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Este texto se centra en el estudio de una serie de prácticas artísticas desarrolladas en el marco del arte correo por creadores de América Latina durante el último tercio del siglo XX, como respuesta a la situación política de sus países de origen y con el objetivo de participar, algunos de ellos desde el exilio voluntario o forzado, en el espacio de lo público controlado por regímenes autoritarios o dictatoriales. El establecimiento de redes y circuitos a través de estas prácticas permitió el surgimiento de una escena artística transnacional e independiente y la relectura del llamado arte latinoamericano, en la medida que su producción artística trascendió las fronteras geográficas y desafió los grandes centros y circuitos hegemónicos del arte, posicionando temas de actualidad de interés social y político de la región a través de sus obras y de sus proyectos editoriales colectivos.

Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co-occurring local drivers will influence temperature sensitivity of plant litter decomposition in lotic ecosystems remains uncertain. Here, we examined the temperature sensitivity of microbial-mediated decomposition, microbial respiration, fungal biomass and leaf nutrients of two plant species varying in litter quality. We also assessed whether the type of microbial community and stream water characteristics influence such responses to temperature. We incubated alder ( Alnus glutinosa ) and eucalypt ( Eucalyptus globulus ) litter discs in three streams differing in autumn–winter water temperature (range 4.6–8.9 °C). Simultaneously, in laboratory microcosms, litter discs microbially conditioned in these streams were incubated at 5, 10 and 15 °C with water from the conditioning stream and with a water control from an additional stream. Both in the field and in the laboratory, higher temperatures enhanced litter decomposition rates, except for eucalypt in the field. Leaf quality modified the response of decomposition to temperature in the field, with eucalypt leaf litter showing a lower increase, whereas it did not in the laboratory. The origin of microbial community only affected the decomposition rates in the laboratory, but it did not modify the response to temperature. Water quality only defined the phosphorus content of the leaf litter or the fungal biomass, but it did not modify the response to temperature. Our results suggest that the acceleration in decomposition by global warming will be shaped by local factors, mainly by leaf litter quality, in headwater streams.

Leaf litter of alder (Alnus glutinosa) is a key resource to detrital stream food webs. Due to its high quality and palatability, it is readily colonised by microorganisms and consumed by detritivores, contributing significantly to carbon and nutrient cycling and to ecosystem functioning. Given that this species has declined due to the spread of the pathogen Phytophthora alni, we investigated how its loss would alter leaf litter decomposition and associated stream assemblages of aquatic hyphomycetes and invertebrates, in a field experiment conducted in three streams. We compared litter mixtures containing alder plus three other species (Corylus avellana, Quercus robur and Salix atrocinerea; that is, 4-species treatments) with mixtures that excluded alder (3-species treatments) and all the monocultures (1-species treatments). The loss of alder reduced decomposition rates, despite the existence of an overall negative diversity effect after 3 weeks of exposure (that is, monocultures decomposed faster than mixtures) and no diversity effect after 6 weeks. Aquatic hyphomycete and detritivore assemblage structure in the mixture without alder differed from those of the mixture with alder and the monocultures, and the former had lower fungal sporulation rate and taxon richness. Our results suggest that alder loss from the riparian vegetation can significantly slow down the processing of organic matter in streams and produce shifts in stream assemblages, with potential consequences on overall ecosystem functioning. We highlight the importance of assessing the ecological consequences of losing single species, particularly those especially vulnerable to stressors, to complement the multiple studies that have assessed the effects of random species loss.

Forest change is a major environmental problem worldwide. Forest streams, with their large aquatic–terrestrial interface and strong dependence on terrestrially derived organic matter, are highly sensitive to forest changes. Fast-wood plantations can be particularly threatening if they markedly differ from native forests. Eucalyptus plantations, in particular, cover large areas worldwide (> 20 million ha, mostly from 35°S to 35°N), but their effects on stream functioning have been addressed mostly in the Iberian Peninsula, which limits generalization to other regions. We assessed the effect of eucalyptus plantations on total (microbial decomposers and macroinvertebrates; in coarse mesh bags) and microbial-driven (in fine mesh bags) leaf litter decomposition by comparing streams flowing through native forests and eucalyptus plantations in seven regions in the Iberian Peninsula, Central Africa and South America. We found an overall significant inhibition of total litter decomposition by 23%. The effect did not significantly differ across regions, although a significant inhibition was found for Spain (-41%), South Brazil (-31%) and Uruguay (-36%) (Portugal had a marginally nonsignificant inhibition by 50%) but not for other regions, suggesting that the effects of plantations in temperate climates are mediated through effects on macroinvertebrate communities. Contrarily, the overall effect for microbial-driven litter decomposition was non-significant, but it significantly differed across regions with a significant stimulation in Central Brazil (110%) and Uruguay (32%), and nonsignificant effects for other regions (Kenya had a marginally nonsignificant inhibition by 48%), suggesting that functional redundancy among microbial communities is not general and effects can occur if plantations induce changes in nutrient availability, solar irradiation or litter characteristics.

1. Understanding how biodiversity loss influences plant litter decomposition—that is, the biologically mediated conversion of coarse to fine particulate organic matteris crucial to predict changes in the functioning of many stream ecosystems, where detrital food webs are dominant. Rates of litter decomposition are influenced by detritivore diversity, but the mechanisms behind this relationship are uncertain. 2. As differences in detritivore body size are a major determinant of interspecific interactions, they should be key for predicting effects of detritivore diversity on decomposition. To explore this question, we manipulated detritivore diversity and body size simultaneously in a microcosm experiment using two small (Leuctra geniculata and Lepidostoma hirtum) and two large detritivore species ( Sericostoma pyrenaicum and Echinogammarus berilloni) in all possible 1-, 2-, and 4-species combinations, and litter discs of Alnus glutinosa. 3. We expected that larger species would facilitate smaller species through the production of smaller litter fragments, resulting in faster decomposition and greater growth of smaller species in polycultures containing species of different body size. To examine this hypothesis, we used a set of “diversity-interaction” models that explored how decomposition was affected by different interspecific interactions and the role of body size, and quantified the magnitude of such effect through ratios of decomposition rates and detritivore growth between polycultures and monocultures. 4. We found a clear positive effect of detritivore diversity on decomposition, which was mainly explained by facilitation and niche partitioning. Facilitation of small animals by larger ones was evidenced by a 12% increase in decomposition rates in polycultures compared to monocultures and the higher growth (20%) of small species, which partly fed on fine particulate organic matter produced by larger animals. When the large species were together in polycultures, decomposition was enhanced by 19%, but there were no changes in growth; niche partitioning was a plausible mechanism behind the increase in decomposition rates, as both species fed on different parts of litter discs, only one species being able to eat less palatable parts. 5. Our study demonstrates that interspecific differences in body size should be taken into account in diversity-decomposition studies. Future studies should also consider differences in species' vulnerability to extinction depending on body size and how this might affect ecosystem functioning in different scenarios of detritivore diversity and more complex food webs.

A partir de la noción de \"pacificación\" como vehículo de comparación de dinámicas en Colombia y Brasil, observo algunos mecanismos del Estado como productor de peligros que estimulan la informalidad y la ilegalidad. Comparo, concretamente, la \"pacificación de Urabá\", en Colombia, y la \"pacificación\" por medio de las Unidades de Policía Pacificadora (UPPs) en Río de Janeiro. Algunos de los mecanismos a los que hago referencia en este artículo, que vislumbra una agenda de investigación para desarrollos futuros, son: la excepcionalidad como mecanismo que permite la activación del valor seguridad y su englobado, la inseguridad; la no diferenciación territorio/población vinculada a ciertas nociones de territorio y soberanía, y la privatización de la cara proveedora del Estado mediante prácticas de militarización.

Summary We are facing major biodiversity loss and there is evidence that such loss can alter ecosystem functioning. However, the effects of plant diversity on decomposition – a key component of the global carbon cycle – are still unclear. A recent study suggested that a plant trait – their nitrogen (N)‐fixing capacity – could mediate effects of litter diversity on decomposition by means of a microbial transfer of N from N‐fixers to non‐fixers. We explored this possibility in a microcosm experiment in which we manipulated litter species richness (one, two or four species), N‐fixing capacity (N‐fixer or non‐fixer species), the presence of detritivores (Sericostoma pyrenaicum larvae present or absent) and water N concentration [natural stream water (0·366 mg L−1 of NO3‐N) or elevated N concentration (five times the natural concentration: 1·835 mg L−1)]. We show that litter diversity accelerated decomposition by micro‐organisms and detritivores (by 7% and 15% respectively), mostly through complementarity effects. However, enhanced decomposition did not result in higher detritivore growth, possibly because all litter combinations provided sufficient resources for their maximum growth. The plant N‐fixing capacity had no effect on decomposition, which varied among species most likely because of differences in a combination of litter traits. Detritivores maximized the consumption of their preferred resource in litter mixtures, but also exploited less preferred resources, and their C : N ratios increased during the experiment regardless of litter type or water N concentration. Microbial decomposition of litter with low N content was enhanced at elevated water N concentration, suggesting that micro‐organisms used nutrients from the water when those nutrients were limiting in leaf litter. In contrast, detritivore growth was impaired at elevated water N concentration, possibly because a stoichiometric imbalance entails metabolic costs. Our findings suggest that loss of plant diversity in riparian forests would mostly affect decomposition in streams of high nutrient status, where effects on microbial decomposition would be more evident and detritivore populations may be reduced. A lay summary is available for this article. Lay Summary

In temperate streams, water temperature and organic matter inputs from surrounding forest vary along the altitude. We tested if the different features of streams of similar size determined by an altitudinal gradient might differentially affect the processing rate of different quality leaves (alder, oak and beech). To distinguish the relative contribution of microbial decomposition from overall decomposition, fine- and coarse-mesh bags were used. We determined decomposition rates, leaf-N and -P concentration, microbial respiration (fine bags), invertebrate colonisation (coarse bags) and density and identity of benthic invertebrates in three second-order streams. Alder decomposed faster than the other species in all three streams and regardless of mesh size due to its lower values of C:N, C:P and N:P. Unexpectedly, microbial decomposition rate did not vary among streams for any of the leaf species. The total decomposition rate of alder and oak showed a negative trend along the altitudinal gradient, the magnitude of the change in decomposition rates being similar for both species. The density and structure of the invertebrate community differed along the altitudinal gradient, related to temperature and surrounding vegetation, determining the decomposition rate. Unexpectedly, sensitivity of decomposition rate of different quality leaves to temperature does not differ along the gradient.

•Parenteral nutrition is associated with the development of several complications.•The cholestasis is one of the most frequent complications of parenteral nutrition.•The amino acids solutions have been proposed as a risk factor in the neonates. In neonates on total parenteral nutrition (TPN), amino acids may be a risk factor for developing total parenteral nutrition–associated cholestasis (TPNAC). We aimed, first, to compare methionine, cysteine, and taurine plasma levels between neonates on TPN who were receiving an intravenous amino acid solution based on a breast milk aminogram and those on an intravenous solution of pediatric amino acids based on an umbilical cord aminogram, and second, to determine the frequency of TPNAC. A double-blind randomized controlled trial was conducted. Ninety-four neonates with a birthweight of 1000g or more and a gestational age of 30 wk or older were admitted and enrolled. Blood samples were obtained at 0, 7, and 14 d of TPN, and plasma amino acid concentrations were determined by ultra-high-resolution liquid chromatography. Continuous variables were compared using the Wilcoxon rank-sum test or Student's t test; categorical variables were compared using the Fisher exact test. Thirty-five neonates completed the study (Primene, n = 14; TrophAmine, n = 21). On day 14, methionine plasma concentrations were significantly lower in the Primene group than in the TrophAmine group (27 µmol/L versus 32.9 µmol/L, P = 0.044); the taurine concentration was significantly higher in the same group (72.4 µmol/L versus 45.3 µmol/L, P < 0.0001). There were no differences in TPNAC incidence. Administering an intravenous solution of pediatric amino acids based on the umbilical cord aminogram yielded a higher taurine and lower methionine plasma concentration than did administering a similar solution based on the breast milk aminogram.

This text focuses on the study of some of the practices developed within the context of Mail Art, by Latin American artists during the final third of the 20th century, in response to the political situation in their home countries and with the aim of participating, some of them from the voluntary or forced exile, in the public space, controlled by authoritarian regimes. The establishment of networks and circuits through these practices made possible the emergence of a transnational and independent artistic scene and the review of the so-called Latin-American art, to the extent that its artistic production transcended geographical boundaries and challenged the major centers and hegemonic art circuits, positioning topical issues of social and political interest in the region, through its collective editorial projects and works.