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1.
Summary Mobilization of soil-borne N, N fertilization and N removal by crops influence EUF-NO3-N contents as well as EUF-Norg contents in the course of a vegetation period. N mobilization alone (no N fertilization) increases the EUF-Norg contents only temporarily (mainly in May and July), while in December they are almost the same as in March (Table 1). The EUF-NO3 contents, on the contrary, increase during the vegetation period, so that an increment in NO3 is registered in unplanted pots in December. This increment is larger the higher the EUF-Norg contents are in March (Table 2).N fertilization increases the contents of both EUF-Norg and EUF-NO3, so that there is an increment in EUF-Norg as well as EUF-NO3 in December (Table 2). This finding also applies to field experiments under fallow (Figs. 4 and 5). However, in contrast to the pot experiment, the EUF-N contents in the field experiment were only temporarily increased by N mobilization alone. This means that N immobilization had taken place which had not been observed in the pot experiment under stable moisture conditions (Fig. 4 and Table 1).A close correlation between hot-water-soluble N contents and EUF-Norg is found only under uniform management conditions (uniform N-fertilizer rates). Depending on the time of sampling different regression equations are, however, obtained because of changes in EUF-Norg due to N mobilization, whereas the hot-water-soluble N contents hardly show any variations during the vegetation period (Fig. 6 and Table 3). 相似文献
2.
Summary Increasing quantities of slurry (30, 60 and 90 m3/ha as well as 60 m3/ha + DIDIN) were applied to two sandy soils both in September and in December 1982. During the 1982/83 winter EUF-N was determined in soil horizons (0–30 cm, 30–60 and 60–90 cm).EUF-NO3 and EUF-Norg clearly reflected the different quantities of slurry applied. The retarding effect of DIDIN on nitrification could also be demonstrated by means of the EUF-N contents.Due to the mild and humid climate prevailing in the winter of 1982/83 slurry-NO3 of the September applications had obviously been leached out of the 0–60 cm soil layer in all treatments by February and even out of the 60–90 cm layer by March 24. Translocation of NO3 was also observed for slurry applied in December. But in this case on March 24 the EUF-NO3 contents in the 60–90 cm layer still reflected the quantities of slurry applied four months earlier.After slurry application the EUF-Norg fraction of a soil initially consists mainly of NH
4
+
which is rapidly oxidized to NO3 and transferred in this form to deeper layers. As a consequence a rapid decline in EUF-Norg fraction is observed. It could therefore be expedient to consider the Norg and EUF-NH
4
+
fractions separately when slurry applications are concerned. 相似文献
3.
秸秆和地膜覆盖对渭北旱作玉米农田土壤氮组分与产量的影响 总被引:5,自引:0,他引:5
基于田间定位试验,研究了秸秆和地膜覆盖措施对旱作春玉米田土壤氮组分和作物产量的影响。试验包括无覆盖对照,秸秆覆盖和地膜覆盖3个处理,观测指标包括土壤全氮(STN)、颗粒有机氮(PON)、潜在可矿化氮(PNM)、微生物量氮(MBN)、硝态氮(NO_3~--N)、铵态氮(NH_4~+-N)含量及作物产量。结果表明:试验进行5到7年后,与对照相比,秸秆覆盖处理0—10 cm土层STN、PON、PNM、MBN和NO_3~--N含量3年平均分别提高了13.11%、64.29%、17.51%、16.94%和55.37%,10—20 cm土层STN、PON、MBN和NO_3~--N含量3年平均分别提高了5.93%、33.33%、15.78%和27.57%(P0.05)。而地膜覆盖处理0—10 cm和10—20 cm土层NO_3~--N的含量较对照分别提高了189.14%和135.75%(P0.05),其他氮组分与对照处理差异不显著。秸秆和地膜覆盖处理玉米产量较对照处理3年平均分别提高了6.90%和36.74%(P0.05)。玉米产量与0—20 cm土层NO_3~--N含量和NO_3~--N/STN值呈显著正相关关系。总的来看,秸秆覆盖能显著增加旱地土壤全氮和活性有机氮含量,促进氮素固定,但需注意作物生长后期补充氮肥以满足作物生长需要。而地膜覆盖能显著提高土壤氮素有效性和作物产量,但不利于土壤有机氮的固定,且表层土壤存在潜在氮淋失风险。 相似文献
4.
Summary An evaluation of the N release by soil organic matter can be obtained by measurements of the course of soil mineral nitrogen on uncropped objects. This N mineralization was studied during several years on some soil types with incorporations of various organic matter. The real N mineralization on a given soil with similar inputs of organic matter varied little from year to year. On the other hand, the net result of NO
3
–
-N increase between spring and autumn showed wider variation, especially due to N losses. 相似文献
5.
Dormant season inorganic nitrogen (N) leaching varies considerably among forested catchments with similar bedrock, forest cover and deposition history. Recent work has highlighted the importance of winter rain-on-snow (ROS) events as a source of winter nitrate (NO3-N) export, but differences among streams are likely due to differences in baseflow NO3-N concentrations, and thus soil N processes. The objective of this study was to investigate rates of N-mineralization and nitrification as well as their potential environmental controls throughout the year, but with particular focus on the winter season in south-central Ontario, Canada. Field incubations were utilized to assess differences in NO3-N and ammonium production over time and across topographic positions in two catchments with contrasting patterns of N export. Rates of nitrification were similar to rates of total mineralization, and nitrification rates were significantly higher during the summer and spring compared with the winter and fall; however, winter nitrification was substantial, and ranged from 19 to 36 % of annual rates. Seasonal differences in nitrification were largely driven by temperature, soil moisture and inorganic N concentration in soil. Rain and melting snow infiltrated the soil during ROS events, which were associated with increased NO3-N availability, particularly in well-drained soils, and ROS-induced increases in stream nitrate concentrations were largest at the catchment dominated by well-drained soil. Annual nitrification fluxes were almost two orders of magnitude greater than N deposition or NO3-N leaching fluxes at either catchment. Similar rates of NO3-N production within the two catchments suggest that consumption of NO3-N within wet soils is responsible for the 10-fold difference in NO3-N export between the two streams. Notably, these results suggest that consumption processes were important for reducing NO3-N export even during winter ROS events. 相似文献
6.
The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40–58 µmol L−1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4
+) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3
−) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4
+ production in winter and spring, and the maximum NO3
− reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4
+ concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3
− fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form. 相似文献
7.
Fate of urine nitrogen on mineral and peat soils in New Zealand 总被引:2,自引:0,他引:2
A field lysimeter experiment was conducted over 150 days to examine the fate of synthetic urinary nitrogen (N) applied to peat and mineral soils, with and without a water table. At the start of the winter season, synthetic urine labelled with 15N, was applied at 500 kg N ha–1. Plant uptake, leaching losses and nitrous oxide (N2O) fluxes were monitored. Total plant uptake ranged from 11% to 35% of the urine-N applied depending on soil type and treatment. Plant uptake of applied N was greater in the presence of a water table in the mineral soil. Nitrate-N (NO3
--N) was only detected in leachates from the mineral soil, at concentrations up to 146 g NO3
--N mL–1. Presence of a water table in the mineral soil reduced leaching losses (as inorganic-N) from 47% to 6%, incrased plant uptake and doubled apparent denitrification losses. In the peat soils leaching losses of applied urine-N as inorganic-N were low (<5%). Losses of N as N2O were greater in the mineral soil than in the peat soils, with losses of 3% and <1% of N applied respectively after 100 days. Apparent denitrification losses far exceeded N2O losses and it is postulated that the difference could be due to dinitrogen (N2) loss and soil entrapment of N2. 相似文献
8.
Carleton S. White 《Biogeochemistry》1991,12(1):43-68
The effects of select monoterpenes on nitrogen (N) mineralization and nitrification potentials were determined in four separate laboratory bioassays. The effect of increasing monoterpene addition was an initial reduction in NO3
–-N production (nitrification inhibition), followed by a reduction in the sum of NH4
+-N and NO3
–-N (inhibition of net N mineralization and net immobilization at high monoterpene additions. Monoterpenes could produce this pattern by inhibiting nitrification, reducing net N mineralization, enhancing immobilization of NO3
–-N relative to NH4
+-N, and/or stimulating overall net immobilization of N by carbon-rich material.Initial monoterpene concentrations in the assay soils were about 5% of the added amount and were below detection after incubation in most samples.Potential N mineralization-immobilization, nitrification, and soil monoterpene concentrations were determined by soil horizon for four collections from a ponderosa pine (Pinus ponderosa) stand in New Mexico. Concentrations of monoterpenes declined exponentially with soil depth and varied greatly within a horizon. Monoterpene content of the forest floor was not correlated with forest floor biomass. Net N mineralization was inversely correlated with total monoterpene content of all sampled horizons. Nitrification was greatest in the mineral soil, intermediate in the F-H horizon, and never occurred in the L horizon. Nitrification in the mineral soil was inversely correlated with the amount of monoterpenes in the L horizon that contain terminal unsaturated carbon-carbon bonds (r
2 = 0.37, P 0.01). This pattern in the field corresponded to the pattern shown in the laboratory assays with increasing monoterpene additions. 相似文献
9.
Nitrogen fertigation of greenhouse-grown cucumber 总被引:2,自引:0,他引:2
I. Papadopoulos 《Plant and Soil》1986,93(1):87-93
Summary This greenhouse study investigated the response of trickle-irrigated cucumber (Cucumis sativa cv. ‘Petita’) to three N levels applied with every irrigation via the irrigation stream. The plants were grown in pots filled
with 12 kg of soil. Water containing 5.8, 11.8, or 17.8 mmol N/l, and uniformly supplied with 2.0 and 3.9 mmol/l of P and
K, respectively, was applied two to three times daily. In all treatments of 0.3 leaching fraction was allowed.
The resulting total N applications were 15.7, 31., and 47.2 g N/plant. The total amount of water applied was 1851/plant. Total
N and NO3-N, in lajinae and petioles, increased with increasing N level whereas P and K in generated decreased. Although different
NO3/NH4 ratios in the treatments may have influeced the response to N, it could be concluded that the highest yield was obtained
with 11.8 mmol N/1 due to increased number of fruit. In the root volume of this treatment the NO3-N concentration in the soil solution was aroun 7 mmol/1 for most of the growing season. The dry matter concentration of fruits
was not affected by the N levels.
It was concluded that 11.8 mmol N/1 applied with every irrigation via the irrigation stream is adequate to cover the needs
of greenhous-grown cucumber for higher yield (9.42 kg/plant over a harvesting period of 93 days). 相似文献
10.
Throughout the summer, abundance of Ulva lactuca L. declined while biomass of Cladophora vagabunda (L.) van den Hoek and Gracilaria tikvahiae McLachlan increased in a New England embayment undergoing eu-trophication (Waquoit Bay, Massachusetts). We investigated the physiological basis for the summer dieback, focusing on temporal variations in photosynthetic performance and tissue nitrogen (N). We also compared photosynthetic and N uptake capabilities of U. lactuca with other abundant species in this eutrophic system. Photosynthetic egiciency and capacity of U. lactuca declined markedly at 25°C, compared with a spring (15°C) peak in photosynthetic performance; Pmax was 4.6 ± 0.3 and 1.8 ± 0.6 μmol O2.m?2.s?1 during spring and summer, respectively. Notably, summer pmax of other abundant species of the embayment was 1.5–3 × higher than that measured for U. lactuca. Ulva lactuca showed a signifciant photosynthetic response to dissolved inorganic carbon enrichment during summer, when water-column-dissolved CO2 levels were 20% of spring values. Although ammonium uptake rates of U. lactuca were extremely high at both subsaturating (15μM) and saturating (75 μM) N concentrations, as predicted by the functional-form hypothesis, tissue N fell to 1% by late summer. We suggest that a carbon imbalance, initiated by rising water temperatures and declining water-column N; thermal stress; and biological factors (competition, grazing) all contribute to the recurrent summer decline of U. lactuca in this shallow, eutrophic embayment. Thus, while the morphology of U. lactuca might be considered a successful strategy for disturbed, or “stressed” (sensu Littler and Littler 1980), habitats, its inability to persist and flourish in this environment emphasizes the complexity of factors at work in natural systems. 相似文献
11.
Peter Sørensen 《Plant and Soil》2004,267(1-2):285-296
About 50–60% of dairy cattle slurry nitrogen is ammonium N. Part of the ammonium N in cattle slurry is immobilised due to
microbial decomposition of organic matter in the slurry after application to soil. The immobilisation and the remineralisation
influence the fertiliser value of slurry N and the amount of organic N that is retained in soil. The immobilisation and the
remineralisation of 15 N-labelled dairy cattle slurry NH4-N were studied through three growing seasons after spring application under temperate conditions. Effects of slurry distribution
(mixing, layer incorporation, injection, surface-banding) and extra litter straw in the slurry on the plant utilisation of
labelled NH4-N from slurry were studied and compared to the utilisation of 15N-labelled mineral fertiliser. The initial immobilisation of slurry N was influenced by the slurry distribution in soil. More
N was immobilised when the slurry was mixed with soil. Surface-banding of slurry resulted in significant volatilisation losses
and less residual 15N in soil. Much more N was immobilised after slurry incorporation than after mineral fertiliser application. After 2.5 years
the recovery of labelled N in soil (0–25 cm) was 46% for slurry mixed with soil, 42% for injected slurry, 22% for surface-banded
slurry and 24% for mineral fertiliser N. The total N uptake in a ryegrass cover crop was 5–10 kg N/ha higher in the autumn
after spring-application of cattle slurry (100–120 kg NH4-N/ha) compared to the mineral fertiliser N reference, but the immobilised slurry N (labelled N) only contributed little to
the extra N uptake in the autumn. Even in the second autumn after slurry application there was an extra N uptake in the cover
crop (0–10 kg N/ha). The residual effect of the cattle slurry on spring barley N uptake was insignificant in the year after
slurry application (equivalent to 3% of total slurry N). Eighteen months after application, 13% of the residual 15N in soil was found in microbial biomass whether it derived from slurry or mineral fertiliser, but the remineralisation rate
(% crop removal of residual 15N) was higher for fertiliser- than for slurry-derived N, except after surface-banding. Extra litter straw in the slurry had
a negligible influence on the residual N effects in the year after application.
It is concluded that a significant part of the organic N retained in soil after cattle slurry application is derived from
immobilised ammonium N, but already a few months after application immobilised N is stabilised and only slowly released. The
immobilised N has negligible influence on the residual N effect of cattle slurry in the first years after slurry application,
and mainly contributes to the long-term accumulation of organic N in soil together with part of the organic slurry N. Under
humid temperate conditions the residual N effects of the manure can only be optimally utilised when soil is also covered by
plants in the autumn, because a significant part of the residual N is released in the autumn, and there is a higher risk of
N leaching losses on soils that receive cattle slurry regularly compared to soils receiving only mineral N fertilisers. 相似文献
12.
High rates of deforestation in the Brazilian Amazon have the potential to alter the storage and cycling of carbon (C) and nitrogen (N) across this region. To investigate the impacts of deforestation, we quantified total aboveground biomass (TAGB), aboveground and soil pools of C and N, and soil N availability along a land-use gradient in Rondônia, Brazil, that included standing primary forest, slashed primary and secondary forest, shifting cultivation, and pasture sites. TAGB decreased substantially with increasing land use, ranging from 311 and 399 Mg ha–1 (primary forests) to 63 Mg ha–1 (pasture). Aboveground C and N pools declined in patterns and magnitudes similar to those of TAGB. Unlike aboveground pools, soil C and N concentrations and pools did not show consistent declines in response to land use. Instead, C and N concentrations were strongly related to percent clay content of soils. Concentrations of NO3-N and NH4-N generally increased in soils following slash-and-burn events along the land-use gradient and decreased with increasing land use. Increasing land use resulted in marked declines in NO3-N pools relative to NH4-N pools. Rates of net nitrification and N-mineralization were also generally higher in postfire treatments relative to prefire treatments along the land-use gradient and declined with increasing land use. Results demonstrate the linked responses of aboveground C and N pools and soil N availability to land use in the Brazilian Amazon; steady reductions in aboveground pools along the land-use gradient were accompanied by declines in inorganic soil N pools and transformation rates. 相似文献
13.
A laboratory incubation experiment was conducted to study the effect of organic amendment and moisture regimes on the immobilization-remineralization
of NO3-N and total N balance in soil fertilized with KNO3. Immobilization of NO3-N was very rapid in soil amended with glucose and sucrose followed by a remineralization of organic N and accumulation of
mineral N. Cellulose caused a slow but continued immobilization and did not show net accumulation of mineral N during 8 weeks
of incubation. At the end of incubation, a significant increase in total N and organic N content of the soil was observed
which is perhaps attributable to the activity of free living N2 fixers. Although N losses seemed to have occurred at 100% WHC through denitrification in soil amended with glucose and sucrose,
main cause of NO3 elimination was microbial immobilization. 相似文献
14.
The influence of the source of inorganic nitrogen (KNO3, (NH4)2SO4 and NH4NO3) and its concentration (5, 10, 20 and 30 mM N) on total N incorporation, as well as on N distribution into different fractions (amminiacal, amino, amide and protein) and on free amino acid levels has been determined in grape vine explants cultured in vitro.Increasing concentrations of the nitrogen source resulted in increased total N content in tissues. This effect was small for KNO3, higher for (NH4)2SO4 and maximal for NH4NO3. In addition, nitrate promoted an increase in amino-N only, whereas ammonium increased both the ammoniacal-N and the amino-N fractions. Incorporation of N into amide-N and protein-N were not affected significantly by the N sources tested.The application of increasing quantities of N enhanced the accumulation of most free amino acids, especially arginine, alanine and proline, but to different extents, depending on both the N source and its concentration. The combination of ammonium and nitrate resulted in a higher accumulation of amino acids than that observed with either one of the two forms alone. 相似文献
15.
Seasonal variation in nitrogen uptake and turnover in two high-elevation soils: mineralization responses are site-dependent 总被引:1,自引:0,他引:1
Amy E. Miller Joshua P. Schimel James O. Sickman Kevin Skeen Thomas Meixner John M. Melack 《Biogeochemistry》2009,93(3):253-270
In arctic and alpine ecosystems, soil nitrogen (N) dynamics can differ markedly between winter and summer months, and nitrogen
losses can be measurable during the spring and fall transitions. To explore the effect of seasonality on biogeochemical processes
in a temperate alpine environment, we used a combination of field incubations (year-round) and 15N tracer additions (late fall, early spring, summer) to characterize soil N dynamics in a wet and dry meadow in the Sierra
Nevada, California. The snowmelt to early summer season marked a period of high 15N uptake and turnover in the two soils, coincident with the increase in microbial N pools at the start of snowmelt (wet and
dry meadow); an increase in net N mineralization and net nitrification as snowmelt progressed (wet meadow only); and measureable
net production of 15N-NH4
+ in mid-summer (wet and dry meadow). Whereas fluctuations in microbial biomass were generally synchronous between the wet
and dry meadow soils, only wet meadow soils appeared to mineralize N in response to declines in the microbial N pool. Net
N mineralization and net nitrification rates in the dry meadow soil were negligible on all but one sampling date, in spite
of periodic decreases in biomass of up to 60%. Across both sites, high 15N recoveries in microbial biomass N, rapid 15N-NH4
+ turnover, and low or negative net 15N-NH4
+ fluxes suggested tight cycling of N, particularly in the late fall and early spring. 相似文献
16.
J. K. R. Gasser 《Plant and Soil》1962,17(2):209-220
Summary The changes in the ammonium-N and nitrate-N contents of bare fallow and soil under the first and third crops of winter wheat after fallow were followed on plots of Broadbalk Field, Rothamsted, which have received for each crop 14 tons farmyard manure (FYM) per acre, complete minerals (P, K, Na, Mg), or complete minerals + nitrogen fertilizers.More mineral N was produced during fallow on the plot receiving FYM than on the other plots. Soil under wheat also contained more mineral N on the FYM plots than elsewhere. Nitrogen fertilizers applied in the spring temporarily increased the mineral-N content of the soil, but were rapidly removed by the crop. Ammonium sulphate applied in the autumn was lost from the surface soil by the following March through nitrification and leaching.Twice as much mineral-N was produced when soil from the FYM plot was incubated as when soils from other plots were similarly treated. Nitrate formed during fallow was leached into the subsoil during the autumn and winter, and recovered by the wheat during the following spring and summer. Its existence is not detected by sampling the surface soil, nor by an incubation test. This source of nitrogen complicates the use of laboratory measurements to assess the fertilizer nitrogen required by winter wheat. Since the crop removed mineral N from the surface soil by March, estimation of the amount then present was also of no value for making fertilizer recommendations. 相似文献
17.
Long-term response of a shallow, moderately flushed lake to reduced external phosphorus and nitrogen loading 总被引:11,自引:2,他引:9
J. KÖHLER S. HILT R. ADRIAN A. NICKLISCH H. P. KOZERSKI N. WALZ 《Freshwater Biology》2005,50(10):1639-1650
1. The responses of nutrient concentrations, plankton, macrophytes and macrozoobenthos to a reduction in external nutrient loading and to contemporary climatic change were studied in the shallow, moderately flushed Lake Müggelsee (Berlin, Germany). Weekly to biweekly data from 1979 to 2003 were compared with less frequently collected historical data. 2. A reduction of more than 50% in both total phosphorus (TP) and total nitrogen (TN) loading from the hypertrophic (1979–90) to the eutrophic period (1997–2003) was followed by an immediate decline in TN concentrations in the lake. TP concentrations only declined during winter and spring. During summer, phosphorus (P) release from the sediments was favoured by a drastic reduction in nitrate import. Therefore, Müggelsee acted as a net P source for 6 years after the external load reduction despite a mean water retention time of only 0.1–0.16 years. 3. Because of the likely limitation by P in spring and nitrogen (N) in summer, phytoplankton biovolume declined immediately after nutrient loading was reduced. The formerly dominant cyanobacteria (Oscillatoriales) Limnothrix redekei and Planktothrix agardhii disappeared, but the mean biovolume of the N2‐fixing species Aphanizomenon flos‐aquae remained constant. 4. The abundance of Daphnia spp. in summer decreased by half, while that of cyclopoid copepod species increased. Abundances of benthic macroinvertebrates (mainly chironomids) decreased by about 80%. A resource control of both phytoplankton and zooplankton is indicated by significant positive correlations between nutrient concentrations and phytoplankton biovolume and between phytoplankton and zooplankton biomass. 5. Water transparency in spring increased after nutrient reduction and resulted in re‐colonisation of the lake by Potamogeton pectinatus. However, this process was severely hampered by periphyton shading and grazing by waterfowl and fish. 6. Water temperatures in Müggelsee have increased in winter, early spring and summer since 1979. The earlier development of the phytoplankton spring bloom was associated with shorter periods with ice cover, while direct temperature effects were responsible for the earlier development of the daphnid maximum in spring. 相似文献
18.
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
19.
Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soils 总被引:7,自引:0,他引:7
MATTHEW D. WALLENSTEIN SHAWNA K. MCMAHON† JOSHUA P. SCHIMEL† 《Global Change Biology》2009,15(7):1631-1639
Arctic soils contain large amounts of organic matter due to very slow rates of detritus decomposition. The first step in decomposition results from the activity of extracellular enzymes produced by soil microbes. We hypothesized that potential enzyme activities are low relative to the large stocks of organic matter in Arctic tundra soils, and that enzyme activity is low at in situ temperatures. We measured the potential activity of six hydrolytic enzymes at 4 and 20 °C on four sampling dates in tussock, intertussock, shrub organic, and shrub mineral soils at Toolik Lake, Alaska. Potential activities of N‐acetyl glucosaminidase, β‐glucosidase, and peptidase tended to be greatest at the end of winter, suggesting that microbes produced enzymes while soils were frozen. In general, enzyme activities did not increase during the Arctic summer, suggesting that enzyme production is N‐limited during the period when temperatures would otherwise drive higher enzyme activity in situ. We also detected seasonal variations in the temperature sensitivity (Q10) of soil enzymes. In general, soil enzyme pools were more sensitive to temperature at the end of the winter than during the summer. We modeled potential in situβ‐glucosidase activities for tussock and shrub organic soils based on measured enzyme activities, temperature sensitivities, and daily soil temperature data. Modeled in situ enzyme activity in tussock soils increased briefly during the spring, then declined through the summer. In shrub soils, modeled enzyme activities increased through the spring thaw into early August, and then declined through the late summer and into winter. Overall, temperature is the strongest factor driving low in situ enzyme activities in the Arctic. However, enzyme activity was low during the summer, possibly due to N‐limitation of enzyme production, which would constrain enzyme activity during the brief period when temperatures would otherwise drive higher rates of decomposition. 相似文献
20.
Effects of 60-year N,P, K and Ca fertilization on EUF-nutrient fractions in the soil and on yields of rye and potato crops 总被引:15,自引:0,他引:15
Summary In field experiments carried out uninterruptedly since 1923 on a sandy, grey-brown luvisol (8% clay) the EUF-nutrient fractions were determined after potato and rye crops in 1982 had been harvested.Annual applications of N fertilizer (90 kg N/ha) over a 60-year period raised both the organic and inorganic EUF-N fractions (Table 1). EUF-Norg values increased depending on crop rotation from 1.1–1.9 to 2.4–3.6 mg/100 g. This increase in EUF-N amounts was higher under rye monoculture than under potato monoculture. N leaching was more intensive under potato monoculture than under rye monoculture.Application of P, K and Ca fertilizers raised the EUF-P, EUF-K and EUF-Ca values at 20°C as well as at 80°C (Figs. 1, 2, 3). Analyses of soil samples from the 25–75 cm layer showed that the contents of EUF-Ca and EUF-K in this layer are as high as in the topsoil or even higher (Table 3).High yields of rye (>4 t/ha) and of potatoes (>30 t/ha) were obtained when in samples taken after harvest EUF-amounts of 3.5 mg N, 2 mg P, 3 mg K (in both topsoil and subsoil), 1.7 mg Mg and 20 mg Ca/100 g were released within 35 min. These levels were obtained with annual fertilizer application rates of 90 kg N, 60 kg P2O5 and 110 kg K2O/ha.Applications of 1.6 t CaO/ha every 4 years were sufficient to maintain the soil pH at 6.0–6.5. Calculated on the basis of EUF-Ca contents, with the amounts of K-selective minerals being taken into account, this rate of liming corresponds with the needs of acid sandy soils. 相似文献