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

Increasing aridity threatens the sexual regeneration of Quercus ilex(holm oak) in Mediterranean ecosystems

Knowledge of the recruitment of dominant forest species is a key aspect for forest conservation and the ecosystem services they provide. In this paper, we address how the simultaneous action of climate change and the intensity of land use in the past influence the recruitment of a forest species that depends on the provision of nurse plants to recruit. We compared the number of saplings (up to 15 years old) and juveniles (16 to 50 years old) of Quercus ilex in 17, 5.3 ha plots in the Iberian System (eastern Spain). We used a gradient of past deforestation intensity crossed with two levels of average annual precipitation, one of them at the lower limit of the species'' precipitation niche (semi-arid) and the other at the optimum (sub-humid). We also examined the association between recruits and nurse plants and the effect on this association of plot-scale factors, such as seed abundance (reproductive Q. ilex), microsites (nurse species and soil availability), and large herbivores. The increase in aridity in the last decades has drastically reduced the recruitment of new individuals in the forests of Q. ilex located in the lower limit of their precipitation niche, regardless of the intensity of past deforestation that they suffered. Recruitment in these climatic conditions depends almost exclusively on large trees and shrubs whose abundance may also be limited by aridity. The lack of regeneration questions the future of these populations, as the number of individuals will decrease over time despite the strong resistance of adult trees to disturbance and drought

Cytotoxic flavonoids and other constituents from the stem bark of Ochna schweinfurthiana

Seven flavonoids, hemerocallone (1), 6,7-dimethoxy-3′,4′-dimethoxyisoflavone (2), amentoflavone (4), agathisflavone (6), cupressuflavone (8), robustaflavone (9) and epicatechin (10), together with three other compounds, lithospermoside (3), β-D- fructofuranosyl-α-D-glucopyranoside (5) and 3β-O-D-glucopyranosyl-β-stigmasterol (7), were isolated from the ethyl acetate extract of the stem bark of Ochna schweinfurthiana F. Hoffm. All the compounds were characterised by spectroscopic and mass spectrometric methods, and by comparison with literature data. Cytotoxicity of the extracts and compounds against cervical adenocarcinoma (HeLa) cells was evaluated by MTT assay. Compounds 4 and 6 exhibited good cytotoxic activity, with IC50 values of 20.7 and 10.0 μM, respectively

Crystal structures of a copper(II) and the isotypic nickel(II) and palladium(II) complexes of the ligand (E)-1-[(2,4,6-tri­bromo­phen­yl)diazen­yl]naphthalen-2-ol

In the copper(II) complex, bis­{(E)-1-[(2,4,6-tri­bromo­phen­yl)diazen­yl]naph­thalen-2- olato}copper(II), [Cu(C₁₆H₈Br₃N₂O)₂], (I), the metal cation is coord­inated by two N atoms and two O atoms from two bidentate (E)-1-[(2,4,6-tri­bromo­phen­yl)diazen­yl]naphthalen-2-olate ligands, forming a slightly distorted square-planar environment. In one of the ligands, the tri­bromo­benzene ring is inclined to the naphthalene ring system by 37.4 (5)°, creating a weak intra­molecular Cu...Br inter­action [3.134 (2) Å], while in the other ligand, the tri­bromo­benzene ring is inclined to the naphthalene ring system by 72.1 (6)°. In the isotypic nickel(II) and palladium(II) complexes, namely bis­{(E)-1-[(2,4,6-tri­bromo­phen­yl)diazen­ yl]naphthalen-2-olato}nickel(II), [Ni(C₁₆H₈Br₃N₂O)₂], (II), and bis­{(E)-1- [(2,4,6-tri­bromo­phen­yl)diazen­yl]naphthalen-2-olato}palladium(II), [Pd(C₁₆H₈Br₃N₂O)₂], (III), respectively, the metal atoms are located on centres of inversion, hence the metal coordination spheres have perfect square-planar geometries. The tri­bromo­benzene rings are inclined to the naphthalene ring systems by 80.79 (18)° in (II) and by 80.8 (3)° in (III). In the crystal of (I), mol­ecules are linked by C-H...Br hydrogen bonds, forming chains along [010]. The chains are linked by C-H...Pi inter­actions, forming sheets parallel to (011). In the crystals of (II) and (III), mol­ecules are linked by C-H...Pi inter­actions, forming slabs parallel to (10-1). For the copper(II) complex (I), a region of disordered electron density was corrected for using the SQUEEZE routine in PLATON [Spek (2015). Acta Cryst. C71, 9-18]. The formula mass and unit-cell characteristics of the disordered solvent mol­ecules were not taken into account during refinement

The success of Quercus ilex plantations in agricultural fields in eastern Spain

Twenty-five years after planting, we measured the survival, growth and reproduction of 153 Quercus ilex plantations promoted by the afforestation programme of the European Union’s Common Agricultural Policy in agricultural fields in the east of the Iberian Peninsula, as a function of climatic aridity and stand characteristics related to water supply and competition among trees for water. Using field sampling, we found that, on average, 80% of the trees in plantations survived, more than 55% had already produced acorns and the tallest tree in each field exceeded 4 m, which are all higher values than those reported for forest plantations of this species in the same area and which represent the overcoming of the limitations imposed by climatic aridity on the natural regeneration of the species. A small proportion of the variation in all success variables was explained by water-related plantation characteristics, such as planting density, drought intensity in the year after planting, and soil permeability. However, climatic aridity only influenced the proportion of reproductive trees, but not the other variables of plantation success. However, most of the variation in planting success variables was linked to who owned the field, which nursery produced the seedlings, and the year of planting. Our results support the idea that the deep soils of agricultural fields counteract the negative effect of climatic aridity on plant performance, but that it is necessary to standardise nursery and planting practices, adapt planting density to the environmental characteristics of the site and provide irrigation supply in the early years to ensure the success of future plantations

Incomplete Punishment Networks in Public Goods Games: Experimental Evidence

Abundant evidence suggests that high levels of contributions to public goods can be sustained through self-governed monitoring and sanctioning. This experimental study investigates the effectiveness of decentralized sanctioning institutions in alternative punishment networks. Our results show that the structure of punishment network significantly affects allocations to the public good. In addition, we observe that network configurations are more important than punishment capacities for the levels of public good provision, imposed sanctions and economic efficiency. Lastly, we show that targeted revenge is a major driver of anti-social punishment

Activity-dependent structural plasticity of perisynaptic astrocytic domains promotes excitatory synapse stability

Excitatory synapses in the CNS are highly dynamic structures that can show activity- dependent remodeling and stabilization in response to learning and memory. Synapses are enveloped with intricate processes of astrocytes known as perisynaptic astrocytic processes (PAPs). PAPs are motile structures displaying rapid actin-dependent movements and are characterized by Ca²⁺ elevations in response to neuronal activity. Despite a debated implication in synaptic plasticity, the role of both Ca²⁺ events in astrocytes and PAP morphological dynamics remain unclear.Results In the hippocampus, we found that PAPs show extensive structural plasticity that is regulated by synaptic activity through astrocytic metabotropic glutamate receptors and intracellular calcium signaling. Synaptic activation that induces long-term potentiation caused a transient PAP motility increase leading to an enhanced astrocytic coverage of the synapse. Selective activation of calcium signals in individual PAPs using exogenous metabotropic receptor expression and two-photon uncaging reproduced these effects and enhanced spine stability. In vivo imaging in the somatosensory cortex of adult mice revealed that increased neuronal activity through whisker stimulation similarly elevates PAP movement. This in vivo PAP motility correlated with spine coverage and was predictive of spine stability.Conclusions This study identifies a novel bidirectional interaction between synapses and astrocytes, in which synaptic activity and synaptic potentiation regulate PAP structural plasticity, which in turn determines the fate of the synapse. This mechanism may represent an important contribution of astrocytes to learning and memory processes

Uniform, Equal Division, and Other Envy-Free Rules between The Two

This paper studies the problem of fairly allocating an amount of a divisible resource when preferences are single-peaked. We characterize the class of envy-free and peak-only rules and show that the class forms a complete lattice with respect to a dominance relation. We also pin down the subclass of strategy-proof rules and show that the subclass also forms a complete lattice. In both cases, the upper bound is the uniform rule, the lower bound is the equal division rule, and any other rule is between the two