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Understanding the drivers of greenhouse gas (GHG) emissions is one of the most critical global environmental challenges to mitigate the increasing global temperature. Nitrous oxide (N2O) emissions are highly variable in space and time and are controlled by multiple proximal drivers, that is, those that affect N2O emissions directly and in short timescales, and distal or indirect drivers that influence emissions over long timescales. Here we present a quantification of N2O emissions in grasslands and forests throughout the Pampas and the Semiarid Chaco in Argentina and reveal distal and proximal drivers, analyzing them in both spatial and temporal models. We measured N2O emissions, soil and climate variables monthly in nine sites over two years. Mean annual temperature and the following soil properties: phosphorous availability, carbon:nitrogen ratio, clay and sand percentages were the main distal drivers controlling N2O emissions in the spatial model, while among proximal drivers, only soil nitrate contents were positively related to N2O emissions. When considering the seasonal variability of N2O emissions (temporal model), we found that emissions were positively related to proximal drivers, such as soil nitrate and soil temperature. Our results show that soil N2O emission drivers differ between spatial and temporal models in natural grasslands and forests, explaining up to 85 and 56% of variations in N2O emissions, respectively. Temperature increased N2O emissions in both spatial and temporal models; therefore, future global warming may increase background emissions from natural ecosystems with important positive feedbacks on the earth system warming.

One- and two-dimensional carbon nanomaterials were tested as adsorbents for the elimination of two anionic dyes, reactive red 2 and methyl orange, and the cationic dye methylene blue from aqueous solutions under the same conditions. Carbon nanomaterials performed well in the removal of dyes. Surface oxygenated groups in the nanomaterials improved the cationic dyes’ adsorption, but not the adsorption of the anionic dye. The interactions between nanomaterials and dyes were verified by infrared and Raman spectroscopy. The pseudo-second order kinetic model was better fitted to the kinetic experimental data than the Elovich and pseudo-first order models. The equilibrium adsorption data were best fitted by the Langmuir model. The dimensions and morphology of the carbon nanomaterials play an important role in the adsorption of the three dyes. The main mechanism of adsorption of anionic dyes is by the interactions of the aromatic rings of the dye structures and π delocalized electrons on carbon nanostructures; the adsorption of cationic dye is mainly due to electrostatic interactions.

Hypothalamic AMPK plays a major role in the regulation of whole body metabolism and energy balance. Present evidence has demonstrated that this canonical mechanism is evolutionarily conserved. Thus, recent data demonstrated that inhibition of AMPKα2 in fish hypothalamus led to decreased food intake and liver capacity to use and synthesize glucose, lipids, and amino acids. We hypothesize that a signal of abundance of nutrients from the hypothalamus controls hepatic metabolism. The vagus nerve is the most important link between the brain and the liver. We therefore examined in the present study whether surgical transection of the vagus nerve in rainbow trout is sufficient to alter the effect in liver of central inhibition of AMPKα2. Thus, we vagotomized (VGX) or not (Sham) rainbow trout and then intracerebroventricularly administered adenoviral vectors tagged with green fluorescent protein alone or linked to a dominant negative isoform of AMPKα2. The inhibition of AMPKα2 led to reduced food intake in parallel with changes in the mRNA abundance of hypothalamic neuropeptides [neuropeptide Y ( npy), agouti-related protein 1 ( agrp1), and cocaine- and amphetamine-related transcript ( cartpt)] involved in food intake regulation. Central inhibition of AMPKα2 resulted in the liver having decreased capacity to use and synthesize glucose, lipids, and amino acids. Notably, these effects mostly disappeared in VGX fish. These results support the idea that autonomic nervous system actions mediate the actions of hypothalamic AMPKα2 on liver metabolism. Importantly, this evidence indicates that the well-established role of hypothalamic AMPK in energy balance is a canonical evolutionarily preserved mechanism that is also present in the fish lineage.

Soil use affects soil organic carbon (OC) stocks by regulating the quantity and quality of incorporated organic matter. Understanding how soil texture and other factors control OC concentration and accumulation would be useful for designing sustainable soil management practices in order to promote and preserve OC storage. The aim of this work was to evaluate the effects of land use and soil texture on the vertical distribution and stock of OC in soils of the Argentinean Mesopotamia. In Entre Rios Province, Argentina, the following sites were selected: native forest in a Typic Halacuept soil (fine to medium texture), agriculture and Eucalyptus grandis plantations of different ages (2–4 and 8–10 years) in Argic Peluderts soils (fine textures) and E. grandis plantations of different ages (2–4 and 8–10 years) in Oxic Udifluvents soils (coarse textures). OC concentration and stock were quantified up to 1 m depth, analysing distribution across the depth of the soil profile. The major differences in OC stock in equivalent mass were associated with texture; the average for coarse Oxic Udifluvents soils was 57.2 Mg OC ha−1 and 162.3 Mg OC ha−1 for Typic Halacuept and Argic Peluderts (fine to medium textures). Forest sites with fine textures stored three times more OC in equivalent mass than coarse textures under similar land use. No significant differences were observed between OC stock in equivalent mass in agricultural versus Eucalyptus plantations of similar texture. Sites with 8–10-year-old forest plantations in coarse soils were a special case, as they presented a great proportion of OC (60%) under 40 cm depth, due to a strong textural gradient with depth.

Mine Tailings of “La Aurora”, a mining site located in central Mexico, display anomalous concentrations of As, Zn, Pb, Cu and Cd. However, data on their potential toxicity is not available. It is known that toxicity is related to elemental speciation. In this work, we evaluated the biogeochemical dynamics of As in terms of mobility and chemical nature. For this purpose, samples of soils, mine tailings, plants and water were collected. Synchrotron based techniques and chemical fractionation extractions were used to determine As speciation, potential mobility, and bioavailability. Our results showed that As is present in concentrations up to 12,672 ± 34 and 326 ± 10 mg kg−1 in mine tailings and nearby soils, respectively. X-ray Absorption Spectroscopy (XAS) analysis demonstrated that As is present as AsV in a structure similar to that of kankite (FeAsO4·3.5H2O) and beudantite (PbFe3 (AsO4)(SO4)(OH)6). The presence of these mineral structures were confirmed by μ X-Ray Fluorescence and X-ray Absorption Near Edge Structure (μ-XRF/XANES). Arsenic was also detected in plant species growing in the tested soils. The highest As concentrations were determined in the roots of Baccharis salicifolia (up to 44 mg kg−1). In a creek nearby the mine tailings, As levels of 163 ± 15 μg L−1 were quantified. In terms of phytoaccessibility and bioaccessibility, As levels can be considered toxic for both plants and humans. According to sequential extraction results, As is associated mainly with the crystalline Fe-Ox fraction.

Zinc speciation, chemical forms, and phytoavailability were determined within mine tailings and soil samples from a historical mining site in the Xichu district, central Mexico. For this purpose, species determination and phase mapping were conducted using XAS, μ-XRF, and μ-XRD, and chemical extraction was performed to assess chemical forms and phytoavailability. High concentrations of Zn were recorded in the mine tailings (4681 mg·kg−1) and relatively high concentrations were observed in the soils (319 mg·kg−1). Soil samples either exceeded the threshold value for exploratory assessment or yielded concentrations that may cause ecological risk. Igeo values indicate that the mine tailings were extremely polluted and soils were unpolluted to moderately polluted. Phytoavailable Zn positively correlated with total Zn content in the mine tailings (34%; 1719 mg·kg−1) and soils (36%; 69.5 mg·kg−1) and exceeded the threshold value for the development of ecotoxicological effects. The average percentages of most mobile fractions (water-soluble, exchangeable, and carbonate-bound) in surficial and composite mine tailings were ~31% and ~34%, respectively, whereas that in the surrounding soils was ~36%. According to XAS and linear combination fitting, the main phases of Zn in mine tailings were residual species, whereas in soils, the main phase was zinc carbonate (hydrozincite). Minor components of Zn were found as sulfate and sorbed onto goethite, which was confirmed by μ-XRD phase mapping. Synchrotron techniques suggest that Zn sulfate and Zn sorbed onto goethite are the main species controlling the mobility and availability of Zn. The potential high mobilization and dispersion of Zn represent potential harm to surrounding ecosystems in the historical mine tailings of central Mexico.

Cattle trampling during grazing of crop residue may cause physical soil damage that may be repaired when animals are excluded. Understanding the interplay between soil deterioration and natural recovery of the soil physical condition allows for a better understanding of grazing management systems. Various soil physical properties (i.e., bulk density (BD), penetration resistance (PR), infiltration rate, structural instability) were determined up to 20 cm depth in a silty loam Typic Argiudoll and a sandy loam Typic Hapludoll of the Argentine Pampas from 2005 to 2008. Sampling was carried out before and after grazing, and at different moments of the crop cycle including harvest event. Grazing winter residues and weeds did not lead to the expected compaction processes (e.g., in average BD difference between after grazing and before grazing was from 0.072 to +0.137 Mg m3 for both soils under grazing). In general, physical soil conditions improved during winter, independently of grazing. This might be related to the intrinsic soil characteristics (organic matter content, moisture, clay content) or grazing system (stocking rate, duration of grazing period), which prevented soil physical damage, suggesting that recovery forces were greater than grazing stress. Cropping to maize and soybean showed similar value or improved soil physical properties respect to the after grazing (e.g., in average PR difference between before harvest and after grazing was from +409 to 2561 kPa for both soils), acting as biotic a recovery factor. However, massive damage was harvest operation led to the highest soil deterioration (e.g., in average PR difference between before harvest and after harvest was 985 kPa). Fil: Fernández, Patricia Lilia. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Manejo y Conservación de Suelos; Argentina Fil: Alvarez, Carina Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Cátedra de Manejo y Conservación de Suelos; Argentina Fil: Taboada, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigación de Recursos Naturales. Instituto de Suelos; Argentina

Nitrous oxide has a key effect on global climate development and 53% of N2O total annual emissions are related to fluxes from the soil. Land use and soil characteristics affect N2O emissions. There are not enough assessments in Argentina to quantify N2O emissions from commercial forest plantations. This research aimed at quantifying N2O fluxes from Eucalyptus grandis plantations and at identifying factors explaining emission variability. The study was carried out in Gualeguaychu, Entre Rios Province, Argentina (33°1′17″S, 58° 13′37″W) on Eucalyptus grandis plantations in four different situations: at two ages (2–4 yr and 8–10 yr), on two contrasting texture soils (coarse and fine), and on a medium-textured sodic soil in a natural forest (shrubland). Greenhouse gas emissions (N2O and CO2) were measured 12 times between August 2016 and October 2017. Emission rates and annual N2O emissions were low in all evaluated treatments (average emission rate: 2.62 µg N2O-N m−2h−1, and average annual emission: 0.226 kg N2O-N ha−1 year−1). These rates are considerably lower than those of agricultural situations in the same region. This can be explained by the null use of nitrogen fertilization and by the absence of atmospheric nitrogen- fixing crops in forestry plantations. The use under natural forest showed the highest cumulative annual emissions (0.698 kg N2O-N ha−1 year−1) possibly because of its woody leguminous species composition and its higher soil water content. N2O emissions in fine 2-4y, coarse 2-4y, and in coarse 8-10y were in average 0.0896 kg N2O-N ha−1 year−1 with no statistically differences between them. The fine 8-10y N2O emissions did not differ from the natural forest neither from the other treatments (0.261 kg N2O-N ha−1 year−1). Soils with higher clay content showed a trend toward higher N2O emissions than sandy soils. NO3-N level in soil was the variable that best explained N2O-N emissions (p

Fil: Osinaga, Natalia Andrea. CONICET. Buenos Aires, Argentina. Fil: Alvarez, Carina Rosa. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Fertilidad y Fertilizantes. Buenos Aires, Argentina. Fil: Taboada, Miguel Angel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Ingeniería Agrícola y Uso de la Tierra. Cátedra de Fertilidad y Fertilizantes. Buenos Aires, Argentina. The subhumid Chaco region of Argentina, originally covered by dry sclerophyll forest, has been subjected to clearing since the end of the 1970s and replacement of the forest by no-till farming. Land use changes produced a decrease in aboveground carbon (C) stored in forests, but little is known about the impact on soil organic C stocks. The aim of this study was to evaluate soil C stocks and C fractions up to 1m depth in soils under different land use: smaller than 10-year continuous cropping, greater than 20-year continuous cropping, warm-season grass pasture and native forest in 32 sites distributed over the Chaco region. The organic C stock content up to 1mdepth expressed as equivalent mass varied as follows: forest (119.3Mgha-1) greater than pasture (87.9Mgha-1) greater than continuous cropping (71.9 and 77.3Mgha-1), with no impact of the number of years under cropping. The coarse particle fraction (2000–212 μm) at 0–5 and 5–20 cm depth layers was the most sensitive organic carbon fraction to land use change. Resistant carbon (smaller than 53 μm) was the main organic matter fraction in all sample categories except in the forest. Organic C stock, its quality and its distribution in the profile were responsive to land use change. The conversion of the Chaco forest to crops was associated with a decrease of organic C stock up to 1m depth and with the decrease of the labile fraction. The permanent pastures of warm-season grasses allowed higher C stocks to be sustained than cropping systems and so could be considered a sustainable land use system in terms of soil C preservation. As soil organic C losses were not restricted to the first few centimetres of the soil, the development of models that would allow the estimation of soil organic C changes in depth would be useful to evaluate the impact of land use change on C stocks with greater precision. grafs., tbls., mapas

To assess the hypothesis of glucosensing systems present in fish telencephalon, we first demonstrated in rainbow trout, by in situ hybridisation, the presence of glucokinase (GK). Then, we assessed the response of glucosensing markers in rainbow trout telencephalon 6 hours after i.c.v. treatment with glucose or 2‐deoxyglucose (inducing glucoprivation). We evaluated the response of parameters related to the mechanisms dependent on GK, liver X receptor (LXR), mitochondrial activity, sweet taste receptor and sodium‐glucose linked transporter 1 (SGLT‐1). We also assessed mRNA abundance of neuropeptides involved in the metabolic control of food intake (agouti‐related protein, neuropeptide Y, pro‐opiomelanocortin, and cocaine‐ and amphetamine‐related transcript), as well as the abundance and phosphorylation status of proteins possibly involved in linking glucosensing with neuropeptide expression, such as protein kinase B (AkT), AMP‐activated protein kinase (AMPK), mechanistic target of rapamycin and cAMP response element‐binding protein (CREB). The responses obtained support the presence in the telencephalon of a glucosensing mechanism based on GK and maybe one based on LXR, although they do not support the presence of mechanisms dependent on mitochondrial activity and SGLT‐1. The mechanism based on sweet taste receptor responded to glucose but in a converse way to that characterised previously in the hypothalamus. In general, systems responded only to glucose but not to glucoprivation. Neuropeptides did not respond to glucose or glucoprivation. By contrast, the presence of glucose activates Akt and inhibits AMPK, CREB and forkhead box01. This is the first study in any vertebrate species in which the response to glucose of putative glucosensing mechanisms is demonstrated in the telencephalon. Their role might relate to processes other than homeostatic control of food intake, such as the hedonic and reward system, Spanish Agencia Estatal de Investigacion and FEDER, Grant/Award Number: AGL2016-74857-C3-1-R, AGL2016-74857-C3-3-R and BES -2014 -068040; the European Fund of Regional Development

To assess the hypothesis that Na+/K+-ATPase (NKA) is involved in the central regulation of food intake in fish, we observed in a first experiment with rainbow trout (Oncorhynchus mykiss) that intracerebroventricular (ICV) treatment with ouabain decreased food intake. We hypothesized that this effect relates to modulation of glucosensing mechanisms in brain areas (hypothalamus, hindbrain, and telencephalon) involved in food intake control. Therefore, we evaluated in a second experiment, the effect of ICV administration of ouabain, in the absence or in the presence of glucose, on NKA activity, mRNA abundance of different NKA subunits, parameters related to glucosensing, transcription factors, and appetite-related neuropeptides in brain areas involved in the control of food intake. NKA activity and mRNA abundance of nkaα1a and nkaα1c in brain were inhibited by ouabain treatment and partially by glucose. The anorectic effect of ouabain is opposed to the orexigenic effect reported in mammals. The difference might relate to the activity of glucosensing as well as downstream mechanisms involved in food intake regulation. Ouabain inhibited glucosensing mechanisms, which were activated by glucose in hypothalamus and telencephalon. Transcription factors and neuropeptides displayed responses comparable to those elicited by glucose when ouabain was administered alone, but not when glucose and ouabain were administered simultaneously. Ouabain might therefore affect other processes, besides glucosensing mechanisms, generating changes in membrane potential and/or intracellular pathways finally modulating transcription factors and neuropeptide mRNA abundance leading to modified food intake.

We previously obtained evidence in rainbow trout peripheral tissues such as liver and Brockmann bodies (BB) for the presence and response to changes in circulating levels of glucose (induced by intraperitoneal hypoglycaemic and hyperglycaemic treatments) of glucosensing mechanisms others than that mediated by glucokinase (GK). There were based on mitochondrial production of reactive oxygen species (ROS) leading to increased expression of uncoupling protein 2 (UCP2), and sweet taste receptor in liver and BB, and on liver X receptor (LXR) and sodium/glucose co-transporter 1 (SGLT-1) in BB. We aimed in the present study to obtain further in vitro evidence for the presence and functioning of these systems. In a first experiment, pools of sliced liver and BB were incubated for 6h at 15°C in modified Hanks' medium containing 2, 4, or 8mM d-glucose, and we assessed the response of parameters related to these glucosensing mechanisms. In a second experiment, pools of sliced liver and BB were incubated for 6h at 15°C in modified Hanks' medium with 8mM d-glucose alone (control) or containing 1mM phloridzin (SGLT-1 antagonist), 20μM genipin (UCP2 inhibitor), 1μM trolox (ROS scavenger), 100μM bezafibrate (T1R3 inhibitor), and 50μM geranyl-geranyl pyrophosphate (LXR inhibitor). The results obtained in both experiments support the presence and functioning of glucosensor mechanisms in liver based on sweet taste receptor whereas in BB the evidence support those based on LXR, mitochondrial activity and sweet taste receptor.

Active fractions of organic matter have been proposed as early indices of changes in soil organic carbon (organic-C) induced by management. We performed a meta-analysis of published results from 31 field experiments conducted in the Pampas in which tillage and rotation effects on organic-C, microbial biomass carbon (microbial-C), light fraction carbon (light-C), particulate carbon (particulate-C) and basal respiration (mineralized-C) were assessed. We compared the changes of organic-C and the four active fractions between management treatments sampled at the same date and depth within each experiment. Pooling all the experiments, active fractions-C varied on average 1.2- to 3.0-fold more than organic-C, depending on the fraction considered, but these average changes were significantly greater than organic-C changes only for particulate-C. This later fraction showed to be more sensitive to agricultural practices than organic-C. In experiments in which organic-C changes were lower than 15–25%, the four labile fractions may show opposite trends than organic-C. Above this threshold, changes of active fractions generally copied organic-C changes and were greater. Consequently, the active fractions may be used as indicators of changes in organic-C only when this latter variable has already suffered a huge change. In these cases, it will be easier to simply measure organic-C. Fil: Alvarez, Carina Rosa. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Alvarez, Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

We previously obtained evidence in rainbow trout for the presence and response to changes in circulating levels of glucose (induced by intraperitoneal hypoglycaemic and hyperglycaemic treatments) of glucosensing mechanisms based on liver X receptor (LXR), mitochondrial production of reactive oxygen species (ROS) leading to increased expression of uncoupling protein 2 (UCP2), and sweet taste receptor in the hypothalamus, and on sodium/glucose co-transporter 1 (SGLT-1) in hindbrain. However, these effects of glucose might be indirect. Therefore, we evaluated the response of parameters related to these glucosensing mechanisms in a first experiment using pooled sections of hypothalamus and hindbrain incubated for 6 h at 15°C in modified Hanks9 medium containing 2, 4 or 8 mmol l −1 d-glucose. The responses observed in some cases were consistent with glucosensing capacity. In a second experiment, pooled sections of hypothalamus and hindbrain were incubated for 6 h at 15°C in modified Hanks9 medium with 8 mmol l −1 d-glucose alone (control) or containing 1 mmol l −1 phloridzin (SGLT-1 antagonist), 20 µmol l −1 genipin (UCP2 inhibitor), 1 µmol l −1 trolox (ROS scavenger), 100 µmol l −1 bezafibrate (T1R3 inhibitor) and 50 µmol l −1 geranyl-geranyl pyrophosphate (LXR inhibitor). The response observed in the presence of these specific inhibitors/antagonists further supports the proposal that critical components of the different glucosensing mechanisms are functioning in rainbow trout hypothalamus and hindbrain.

One of the expected benefits of no-tillage systems is a higher rate of soil C sequestration. However, higher C retention in soil is not always apparent when notillage is applied, due e.g., to substantial differences in soil type and initial C content. The main purpose of this study was to evaluate the potential of no-tillage management to increase the stock of total organic C in soils of the Pampas region in Argentina. Forty crop fields under no-tillage and conventional tillage systems and seven undisturbed soils were sampled. Total organic C, total N, their fractions and stratification ratios and the C storage capacity of the soils under different managements were assessed in samples to a depth of 30 cm, in three layers (0-5, 5-15 and 15-30 cm). The differences between the C pools of the undisturbed and cultivated soils were significant (p < 0.05) and most pronounced in the top (0-5 cm) soil layer, with more active C near the soil surface (undisturbed > no-tillage > conventional tillage). Based on the stratification ratio of the labile C pool (0-5/5-15 cm), the untilled were separated from conventionally tilled areas. Much of the variation in potentially mineralizable C was explained by this active C fraction (R 2 = 0.61) and by total organic C (R 2 = 0.67). No-till soils did not accumulate more organic C than conventionally tilled soils in the 0-30 cm layer, but there was substantial stratification of total and active C pools at no till sites. If the C stratification ratio is really an indicator of soil quality, then the C storage potential of no-tillage would be greater than in conventional tillage, at least in the surface layers. Particulate organic C and potentially mineralizable C may be useful to evaluate variations in topsoil organic matter. Um dos benefícios esperados do uso do plantio direto é um maior sequestro de C. Contudo, nem sempre se observa maior retenção de C no solo quando esse sistema de preparo é utilizado, devido principalmente às diferenças em tipo de solo e conteúdo inicial de C, entre outras. O objetivo deste trabalho foi avaliar o potencial do plantio direto para estocar C orgânico nos solos da Região do Pampa Argentino. Foram coletadas amostras de solo em 40 áreas sob plantio direto ou preparo convencional e em sete campos não cultivados por vários anos. Determinaram-se o C orgânico total, N total, suas frações lábeis, sua taxa de estratificação e a capacidade de estocar C dos solos sob diferentes manejos, na camada de 0-30 cm de profundidade, a qual foi dividida, para fins de amostragem, em três profundidades (0-5, 5-15 e 15-30 cm). Verificou-se diferença significativa (p < 0,05) para todos os pools de C entre os solos não cultivados e os cultivados. A diferença mais pronunciada foi verificada na camada superficial (0-5 cm), sendo determinado o maior teor de C lábil próximo da superfície do solo (não perturbado > plantio direto > preparo convencional). A taxa de estratificação do C lábil (0-5/5-15 cm) permitiu separar as áreas sob plantio direto daquelas sob preparo convencional. Boa parte da variação em C potencialmente mineralizável foi explicada pela fração lábil do C (R2 = 0,61), assim como pelo C orgânico total (R2 = 0,67). Os solos sob plantio direto não estocaram mais C orgânico do que os preparados de maneira convencional, na camada de 0-30 cm. Entretanto, houve substancial estratificação dos pools de C lábil nos locais sob plantio direto, indicando que, se a taxa de estratificação for realmente um indicador de qualidade de solos, as áreas sob plantio direto poderiam ter maior potencial de acúmulo de C, pelo menos nas camadas superficiais de solo, se comparada com as áreas sob preparo convencional. O C orgânico particulado e o C potencialmente mineralizável podem ser utilizados para avaliar variações na matéria orgânica da camada superficial do solo. Fil: Alvarez, Carina Rosa. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Costantini, Alejandro Oscar. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina Fil: Bono, Alfredo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina Fil: Taboada, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnología Agropecuaria; Argentina. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Gutiérrez Boem, Flavio Hernán. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Fernández, Patricia Lilia. Universidad de Buenos Aires. Facultad de Agronomía; Argentina Fil: Prystupa, Pablo. Universidad de Buenos Aires. Facultad de Agronomía; Argentina

Decreasing P buffer capacity of the soil surface in no-tilled soils has been attributed to enrichment of both P and OM (OM). As soil surface enrichment with P and OM usually occurs simultaneously in no-tilled soils, it is not clearly established whether the increase of soil OM affects the capacity of soils to retain P. A study was conducted to assess whether the variations in soil OM (total and particulate) at soil surface affects P retention capacity. Thirty five soils from the Rolling Pampa (17 tilled and 18 no-tilled) were selected. All soils had medium to low levels of available P (P Bray1 53 μm), particle size distribution, and pH. Tilled and no-tilled soils did not differ in soil texture, pH, total and available P content. On the contrary, no-tilled soils had more OM (+14%) and POM (+56%) than tilled soils. The capacity of soils to retain added P was not different in both groups of soils. Phosphorus sorption index was not related to soil content of total OM or POM. Variation in P sorption index was only related to soil clay content (r 2 = 0.44). This study provides evidence contradicting the long held assumption that the reported decrease in P sorption at the surface of no-tilled soils was caused in part by OM enrichment.

Nitrogen (N) management may be improved by a thorough understanding of the nutrient dynamics during previous‐crop residue decomposition and its impact on fertilizer N fate in the soil–plant system. An experiment was conducted in the Argentine Pampas to evaluate the effect of maize and soybean as previouscrops and plow‐till and no‐till methods on N dynamics and 15N‐labeled fertilizer uptake during a wheat growing season. Maize and soybean residues released N under both tillage treatments, but N release was faster from soybean residues and when residues were buried by tillage. Net immobilization of N on decomposing residues was not detected. A regression model that accounted for 92% of remaining N variability included time, previous crop, and tillage treatment as independent variables. The rapid residue decomposition with N release was attributed to the high temperatures of the agroecosystem. The recovery of 15N‐labeled fertilizer in the wheat crop, soil organic matter, and decomposing residues was...

The knowledge of nitrogen (N) losses in direct‐drilling agrosystems is essential to develop strategies to increase fertilizer efficiency and to minimize environmental damage. The objectives were i) to quantify the magnitude of N volatilization and leaching simultaneously as affected by different urea fertilization rates and ii) to evaluate the capacity of these specific plant–soil systems to act as a buffer to prevent nitrate leaching. Two experiments were conducted during 2001/02 and 2002/03 growing seasons in Alberti, Argentina. The crop was direct‐drilled maize and the soil a Typic Argiudoll. Ammonia losses, N uptake by crop at flowering and harvest, grain yield, N in previous crop residues, and soil nitrate content up to 2‐m depths were determined. Nitrogen availability, soil nitrate (NO3)‐N up to 1 m plus fertilizer N, was linearly and highly associated with crop N uptake at flowering (R2=0.93, P

There is no evidence in fish brain demonstrating the existence of changes in lactate metabolism in response to alterations in glucose levels. We induced in rainbow trout through intraperitoneal (IP) treatments, hypoglycaemic or hyperglycaemic changes to assess the response of parameters involved in lactate metabolism in glucosensing areas like hypothalamus and hindbrain. To distinguish those effects from those induced by peripheral changes in the levels of metabolites or hormones, we also carried out intracerebroventricular (ICV) treatments with 2-deoxy-D-glucose (2-DG, a non-metabolizable glucose analogue thus inducing local glucopenia) or glucose. Finally, we also incubated hypothalamus and hindbrain in vitro in the presence of increased glucose concentrations. The changes in glucose availability were in general correlated to changes in the amount of lactate in both areas. However, when we assessed in these areas the response of parameters related to lactate metabolism, the results obtained were contradictory. The increase in glucose levels did not produce in general the expected changes in those pathways with only a minor increase in their capacity of lactate production. The decrease in glucose levels was, however, more clearly related to a decreased capacity of the pathways involved in the production and use of lactate, and this was especially evident after ICV treatment with 2-DG in both areas. In conclusion, the present results while addressing the existence of changes in lactate metabolism after inducing changes in glucose levels in brain glucosensing areas only partially support the possible existence of an astrocyte-neuron lactate shuttle in hypothalamus and hindbrain of rainbow trout relating glucose availability to lactate production and use.

The Rolling and Flat Pampas are vast plains located in Argentina. Wheat is one of the most economically important crops of these regions. Two extensive studies have been preformed to evaluate the effects of nitrogen fertilization on wheat yield at field scale. We pooled these published data to establish relationships between wheat yield and soil and climate variables under a wide range of soils and management conditions. Total soil carbon was the variable more associated with yield (r 2=0.25). The increase in grain production expected between soils with low and high carbon levels rounded 2,200 kg ha− 1. A multivariate model which included carbon in the light fraction, potential mineralizaable nitrogen, available mineral nitrogen, and rainfall was obtained, explaining 50% of wheat yield variability. These results highlight the importance of organic matter on grain production in the Humid Pampas. This effect can be due to the role of organic soil components as source of nutrients for crops.

The Rolling and Flat Pampas are vast plains which contribute with more than half of the Argentine wheat production. In the 80's three extensive studies were preformed in these regions, which determined nitrate content in the 0–20, 20–40, and 40–60 cm soil layers, comprising a wide range of soil, climatic and cultural variables. More recently, we determined the mineral-N (N) content at 0–30 and 30–60 cm depths, in a set of farmer's plots under different tillage systems and previous crop. These datasets were used in order to establish simple equations to predict N availability in the 0–60 cm stratum, from the N availability in the upper layer. Nitrate content at wheat presowing time presented a clear stratification pattern with depth. For the fist dataset, strong relationships were obtained between the nitrate content at different soil depths, with previous crops of corn, sunflower or sorghum (R2=0.52 to 0.90, P

The labile component of soil organic matter (SOM) plays an important role in short-term nutrient turnover. Our objectives were (i) to establish the relationships between carbon in soil density fractions with carbon mineralization and the microbial biomass under contrasting conditions, (it) to compare the goodness of fit of different mathematical models to describe carbon mineralization, and (iii) to evaluate the relationships of the SOM pools and the mineralization parameters estimated by the best kinetic model. Twenty-eight soil samples were collected from a fine, illitic, thermic Typic Argiudoll localized in Argentina. These samples differed in the soil management (pasture and agriculture), tillage systems (chisel tillage, plough tillage, and no-tillage), crop rotation, or depths. Microbial biomass was highly correlated with total carbon (r 2 = 0.777, P 2.0 g mL -1 ) soil fractions. Carbon in the soil light fraction was strongly related to the carbon mineralized at 10 and 160 d of incubation. The exponential and hyperbolic models showed a good description of the mineralization data (r 2 >0.982). The application of models which considered two organic matter pools could not describe the mineralization of some samples. The hyperbolic model estimated higher potentially carbon mineralizable pools (C 0 ) and semidecomposition time periods than the exponential one. The C 0 estimated by the exponential model were similar to the carbon content in the soil light fraction. This soil organic component seemed to be the driving variable of microbial activity and a good predictor of soil potential carbon mineralization.

The active pool of organic matter plays an essential role in the short-term of nutrients turnover in soil. An approach to characterizing this fraction is through densimetric techniques which isolate soil light fractions. Cropping and tillage systems are determinants of the amount and distribution of soil organic matter, especially in the upper layers of the soil profile. Our objectives were to evaluate the distribution and dynamics of carbon in different density fractions in order to provide a better understanding of soil fertility changes induced by contrasting types of soil management: plow tillage, no-tillage and pasture. The total and active microbial biomass pools and microbial activity were also determined. The experiment was performed on a Typic Argiudoll from the Argentinean Pampa. Organic carbon was highest under pasture, but there were no differences between the others two treatments for the 0–15 cm layer. Under the pasture and no-tillage treatments, organic carbon decreased with depth. The light fraction (density ≤1.6 g ml−1) was higher under no-tillage than in the plowed soil, indicating that this fraction was more sensitive to management than was total carbon. The carbon mineralized in 160 d of incubation from different density fractions followed the order: light fraction>medium fraction (1.6–2 g ml−1)>heavy fraction (≥2 g ml−1), presumably because of an increase in chemical and physical protection of organic matter in the heavier fractions. Total soil microbial biomass was stratified under the pasture and no-tillage treatments. Basal respiration was significantly associated with the availability of carbon in the light fraction (r2=0.98, P

The esterification of lauric acid and methanol is explored using a thermally coupled distillation sequence with a side rectifier and the Petlyuk distillation column. The study was conducted using as a design tool a multi objective genetic algorithm with restrictions. The product of the esterification can be used as biodiesel. It was found that the thermally coupled distillation sequence involving a side rectifier can produce biodiesel with a high purity (around 0.999) and also pure water, and the excess of methanol is recovered in a side rectifier. The results indicate that the energy consumption of the complex distillation sequence with a side rectifier can be reduced significantly by varying operational conditions. These reductions in energy consumption can be interpreted as reductions in carbon dioxide emissions.

Calcium carbonate is the most widespread mineral phase involved in the biomineralization processes occurring in invertebrates. Besides the usual CaCO3 crystalline modifications, i.e. vaterite, calcite and aragonite, an increasing number of investigations have demonstrated the presence of amorphous calcium carbonate (ACC) as a transient phase that plays an important role in the initiation of the biomineralization process.

Waterlogging is a common feature in some natural grazed grasslands of Argentina. Phosphorus is the most limiting element. The response of two representative grasses, Danthonia montevidensis and Paspalum dilatatum, to waterlogging and application of phosphorus and nitrogen fertilizer, was studied in a pot experiment. Both species tolerated waterlogging and both increased their herbage production when waterlogged, especially when phosphorus fertilizer was applied.