Capacidad de las raíces para penetrar sustratos compactados y detectar grietas. Metodología y aplicación a la colonización vegetal de laderas erosionadas en ambiente semiárido

En el presente trabajo, proponemos profundizar en el conocimiento sobre los procesos que limitan la colonización vegetal de laderas erosionadas en ambientes semiáridos, y más específicamente sobre la penetración de raíces en suelos compactados. Para ello, hemos desarrollado una metodología para el estudio de la capacidad de las raíces para penetrar sustratos y detectar grietas en un rango amplio de compactaciones. Hemos analizado además el efecto de la morfología de las raíces, del nivel de resistencia a la penetración y del espesor del nivel más superficial del sustrato en la penetración de las raíces y en la detección de grietas por las raíces. Esta metodología se basa en el uso de discos de cera cuyo nivel de resistencia a la penetración depende de las proporciones de mezcla de parafina y vaselina en condiciones controladas de laboratorio. Para el estudio se utilizó un diseño factorial cruzado 2 x 2 x 5, con dos especies de distinta morfología radicular (pivotante vs. fasciculada), dos espesores de sustrato (3 y 7 mm) y cinco niveles de resistencia a la penetración comprendidos entre 60 y 1500 kPa. Los resultados indican que el nivel de resistencia a la penetración y el espesor del sustrato influyen sobre la tasa (número de raíces por semilla que penetran el sustrato) y velocidad (número de días para que se produzca la primera penetración) de penetración de las raíces para las dos morfologías de raíces estudiadas. Al contrario, no se aprecia ningún efecto del tipo de raíz en la velocidad para penetrar el sustrato. Por otro lado, se ha puesto de manifiesto el papel importante del nivel de resistencia a la penetración y de la morfología de las raíces en la detección de grietas superficiales por las raíces. A partir de los resultados obtenidos, se discuten las distintas estrategias posibles que podrían explicar el éxito de las especies colonizadoras de taludes de carreteras. Asimismo, una estrategia mixta, que contempla la penetración del suelo o la detección de grietas superficiales por las raíces, podría tener éxito en los terraplenes, mientras que en los desmontes con valores limitantes de resistencia a la penetración por las raíces en las capas superficiales del sustrato geológico, la capacidad de las raíces para detectar grietas con un microambiente más favorable podría ser una estrategia de éxito para las plantas.Este trabajo ha sido realizado con la financiación del Ministerio de Ciencia y Tecnología (Proyecto REN 2001-2313 y Programa Ramón y Cajal co-financiado por el Fondo Social Europeo).Peer Reviewe

The Stokes-Einstein Relation at Moderate Schmidt Number

The Stokes-Einstein relation for the self-diffusion coefficient of a spherical particle suspended in an incompressible fluid is an asymptotic result in the limit of large Schmidt number, that is, when momentum diffuses much faster than the particle. When the Schmidt number is moderate, which happens in most particle methods for hydrodynamics, deviations from the Stokes-Einstein prediction are expected. We study these corrections computationally using a recently-developed minimally-resolved method for coupling particles to an incompressible fluctuating fluid in both two and three dimensions. We find that for moderate Schmidt numbers the diffusion coefficient is reduced relative to the Stokes-Einstein prediction by an amount inversely proportional to the Schmidt number in both two and three dimensions. We find, however, that the Einstein formula is obeyed at all Schmidt numbers, consistent with linear response theory. The numerical data is in good agreement with an approximate self-consistent theory, which can be used to estimate finite-Schmidt number corrections in a variety of methods. Our results indicate that the corrections to the Stokes-Einstein formula come primarily from the fact that the particle itself diffuses together with the momentum. Our study separates effects coming from corrections to no-slip hydrodynamics from those of finite separation of time scales, allowing for a better understanding of widely observed deviations from the Stokes-Einstein prediction in particle methods such as molecular dynamics.Comment: Submitte

Biases in global effects of exotic species on local invertebrates: a systematic review

Historical gaps and biases in the literature may have influenced the current knowledge of the impacts of invaders on global biodiversity. We performed a systematic review and compiled the main gaps and biases in the literature and the reported negative, neutral and positive effects of exotic species on local invertebrates worldwide. We analysed the relation of these reported effects to the biogeographical origin of the exotic species, the environmental characteristics of the invaded area, the trophic level of the exotic species and of the invaded local fauna, and the elapsed time after first introduction. We analysed 1276 publications comprising 2984 study cases. From these, 1786 cases included “control” situations (without exotics) and provided quantitative supporting evidence of the effects of exotic species on local invertebrates. The main gaps in the literature included tropical and arid climates, estuaries and marine ecosystems, as well as exotic species coming from Neotropical, Australian, Oriental, Ethiopian and Antarctic regions. Carnivorous and herbivorous species were underreported as exotic species and as impacted invertebrates. The considered variables were mostly unrelated to the reported effects, suggesting that the effects of exotic species on local invertebrates are heterogeneous and not unidirectional. Many impacted invertebrates were assemblages of undefined composition in terms of the native or exotic nature of the invaded organisms. Further avenues to reduce the identified biases in the current knowledge about the effects of exotic species on local invertebrates are also indicatedThe MF’s grant was supported by the Conselho Nacional de Desenvolvimento Cientı´fico e Tecnológico-CNPq (401045/2014-5), program Ciência sem Fronteiras, and by the Universidad de Alcala´. LMB has been supported by the National Institutes for Science and Technology (INCT) in Ecology, Evolution and Biodiversity Conservation (MCTIC/CNPq, 465610/2014-5, FAPEG) and by a CNPq Grant (304314/2014-5

The Space of Countably Simple Bounded Functions with Values in a DF-Space

Sin resume

The exotic weevil Stenopelmus rufinasus Gyllenhal, 1835 (Coleoptera: Curculionidae) across a "host-free" pond network

The presence of the exotic weevil Stenopelmus rufinasus (Coleoptera: Curculionidae) is closely related to the occurrence of the exotic red water fern, Azolla filiculoides. In this paper, we present the first records of S. rufinasus in Doñana National Park (SW Spain), based on sampling of macroinvertebrates in 91 temporary ponds, including monthly samples of 22 ponds, during two successive years (2005-2007). The exotic weevil was present in 21% of the sampled ponds where the host plant, A. filiculiodes, was not detectable. Because A. filiculoides can reach high densities in an adjacent area of marsh, we suggest that the occurrence of the exotic weevil in these ponds is a consequence of dispersal from nearby marshes. Our study demonstrates that S. rufinasus adults can occur at relatively high densities in ponds where the host plant is not present, suggesting that such apparently “host-free” sites may act as stepping stones for the spread of this speciesLa presencia de la especie de gorgojo exótico Stenopelmus rufinasus (Coleoptera: Curculionidae) está íntimamente rela- cionada con la planta acuática exótica Azolla filiculoides. En este estudio se registró por primera vez la presencia de S. rufinasus en el Parque Nacional de Doñana (SO España) tras realizar un muestreo de macroinvertebrados en 91 lagunas que incluye muestreos mensuales de 22 de las mismas durante dos años consecutivos (2005-2007). El gorgojo exótico estuvo presente en el 21% de las lagunas muestreadas a pesar de que su supuesto hospedador, A. filiculiodes, no fue detectado. Dado que A. filiculiodes puede alcanzar grandes densidades en la marisma adyacente, sugerimos que la presencia del gor- gojo exótico en las lagunas temporales se debe a su dispersión desde la marisma. Este estudio demuestra que individuos adultos de S. rufinasus pueden aparecer con densidades relativamente altas en lagunas donde su hospedador potencial no está presente, lo que sugiere que estos sitios libres de hospedador podrían actuar como zonas de paso para la dispersión de la especiePeer reviewe

Interannual variation in filling season affects zooplankton diversity in Mediterranean temporary ponds

In Mediterranean temporary ponds, the timing of annual flooding is highly variable and depends on heavy seasonal rains. Ponds can flood in the autumn, winter, or spring, and thus the environmental conditions faced by emerging zooplankton can be very different. We performed an experiment in a climatic chamber where we simulated annual variation in natural temperature and light conditions to study how differences in pond-filling season affected zooplankton assemblage composition. We sampled sediments from a temporary pond and placed them in aquariums that were filled with water during three different seasons: autumn (October), winter (January), and spring (March). Zooplankton abundance, species richness, diversity, and assemblage composition differed significantly among treatments, and post-inundation temperature and pH appeared to be the main drivers of these differences. Diversity was highest in the winter treatment. It was lower in the autumn treatment and the spring treatment, and no indicator species were present in the latter. Our results suggest that interannual variability in initial inundation conditions favours the emergence of different species and thus contributes to high species richness in the egg bank. However, climate change and/or groundwater drawdown could delay pond flooding, impoverishing the zooplankton assemblage in the long ter

Nucleation and growth of precipitates in a V-microalloyed steel according to physical theory and experimental results

Using a theoretical model, the nucleus number and nucleation time were determined for a V-microalloyed steel. The calculated data has made it possible to plot the nucleus number vs. temperature, nucleation critical time vs. temperature, and precipitate critical radius vs. temperature. The nucleus number was calculated by integration of the nucleation rate expression. On the other hand, an experimental study was performed and the nucleation time vs. temperature was plotted (PTT diagram), thus allowing a comparison between the theoretical values and experimental results. It has been found that the growth of precipitates during precipitation obeys a quadratic growth equation and not a cubic coalescence equation. The experimentally determined growth rate coincides with the theoretically predicted growth rate. The experimental nucleation time is longer than the calculated time due to conceptual differences.Peer ReviewedPostprint (author's final draft

A core of three amino acids at the carboxyl-terminal region of glutamine synthetase defines its regulation in cyanobacteria

© 2015 John Wiley & Sons Ltd. Glutamine synthetase (GS) type I is a key enzyme in nitrogen metabolism, and its activity is finely controlled by cellular carbon/nitrogen balance. In cyanobacteria, a reversible process that involves protein-protein interaction with two proteins, the inactivating factors IF7 and IF17, regulates GS. Previously, we showed that three arginine residues of IFs are critical for binding and inhibition of GS. In this work, taking advantage of the specificity of GS/IFs interaction in the model cyanobacteria Synechocystis sp. PCC 6803 and Anabaena sp. PCC 7120, we have constructed a different chimeric GSs from these two cyanobacteria. Analysis of these proteins, together with a site-directed mutagenesis approach, indicates that a core of three residues (E419, N456 and R459) is essential for the inactivation process. The three residues belong to the last 56 amino acids of the C-terminus of SynechocystisGS. A protein-protein docking modeling of SynechocystisGS in complex with IF7 supports the role of the identified core for GS/IF interaction.Peer Reviewe