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1.
Policy implications of human-accelerated nitrogen cycling   总被引:9,自引:2,他引:7  
The human induced input of reactive N into the globalbiosphere has increased to approximately 150 Tg N eachyear and is expected to continue to increase for theforeseeable future. The need to feed (125 Tg N) andto provide energy (25 Tg N) for the growing worldpopulation drives this trend. This increase inreactive N comes at, in some instances, significantcosts to society through increased emissions of NOx,NH3, N2O and NO3 and deposition of NOy and NHx.In the atmosphere, increases in tropospheric ozone andacid deposition (NOy and NHx) have led toacidification of aquatic and soil systems and toreductions in forest and crop system production. Changes in aquatic systems as a result of nitrateleaching have led to decreased drinking water quality,eutrophication, hypoxia and decreases in aquatic plantdiversity, for example. On the other hand, increaseddeposition of biologically available N may haveincreased forest biomass production and may havecontributed to increased storage of atmospheric CO2 inplant and soils. Most importantly, syntheticproduction of fertilizer N has contributed greatly tothe remarkable increase in food production that hastaken place during the past 50 years.The development of policy to control unwanted reactiveN release is difficult because much of the reactive Nrelease is related to food and energy production andreactive N species can be transported great distancesin the atmosphere and in aquatic systems. There aremany possibilities for limiting reactive N emissionsfrom fuel combustion, and in fact, great strides havebeen made during the past decades. Reducing theintroduction of new reactive N and in curtailing themovement of this N in food production is even moredifficult. The particular problem comes from the factthat most of the N that is introduced into the globalfood production system is not converted into usableproduct, but rather reenters the biosphere as asurplus. Global policy on N in agriculture isdifficult because many countries need to increase foodproduction to raise nutritional levels or to keep upwith population growth, which may require increaseduse of N fertilizers. Although N cycling occurs atregional and global scales, policies are implementedand enforced at the national or provincial/statelevels. Multinational efforts to control N loss tothe environment are surely needed, but these effortswill require commitments from individual countries andthe policy-makers within those countries.  相似文献   

2.
Mosier  Arvin R 《Plant and Soil》2001,228(1):17-27
Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH3, NOx (NO + NO2) and N2O. Emissions of NH3 and NOx (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to local and regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NOx also contribute to local elevated ozone concentrations while N2O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion.Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the 55 Tg N yr–1 NH3 from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and synthetic fertilizer application. About half of the 50 Tg N yr–1 of NOx emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NOx emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N2O. About 5% of the total atmospheric greenhouse effect is attributed to N2O from which 70% of the annual global anthropogenic emissions come from animal and crop production.The coupling of increased population with a move of a large sector of the world population to diets that require more energy and N input, will lead to continued increases in anthropogenic input into the global N cycle. This scenario suggests that emissions of NH3, NOx and N2O from agricultural systems will continue to increase and impact global terrestrial and aquatic systems, even those far removed from agricultural production, to an ever growing extent, unless N resources are used more efficiently or food consumption trends change.  相似文献   

3.
Atmospheric deposition of nutrients to the North Atlantic Basin   总被引:18,自引:6,他引:12  
Atmospheric chemical models are used to estimate the deposition rate of various inorganic oxides of nitrogen (NOy), reduced nitrogen species (NHx) and mineral dust to the North Atlantic Ocean (NAO). The estimated deposition of NOy to the NAO (excluding the coastal ocean) and the Caribbean is 360 × 109 Moles-N m–2 yr–1 (5.0 Tg N); this is equivalent to about 13% of the estimated global emission rate (natural and anthropogenic) and a quarter of the emission rate from sources in North America and Europe. In the case of NHx, 258 Moles-N m–2 yr–1 (3.6 Tg N) are deposited to the NAO and the Caribbean; this is about 6% of the global continental emissions. There is relatively little data on the deposition rate of organic nitrogen species; nonetheless, this evidence suggests that concentrations and deposition rates are comparable to those for inorganic nitrogen.Because of anthropogenic emissions, the present-day deposition rate of NOy to the NAO is about five times greater than pre-industrial times largely due to emissions from energy production and biomass burning. The present-day emissions of NHx from continental anthropogenic sources are about four-to-five times greater than natural sources, mostly due to the impact of emissions from animal wastes associated with food production. Indeed, present-day emissions of NHx from animal waste are estimated to be about 10 times greater than the pre-human era. The deposition rate of mineral dust to the NAO is about 170 Tg yr–1; deposited with the dust (assuming average crustal abundances) is about 6 Tg yr–1 of Fe and 0.2 Tg yr–1 of P. Dust deposition in the NAO is almost completely attributable to transport from North African sources; a substantial fraction of the dust over the NAO is probably mobilized as a consequence of land use practices in arid regions and, consequently, it should be regarded as a pollutant.  相似文献   

4.
Contemporary and pre-industrial global reactive nitrogen budgets   总被引:56,自引:6,他引:50  
Increases and expansion of anthropogenic emissions of both oxidized nitrogen compounds, NOx, and a reduced nitrogen compound, NH3, have driven an increase in nitrogen deposition. We estimate global NOx and NH3 emissions and use a model of the global troposphere, MOGUNTIA, to examine the pre-industrial and contemporary quantities and spatial patterns of wet and dry NOy and NHx deposition. Pre-industrial wet plus dry NOx and NHx deposition was greatest for tropical ecosystems, related to soil emissions, biomass burning and lightning emissions. Contemporary NOy+NHx wet and dry deposition onto Northern Hemisphere (NH) temperate ecosystems averages more than four times that of preindustrial N deposition and far exceeds contemporary tropical N deposition. All temperate and tropical biomes receive more N via deposition today than pre-industrially. Comparison of contemporary wet deposition model estimates to measurements of wet deposition reveal that modeled and measured wet deposition for both NO 3 and NH 4 + were quite similar over the U.S. Over Western Europe, the model tended to underestimate wet deposition of NO 3 and NH 4 + but bulk deposition measurements were comparable to modeled total deposition. For the U.S. and Western Europe, we also estimated N emission and deposition budgets. In the U.S., estimated emissions exceed interpolated total deposition by 3-6 Tg N, suggesting that substantial N is transported offshore and/or the remote and rural location of the sites may fail to capture the deposition of urban emissions. In Europe, by contrast, interpolated total N deposition balances estimated emissions within the uncertainty of each.Abbreviations EMEP European Monitoring and Evaluation Program - GEIA Global Emissions Inventory Activity - NADP/NTN National Atmospheric Deposition Program/National Trends Network in the US - NH Northern Hemisphere - NHx=NH3+NH + 4 NOx=NO+NO2 NOy total odd nitrogen=NOx+HNO3+HONO+HO2NO2+NO3+radical (NO3 .)+Peroxyacetyl nitrates+N2O5+organic nitrates - SH Southern Hemisphere - Gg 109 g - Tg 1012 g  相似文献   

5.
Summary The purpose of this study was to investigate the phytotoxicity of nitrapyrin 2-chloro-6-(trichloromethyl)pyridine to sunflower (Helianthus annuus L.) under different N regimes and to see if N forms affect the phytotoxicity of nitrapyrin. Sunflower was grown in pot culture for 21 days and was fertilized with (NH4)2SO4, NH4NO3 and NaNO3 to provide 0, 100 and 200 ppm N and with nitrapyrin application of 0 and 20 ppm. All N-treated sunflower plants in all N regimes and regardless of titrapyrin treatment produced more root and shoot dry weights and contained a significantly higher N than untreated check. Nitrapyrin toxicity appeared as a curling of leaf margin and a tendril type of stem growth, the visible toxicity symptoms decreased in the order: (NH4)2SO4>NH4NO3>NaNO3. Furthermore nitrapyrin addition suppressed sunflower growth in each N regime, the suppressing effect being greater with (NH4)2SO4 and NH4NO3 than as with NaNO3. Although, shoot growth from plants receiving nitrapyrin was not significantly affected by any N regime, root growth of nitrapyrin-treated plants was somewhat restricted by NH4 +−N nutrition relative to NO3 −N nutrition.  相似文献   

6.
The chemical compositions of ground water and organic matter in sediments were investigated at a sandy shore of Tokyo Bay, Japan to determine the fate of ground water NO3 . On the basis of Cl distribution in ground water, the beach was classified into freshwater (FR)-, transition (TR)-, and seawater (SW)-zones from the land toward the shoreline. The NO3 and N2O did not behave conservatively with respect to Cl during subsurface mixing of freshwater and seawater, suggesting NO3 consumption and N2O production in the TR-zone. Absence of beach vegetation indicated that NO3 assimilation by higher plants was not as important as NO3 sink. Low NH4 + concentrations in ground water revealed little reduction of NO3 to NH4 +. These facts implied that microbial denitrification and assimilation were the likely sinks for ground water NO3 . The potential activity and number of denitrifiers in water-saturated sediment were highest in the low-chlorinity part of the TR-zone. The location of the highest potential denitrification activity (DN-zone) overlapped with that of the highest NO3 concentration. The C/N ratio and carbon isotope ratio (13C) of organic matter in sediment (< 100 -m) varied from 12.0 to 22.5 and from –22.5 to –25.5, respectively. The 13C value was inversely related to the C/N ratio (r 2 = 0.968, n = 11), which was explained by the mixing of organic matters of terrestrial and marine origins. In the DN-zone, the fine sediments were rich in organic matters with high C/N ratios and low 13C values, implying that dissolved organic matters of terrestrial origin might have been immobilized under slightly saline conditions. A concurrent supply of NO3 and organic matter to the TR-zone by ground water discharge probably generates favorable conditions for denitrifiers. Ground water NO3 discharged to the beach is thus partially denitrified and fixed as microbial biomass before it enters the sea. Further studies are necessary to determine the relative contribution of these processes for NO3 removal.  相似文献   

7.
Regional nitrogen budgets for China and its major watersheds   总被引:22,自引:5,他引:22  
Xing  G.X.  Zhu  Z.L. 《Biogeochemistry》2002,(1):405-427
Since the Changjiang River, Huanghe River and Zhujiang River are the three major rivers in China that are flowing into the Pacific Ocean, this paper addresses nitrogen budgeting, source (input) and sink (output and storage), in these three river valleys, and the China watershed as well. In the China watershed, the anthropogenic reactive N has far exceeded the terrestrial bio-fixed N in nature, and human activities have significantly altered the N cycling in this region. In 1995, the total amount of anthropogenic reactive N in China reached 31.2 Tg with 22.2 Tg coming from synthetic fertilizers and 4.18 Tg from NOx emission from fossil fuel combustion, and the input of recycling N amounted to 30.5 Tg, consisting mainly of human and animal excrement N, reflecting the intensity of the human activity. The sink of N includes N in the harvested crop, denitrification and storage in agricultural soils, transportation into waterbodies and volatilization of NH3. N output and storage in soil reached up to 48–53 Tg. Of this amount, 14 Tg was in the harvested crops, 12 Tg stored in agricultural soils, 11 Tg transported into waterbodies, 5 – 10 Tg denitrified in the soils and a limited amount exported through food/feed.In this paper – besides the N budget in the China watershed – the N budgets and especially N transports into waterbodies in the Changjiang, Huanghe and Zhujiang river valleys are estimated.  相似文献   

8.
In life cycle impact assessment (LCIA), limited attention is generally given to a consistent inclusion of a fate analysis in the derivation of aquatic eutrophication potentials. This paper includes fate and potential effects in the calculation of aquatic eutrophication potentials of NH3 and NOx emitted to the ait, N and P emitted to water, and N and P emitted to soil. These characterisation factors were calculated for the Netherlands, West-Europe and the world, respectively. Implementation in current LCIA practice is further facilitated by calculating normalisation scores for the Netherlands in 1997, West-Europe in 1995 and the world in 1990. Although the results presented may be a step forward, significant improvements are still needed in the assessment of pollutants causing aquatic eutrophication. In particular, the fate factors representing transport of NOx and NH3, air emissions via soils to the aquatic environment should be improved. In addition, differences in the biological availability of nutrients and differences in the sensitivity of aquatic environments should be included in the calculation of effect factors for aquatic eutrophication.  相似文献   

9.
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively. The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers.  相似文献   

10.

Background and aims

Plant responses to S supply are highly dependent on N nutrition. We investigated the effect of S status on metabolic, nutritional, and production variables in Brachiaria brizantha treated with different N forms. Additionally, 15N and 34S root influx were determined in plants under short- and long-term S deprivation.

Methods

Plants were submitted to soil fertilization treatments consisted of combinations of N forms [without N, ammonium (NH4 +), nitrate (NO3 ?) or NH4 ++NO3 ?] at S rates (0, 15, 30, or 45 mg dm?3). N and S influx capacity was determined in hydroponically-grown plants.

Results

Shoot production due to S supply increased 53, 145 and 196 % with NH4 +, NH4 ++NO3 ? and NO3 ? treatments, respectively. No or low S impaired protein synthesis and led to high accumulation of N-NO3 ? and asparagine in NO3 ?-fed plants, both alone and with NH4 +. Proline accumulation was observed in NH4 +-fed plants. Short- and long-term S deprivation did not promote considerable changes in 15N influx. 34S absorption decreased depending on the N form provided: NH4 ++NO3 ? > only NH4 + > only NO3 ? > low N.

Conclusions

Including both NH4 + and NO3 ? forms in fertilizer increases N and S intake potential and thereby enhances plant growth, nutritional value and production.  相似文献   

11.
Global nitrogen fixation contributes 413 Tg of reactive nitrogen (Nr) to terrestrial and marine ecosystems annually of which anthropogenic activities are responsible for half, 210 Tg N. The majority of the transformations of anthropogenic Nr are on land (240 Tg N yr−1) within soils and vegetation where reduced Nr contributes most of the input through the use of fertilizer nitrogen in agriculture. Leakages from the use of fertilizer Nr contribute to nitrate (NO3) in drainage waters from agricultural land and emissions of trace Nr compounds to the atmosphere. Emissions, mainly of ammonia (NH3) from land together with combustion related emissions of nitrogen oxides (NOx), contribute 100 Tg N yr−1 to the atmosphere, which are transported between countries and processed within the atmosphere, generating secondary pollutants, including ozone and other photochemical oxidants and aerosols, especially ammonium nitrate (NH4NO3) and ammonium sulfate (NH4)2SO4. Leaching and riverine transport of NO3 contribute 40–70 Tg N yr−1 to coastal waters and the open ocean, which together with the 30 Tg input to oceans from atmospheric deposition combine with marine biological nitrogen fixation (140 Tg N yr−1) to double the ocean processing of Nr. Some of the marine Nr is buried in sediments, the remainder being denitrified back to the atmosphere as N2 or N2O. The marine processing is of a similar magnitude to that in terrestrial soils and vegetation, but has a larger fraction of natural origin. The lifetime of Nr in the atmosphere, with the exception of N2O, is only a few weeks, while in terrestrial ecosystems, with the exception of peatlands (where it can be 102–103 years), the lifetime is a few decades. In the ocean, the lifetime of Nr is less well known but seems to be longer than in terrestrial ecosystems and may represent an important long-term source of N2O that will respond very slowly to control measures on the sources of Nr from which it is produced.  相似文献   

12.
In short-term water culture experiments with different 15N labeled ammonium or nitrate concentrations, citrus seedlings absorbed NH4 + at a higher rate than NO3 . Maximum NO3 uptake by the whole plant occurred at 120 mg L–1 NO3 -N, whereas NH4 + absorption was saturated at 240 mg L–1 NH4 +-N. 15NH4 + accumulated in roots and to a lesser degree in both leaves and stems. However, 15NO3 was mostly partitioned between leaves and roots.Adding increasing amounts of unlabeled NH4 + (15–60 mg L–1 N) to nutrient solutions containing 120 mg L–1 N as 15N labeled nitrate reduced 15NO3 uptake. Maximum inhibition of 15NO3 uptake was about 55% at 2.14 mM NH4 + (30 mg L–1 NH4 +-N) and it did not increase any further at higher NH4 + proportions.In a long-term experiment, the effects of concentration and source of added N (NO3 or NH4 +) on nutrient concentrations in leaves from plants grown in sand were evaluated. Leaf concentration of N, P, Mg, Fe and Cu were increased by NH4 + versus NO3 nutrition, whereas the reverse was true for Ca, K, Zn and Mn.The effects of different NO3 -N:NH4 +-N ratios (100:0, 75:25, 50:50, 25:75 and 0:100) at 120 mg L–1 total N on leaf nutrient concentrations, fruit yield and fruit characteristics were investigated in another long-term experiment with plants grown in sand cultures. Nitrogen concentrations in leaves were highest when plants were provided with either NO3 or NH4 + as a sole source of N. Lowest N concentration in leaves was found with a 75:25 NO3 -N/NH4 +-N ratio. With increasing proportions of NH4 + in the N supply, leaf nutrients such as P, Mg, Fe and Cu increased, whereas Ca, K, Mn and Zn decreased. Yield in number of fruits per tree was increased significantly by supplying all N as NH4 +, although fruit weight was reduced. The number of fruits per tree was lowest with the 75:25 NO3 -N:NH4 +-N ratio, but in this treatment fruits reached their highest weight. Rind thickness, juice acidity, and colour index of fruits decreased with increasing NH4 + in the N supply, whereas the % pulp and maturity index increased. Percent of juice in fruits and total soluble solids were only slightly affected by NO3 :NH4 + ratio.  相似文献   

13.
We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH4PO3, whereas ginsenoside accumulation was highest (9.90 mg g-1 DW) in the absence of NH4PO3. At levels of 1.0-strength KNO3, root growth was maximum, but a 2.0 strength of KNO3 led to the greatest ginsenoside content (9.85 mg g-l). High concentrations of MgSO4 were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI2 in the medium, with the greatest accumulation of ginsenoside (8.91 mg g-1 DW) occurring at a 2.0 strength. The NH4/NO3 -- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO3 - concentration was higher than that of NH4 +. Maximum root growth was achieved at an NH4 +/NO3 - ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L-1) when NO3 - was used as the sole N source.  相似文献   

14.
Differences in 15N among ten white spruce [Picea glauca (Moench) Voss] families were examined in hydroponic experiments testing (1) three N sources [100 M N as (i) NH4+, (ii) NO3 or (iii) NH4NO3] and (2) two supply regimes [200 M NH4+ (i) maintained steadily or (ii) recurrently drawn-down]. In the N-source experiment, the NH4+ treatment resulted in superior growth and lower C/N ratios. Whole plant 15N was higher on NH4+ and NH4NO3, reflecting higher NH4+ removal rates from the media. Families expressed differences in biomass, C/N, 15N and 13C. Family 15N and 13C were positively correlated in the NH4NO3 treatment and the steady-state regime. Supply regime did not affect total biomass, but higher root/shoot ratios implied N was more limiting under the draw-down regime. Family rank changed with supply regime, but not with N source. Analysis of media isotope enrichment during substrate depletion revealed relationships between net discrimination and external N concentration. Discrimination against 15NH4+ was about twice that of 15NO3. A simple model relating isotope discrimination to relative rates of ion efflux and influx predicted efflux/influx ratios consistent with published values for white spruce. We propose that genetic differences in discrimination are caused by different demands on assimilation and in uptake capacity which interact, influencing the balance between N influx and efflux.  相似文献   

15.
The exudation of certain organic anions and protons by roots which may affect solubility of metals and P and uptake by plants, is affected by nitrogen form and pH. The objective of this work was to study exudation of carboxylates and H+/OH by tomato plants in response to NH4/NO3 ratio and pH in nutrient solution. Four NH4/(NH4+NO3) ratios (R= 0, 0.33, 0.67 and 1) and constant vs. variable solution pH treatments were investigated. The sum of the exudation rates of all carboxylates tended to decline with increasing R, particularly tri- and dicarboxylates. The molar fraction of the exuded tri- and dicarboxylates, averaged over all treatments and plant ages, increased in the order tartarate 2%), malate (6%), succinate (15%), citrate (26%) and fumarate (46%). At R=1 the solution pH dropped from 5.2 to 3 and at R=0 increased to 8. The R corresponding to the pH stat of tomato plant was 0.3. For the constant solution pH treatment, the effect of solution pH on carboxylate exudation rate was small as compared to the effect of R. The exudation of citrate and H+ efflux which were initiated when NO3 and NH4 uptake rates per plant exceeded certain threshold values, increased with plant age.  相似文献   

16.
Nitrite (NO2 ) is an intermediate in a variety of soil N cycling processes. However, NO2 dynamics are often not included in studies that explore the N cycle in soil. Within the presented study, nitrite dynamics were investigated in a Nothofagus betuloides forest on an Andisol in southern Chile. We carried out a 15N tracing study with six 15N labeling treatments, including combinations of NO3 , NH4 + and NO2 . Gross N transformation rates were quantified with a 15N tracing model in combination with a Markov chain Monte Carlo optimization routine. Our results indicate the occurrence of functional links between (1) NH4 + oxidation, the main process for NO2 production (nitritation), and NO2 reduction, and (2) oxidation of soil organic N, the dominant NO3 production process in this soil, and dissimilatory NO3 reduction to NH4 + (DNRA). The production of NH4 + via DNRA was approximately ten times higher than direct mineralization from recalcitrant soil organic matter. Moreover, the rate of DNRA was several magnitudes higher than the rate of other NO3 reducing processes, indicating that DNRA is able to outcompete denitrification, which is most likely not an important process in this ecosystem. These functional links are most likely adaptations of the microbial community to the prevailing pedo-climatic conditions of this Nothofagus ecosystem.  相似文献   

17.
Summary The effects of concentration and source (NH4, NO3, and NO3 plus NH4) of added N on the rate of growth, final yield, and content and rate of intake of N, P, K, Ca, Mg and S by wheat seedlings were evaluated. Rate of growth in dilute liquid cultures differed among the N sources giving yields relative to those of the all-NO3 system of 92 per cent for the all-NH4 system, and of 154 per cent for the NO3 plus NH4 system. At low rates of NH4 intake in the all-NH4 systems growth rates were equal to or slightly better than those of plants supplied equivalent concentrations of NO3. Rates of NH4 intake exceeding 100 mole g–1 h–1 resulted in reduced growth rates and incipient NH4 toxicity. Yields at 95 per cent of maximum resulted with steady-state N concentrations of 80 M in all NO3 systems, 30 M NH4 in all-NH4 systems, and in combined source systems when 200M NO3 plus 30 M NH4 were supplied. The rate of N intake and plant protein content, were maximal when both NO3 and NH4 were supplied. Increasing rates of NO3 intake were associated with increases in the rates of Ca, Mg, and K intake; but with increasing rates of NH4 absorption, intake of Ca and Mg decreased. The yield and growth rate enhancement observed from the addition of low concentrations of NH4 to cultures supplying adequate NO3 is suggested to result from the reduced energy requirement for utilization of NH4, as compared to NO3 in protein synthesis and from the increased photosynthetic capacity of the higher-protein NH4-fed plants. In the all-NH4 systems the maximum attainable growth rate was limited by NH4 toxicity; whereas in the all-NO3 systems the rate of NO3 reduction was limiting.Contribution from the Department of Soils and Plant Nutrition, University of California, Davis, California 95616.  相似文献   

18.
Labelled fertilizer N applied to winter wheat as Na15NO3 and (15NH4)2SO4 at a total N dressing of 100kg ha−1 was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO3 and 32.3%, 48.4% and 52.5% for the NH4 carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO3 and 51.7%, 63.5% and 66.1% for the NH4 carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO3−N and to 22.5%, 12.7% and 15.2% of the applied NH4−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.  相似文献   

19.
The 1:1 and 1:2 complexes of cis-(NH3)2PtII with 9-methyladeninium cations, 9-MeAH+, have been prepared and characterized by X-ray crystallography: cis-[(NH3)2Pt(9-MeAH-N7)Cl](NO3)2 (1) and cis-[(NH3)2Pt(9-MeAH-N7)2](NO3)4 · 2HNO3 · 2H2O (2). The pKa values for 9-MeAH+ in H2O are 1.7 in 1 as well as 0.4 (pKa1) and 1.3 (pKa2) for 2, as determined by pD dependent 1H NMR spectroscopy. Compound 2 is special in that it crystallizes with two equivalents of HNO3 per Pt entity. The HNO3 molecules are stacked in rectangular channels provided by cis-(NH3)2PtII units, 9-methyladeninium ligands and nitrate anions, which form a porous network of hydrogen bonds.  相似文献   

20.
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   

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