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Like obese humans, Zucker diabetic fatty (ZDF) rats exhibit early β cell compensation for insulin resistance (4-fold β cell hyperplasia) followed by decompensation (>50% loss of β cells). In prediabetic and diabetic ZDF islets, apoptosis measured by DNA laddering is increased 3- and >7-fold, respectively, compared with lean ZDF controls. Ceramide, a fatty acid-containing messenger in cytokine-induced apoptosis, was significantly increased (P < 0.01) in prediabetic and diabetic islets. Free fatty acids (FFAs) in plasma are high (>1 mM) in prediabetic and diabetic ZDF rats; therefore, we cultured prediabetic islets in 1 mM FFA. DNA laddering rose to 19.6% vs. 4.6% in lean control islets, preceded by an 82% increase in ceramide. C2-Ceramide without FFA induced DNA laddering, but fumonisin B1, a ceramide synthetase inhibitor, completely blocked FFA-induced DNA laddering in cultured ZDF islets. [3H]Palmitate incorporation in [3H]ceramide in ZDF islets was twice that of controls, but [3H]palmitate oxidation was 77% less. Triacsin C, an inhibitor of fatty acyl-CoA synthetase, and troglitazone, an enhancer of FFA oxidation in ZDF islets, both blocked DNA laddering. These agents also reduced inducible nitric oxide (NO) synthase mRNA and NO production, which are involved in FFA-induced apoptosis. In ZDF obesity, β cell apoptosis is induced by increased FFA via de novo ceramide formation and increased NO production.

The abundance of genes related to the nitrogen biogeochemical cycle and the microbial community in forest soils (bacteria, archaea, fungi) were quantitatively analyzed via real-time PCR using 11 sets of specific primers amplifying nifH, bacterial amoA, archaeal amoA, narG, nirS, nirK, norB, nosZ, bacterial 16S rRNA gene, archaeal 16S rRNA gene, and the ITS sequence of fungi. Soils were sampled from Bukhan Mountain from September of 2010 to July of 2011 (7 times). Bacteria were the predominant microbial community in all samples. However, the abundance of archaeal amoA was greater than bacterial amoA throughout the year. The abundances of nifH, nirS, nirK, and norB genes changed in a similar pattern, while narG and nosZ appeared in sensitive to the environmental changes. Clone libraries of bacterial 16S rRNA genes were constructed from summer and winter soil samples and these revealed that Acidobacteria was the most predominant phylum in acidic forest soil environments in both samples. Although a specific correlation of environmental factor and gene abundance was not verified by principle component analysis, our data suggested that the combination of biological, physical, and chemical characteristics of forest soils created distinct conditions favoring the nitrogen biogeochemical cycle and that bacterial communities in undisturbed acidic forest soils were quite stable during seasonal change.

In this paper we discuss three topics concerning N₂O emissions from agricultural systems. First, we present an appraisal of N₂O emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N₂O flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N₂O emissions from N-fertilized fields (Mitigation). To assess the global emission of N₂O from agricultural soils, the total flux should represent N₂O from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N₂O from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N₂O production. The assessment of direct and indirect N₂O emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N₂O-N ha⁻¹. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales. Several N₂O flux measurement techniques have been used in recent field studies which utilize small and ultralarge chambers and micrometeorological along with new analytical techniques to measure N₂O fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N₂O flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability. There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N₂O emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N₂O emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N₂O emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers.

Highest rates of N2O emissions from fertilized as well as natural ecosystems have often been measured at spring thaw. But, it is not clear if management practices have an effect on winter and spring thaw emissions, or if measurements conducted over several years would reveal different emission patterns depending on winter conditions. In this study, we present N2O fluxes obtained using the flux-gradient approach over four winter and spring thaw periods, spanning from 1993 to 1996, at two locations in Ontario, Canada. Several agricultural fields (bare soil, barley, soybean, canola, grass, corn) subjected to various management practices (manure and nitrogen fertilizer addition, alfalfa ploughing, fallowing) were monitored. Nitrous oxide emissions from these fields from January to April over four years ranged between 0 and 4.8 kg N ha-1. These thaw emissions are substantial and should be considered in the nitrous oxide budgets in regions where thaw periods occur. Our study indicates that agricultural management can play a role in mitigating these emissions. Our data show that fallowing, manure application and alfalfa incorporation in the fall lead to high spring emissions, while the presence of plants (as in the case of alfalfa or grass) can result in negligible emissions during thaw. This presents an opportunity for mitigation of N2O emissions through the use of over-wintering cover crops.

Three-year-old seedlings of black alder (Alnus glutinosa (L.) Gaertn.), a common European wetland tree species, were grown in native soil taken from an alder swamp. Fluxes of methane (CH₄) and nitrous oxide (N₂O) between the tree stem and the atmosphere were determined under controlled conditions. Both CH₄ and N₂O were emitted through the bark of the stem into the atmosphere when the root zone exhibited 'higher-than-ambient' CH₄ and N₂O gas mixing ratios. Flooding of the soil caused a decreased N₂O emission but an increased CH₄ efflux from the stem. Immediately after flooding of the soil, N₂O was emitted from the seedlings' bark at a rate of 350 μmol N₂O m⁻² h⁻¹ whereas CH₄ flux could not be detected. After more than 40 days of flooding CH₄ fluxes up to 3750 μmol CH₄ m⁻² h⁻¹ from the stem were measured, while N₂O emission had decreased below the limit of detection. Gas efflux decreased with increasing stem height and correlated with gas mixing ratios in the soil, indicating diffusion through the aerenchyma as the major path of gas transport. From these results it is assumed that woody species with aerenchyma can serve as conduits for soil-derived trace gases into the atmosphere, to date only shown for herbaceous plants. This, yet unidentified, 'woody plant pathway' contributes to the total greenhouse gas source strength of wetlands.

Nitrous oxide (N2O) produced from agricultural activities must be determined if management procedures to reduce emissions are to be established. From 1994 to 1996, N2O emissions were determined using a closed chamber technique. Continuous corn (Zea mays L.) at four N rates of 0, 170, 285, and 400 kg of N ha-1 was used on a Ste. Rosalie heavy clay (a very-fine-silty, mixed, nonacid, frigid Typic Humaquept) and a Chicot sandy loam (a fine-loamy, frigid, Typic Hapludalf). On two additional sites, a Ste. Rosalie clay and an Ormstown silty clay loam (a fine-silty, mixed, nonacid, frigid Humaquept) no-till (NT) and conventional tillage (CT); monocultural corn (CCC), monocultural soybean (Glycine max L.) (SSS); corn-soybean (SSC, CCS); and soybean-corn-alfalfa (Medicago sativa L.) phased rotations (SAC, CSA, and ACS) were used. Nitrogen rates of 0, 90, and 180 kg of N ha-1 for corn and 0, 20, and 40 kg of N ha-1 for SSS were used. Rates of N2P emission were measured from April to November in 1994 and 1995, and from mid-March to mid-November in 1996. Maximum N2O emissions reached from 120 to 450 ng of N m-2 s-1 at the Ormstown site to 50 to 240 ng of N m-2 s-1 at the Ste. Rosalie soil. Generally, N2O emissions were higher in the NT systems, with corn, and increased linearly with increasing N rates, and amounted to 1.0 to 1.6% of fertilizer N applied. The N2O emission rates were significantly related to soil denitrification rates, water-filled pore space, and soil NH4 and NO3 concentrations. A corn system using conventional tillage, legumes in rotation, and reduced N fertilizer would decrease N2O emission from agricultural fields

Nitrous oxide can be produced during nitrification, denitrification, dissimilatory reduction of NO3- to NH4+ and chemo-denitrification. Since soils are a mosaic of aerobic and anaerobic zones, it is likely that multiple processes are contributing simultaneously to N2O production in a soil profile. The N2O produced by all processes may mix to form one pool before being reduced to N2 by denitrification. Reliable methods are needed for measuring the fluxes of N2O and N2 simultaneously from agricultural soils. The C2H2 inhibition and 15N gas-flux methods are suitable for use in undisturbed soils in the field. The main disadvantage of C2H2 is that as well as blocking N2O reductase, it also blocks nitrification and dissimilatory reduction of NO3- to NH4+. Potentially the 15 N gas-flux method can give reliable measurements of the fluxes of N2O and N2 when all N transformation processes proceed naturally. The analysis of 15N in N2 and N2O is now fully automated by continuous-flow isotope-ratio mass spectrometry for 12-ml gas samples contained in septum-capped vials. Depending on the methodology, the limit of detection ranges from 4 to 11 g N ha-1day-1 for N2 and 4 to 15 g N ha-1day-1 for N2O. By measuring the 15N content and distribution of 15N atoms in the N2O molecules, information can also be obtained to help diagnose the sources of N2O and the processes producing it. Only a limited number of field studies have been done using the 15N gas-flux method on agricultural soils. The measured flux rates and mole fractions of N2O have been highly variable. In rain-fed agricultural soils, soil temperature and water-filled pore space change with the weather and so are difficult to modify. Soil organic C, NO3- and pH should be amenable to more control. The effect of organic C depends on the degree of anaerobiosis generated as a result of its metabolism. If conditions for denitrification are not limiting, split applications of organic C will produce more N2O than a single application because of the time lag in the synthesis of N2O reductase. Increasing the NO3- concentration above the Km value for NO3- reductase, or decreasing soil pH from 7 to 5, will have little effect on denitrification rate but will increase the mole fraction of N2O. The effect of NO3- concentration on the mole fraction of N2O is enhanced at low pH. Manipulating the interaction between NO3- supply and soil pH offers the best hope for minimising N2O and N2 fluxes.

Introducción/objetivo: las emisiones de gases de efecto invernadero (GEI) de origen natural han aumentado por las acciones antropogénicas, y amenazan al planeta con un desequilibrio ambiental. Los embalses para almacenar agua, que después se utiliza para mover las turbinas de centrales hidroeléctricas, acumulan sedimentos generando GEI. En este trabajo se analizan los métodos empleados para estimar las emisiones de GEI en embalses, clasificando las publicaciones científicas encontradas en los motores de búsqueda de ScienceDirect y Google Scholar. Metodología: el método analítico utiliza una expresión booleana para recopilar información en los motores de búsqueda indicados y extraer la bibliografía relevante, considerando factores como la temperatura del agua, la ubicación geográfica, el tipo y la superficie del embalse, el tipo de gas y la tecnología, lo que atribuye un valor de pertinencia a cada característica para elaborar una matriz de resultados. Resultados: los resultados muestran que más del 50 % se basan en estimaciones de GEI y el resto en mediciones directas en los embalses. Además, la contribución de la inteligencia artificial como técnica de estimación es menor al 6 %. Conclusiones: finalmente, las regiones mundiales donde se realizan los estudios están distribuidas proporcionalmente y el análisis de literatura científica indica versatilidad en los métodos de estimación de GEI en embalses hidroeléctricos. Abstract Introduction/objective: greenhouse gases (GHG) emissions of natural origin have increased due to anthropogenic actions, and threaten the planet with environmental imbalance. Reservoirs for storing water, which is later used to drive the turbines of hydroelectric power plants, accumulate sediments, generating GHG. This paper analyzes the methods used to estimate GHG emissions in reservoirs, classifying scientific publications found in the ScienceDirect and Google Scholar search engines. Methodology: the analytical method uses a Boolean expression to collect information in the indicated search engines and extract the relevant literature considering factors such as water temperature, geographic location, reservoir type and surface area, gas type and technology, which attributes a relevance value to each characteristic to elaborate a matrix of results. Results: the results show that more than 50 % are based on GHG estimates and the rest on direct measurements in the reservoirs. In addition, the contribution of artificial intelligence as an estimation technique is less than 6 %. Conclusions: finally, the world regions where studies are conducted are proportionally distributed and the analysis of scientific literature indicates versatility in GHG estimation methods in hydropower reservoirs.