The biogeochemical cycles of carbon (C), nitrogen (N) and phosphorus (P) are interlinked by primary production, respiration and decomposition in terrestrial ecosystems. It has been suggested that the C, N and P cycles could become uncoupled under rapid climate change because of the different degrees of control exerted on the supply of these elements by biological and geochemical processes. Climatic controls on biogeochemical cycles are particularly relevant in arid, semi-arid and dry sub-humid ecosystems (drylands) because their biological activity is mainly driven by water availability. The increase in aridity predicted for the twenty-first century in many drylands worldwide may therefore threaten the balance between these cycles, differentially affecting the availability of essential nutrients. Here we evaluate how aridity affects the balance between C, N and P in soils collected from 224 dryland sites from all continents except Antarctica. We find a negative effect of aridity on the concentration of soil organic C and total N, but a positive effect on the concentration of inorganic P. Aridity is negatively related to plant cover, which may favour the dominance of physical processes such as rock weathering, a major source of P to ecosystems, over biological processes that provide more C and N, such as litter decomposition. Our findings suggest that any predicted increase in aridity with climate change will probably reduce the concentrations of N and C in global drylands, but increase that of P. These changes would uncouple the C, N and P cycles in drylands and could negatively affect the provision of key services provided by these ecosystems.
Abstract1. Dryland vegetation is characterized by discrete plant patches that accumulate and capture soil resources under their canopies. These "fertile islands" are major drivers of dryland ecosystem structure and functioning, yet we lack an integrated understanding of the factors controlling their magnitude and variability at the global scale.2. We conducted a standardized field survey across 236 drylands from five continents.At each site, we measured the composition, diversity and cover of perennial plants.Fertile island effects were estimated at each site by comparing composite soil
The agricultural activities practice often demands an intensive application of fertilizers. Phosphate and nitrogen fertilizers are the most employed in the corn growing areas of the central Mexico highlands. The first ones presents an uranium content ranging from 50 to 200 mg · kg −1 depending on the origin of the phosphate rock used in its production. It is crucial to analyze the rainwater, surface water, soil water at several depths, groundwater and soil to determine the simultaneous behavior of phosphate, nitrate and uranium, and their leaching in a specific agricultural land. Uranium concentration, 16 mg · kg −1 , in the soil water was higher than that in the surface water and groundwater. The different concentrations are due to an unequal uranium distribution in the environment. The phosphate concentration, 37.4 mg · kg −1 , diminished throughout the profile of the soil due to a sorption-precipitation process. The nitrates were leached toward groundwater after the application of fertilizers, but the nitrate concentration in it did not exceed the limit for drinking water.
Natural fluorapatite samples were contacted with uranyl nitrate solutions (from 10 -2 to 10 -6 M), adjusted to pH 6.0, then, shaken for times varying between 15 minutes to 72 hours, at room temperature. After that, the solid and liquid phases were separated by centrifugation and the solid was dried at 80 ~ overnight. The uranium analysis of the solid samples and solutions revealed that uranium was incorporated over fluorapatite. Selected solid samples produced by contacting treatments were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. XRD patterns showed the growth of uranyl species in the fluorapatite. Imaging by SEM at 20000x showed the location of uranyl compounds in a crystalline layer in the surface of fluorapatite grains, This layer was well defined for the 10-2M of U-contacting solution, but a saturation value was attained at 64% of uranium uptake yield. In the case of 10 -4 M and lower U-contacting solution, the uranium uptake yield was near of 90% after 45 minutes. This fact suggests that natural fluorapatite has excellent properties to immobilize uranium compounds in a solution. Afterwards, the pregnant fluorapatite mineral was regenerated using an alkaline-leaching process. The uranium separated in this way is concentrated and can be handled to a final disposition.
Objetivo: Comparar la eficacia de la prevención no farmacológica estándar (PnFE) versus la prevención no farmacológica reforzada (PnFR), consistente en prevención no farmacológica estándar más Terapia Ocupacional (TO) precoz e intensiva, en la incidencia del delirium en adultos mayores (AM) ingresados a unidad de pacientes críticos (UPC). Diseño: Ensayo clínico randomizado, en UPC del Hospital Clínico de la Universidad de Chile (HCUCH). Sujetos: 70 pacientes de edad igual o superior a 60 años, ingresados al HCUCH entre abril y octubre del 2011, con necesidad de ingreso a UPC para monitorización, hospitalización por enfermedad aguda/crónica descompensada, con consentimiento del paciente o familiar y sin presencia de delirium al ingreso ni deterioro cognitivo previo al estudio. Materiales y Métodos: PnFE (grupo control) consiste en: reorientación, movilización precoz, corrección de déficit sensoriales, manejo ambiental, protocolo de sueño y reducción de fármacos anticolinérgicos, versus PnFR (grupo experimental), que considera las siguientes áreas de intervención de TO: estimulación polisensorial, posicionamiento, estimulación cognitiva, entrenamiento en actividades de la vida diaria básica, estimulación motora de extremidades superiores y participación familiar; durante 5 días, dos veces al día. Se evaluó la presencia del delirium, con el CAM dos veces al día durante 5 días, y la severidad de éste con DRS; previo al alta se evaluó, independencia funcional con FIM, estado cognitivo con MMSE y fuerza de garra con dinamómetro de Jamar. Resultados: La PnFR de TO se asocia a menor incidencia de delirium, afectando al 16,1% del grupo con prevención no farmacológica estándar versus un 3,1% del con prevención no farmacológica reforzada, así como a menos días de hospitalización (20,6 días versus 10,4 p=.009). La independencia funcional al alta se mantiene en aspectos cognitivos (32,5 versus 32,9) mientras que en aspectos motores aumenta significativamente (46,5 versus 58,3l, P=.03). Conclusión: La intervención precoz e intensiva de TO es efectiva en la prevención del delirium en AM hospitalizados, reduce su estadía y aumenta niveles de independencia funcional motora al alta.
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