Diminution of Voltage Threshold Plays a Key Role in Determining Recruitment of Oculomotor Nucleus Motoneurons during Postnatal Development

The size principle dictates the orderly recruitment of motoneurons (Mns). This principle assumes that Mns of different sizes have a similar voltage threshold, cell size being the crucial property in determining neuronal recruitment. Thus, smaller neurons have higher membrane resistance and require a lower depolarizing current to reach spike threshold. However, the cell size contribution to recruitment in Mns during postnatal development remains unknown. To investigate this subject, rat oculomotor nucleus Mns were intracellularly labeled and their electrophysiological properties recorded in a brain slice preparation. Mns were divided into 2 age groups: neonatal (1–7 postnatal days, n = 14) and adult (20–30 postnatal days, n = 10). The increase in size of Mns led to a decrease in input resistance with a strong linear relationship in both age groups. A well-fitted inverse correlation was also found between input resistance and rheobase in both age groups. However, input resistance versus rheobase did not correlate when data from neonatal and adult Mns were combined in a single group. This lack of correlation is due to the fact that decrease in input resistance of developing Mns did not lead to an increase in rheobase. Indeed, a diminution in rheobase was found, and it was accompanied by an unexpected decrease in voltage threshold. Additionally, the decrease in rheobase co-varied with decrease in voltage threshold in developing Mns. These data support that the size principle governs the recruitment order in neonatal Mns and is maintained in adult Mns of the oculomotor nucleus; but during postnatal development the crucial property in determining recruitment order in these Mns was not the modifications of cell size-input resistance but of voltage threshold

Global ecological predictors of the soil priming effect

Identifying the global drivers of soil priming is essential to understanding C cycling in terrestrial ecosystems. We conducted a survey of soils across 86 globally-distributed locations, spanning a wide range of climates, biotic communities, and soil conditions, and evaluated the apparent soil priming effect using 13C-glucose labeling. Here we show that the magnitude of the positive apparent priming effect (increase in CO2 release through accelerated microbial biomass turnover) was negatively associated with SOC content and microbial respiration rates. Our statistical modeling suggests that apparent priming effects tend to be negative in more mesic sites associated with higher SOC contents. In contrast, a single-input of labile C causes positive apparent priming effects in more arid locations with low SOC contents. Our results provide solid evidence that SOC content plays a critical role in regulating apparent priming effects, with important implications for the improvement of C cycling models under global change scenarios

EFECTO DE AUXINAS Y CITOQUININAS EN EL CULTIVO DE TEJIDO DE AHNFELTIA PLICATA (HUDSON) FRIES, 1836 (AHNFELTIALES, RHODOPHYTA) DE LA REGIÓN DE MAGALLANES

Ahnfeltia plicata (Hudson) Fries, 1836, es una agarófita comercialmente importante, que ocurre en la Región de Magallanes y caracterizada por presentar un ciclo de vida heteromórfico. Se han utilizado técnicas de cultivo in vitro para la micropropagación de diferentes especies de microalgas, sin embargo, no hay antecedentes del uso de estas tecnologías con A. plicata. El objetivo de este estudio fue desarrollar técnicas de cultivo in vitro de tejido vegetativo de A. plicata para micropropagación utilizando 2 reguladores de crecimiento de plantas superiores: 6-Bencilaminopurina (BAP) y ácido Indolacético (IAA) bajo diferentes condiciones de cultivo. Fueron utilizados talos gametofíticos no reproductivos de regiones apicales y porciones medias, de los cuales se obtuvieron explantes de 5 mm. Los reguladores de crecimiento de plantas superiores fueron utilizados en 3 concentraciones: 0.1 mg/L, 1.0 mg/L y 5.0 mg/L, preparadas en medio de cultivo Provasoli. El experimento se realizó en triplicado para cada concentración de estos reguladores de crecimiento y para cada sección del talo, utilizando un n= 4 explantes por placa de cultivo en dos fotoperiodos (16:8 y 12:12, luz: oscuridad), a una temperatura de 10°C e intensidad luminosa de 9 - 10 μmol seg-1 m-2. Se realizaron monitoreos y mediciones de cada explante cada siete días. Se observó que ambos reguladores de crecimiento de plantas superiores promueven el crecimiento de Ahnfeltia plicata. El medio de cultivo enriquecido con IAA estimuló el crecimiento en regiones polares de los explantes de A. plicata, mientras que al utilizar BAP se observó crecimiento tanto en regiones polares como formación de ramificaciones laterales. El proceso de regeneración de explantes mostró mejor resultados con BAP 1 mg/L en fotoperíodo 12:12 (luz: oscuridad). Los tejidos cultivados en fotoperiodo corto, presentaron decoloración y mayor porcentaje de mortalidad

Can we infer plant facilitation from remote sensing? A test across global drylands

Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely-sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely-sensed images freely available through Google EarthTM with detailed field assessments, and used a simple individual-based model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely-sensed images were more right-skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google EarthTM images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely-sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems

Spread dynamics of invasive species

Species invasions are a principal component of global change, causing large losses in biodiversity as well as economic damage. Invasion theory attempts to understand and predict invasion success and patterns of spread. However, there is no consensus regarding which species or community attributes enhance invader success or explain spread dynamics. Experimental and theoretical studies suggest that regulation of spread dynamics is possible; however, the conditions for its existence have not yet been empirically demonstrated. If invasion spread is a regulated process, the structure that accounts for this regulation will be a main determinant of invasion dynamics. Here we explore the existence of regulation underlying changes in the rate of new site colonization. We employ concepts and analytical tools from the study of abundance dynamics and show that spread dynamics are, in fact, regulated processes and that the regulation structure is notably consistent among invasions occurring in widely different contexts. We base our conclusions on the analysis of the spread dynamics of 30 species invasions, including birds, amphibians, fish, invertebrates, plants, and a virus, all of which exhibited similar regulation structures. In contrast to current beliefs that species invasions are idiosyncratic phenomena, here we provide evidence that general patterns do indeed exist

Climatic vulnerabilities and ecological preferences of soil invertebrates across biomes

Unlike plants and vertebrates, the ecological preferences, and potential vulnerabilities of soil invertebrates to environmental change, remain poorly understood in terrestrial ecosystems globally. We conducted a cross-biome survey including 83 locations across six continents to advance our understanding of the ecological preferences and vulnerabilities of the diversity of dominant and functionally important soil invertebrate taxa, including nematodes, arachnids and rotifers. The diversity of invertebrates was analyzed through amplicon sequencing. Vegetation and climate drove the diversity and dominant taxa of soil invertebrates. Our results suggest that declines in forest cover and plant diversity, and reductions in plant production associated with increases in aridity, can result in reductions of the diversity of soil invertebrates in a drier and more managed world. We further developed global atlases of the diversity of these important soil invertebrates, which were cross-validated using an independent database. Our study advances the current knowledge of the ecological preferences and vulnerabilities of the diversity and presence of functionally important soil invertebrates in soils from across the globe. This information is fundamental for improving and prioritizing conservation efforts of soil genetic resources and management policies

Astrocytic modulation of cortical oscillations

Brain waves are rhythmic voltage oscillations emerging from the synchronization of individual neurons into a neuronal network. These oscillations range from slow to fast fluctuations, and are classified by power and frequency band, with different frequency bands being associated with specific behaviours. It has been postulated that at least ten distinct mechanisms are required to cover the frequency range of neural oscillations, however the mechanisms that gear the transition between distinct oscillatory frequencies are unknown. In this study, we have used electrophysiological recordings to explore the involvement of astrocytic K+ clearance processes in modulating neural oscillations at both network and cellular levels. Our results indicate that impairment of astrocytic K+ clearance capabilities, either through blockade of K+ uptake or astrocytic connectivity, enhance network excitability and form high power network oscillations over a wide range of frequencies. At the cellular level, local increases in extracellular K+ results in modulation of the oscillatory behaviour of individual neurons, which underlies the network behaviour. Since astrocytes are central for maintaining K+ homeostasis, our study suggests that modulation of their inherent capabilities to clear K+ from the extracellular milieu is a potential mechanism to optimise neural resonance behaviour and thus tune neural oscillations