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NITROGEN FLUXES IN A NOTHOFAGUS OBLIQUA FOREST AND A PINUS RADIATA PLANTATION IN THE CENTRAL VALLEY OF SOUTHERN CHILE
No full textForest structure and tree species can have a significant impact on total atmospheric nitrogen (N) deposition; for example, deciduous forests have higher N requirements than coniferous forests. However, knowledge about the effect of the conversion of native Chilean vegetation cover by exotic plantations on N cycling is scarce. The aim of this study was to determine the effect of the replacement of a Nothofagus obliqua native forest by a Pinus radiata plantation in southern Chile on the chemistry of throughfall, stemflow, soil water infiltration and percolation. Pinus radiata stemflow was more acidic (pH 4.7) than precipitation (pH 5.2) and throughfall (pH 5.6), while in the Nothofagus forest stemflow and throughfall pH were 6.3 and 6.1, respectively. In the Nothofagus forest, the soil water infiltration and percolation at 150 cm depth pH were 6.2 and 6.3, while in the Pinus plantation pH were 5.9 and 6.0, respectively. Throughfall and stemflow were enriched in DIN (NH4+-N + NO3--N) and DON in both forests. DIN fluxes were higher in throughfall in the Nothofagus forest (7.5 kg ha-1 yr-1) than in the Pinus plantation (6.4 kg ha-1 yr-1). DIN infiltration fluxes were much higher in the Pinus plantation (NH4+-N = 3.1 kg ha-1 yr-1, NO3--N = 5.4 kg ha-1 yr-1) than in the Nothofagus forest (NH4+-N = 0.4 kg ha-1 yr-1, NO3--N = 1.5 kg ha-1 yr-1), suggesting a lower N immobilization and/or plant uptake in the Pinus plantatio
EL CARIOTIPO DE CHAETANTHERA INCANA POEPP. EX LESS. (ASTERACEAE)
No full textThe karyotype oí Chaetanthera incana Poepp. ex Less, from Chile was examined. This species belong to the subgenus Chaetanthera. The species has 2n = 2x = 22 chromosomes, with 10m + Ism chromosomes. The reported karyotype is symmetric (Asi % = 56.0). These results were compared with Ch. chilensis and Ch. ciliata
NO AND N2O FLUXES FROM A BELGIAN FOREST AFFECTED BY ELEVATED NITROGEN DEPOSITION
No full textNitrous oxide (N2O) and nitric oxide (NO) are important atmospheric trace gases, and soils (including forest soils) are a substantial source of both gases. In forests subjected to elevated N deposition these emissions are considered as indirect emissions from agricultural N sources (mainly NH3) or combustion (e.g. NOx from traffic). However, knowledge about N2O and NO exchange between forests and the atmosphere is scarce. The aim of this study was to determine N2O and NO emission rates from a deciduous forest in Belgium, receiving a high N-deposition (ca. 40 kg N ha-1 yr-1). In April 2000, the NO emission from the forested location was 17.3 (± 1.2) and 17.05 (± 0.7) ng NO-N m-2 s-1, respectively, for the soil including the organic layer and the mineral soil only. In June 2000, the NO flux from the same location was 94.3 (± 14.1) and 53.8 (± 10.3) ng NO-N m-2 s-1, respectively, for the soil with organic layer and the mineral soil only. In April 2000, the NO emission from a clear-cut location in the same forest for the soil with organic layer was 30.5 (±1.52) ng NO-N m-2 s-1, whereas the flux from the mineral soil was 42.3 (± 1.33) ng NO-N m-2 s-1. In June 2000, however, the mineral soil emitted a significantly higher amount of NO than the clear-cut soil with organic layer (145.8 ± 7.2 ng NO-N m-2 s-1 versus 22.6 ± 3.1 ng NO-N m-2 s-1). The soil at the forested location acted as a net sink for N2O, with a mean annual flux of -0.63 ± 0.57 ng N2O-N m-2 s-1. In contrast the soil at the clear-cut site acted as a net N2O source, with a mean annual flux of 1.55 ± 0.90 ng N2O-N m-2 s-1. From these measurements it could be concluded that the forested soil was a significant secondary NO source and a N2O source or sink. However, more research is needed to investigate how N deposition, climate and forest management can affect N trace gas exchange in forest soil
Negative photoblastism in the invasive specie Eschscholzia californica Cham. (Papaveraceae): Patterns of altitudinal variation in native and invasive range
No full textNegative photoblastism is defined as the inhibitory effect of light on seed germination. This effect can be modulated by abiotic variables, such as temperature, light condition and water potential. This conditions change notoriously at higher altitudes, could promote differentiations in the photoblastic response among populations. Also, this physiological attribute poses an interesting conflict for plant regeneration, because prevents seed germination on the soil surface, however, it can also to reduce the mortality of seeds germinants in unsuitable conditions and consequently, seedling mortality. Eschscholzia californica is one of the few species with negative photoblastism and it is invasive in Chile, growing primarily in open and disturbed places. Some invasive species have the potential to adapt their morphological and ecophysiological characteristics faced to new environmental conditions. In this study, we examined variation in negative photoblastism between populations from central Chile (invasive) and California (native) located at the extremes of their altitudinal distribution. We used common garden experiments where seeds from different origins were germinated under controlled lab condition in Chile. If negative photoblastism is conserved, we would see similar responses among seeds original from this climatic analogues regions. Also, we evaluated whether seed burial increases seed germination of this species as a mechanism for escaping the intense luminosity at the soil surface, by planting seeds at different soil depths. For this experiment, we expected an increase of germination at higher soil depth. The results indicate no differences in negative photoblastism between Chilean and Californian populations. A significant variation across altitudinal range in California suggests the existence of genetic differentiation in the native region, however, the absence of differences across the altitudinal range in Chile suggests trait conservatism at local scale. Seed germination was zero at the soil surface and increased when seeds were experimentally buried, suggesting that negative photoblastism is inhibited. Three possible explanations are given to explain the pattern of establishment of E. californica despite having negative photoblastism. This is a fairly specialist trait, related with Mediterranean climates and does not explain by itself the invasiveness described for this specie. In any case, is clear that more studies are necessary to disentangle the adaptive value of this physiological trait
Heliotropium geissei (Heliotropiaceae): nuevos registros, tipificación, posición sistemática y estado de conservación
No full textSe reportan nuevos registros de Heliotropium geissei, una especie rara de Chile central. La nomenclatura de la especie es revisada y se refina su lectotipificación. Análisis filogenéticos moleculares confirman su posición sistemática como miembro de la sección Plagiomeris. Se proporciona una clave de identificación de las especies de la sección Plagiomeris. Se evalúa su estado de conservación y se sugiere la categoría UICN de En Peligro (EN)
MORPHOLOGY OF THE SYMMETRICAL MORPHOTYPES OF CENTRONELLA REICHELTII VOIGT (FRAGILARIACEAE, BACILLARIOPHYCEAE) FROM PATAGONIAN ENVIRONMENTS
No full textThe ultrastructure of symmetrical valves of Centronella reicheltii Voigt, resembling the former C. rostafinskii Woloszynska, is studied for the first time, and their morphology is compared with the asymmetrical forms. Valve morphology and morphometry of both morphotypes are similar and only differ in the shape and striation pattern of the valve centre and the arrangement of the arm bases. However, since they occur in environments with different trophic status, the new combination C. reicheltii f. rostafinskii is proposed for the symmetrical valves, because this distinction may provide ecologically useful information
La flora exótica ruderal del Parque Nacional La Campana, Región de Valparaíso, Chile central
No full textRESUMEN Los ecosistemas mediterráneos, entre los que se cuenta la zona central de Chile, se consideran globalmente entre los más afectados por las invasiones biológicas. Si bien no todas las especies de plantas exóticas se pueden considerar invasoras, en ellas se encuentra el potencial de invasibilidad que eventualmente puede significar cambios sustanciales en la composición de los ecosistemas y las relaciones entre sus especies. Ello es especialmente crítico en espacios protegidos en los cuales se pretende asegurar la conservación presente y futura de las poblaciones de especies nativas y endémicas. En esta investigación se estudió la presencia de plantas exóticas ruderales en los márgenes de los senderos del Parque Nacional La Campana, con el método de transectos. Las familias mejor representadas en la flora exótica ruderal del Parque son Poaceae, Asteraceae y Fabaceae. En cuanto a su forma de vida, el 71% corresponde a terófitos. La gran mayoría (92,7%) es de origen euroasiático-norafricano. Al examinar la presencia de las plantas exóticas ruderales en las diferentes unidades de vegetación se obtiene que el Puyal con suculentas es la unidad más afectada. En cambio, las unidades a mayor altitud como el Bosque caducifolio y el Matorral altoandino son las que muestran una menor presencia de especies introducidas. Hay dos factores que parecen ejercer una influencia importante en el grado de invasibilidad: la cantidad de luz disponible y la altitud a la que se encuentra la unidad de vegetación. Para poder evaluar la tasa de expansión y los posibles efectos sobre las especies nativas y el ecosistema del PN La Campana, conviene diseñar un plan de monitoreo, sobre todo de las especies que están más difundidas en el Parque y que aparecen sistemáticamente en los muestreos en distintos tipos de vegetación
Descripción de las normas y equipos de laboratorio utilizados para la caracterización física y mecánica de los tableros OSB en el mercado de los Estados Unidos
Get PDFpáginas 83-92El Estándar Voluntario de Productos PS 2-10, emitido por la Asociación de Fabricantes de Tableros Contrachapados de los Estados Unidos (APA), identifica las normas y los requisitos de calidad que deben cumplir los tableros de madera estructurales que se producen y comercializan en ese país. El estándar PS 2-10 hace referencia a una serie de normas ASTM.
En este documento se recopilan las normas ASTM utilizadas en la caracterización física y mecánica de los tableros OSB
Nuevas combinaciones en los géneros sudamericanos Lepidaploa y Lessingianthus (Vernonieae, Asteraceae)
No full textLos géneros Lepidaploa (Cass.) Cass. y Lessingianthus H. Rob. (Vernonieae, Asteraceae) fueron establecidos para separar a las especies inicialmente ubicadas en Vernonia Schreb. sect. Lepidaploa (Cass.) DC. subsect. Axilliflorae Benth. & Hook. y Vernonia sect. Lepidaploa subsect. Macrocephalae Benth. & Hook., respectivamente. Tal como se delimitan actualmente, Lepidaploa está compuesto por alrededor de 150 especies ampliamente distribuidas en Sudamérica, mientras que Lessingianthus presenta 120 especies con una gran concentración en el sudeste de Brasil. Se estima que gran cantidad de especies todavía incluidas en Vernonia no han sido estudiadas apropiadamente y en consecuencia su posición y estatus taxonómicos permanecen inciertos. En este trabajo se analizó la morfología de los granos de polen y de algunos microcaracteres florales para aportar datos que permitieron transferir seis taxones de Vernonia al género Lessingianthus y otras dos especies del mismo género a Lepidaploa