Data-driven estimation of nitric oxide emissions from global soils based on dominant vegetation covers

Soils are a major source of global nitric oxide (NO) emissions. However, estimates of soil NO emissions have large uncertainties due to limited observations and multifactorial impacts. Here, we mapped global soil NO emissions, integrating 1356 in-situ NO observations from globally distributed sites with high-resolution climate, soil, and management practice data. We then calculated global and national total NO budgets and revealed the contributions of cropland, grassland, and forest to global soil NO emissions at the national level. The results showed that soil NO emissions were explained mainly by N input, water input and soil pH. Total above-soil NO emissions of the three vegetation cover types were 9.4 Tg N year⁻¹ in 2014, including 5.9 Tg N year⁻¹ (1.04, 95% confidence interval [95% CI]: 0.09–1.99 kg N ha⁻¹ year⁻¹) emitted from forest, 1.7 Tg N year⁻¹ (0.68, 95% CI: 0.10–1.26 kg N ha⁻¹ year⁻¹) from grassland, and 1.8 Tg N year⁻¹ (0.98, 95% CI: 0.42–1.53 kg N ha⁻¹ year⁻¹) from cropland. Soil NO emissions in approximately 57% of 213 countries surveyed were dominated by forests. Our results provide updated inventories of global and national soil NO emissions based on robust data-driven models. These estimates are critical to guiding the mitigation of soil NO emissions and can be used in combination with biogeochemical models.     

Nitrous oxide emissions following application of residues and fertiliser under zero and conventional tillage

Emissions of N₂O were measured following combined applications of inorganic N fertiliser and crop residues to a silt loam soil in S.E. England, UK. Effects of cultivation technique and residue application on N₂O emissions were examined over 2 years. N₂O emissions were increased in the presence of residues and were further increased where NH₄NO₃ fertiliser (200 kg N ha^–1) was applied. Large fluxes of N₂O were measured from the zero till treatments after residue and fertiliser application, with 2.5 kg N₂O-N ha^–1 measured over the first 23 days after application of fertiliser in combination with rye (Secale cereale) residues under zero tillage. CO₂ emissions were larger in the zero till than in the conventional till treatments. A significant tillage/residue interaction was found. Highest emissions were measured from the conventionally tilled bean (Vicia faba) (1.0 kg N₂O-N ha^–1 emitted over 65 days) and zero tilled rye (3.5 kg N₂O-N ha^–1 over 65 days) treatments. This was attributed to rapid release of N following incorporation of bean residues in the conventionally tilled treatments, and availability of readily degradable C from the rye in the presence of anaerobic conditions under the mulch in the zero tilled treatments. Measurement of ¹⁵N-N₂O emission following application of ¹⁵N-labelled fertiliser to microplots indicated that surface mulching of residues in zero till treatments resulted in a greater proportion of fertiliser N being lost as N₂O than with incorporation of residues. Combined applications of ¹⁵N fertiliser and bean residues resulted in higher or lower emissions, depending on cultivation technique, when compared with the sum of N₂O from single applications. Such interactions have important implications for mitigation of N₂O from agricultural soils.     

Nitrous oxide and dinitrogen emissions from urine-affected soil under controlled conditions

A ¹⁵N labelling technique was used to measure N₂O and N₂ emissions from an undisturbed grassland soil treated with cow urine and held at 30 cm water tension and 20°C in a laboratory. Large emissions of dinitrogen were detected immediately following urine application to pasture. These coincided with a rapid and large increase in soil water-soluble carbon levels, some of this increase being attributed to solubilization of soil organic matter by high pH and ammonia concentrations. Emissions of nitrous oxide generally increased with time in contrast to dinitrogen fluxes which decreased as time progressed. Estimated losses of N₂O and N₂ over a 30 day period were between 1 to 5% and 30 to 65% of the urine N applied plus N mineralized from soil organic matter, respectively. Most of the N₂ and N₂O originated from denitrification with nitrification-denitrification being of minor significance as a source of N₂O. Comparisons of the ¹⁵N enrichments in the soil mineral N pools and the evolved N₂O suggested that much of the N₂O was produced in the 5–8 cm zone of the soil. It is concluded that established grassland soils contain large amounts of readily-oxidizable organic carbon which may be used by soil denitrifying organisms when nitrate is non-limiting and soil redox potential is lowered due to high rates of biological activity and high soil moisture contents. ei]{gnR}{fnMerckx}     

Short-term nitrous oxide emissions from pasture soil as influenced by urea level and soil nitrate

Nitrogen excreted by cattle during grazing is a significant source of atmospheric nitrous oxide (N₂O). The regulation of N₂O emissions is not well understood, but may vary with urine composition and soil conditions. This laboratory study was undertaken to describe short-term effects on N₂O emissions and soil conditions, including microbial dynamics, of urea amendment at two different rates (22 and 43 g N m⁻²). The lower urea concentration was also combined with an elevated soil NO ₃ ⁻ concentration. Urea solutions labelled with 25 atom%¹⁵N were added to the surface of repacked pasture soil cores and incubated for 1, 3, 6 or 9 days under constant conditions (60% WFPS, 14 °C). Soil inorganic N (NH ₄ ⁺ , NO ₂ ⁻ and NO ₃ ⁻ ), pH, electrical conductivity and dissolved organic C were quantified. Microbial dynamics were followed by measurements of CO₂ evolution, by analyses of membrane lipid (PLFA) composition, and by measurement of potential ammonium oxidation and denitrifying enzyme activity. The total recovery of¹⁵N averaged 84%. Conversion of urea-N to NO ₃ ⁻ was evident, but nitrification was delayed at the highest urea concentration and was accompanied by an accumulation of NO ₂ ⁻ . Nitrous oxide emissions were also delayed at the highest urea amendment level, but accelerated towards the end of the study. The pH interacted with NH ₄ ⁺ to produce inhibitory concentrations of NH₃(aq) at the highest urea concentration, and there was evidence for transient negative effects of urea amendment on both nitrifying and denitrifying bacteria in this treatment. However, PLFA dynamics indicated that initial inhibitory effects were replaced by increased microbial activity and net growth. It is concluded that urea-N level has qualitative, as well as quantitative effects on soil N transformations in urine patches.     

Nitrous oxide and carbon dioxide emissions from pelletized and nonpelletized poultry litter incorporated into soil

While several studies have shown that the addition of animal manures to soil can increase N₂O and CO₂ emissions, limited information is available on the effect that manure physical characteristics can have on these emissions. This study compared N₂O and CO₂ emissions from poultry litter incorporated as pellets (5.5 mm OD, 7 mm long) or fine particles (<0.83 mm) into Cecil soil samples. The soil-litter mixture was packed in acrylic plastic cylinders and adjusted to 55 or 90 % water-filled porosity (WFP). The cylinders were placed inside jars that were sealed and placed in an incubator at 25°C for 35 d, with periodic air samplings conducted for N₂O and CO₂ analyses. At 55% WFP, cumulative emission of CO₂ was similar for both litter types, but cumulative emission of N₂O was slightly higher for pelletized (6.8 % of applied N) than for fine-particle litter (5.5 %). In contrast, at 90 % WFP, cumulative emission of N₂O was larger for fine-particle litter (3.4 % of applied N) than for pelletized litter (1.5 %). These results indicate that the effect of poultry litter physical characteristics on N₂O emissions from incorporated applications can be expected to vary depending on the soil water regime.     

Effects of soil temperature on nitric oxide emission from a typical Chinese rice–wheat rotation during the non-waterlogged period

Measurements of nitric oxide (NO) emission from a typical Chinese rice–wheat rotation are continuously made during the non‐waterlogged period by using an automatic system based on static chamber techniques. A positive correlation exists between NO emission and soil moisture content when surface soil temperature is > 20 °C. The diurnal variability in NO emission is characterized with day‐peak, night‐peak and irregular patterns, which are in close association with wheat growth. The diurnal NO emission under the day‐peak pattern is correlated with the simultaneously observed surface soil temperature, whereas that under the night‐peak and irregular pattern is dependent on surface soil temperature at 7 ± 2 and 3 ± 2 h before NO observation, respectively. The effect of soil temperature on NO emission is well described by F = α·e^β·T, where F is NO flux, T soil temperature, and α and b empirical coefficients. The parameter Q₁₀; that is, the change in NO emission per 10 °C soil temperature, is correlated with the rates of fertilizer‐N application. An approach orientated from the Arrhenius equation, , is developed in order to predict diurnal NO emission, where T_K is the daily average soil temperature, ΔT_K the deviation of soil temperature from the daily average, E_a the apparent activation energy, R the gas constant, t a given time within the one‐day cycle, t delayed time for appearance of the diurnal NO emission peak, and k an empirical coefficient. Based on the results, the authors recommend that intermittent measurement of NO emission from a similar ecosystem would be best taken around 17:00. The molar ratio of NO/N₂O over the non‐waterlogged period is > 1 when soil moisture content was less than the field capacity, suggesting that NO emission was mainly derived from nitrification under this condition.     

Estimation of nitrous oxide, nitric oxide and ammonia emissions from croplands in East, Southeast and South Asia

Agricultural activities have greatly altered the global nitrogen (N) cycle and produced nitrogenous gases of environmental significance. More than half of all chemical N fertilizer produced globally is used in crop production in East, Southeast and South Asia, where rice is central to nutrition. Emissions of nitrous oxide (N₂O), nitric oxide (NO) and ammonia (NH₃) from croplands in this region were estimated by considering background emission and emissions resulting from N added to croplands, including chemical N, animal manure, biologically fixed N and N in crop residues returned to fields. Background emission fluxes of N₂O and NO from croplands were estimated to be 1.22 and 0.57 kg N ha^?1 yr^?1, respectively. Separate fertilizer‐induced emission factors were estimated for upland fields and rice fields. Total N₂O emission from croplands in the study region was estimated to be 1.19 Tg N yr^?1, with 43% contributed by background emissions. The average fertilizer‐induced N₂O emission, however, accounts for only 0.93% of the applied N, which is less than the default IPCC value of 1.25%, because of the low emission factor from paddy fields. Total NO emission was 591 Gg N yr^?1 in the study region, with 40% from background emissions. The average fertilizer‐induced NO emission factor was 0.48%. Total NH₃ emission was estimated to be 11.8 Tg N yr^?1. The use of urea and ammonium bicarbonate and the cultivation of rice led to a high average NH₃ loss rate from chemical N fertilizer in the study region. Emissions were displayed at a 0.5° × 0.5° resolution with the use of a global landuse database.     

Factors promoting emissions of nitrous oxide and nitric oxide from denitrifying sequencing batch reactors operated with methanol and ethanol as electron donors

The emissions of nitrous oxide (N₂O) and nitric oxide (NO) from biological nitrogen removal (BNR) operations via nitrification and denitrification is gaining increased prominence. While many factors relevant to the operation of denitrifying reactors can influence N₂O and NO emissions from them, the role of different organic carbon sources on these emissions has not been systematically addressed or interpreted. The overall goal of this study was to evaluate the impact of three factors, organic carbon limitation, nitrite concentrations, and dissolved oxygen concentrations on gaseous N₂O and NO emissions from two sequencing batch reactors (SBRs), operated, respectively, with methanol and ethanol as electron donors. During undisturbed ultimate‐state operation, emissions of both N₂O and NO from either reactor were minimal and in the range of <0.2% of influent nitrate‐N load. Subsequently, the two reactors were challenged with transient organic carbon limitation and nitrite pulses, both of which had little impact on N₂O or NO emissions for either electron donor. In contrast, transient exposure to oxygen led to increased production of N₂O (up to 7.1% of influent nitrate‐N load) from ethanol grown cultures, owing to their higher kinetics and potentially lower susceptibility to oxygen inhibition. A similar increase in N₂O production was not observed from methanol grown cultures. These results suggest that for dissolved oxygen, but not for carbon limitation or nitrite exposure, N₂O emission from heterotrophic denitrification reactors can vary as a function of the electron donor used. Biotechnol. Bioeng. 2010; 106: 390–398. © 2010 Wiley Periodicals, Inc.     

15N natural abundance in forest and pasture soils of the Brazilian Amazon Basin

The natural abundance of ¹⁵N was examined in soil profiles from forests and pastures of the Brazilian Amazon Basin to compare tropical forests on a variety of soil types and to investigate changes in the sources of nitrogen to soils following deforestation for cattle ranching. Six sites in the state of Rondônia, two sites in Pará and one in Amazonas were studied. All sites except one were chronosequences and contained native forest and one or more pastures ranging from 2 to 27 years old. Forest soil ¹⁵N values to a depth of 1 m ranged from 8 to 23 and were higher than values typically found in temperate forests. A general pattern of increasing ¹⁵N values with depth near the soil surface was broadly similar to patterns in other forests but a decrease in ¹⁵N values in many forest profiles between 20 and 40 cm suggests that illuviation of ¹⁵N-depleted nitrate may influence total soil ¹⁵N values in deeper soil where total N concentrations are low. In four chronosequences in Rondônia, the ¹⁵N values of surface soil from pastures were lower than in the original forest and ¹⁵N values were increasingly depleted in older pastures. Inputs of atmospheric N by dinitrogen fixation could be an important N source in these pastures. Other pastures in Amazonas and Pará and Rondônia showed no consistent change from forest values. The extent of fractionation that leads to ¹⁵N enrichment in soils was broadly similar over a wide range of soil textures and indicated that similar processes control N fractionation and loss under tropical forest over a broad geographic region. Forest ¹⁵N profiles were consistent with conceptual models that explain enrichment of soil ¹⁵N values by selective loss of ¹⁴N during nitrification and denitrification.     

耕作和覆盖对黄土高原果园土壤水分和温度的影响

研究了几种不同耕作方式（免耕、旋耕和翻耕）和覆盖措施（覆草、生草和覆膜）对黄土高原果园土壤水分和温度的影响.结果表明：5月不同耕作方式下0～1 m土层土壤水分差异极显著,表现为免耕（14.28%）>旋耕（14.13%）>翻耕（13.57%）,9月差异不明显;不同覆盖措施中,覆草处理的土壤水分最高,且与生草、覆膜、裸地处理间差异极显著;不同耕作方式和覆盖组合处理中以免耕覆草保水效果最好.不同覆盖处理白天土壤平均温度表现为覆膜>裸地>生草>覆草,土壤温度变幅表现为裸地>覆膜>生草>覆草.各覆盖处理的蓄水量与其土壤温度并不都呈负相关,而是由不同覆盖物的保水效果和保温性质共同决定.综上所述,黄土高原果园的保护性耕作体系应以免耕覆草为主.     

Role of nitric oxide in chick embryonic organogenesis and dysmorphogenesis

BACKGROUND: Nitric oxide (NO), produced by the nitric oxide synthase family of enzymes, mediates multiple signaling functions, and when unchecked, NO causes pathological damage. Exposure of embryos to a variety of teratogens, including carbon monoxide (CO), has been shown to increase reactive intermediates, such as NO, and recent work showed that either the excess or absence of NO caused morphological defects. While endogenous NO is known to regulate many adult tissues, its role during embryonic organogenesis and/or in mediating responses to teratogen exposure has not been explored. METHODS: We have examined here the presence of NO during normal chick embryonic organogenesis, and investigated the teratogenicity of NO through the application of sodium nitroprusside (SNP), which mimics NO overproduction, and NG-monomethyl-L-arginine (L-NMMA), which inhibits endogenous NOS activity. RESULTS: Topical treatment with SNP or L-NMMA for 18 h resulted in morphological defects, specifically in the neural tube and somites, which corresponded to sites of altered apoptosis. The location of NO was histochemically correlated with the observed morphological defects. Coadministration of SNP or L-NMMA with CO showed functional coregulation and interaction between NO and CO in chick embryonic development. CONCLUSIONS: Our results showed that regulation of NO is essential for normal axial development, that sites of altered NO expression correlate to those of altered apoptosis and dysmorphogenesis, and that CO coadministration resulted in a rectification of normal NO expression. Collectively, these results suggest that alteration in endogenous NO/CO signaling is responsible, at least in part, for the observed NO-induced teratogenesis.     

Denitrification and N2O emissions from a UK pasture soil following the early spring application of cattle slurry and mineral fertiliser

Total denitrification and nitrous oxide (N₂O) losses were measured from three contrasting dairy management systems representing good commercial practice (system 1), production maintained but with reduced N losses (system 2); and nitrate leaching less than 50 mg L^-1 but with reduced production (system 3). Measurements were made following mineral fertiliser application and from two plot experiments where four treatments were applied: control, NH₄NO₃ at 60 kg N ha^-1, cattle slurry applied to the surface (equivalent to 45 kg N ha^-1), and cattle slurry injected. Despite low soil temperatures (<6 °C) and low rainfall (<3 mm), total denitrification and N₂O losses peaked at 56 and 16 g N ha^-1 d^-1, respectively. Total denitrification losses decreased: system 1 system 2 > system 3, whereas N₂O losses decreased: system 2 > system 3 > system 1. Total denitrification losses tended to decrease with decreasing fertiliser application rate, whereas fertiliser application rate was not the sole determinant of the N₂O loss. The system 3 field was injected with cattle slurry for 2 yr, system 2 received some slurry by injection and system 1 received slurry to the surface. Thus, the amount, timing and method of previous cattle slurry application was important in determining the loss following subsequent fertiliser application. For the plot experiments, total denitrification and N₂O losses decreased in the order: slurry injected > mineral fertiliser > slurry applied to the surface > control for 5 days following application. However, 16 and 19 days after application, N₂O losses above the control were measured from plots that had received cattle slurry. It was inferred that the application of cattle slurry to the pasture soil stimulated greater N₂O production and increased losses over a longer time period compared with mineral fertiliser additions.     

Diurnal fluctuations of dissolved nitrous oxide (N2O) concentrations and estimates of N2O emissions from a spring-fed river: implications for IPCC methodology

There is uncertainty in the estimates of indirect nitrous oxide (N₂O) emissions as defined by the Intergovernmental Panel on Climate Change (IPCC). The uncertainty is due to the challenge and dearth of in situ measurements. Recent work in a subtropical stream system has shown the potential for diurnal variability to influence the downstream N transfer, N form, and estimates of in‐stream N₂O production. Studies in temperate stream systems have also shown diurnal changes in stream chemistry. The objectives of this study were to measure N₂O fluxes and dissolved N₂O concentrations from a spring‐fed temperate river to determine if diurnal cycles were occurring. The study was performed during a 72 h period, over a 180 m reach, using headspace chamber methodology. Significant diurnal cycles were observed in radiation, river temperature and chemistry including dissolved N₂O‐N concentrations. These data were used to further assess the IPCC methodology and experimental methodology used. River NO₃‐N and N₂O‐N concentrations averaged 3.0 mg L⁻¹ and 1.6 μg L⁻¹, respectively, with N₂O saturation reaching a maximum of 664%. The N₂O‐N fluxes, measured using chamber methodology, ranged from 52 to 140 μg m⁻² h⁻¹ while fluxes predicted using the dissolved N₂O concentration ranged from 13 to 25 μg m⁻² h⁻¹. The headspace chamber methodology may have enhanced the measured N₂O flux and this is discussed. Diurnal cycles in N₂O% saturation were not large enough to influence downstream N transfer or N form with variability in measured N₂O fluxes greater and more significant than diurnal variability in N₂O% saturation. The measured N₂O fluxes, extrapolated over the study reach area, represented only 6 × 10⁻⁴% of the NO₃‐N that passed through the study reach over a 72 h period. This is only 0.1% of the IPCC calculated flux.     

Changes in the level of cytosolic calcium, nitric oxide and nitric oxide synthase activity during platelet aggregation: an in vitro study in platelets from normal subjects and those with cirrhosis

Variceal bleeding due to abnormal platelet function is a well-known complication of cirrhosis. Nitric oxide-related stress has been implicated in the pathogenesis of liver cirrhosis.In the present investigation,we evaluated the level of platelet aggregation and concomitant changes in the level of platelet cytosolic calcium (Ca2+), nitric oxide (NO) and NO synthase (NOS) activity in liver cirrhosis.The aim of the present study was to investigate whether the production of NO by NOS and level of cytosolic Ca2+ influence the aggregation of platelets in patients with cirrhosis of the liver.Agonist-induced aggregation and the simultaneous changes in the level of cytosolic Ca2+, NO and NOS were monitored in platelets of patients with cirrhosis.Platelet aggregation was also measured in the presence of the eNOS inhibitor,diphenylene iodinium chloride (DIC).The level of agonist-induced platelet aggregation was significantly low in the platelets of patients with cirrhosis compared with that in platelets from normal subjects.During the course of platelet aggregation,concomitant elevation in the level of cytosolic Ca2+ was observed in normal samples,whereas the elevation was not significant in platelets of patients with cirrhosis.A parallel increase was observed in the levels of NO and NOS activity.In the presence of the eNOS inhibitor,platelet aggregation was enhanced and accompanied by an elevated calcium level.The inhibition of platelet aggregation in liver cirrhosis might be partly due to greater NO formation by eNOS.Defective Ca2+ release from the internal stores to the cytosol may account for inhibition of aggregation of platelets in cirrhosis.The NO-related defective aggregation of platelets in patients with cirrhosis found in our study is of clinical importance,and the underlying mechanism of such changes suggests a possible therapeutic strategy with cell-specific NO blockers.     

Large losses of soil C and N from soil profiles under pasture in New Zealand during the past 20 years

The conversion of two‐thirds of New Zealand's native forests and grasslands to agriculture has followed trends in other developed nations, except that pastoral grazing rather than cropping dominates agriculture. The initial conversion of land to pasture decreased soil acidity and elevated N and P stocks, but caused little change in soil organic C stocks. However, less is known about C and nutrient stock changes during the last two decades under long‐term pastoral management. We resampled 31 whole soil profiles in pastures spanning seven soil orders with a latitudinal range of 36–46°S, which had originally been sampled 17–30 years ago. We measured total C, total N, and bulk density for each horizon (generally to 1 m) and also reanalyzed archived soil samples of the same horizons for C and N. On average, profiles had lost significant amounts of C (− 2.1 kg C m⁻²) and N (− 0.18 kg N m⁻²) since initial sampling. Assuming a continuous linear decline in organic matter between sampling dates, significant losses averaged 106 g C m⁻² yr⁻¹ (P=0.01) and 9.1 g N m⁻² yr⁻¹ (P=0.002). Removal of C through leaching and erosion appears too small to explain these losses, suggesting losses from respiration exceed the inputs of photosynthate in the soil profile. These results emphasize that resampling soil profiles provide a robust method for detecting soil C changes, and add credence to the suggestion that soil C losses may be occurring in some temperate soil profiles. Further work is required to determine whether these losses are continuing and how losses might be extrapolated across landscapes to determine the implications for New Zealand's national CO₂ emissions and the sustainability of the implied rates of soil N loss.     

Initial nitrous oxide,carbon dioxide,and methane costs of converting conservation reserve program grassland to row crops under no‐till vs. conventional tillage

Around 4.4 million ha of land in USDA Conservation Reserve Program (CRP) contracts will expire between 2013 and 2018 and some will likely return to crop production. No‐till (NT) management offers the potential to reduce the global warming costs of CO₂, CH₄, and N₂O emissions during CRP conversion, but to date there have been no CRP conversion tillage comparisons. In 2009, we converted portions of three 9–21 ha CRP fields in Michigan to conventional tillage (CT) or NT soybean production and reserved a fourth field for reference. Both CO₂ and N₂O fluxes increased following herbicide application in all converted fields, but in the CT treatment substantial and immediate N₂O and CO₂ fluxes occurred after tillage. For the initial 201‐day conversion period, average daily N₂O fluxes (g N₂O‐N ha^?1 d^?1) were significantly different in the order: CT (47.5 ± 6.31, n = 6) ? NT (16.7 ± 2.45, n = 6) ? reference (2.51 ± 0.73, n = 4). Similarly, soil CO₂ fluxes in CT were 1.2 times those in NT and 3.1 times those in the unconverted CRP reference field. All treatments were minor sinks for CH₄ (?0.69 ± 0.42 to ?1.86 ± 0.37 g CH₄–C ha^?1 d^?1) with no significant differences among treatments. The positive global warming impact (GWI) of converted soybean fields under both CT (11.5 Mg CO₂e ha^?1) and NT (2.87 Mg CO₂e ha^?1) was in contrast to the negative GWI of the unconverted reference field (?3.5 Mg CO₂e ha^?1) with on‐going greenhouse gas (GHG) mitigation. N₂O contributed 39.3% and 55.0% of the GWI under CT and NT systems with the remainder contributed by CO₂ (60.7% and 45.0%, respectively). Including foregone mitigation, we conclude that NT management can reduce GHG costs by ~60% compared to CT during initial CRP conversion.     

Biochemical and functional changes of rat liver spheroids during spheroid formation and maintenance in culture: II. nitric oxide synthesis and related changes

Liver cells isolated from intact tissue can reaggregate to form three-dimensional, multicellular spheroids in vitro. During this process, cells undergo a histological and environmental change. How cells respond biochemically to this change has not been studied in detail previously. We have investigated some biochemical changes in rat liver cells during the formation and maintenance of spheroids. Liver cells were isolated from male Sprague rats and spheroids cultured by a gyrotatory-mediated method. Liver cells were shown to respond to the isolation procedure and the formation of spheroids triggered histological environmental changes that increased arginine uptake, nitric oxide (NO) and urea syntheses, as well as raised levels of GSH, GSSG, glutamic acid and aspartic acid secretion within the first couple of days after cell isolation. Levels were maintained at a relatively stable level in the mature spheroids (>5 days) over the 3 week period of observation. P450 1A1 activity was lost in the first 2 days and gradually recovered thereafter. This study, for the first time, shows that liver cells after isolation and during spheroid formation actively uptake arginine and increase NO and urea syntheses. A high level of NO is likely to play an important role in modulating a series of biochemical changes in liver cells. It is considered that liver cells actively respond to the 'challenge' induced by the isolation procedure and subsequent histological environmental changes, and biochemical modulation and instability result. The stable cell-cell contacts and histological environment in mature spheroids permit and support functional recovery and maintenance in vitro. This period of stability permits the use of spheroids in toxicity studies to establish acute and chronic paradigms.     

Role of nitrate and nitrite for production and consumption of nitric oxide during denitrification in soil

Abstract Anaerobic production and consumption of NO was measured in a calcic cambisol (KBE; pH 7.3) and a forest luvisol (PBE; pH 4.4) which were incubated at 80% water-holding capacity and continuously flushed with N₂. Both NO production and NO consumption were negligibly low when nitrate and nitrite concentrations in the soil were exhausted. Addition of glucose alone had no effect, but addition of nitrate ± glucose greatly stimulated both NO production and NO consumption. NO consumption followed an apparent first-order reaction at low NO mixing ratios (1–3 ppmv), but a higher NO mixing ratios it followed Michaelis-Menten kinetics. In PBE the apparent K _m was 980 ppbv NO (1.92 nM in soil water). During reduction of nitrate, nitrite intermediately accumulated and simultaneously, production rates of NO and N₂O were at the maximum. Production rates of NO plus N₂O amounted to 20% and 34% of the nitrate reduction rate in KBE and PBE, respectively. NO production was hyperbolically related to the nitrite concentration, indicating an apparent K_m of 1.6 μg nitrite-N g⁻¹ d.w. soil (equivalent to 172 μM nitrite in soil solution) for the reduction of nitrite to NO in KBE. Under nitrate and nitrite-limiting conditions, 62–76% and 93–97% of the consumed NO-N were recovered as N₂O-N in KBE and PBE, respectively. Gassing of nitrate plus nitrite-depretsu KBE with increasing mixing ratios of NO₂ resulted in increasing rates of NO₂ uptake and presumably in the formation of low concentrations of nitrite and nitrate. This NO₂ uptake resulted in increasing rates of both NO production and NO consumption indicating that nitrite or nitrate was limiting for both reactions.     

Nitrite-driven nitrous oxide production under aerobic soil conditions: kinetics and biochemical controls

Nitrite (NO₂⁻) can accumulate during nitrification in soil following fertilizer application. While the role of NO₂⁻ as a substrate regulating nitrous oxide (N₂O) production is recognized, kinetic data are not available that allow for estimating N₂O production or soil‐to‐atmosphere fluxes as a function of NO₂⁻ levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N₂O production rate () to NO₂⁻ was observed at concentrations below 60 μg N g⁻¹ soil in both nonsterile and sterilized soils. Rate coefficients (K_p) relating to NO₂⁻ varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in K_p across all samples. Abiotic processes accounted for 31–75% of total N₂O production. Biological reduction of NO₂⁻ was enhanced as oxygen (O₂) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO₃⁻)‐reduction, and the reduction of N₂O itself, were only stimulated at O₂ levels below 5%. Greater temperature sensitivity was observed for biological compared with chemical N₂O production. Steady‐state model simulations predict that NO₂⁻ levels often found after fertilizer applications have the potential to generate substantial N₂O fluxes even at ambient O₂. This potential derives in part from the production of N₂O under conditions not favorable for N₂O reduction, in contrast to N₂O generated from NO₃⁻ reduction. These results have implications with regard to improved management to minimize agricultural N₂O emissions and improved emissions assessments.     

Amazon Basin climate under global warming: the role of the sea surface temperature

The Hadley Centre coupled climate-carbon cycle model (HadCM3LC) predicts loss of the Amazon rainforest in response to future anthropogenic greenhouse gas emissions. In this study, the atmospheric component of HadCM3LC is used to assess the role of simulated changes in mid-twenty-first century sea surface temperature (SST) in Amazon Basin climate change. When the full HadCM3LC SST anomalies (SSTAs) are used, the atmosphere model reproduces the Amazon Basin climate change exhibited by HadCM3LC, including much of the reduction in Amazon Basin rainfall. This rainfall change is shown to be the combined effect of SSTAs in both the tropical Atlantic and the Pacific, with roughly equal contributions from each basin. The greatest rainfall reduction occurs from May to October, outside of the mature South American monsoon (SAM) season. This dry season response is the combined effect of a more rapid warming of the tropical North Atlantic relative to the south, and warm SSTAs in the tropical east Pacific. Conversely, a weak enhancement of mature SAM season rainfall in response to Atlantic SST change is suppressed by the atmospheric response to Pacific SST. This net wet season response is sufficient to prevent dry season soil moisture deficits from being recharged through the SAM season, leading to a perennial soil moisture reduction and an associated 30% reduction in annual Amazon Basin net primary productivity (NPP). A further 23% NPP reduction occurs in response to a 3.5 degrees C warmer air temperature associated with a global mean SST warming.