46 research outputs found
Global patterns of phosphatase activity in natural soils
Soil phosphatase levels strongly control the biotic pathways of phosphorus (P), an essential element for life, which is often limiting in terrestrial ecosystems. We investigated the influence of climatic and soil traits on phosphatase activity in terrestrial systems using metadata analysis from published studies. This is the first analysis of global measurements of phosphatase in natural soils. Our results suggest that organic P (Porg), rather than available P, is the most important P fraction in predicting phosphatase activity. Structural equation modeling using soil total nitrogen (TN), mean annual precipitation, mean annual temperature, thermal amplitude and total soil carbon as most available predictor variables explained up to 50% of the spatial variance in phosphatase activity. In this analysis, Porg could not be tested and among the rest of available variables, TN was the most important factor explaining the observed spatial gradients in phosphatase activity. On the other hand, phosphatase activity was also found to be associated with climatic conditions and soil type across different biomes worldwide. The close association among different predictors like Porg, TN and precipitation suggest that P recycling is driven by a broad scale pattern of ecosystem productivity capacity
Brightness, distribution, and evolution of sunspot umbral dots
We present a 106-minute TiO (705.7nm) time series of high spatial and
temporal resolution that contains thousands of umbral dots (UDs) in a mature
sunspot in the active region NOAA 10667 at =0.95. The data were acquired
with the 1-m Swedish Solar Telescope on La Palma. With the help of a multilevel
tracking (MLT) algorithm the sizes, brightnesses, and trajectories of 12836
umbral dots were found and analyzed. The MLT allows UDs with very low contrast
to be reliably identified. Inside the umbra we determine a UD filling factor of
11%. The histogram of UD lifetimes is monotonic, i.e. a UD does not have a
typical lifetime. Three quarters of the UDs lived for less than 150s and showed
no or little motion. The histogram of the UD diameters exhibits a maximum at
225km, i.e. most of the UDs are spatially resolved. UDs display a typical
horizontal velocity of 420m/s and a typical peak intensity of 51% of the mean
intensity of the quiet photosphere, making them on average 20% brighter than
the local umbral background. Almost all mobile UDs (large birth-death distance)
were born close to the umbra-penumbra boundary, move towards the umbral center,
and are brighter than average. Notably bright and mobile UDs were also observed
along a prominent UD chain, both ends of which are located at the
umbra-penumbra boundary. Their motion started primarily at either of the ends
of the chain, continued along the chain, and ended near the chain's center. We
observed the splitting and merging of UDs and the temporal succession of both.
For the first time the evolution of brightness, size, and horizontal speed of a
typical UD could be determined in a statistically significant way. Considerable
differences between the evolution of central and peripheral UDs are found,
which point to a difference in origin
Improved SOT (Hinode mission) high resolution solar imaging observations
We consider the best today available observations of the Sun free of
turbulent Earth atmospheric effects, taken with the Solar Optical Telescope
(SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the
observed stray light are analyzed in order to improve the resolution. The Point
Spread Function (PSF) corresponding to the blue continuum Broadband Filter
Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/
images taken during the transit of the planet Venus in 2012. A combination of
Gaussian and Lorentzian functions is selected to construct a PSF in order to
remove both smearing due to the instrumental diffraction effects (PSF core) and
the large-angle stray light due to the spiders and central obscuration (wings
of the PSF) that are responsible for the parasitic stray light. A
Max-likelihood deconvolution procedure based on an optimum number of iterations
is discussed. It is applied to several solar field images, including the
granulation near the limb. The normal non-magnetic granulation is compared to
the abnormal granulation which we call magnetic. A new feature appearing for
the first time at the extreme- limb of the disk (the last 100 km) is discussed
in the context of the definition of the solar edge and of the solar diameter. A
single sunspot is considered in order to illustrate how effectively the
restoration works on the sunspot core. A set of 125 consecutive deconvolved
images is assembled in a 45 min long movie illustrating the complexity of the
dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi
Physics of Solar Prominences: II - Magnetic Structure and Dynamics
Observations and models of solar prominences are reviewed. We focus on
non-eruptive prominences, and describe recent progress in four areas of
prominence research: (1) magnetic structure deduced from observations and
models, (2) the dynamics of prominence plasmas (formation and flows), (3)
Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and
large-scale patterns of the filament channels in which prominences are located.
Finally, several outstanding issues in prominence research are discussed, along
with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape
Neurons of the Dentate Molecular Layer in the Rabbit Hippocampus
The molecular layer of the dentate gyrus appears as the main entrance gate for information into the hippocampus, i.e., where the perforant path axons from the entorhinal cortex synapse onto the spines and dendrites of granule cells. A few dispersed neuronal somata appear intermingled in between and probably control the flow of information in this area. In rabbits, the number of neurons in the molecular layer increases in the first week of postnatal life and then stabilizes to appear permanent and heterogeneous over the individuals’ life span, including old animals. By means of Golgi impregnations, NADPH histochemistry, immunocytochemical stainings and intracellular labelings (lucifer yellow and biocytin injections), eight neuronal morphological types have been detected in the molecular layer of developing adult and old rabbits. Six of them appear as interneurons displaying smooth dendrites and GABA immunoreactivity: those here called as globoid, vertical, small horizontal, large horizontal, inverted pyramidal and polymorphic. Additionally there are two GABA negative types: the sarmentous and ectopic granular neurons. The distribution of the somata and dendritic trees of these neurons shows preferences for a definite sublayer of the molecular layer: small horizontal, sarmentous and inverted pyramidal neurons are preferably found in the outer third of the molecular layer; vertical, globoid and polymorph neurons locate the intermediate third, while large horizontal and ectopic granular neurons occupy the inner third or the juxtagranular molecular layer. Our results reveal substantial differences in the morphology and electrophysiological behaviour between each neuronal archetype in the dentate molecular layer, allowing us to propose a new classification for this neural population
Microglial cells during the lesion-regeneration of the lizard medial cortex
The lizard medial cortex (lizard fascia dentata) is capable of neural regeneration after being lesioned by the anti-metabolite 3-acetylpyridine (3AP). This study was aimed at detecting microglial behaviour during the medial cortex lesion-regeneration process using tomato lectin histochemistry to label microglia (both with light and electron microscopy) and proliferating cell nuclear antigen (PCNA) immunocytochemistry to label proliferating cells. As expected, 1-2 days post-injection lectin-labelled microglia cells could not be observed in the medial cortex plexiform layers, but later (7 days post-injection) abundant lectin-labelled microglia cells re-populated the regenerating medial cortex. Abundant PCNA-immunolabelled nuclei were detected both in the subjacent ependymal neuroepithelium (neuroblasts, maximum at 2 days postinjection) as well as in some parenchyma1 cells which were also lectin-labelled (microglia, maximum at 7-15 days post-injection). Re-invasive microglia were also detected in the vicinity of ventricular ependymal lining, blood vessels and meninges. The electron microscope demonstrated that these microglial cells participate in cell debris removal, especially of neural granular cell somata. Other cell types related to microglia (mast cells, peri-vascular cells and meningeal cells) were also present during the scavenging process. Significant numbers of microglial cells remained in close relationship with the ependymal proliferative areas, even in control non-lesioned animals. This is indirect evidence for the working hypothesis that microglia are not only implicated in cell debris removal, but also in the regulation of newly generated neuroblast incorporation onto the cortical areas. Whether they phagocytose immature neuroblasts or induce cell death in them or even prevent their migration onto the principal layer areas are likely possibilities that remain to be proven
Radial glia and cell debris removal during lesion-regeneration of the lizard medial cortex
Intraperitoneal injection of the neurotoxin 3- acetylpyridine (3AP) induces a rapid degeneration of the medial cerebral cortex (lizard fascia dentata) granular layer and of its zinc enriched axonal projection (lizard mossv fibres). After 6-8 weeks ~ost-lesionth e cell debris have ieen rekoved and the grakular layer is repopulated by neurons generated in the subjacent ependyma. Both processes, neuron incorporation and debris removal, seem to be crucial for successful regeneration. Scavenging processes in the lesioned mammalian CNS are usually carried out by microglia andlor astrocytes. In the lizard cerebral cortex there are no free astrocytes and the only glial fibrillary acid (GFAP) immunoreactive cells are radial glia-ependymocytes, similar to those present during mammalian CNS development. Ependymocytes, in addition to their help in vertical migrations of just generated immature neurons, built the cortical glial scaffold, insulate the blood capillaries, form the outer glial limiting membrane, thus playing an essential role in the lizard cortical blood-brain barrier. In this study, by means of GFAP-immunocytochemistry and electron microscopy, we have shown that radial glial cells participate actively in the removal/phagocytosis of cellular debris generated in the lesion process: mainly degenerated synapses, but interestingly, also some neuronal somata. Cell debris taken up by ependymocyte lateral processes seem to be progressively transported to either distal (pial) or proximal (ventricular) poles of the cell, where they result in lipofuscin accumulations. The hypothetical subsequent exchange of debris from ependymoglia by microglia/macrophages and Kolmer cells is discussed
Contrasting winter and summer VOC mixing ratios at a forest site in the Western Mediterranean Basin: the effect of local biogenic emissions.
43 páginas, 9 figuras, 2 tablas.Atmospheric volatile organic compounds (VOCs) are involved in ozone and aerosol
generation, thus having implications for air quality and climate. VOCs and their emissions by vegetation also have important ecological roles as they can protect plants from
5 stresses and act as communication cues between plants and between plants and animals. In spite of these key environmental and biological roles, the reports on seasonal
and daily VOC mixing ratios in the literature for Mediterranean natural environments
are scarce.
We conducted seasonal (winter and summer) measurements of VOC mixing ratios
10 in an elevated (720 m a.s.l.) holm oak Mediterranean forest site near the metropolitan
area of Barcelona (NE Iberian peninsula). Methanol was the most abundant compound
among all the VOCs measured in both seasons. While aromatic VOCs showed almost
no seasonal variability, short-chain oxygenated VOCs presented higher mixing ratios
in summer, presumably due to greater emission by vegetation and increased photo-
15 chemistry, both enhanced by the high temperatures and solar radiation in summer. Isoprenoid VOCs showed the biggest seasonal change in mixing ratios: they increased by
one order of magnitude in summer, as a result of the vegetation’s greater physiological
activity and emission rates. The maximum diurnal concentrations of ozone increased
in summer too, most likely due to more intense photochemical activity and the higher
20 levels of VOCs in the air.
The daily variation of VOC mixing ratios was mainly governed by the wind regime of
the mountain, as the majority of the VOC species analyzed followed a very similar diel
cycle. Mountain and sea breezes that develop after sunrise advect polluted air masses
to the mountain. These polluted air masses had previously passed over the urban
25 and industrial areas surrounding the Barcelona metropolitan area, where they were
enriched in NOx and in VOCs of biotic and abiotic origin. Moreover, these polluted air
masses receive additional biogenic VOCs emitted in the local valley by the vegetation,
thus enhancing O3
formation in this forested site. The only VOC species that showed a somewhat different daily pattern were monoterpenes because of their local biogenic
emission. Isoprene also followed in part the daily pattern of monoterpenes, but only in
summer when its biotic sources were stronger. The increase by one order of magnitude
in the concentrations of these volatile isoprenoids highlights the importance of local
5 biogenic summer emissions in these Mediterranean forested areas which also receive
polluted air masses from nearby or distant anthropic sources.This study was supported by the Spanish Government grants CGL2006-
04025/BOS, CGL2010-17172, Consolider-Ingenio Montes CSD2008-00040 and Accion Com- ´
plementaria DAURE CGL2007-30502-E/CLI, and the Catalan Government grant SGR 2009-
10 458. Roger Seco gratefully acknowledges an FPI fellowship (BES-2005-6989) from the Spanish Government.
This research has received funding from the EC Seventh Framework Programme under grant
agreement no. 215072 (Marie Curie Initial Training Network, “CLOUD-ITN”). Helpful discussion
concerning the PTR-TOF evaluation with Martin Graus and Ralf Schnitzhofer from the Univer-
15 sity of Innsbruck was much appreciated.Peer reviewe
Structural-changes in the ovary of pisum-sativum induced by pollination and gibberellic-acid
Peer reviewe