):123-142
Relatively high deposition ofnitrogen (N) in the northeastern United States hascaused concern because sites could become N saturated.In the past, mass-balance studies have been used tomonitor the N status of sites and to investigate theimpact of increased N deposition. Typically, theseefforts have focused on dissolved inorganic forms ofN (DIN = NH4-N + NO3-N) and have largelyignored dissolved organic nitrogen (DON) due todifficulties in its analysis. Recent advances in themeasurement of total dissolved nitrogen (TDN) havefacilitated measurement of DON as the residual of TDN– DIN. We calculated DON and DIN budgets using data onprecipitation and streamwater chemistry collected from9 forested watersheds at 4 sites in New England. TDNin precipitation was composed primarily of DIN. Netretention of TDN ranged from 62 to 89% (4.7 to 10 kghaminus 1 yrminus 1) of annual inputs. DON made up themajority of TDN in stream exports, suggesting thatinclusion of DON is critical to assessing N dynamicseven in areas with large anthropogenic inputs of DIN.Despite the dominance of DON in streamwater,precipitation inputs of DON were approximately equalto outputs. DON concentrations in streamwater did notappear significantly influenced by seasonal biologicalcontrols, but did increase with discharge on somewatersheds. Streamwater NO3-N was the onlyfraction of N that exhibited a seasonal pattern, withconcentrations increasing during the winter months andpeaking during snowmelt runoff. Concentrations ofNO3-N varied considerably among watersheds andare related to DOC:DON ratios in streamwater. AnnualDIN exports were negatively correlated withstreamwater DOC:DON ratios, indicating that theseratios might be a useful index of N status of uplandforests. 相似文献
9.
Jirko Holst Chunyan Liu Nicolas Brüggemann Klaus Butterbach-Bahl Xunhua Zheng Yuesi Wang Shenghui Han Zhisheng Yao Jin Yue Xingguo Han 《Ecosystems》2007,10(4):623-634
Gross rates of N mineralization and nitrification, and soil–atmosphere fluxes of N2O, NO and NO2 were measured at differently grazed and ungrazed steppe grassland sites in the Xilin river catchment, Inner Mongolia, P. R.
China, during the 2004 and 2005 growing season. The experimental sites were a plot ungrazed since 1979 (UG79), a plot ungrazed
since 1999 (UG99), a plot moderately grazed in winter (WG), and an overgrazed plot (OG), all in close vicinity to each other.
Gross rates of N mineralization and nitrification determined at in situ soil moisture and soil temperature conditions were
in a range of 0.5–4.1 mg N kg−1 soil dry weight day−1. In 2005, gross N turnover rates were significantly higher at the UG79 plot than at the UG99 plot, which in turn had significantly
higher gross N turnover rates than the WG and OG plots. The WG and the OG plot were not significantly different in gross ammonification
and in gross nitrification rates. Site differences in SOC content, bulk density and texture could explain only less than 15%
of the observed site differences in gross N turnover rates. N2O and NO
x
flux rates were very low during both growing seasons. No significant differences in N trace gas fluxes were found between
plots. Mean values of N2O fluxes varied between 0.39 and 1.60 μg N2O-N m−2 h−1, equivalent to 0.03–0.14 kg N2O-N ha−1 y−1, and were considerably lower than previously reported for the same region. NO
x
flux rates ranged between 0.16 and 0.48 μg NO
x
-N m−2 h−1, equivalent to 0.01–0.04 kg NO
x
-N ha−1 y−1, respectively. N2O fluxes were significantly correlated with soil temperature and soil moisture. The correlations, however, explained only
less than 20% of the flux variance. 相似文献
10.
Biogeochemistry of unpolluted forested watersheds in the Oregon Cascades: temporal patterns of precipitation and stream nitrogen fluxes 总被引:10,自引:6,他引:4
We analyzed long-term organic and inorganic nitrogen inputs and outputs in precipitation and streamwater in six watersheds at the H.J. Andrews Experimental Forest in the central Cascade Mountains of Oregon. Total bulk N deposition, averaging 1.6 to 2.0 kg N ha–1 yr–1, is low compared to other sites in the United States and little influenced by anthropogenic N sources. Streamwater N export is also low, averaging <1 kg ha–1 yr–1. DON is the predominant form of N exported from all watersheds, followed by PON, NH4-N, and NO3-N. Total annual stream discharge was a positive predictor of annual DON output in all six watersheds, suggesting that DON export is related to regional precipitation. In contrast, annual discharge was a positive predictor of annual NO3-N output in one watershed, annual NH4-N output in three watersheds, and annual PON output in three watersheds. Of the four forms of N, only DON had consistent seasonal concentration patterns in all watersheds. Peak streamwater DON concentrations occurred in November-December after the onset of fall rains but before the peak in the hydrograph, probably due to flushing of products of decomposition that had built up during the dry summer. Multiple biotic controls on the more labile nitrate and ammonium concentrations in streams may obscure temporal DIN flux patterns from the terrestrial environment. Results from this study underscore the value of using several watersheds from a single climatic zone to make inferences about controls on stream N chemistry; analysis of a single watershed may preclude identification of geographically extensive mechanisms controlling N dynamics. 相似文献
11.
Quanxiao Fang Qiang Yu Enli Wang Yuhai Chen Guoliang Zhang Jing Wang Longhui Li 《Plant and Soil》2006,284(1-2):335-350
There is a growing concern about excessive nitrogen (N) and water use in agricultural systems in North China due to the reduced
resource use efficiency and increased groundwater pollution. A two-year experiment with two soil moisture by four N treatments
was conducted to investigate the effects of N application rates and soil moisture on soil N dynamics, crop yield, N uptake
and use efficiency in an intensive wheat–maize double cropping system (wheat–maize rotation) in the North China Plain. Under
the experimental conditions, crop yield of both wheat and maize did␣not␣increase significantly at N rates above 200 kg N ha−1. Nitrogen application rates affected little on ammonium-N (NH4-N) content in the 0–100 cm soil profiles. Excess nitrate-N (NO3-N), ranging from 221 kg N ha−1 to 620 kg N ha−1, accumulated in the 0–100 cm soil profile at the end of second rotation in the treatments with N rates of 200 kg N ha−1 and 300 kg N ha−1. In general, maize crop has higher N use efficiency than wheat crop. Higher NO3-N leaching occurred in maize season than in wheat season due to more water leakage caused by the concentrated summer rainfall.
The results of this study indicate that the optimum N rate may be much lower than that used in many areas in the North China
Plain given the high level of N already in the soil, and there is great potential for reducing N inputs to increase N use
efficiency and to mitigate N leaching into the groundwater. Avoiding excess water leakage through controlled irrigation and
matching N application to crop N demand is the key to reduce NO3-N leaching and maintain crop yield. Such management requires knowledge of crop water and N demand and soil N dynamics as
they change with variable climate temporally and spatially. Simulation modeling can capture those interactions and is considered
as a powerful tool to assist in␣the␣future optimization of N and irrigation managements.
Section Editor: L. Wade 相似文献
12.
The Ferrous Wheel Hypothesis (Davidson et al. 2003) postulates the abiotic formation of dissolved organic N (DON) in forest floors, by the fast reaction of NO2
− with dissolved organic C (DOC). We investigated the abiotic reaction of NO2
− with dissolved organic matter extracted from six different forest floors under oxic conditions. Solutions differed in DOC
concentrations (15–60 mg L−1), NO2
− concentrations (0, 2, 20 mg NO2
−-N L−1) and DOC/DON ratio (13.4–25.4). Concentrations of added NO2
− never decreased within 60 min, therefore, no DON formation from added NO2
− took place in any of the samples. Our results suggest that the reaction of NO2
− with natural DOC in forest floors is rather unlikely. 相似文献
13.
The responses of soil-atmosphere carbon (C) exchange fluxes to growing atmospheric nitrogen (N) deposition are controversial, leading to large uncertainty in the estimated C sink of global forest ecosystems experiencing substantial N inputs. However, it is challenging to quantify critical load of N input for the alteration of the soil C fluxes, and what factors controlled the changes in soil CO2 and CH4 fluxes under N enrichment. Nine levels of urea addition experiment (0, 10, 20, 40, 60, 80, 100, 120, 140 kg N ha−1 yr−1) were conducted in the needle-broadleaved mixed forest in Changbai Mountain, Northeast China. Soil CO2 and CH4 fluxes were monitored weekly using the static chamber and gas chromatograph technique. Environmental variables (soil temperature and moisture in the 0–10 cm depth) and dissolved N (NH4+-N, NO3−-N, total dissolved N (TDN), and dissolved organic N (DON)) in the organic layer and the 0–10 cm mineral soil layer were simultaneously measured. High rates of N addition (≥60 kg N ha−1 yr−1) significantly increased soil NO3−-N contents in the organic layer and the mineral layer by 120%-180% and 56.4%-84.6%, respectively. However, N application did not lead to a significant accumulation of soil NH4+-N contents in the two soil layers except for a few treatments. N addition at a low rate of 10 kg N ha−1 yr−1 significantly stimulated, whereas high rate of N addition (140 kg N ha−1 yr−1) significantly inhibited soil CO2 emission and CH4 uptake. Significant negative relationships were observed between changes in soil CO2 emission and CH4 uptake and changes in soil NO3−-N and moisture contents under N enrichment. These results suggest that soil nitrification and NO3−-N accumulation could be important regulators of soil CO2 emission and CH4 uptake in the temperate needle-broadleaved mixed forest. The nonlinear responses to exogenous N inputs and the critical level of N in terms of soil C fluxes should be considered in the ecological process models and ecosystem management. 相似文献
14.
Qing Liu Huajun Yin Jinsong Chen Chunzhang Zhao Xinying Cheng Yunyan Wei Bo Lin 《Ecological Research》2011,26(3):637-648
The impacts of global climatic change on belowground ecological processes of terrestrial ecosystems are still not clear. We
therefore conducted an experiment in the subalpine coniferous forest ecosystem of the eastern edges of the Tibetan Plateau
to study roots of Picea asperata seedlings and rhizosphere soil responses to soil warming and nitrogen availability from April 2007 to December 2008. The
seedlings were subjected to two levels of temperature (ambient; infrared heater warming) and two nitrogen levels (0 or 25 g m−2year−1 N). We used a free air temperature increase from an overhead infrared heater to raise both air and soil temperature by 2.1
and 2.6°C, respectively. The results showed that warming alone significantly increased total biomass, coarse root biomass
and fine root biomass of P. asperata seedlings. Both total biomass and fine root biomass were increased, but coarse root biomass was significantly decreased by
nitrogen fertilization and warming combined with nitrogen fertilization. Warming induced a prominent increase in soil organic
carbon (SOC) and NO3
−-N of rhizosphere soil, while nitrogen fertilization significantly decreased SOC and NH4
+-N of rhizosphere soil. The warming, fertilization and warming × N fertilization interaction decreased soil microbial C significantly,
but substantially increased soil microbial N. These results suggest that nitrogen deposition combined with warmer temperatures
under future climatic change possibly will have no effect on fine root production of P. asperata seedlings, but could enhance the nitrification process of their rhizosphere soils in subalpine coniferous forests. 相似文献
15.
We are studying the chemical quality of dissolved organic nitrogen (DON) in a high-elevation watershed in the Colorado Front Range. Samples were collected over the 2000 snowmelt runoff season at two sites across an alpine/subalpine ecotone to understand how the transition between the lightly vegetated alpine and forested reaches of the catchment influences the chemical character of DON. Samples were analyzed approximately weekly for dissolved organic material (DOM) content and chemical character. A subset of samples was analyzed for the elemental content of fulvic and hydrophilic acids. Concentrations of DON at both sites were highest in the spring at the initiation of snowmelt, decreased during snowmelt, and increased again during the late summer and fall. In contrast, concentrations of dissolved organic carbon (DOC) peaked on the ascending limb of the hydrograph and declined to seasonal minima on the descending limb of the hydrograph. The ratio of DOC:DON showed a seasonal shift at both sites with high values (40 to 55) during peak runoff in early summer and lower values (15 to 25) during low flows late in the runoff season. These results indicate that there was a seasonal change in the relative N content of DOM at both sites. Chemical fractionation of DOC showed that there were temporal and longitudinal changes in the chemical character of DOC. At the alpine site, the fulvic acid content of DOC decreased from 57% in June to 35% in September. The change in fulvic acid was less pronounced at the forested site, from 66% in June to 54% in September. Elemental analysis of fulvic and hydrophilic acids indicated that hydrophilic acids were N rich compared to fulvic acids. Additionally, fulvic and hydrophilic acids isolated at the alpine site had a lower C:N ratio than those isolated at the forested site. Similarly, the C:N ratio of organic acids at both sites was lower in September than in June during peak runoff. These differences appear to be a result of changes in both DOM precursor material and hydrologic flowpaths. Using C:N ratios of fulvic and hydrophilic acids, we estimate that nonhumic material carried between 54 to 73% of the organic N in surface water at the alpine site and 44 to 58% of the organic N in surface water at the subalpine site. 相似文献
16.
Anthony Darrouzet-Nardi Joseph Erbland William D. Bowman Joel Savarino Mark W. Williams 《Biogeochemistry》2012,109(1-3):271-285
Knowledge of import, export, and transport of nitrogen (N) in headwater catchments is essential for understanding ecosystem function and water quality in mountain ecosystems, especially as these ecosystems experience increased anthropogenic N deposition. In this study, we link spatially explicit soil and stream data at the landscape scale to investigate import, export and transport of N in a 0.89?km2 site at the alpine-subalpine ecotone in the Front Range of the Rocky Mountains, Colorado, U.S.A. For two of the major N inputs to our site, N deposition in the snowpack and N fixation, a complementary relationship was found across the study site, with greater abundance of N-fixing plants in areas with less snow and substantial snow inputs in areas with low N fixer abundance. During the initial phases of snowmelt, mixing model end members for oxygen isotopes in nitrate (NO3 ?) indicated that a substantial quantity of NO3 ? is transported downhill into the forested subalpine without being assimilated by soil microbes. After this initial pulse, much less NO3 ? entered the stream and most but not all of it was microbial in origin. Rising δ15N in stream NO3 ? indicated greater influence of fractionating processes such as denitrification later in the season. NO3 ? from both atmospheric and microbial sources was not exported from our site because it was consumed within the first several hundred meters of the stream; ultimately, N exports were in the form of dissolved organic nitrogen (DON) and particulate N (PN). The results of this study suggest that the highest elevation dry alpine meadows rely more heavily on N fixation as an N source and experience less of the effects of anthropogenic N deposition than mid and lower elevation areas that have more snow. Our data also suggest that mid-elevation krummholz, moist meadows, and talus slopes are exporting N as NO3 ? shortly after the onset of snowmelt, but that this NO3 ? is rapidly consumed as the stream flows through the subalpine forest. This consumption by assimilation and/or denitrification currently provides a buffer against increased inorganic N availability downstream. 相似文献
17.
The lignite and pyrite containing spoil substrates of the Lusatian mining district are marked by very high acidity and salt
concentrations due to pyrite oxidation and by a very low content of pedogenic organic matter and nutrients. The effects of
fly ash application to neutralize the produced acid and of organic waste material application to improve the ecological soil
functions were studied considering the carbon and nitrogen cycling. Nineteen, 38 and 57 t ha−1 sewage sludge and 22, 44 and 66 t ha−1 compost were applied to ameliorated lignite and pyrite containing substrate. An automated soil microcosm system was used
to analyse the solid, gaseous and liquid phases. Almost 9% of total N applied with sewage sludge (620, 1240 and 1860 t N ha−1 applied) were lost over a period of 150 days mainly as NO3-N. The total N losses from compost treatments were three times lower (2.8–3.1% of applied Nt) and occurred in similar quantities
as NH4-N and NO3-N. Only sewage sludge treatments showed slightly increased N2O emissions at the beginning of the experiment. CO2 emissions determined the carbon losses of all treatments. The C losses amounted to 3.2–4.7% and 1.5–2.7% of Ct applied with sewage sludge and with compost, respectively.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
18.
Temperature sensitivity of soil carbon and nitrogen mineralization: impacts of nitrogen species and land use type 总被引:3,自引:0,他引:3
Background and aims
Climate warming, nitrogen (N) deposition and land use change are some of the drivers affecting ecosystem processes such as soil carbon (C) and N dynamics, yet the interactive effects of those drivers on ecosystem processes are poorly understood. This study aimed to understand mechanisms of interactive effects of temperature, form of N deposition and land use type on soil C and N mineralization.Methods
We studied, in a laboratory incubation experiment, the effects of temperature (15 vs. 25 °C) and species of N deposition (NH4 +-N vs. NO3 ?-N) on soil CO2 efflux, dissolved organic C (DOC) and N (DON), NH4 +-N, and NO3 ?-N concentrations using intact soil columns collected from adjacent forest and grassland ecosystems in north-central Alberta.Results
Temperature and land use type interacted to affect soil CO2 efflux, concentrations of DON, NH4 +-N and NO3 ?-N in most measurement times, with the higher incubation temperature resulted in the higher CO2 efflux and NH4 +-N concentrations in forest soils and higher DON and NO3 ?-N concentrations in grassland soils. Temperature and land use type affected the cumulative soil CO2 efflux, and DOC, DON, NH4 +-N and NO3 ?-N concentrations. The form of N added or its interaction with the other two factors did not affect any of the C and N cycling parameters.Conclusions
Temperature and land use type were dominant factors affecting soil C loss, with the soil C in grassland soils more stable and resistant to temperature changes. The lack of short-term effects of the deposition of different N species on soil C and N mineralization suggest that maybe there was a threshold for the N effect to kick in and long-term experiments should be conducted to further elucidate the species of N deposition effects on soil C and N cycling in the studied systems. 相似文献19.
The effects of a slow-release N-enriched rock powder on soil chemistry, on the development of the soil vegetation (field layer
vegetation), on the nutritional status of pine seedlings (Pinus sylvestris L.), and on decomposition rates of cellulose in
lignite-poor mine spoils were studied. In the initial phase after afforestation fertilization caused a significant increase
in NO3
−-N concentrations in the soil solution of the top-soil (0–60 cm). Subsequently, NO3
−-N concentrations of all N fertilized treatments decreased with the exception of the highest N application area (500 kg N
ha−1). This decrease of NO3
−-N concentrations was related to the establishment of a field layer vegetation, which developed according to the amount of
N applied. In the above-ground phytomass of the field layer vegetation a maximum N accumulation amount of 22 kg ha−1 was measured. Cellulose decomposition increased with higher N application rates. In the second year after N-fertilization,
the pine needles indicated insufficient supply for almost all nutrients except for N. The deficiency symptoms were most pronounced
at the plots that had received the highest amounts of nitrogen. This phenomenon appears to be related to the competition by
the field layer vegetation.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
增氮对青藏高原东缘高寒草甸土壤甲烷吸收的早期影响 总被引:1,自引:0,他引:1
研究大气氮沉降对青藏高原高寒草甸土壤CH4吸收的影响,对于揭示氮素调节土壤CH4吸收的机制和评价氮沉降增加背景下大气CH4收支平衡至关重要.通过构建多形态、低剂量的增氮控制试验,测定土壤CH4净交换通量和相关土壤理化性质,分析高寒草甸土壤CH4通量变化特征及其主要驱动因子.研究结果表明:自然状态下高寒草甸土壤是大气CH4汇,CH4平均吸收量为(35.40±1.92) μg· m-2· h-1.土壤CH4吸收主要受水分驱动,其次为土壤NH4+-N和NO3-N含量.NH4+-N抑制CH4吸收,NO3--N促进CH4吸收;不同剂量氮素输入对土壤CH4吸收影响也不尽相同,低氮处理促进土壤CH4吸收,而中氮和高氮处理抑制土壤CH4吸收.结果显示青藏高原高寒草甸土壤是重要的大气CH4汇,在未来大气氮沉降加倍的情景下CH4汇功能增强,但当氮沉降量增加两倍以上时CH4汇功能将会减弱. 相似文献