ResumenEn la llanura inundable de la Orinoquía colombiana (departamento de Arauca) se realizó la caracterización de cuatro tipos ecosistémicos con diferentes grados de intervención por ganadería, durante la intensa temporada seca de enero a marzo 2010: sabana de pastizal, sabana arbolada, bosque de galería y bosque conservado del piedemonte. En cada uno de ellos se evaluaron las condiciones microclimáticas (humedad y temperatura del aire), las características físico químicos del suelo (capacidad de retención de agua, capacidad de intercambio catiónico, pH, contenido de fósforo y de micronutrientes), la diversidad vegetal (riqueza y abundancia) y el potencial regenerativo (diversidad y porcentaje de germinación del banco de semillas del suelo), con el fin de establecer cuáles parámetros ecosistémicos son los más afectados por la ganadería durante la sequía, y evaluar la capacidad de regulación ambiental y el potencial de recuperación natural. Los resultados demostraron que en casi todos los aspectos el tipo ecosistémico de pastizal es ampliamente contrastante con relación a los bosques conservados del piedemonte, siendo estos últimos los lugares con mayor biodiversidad, menor variabilidad en temperatura y humedad relativa, mayor capacidad de retención de agua, mayor variabilidad topográfica que brinda sitios específicos de regeneración y contenidos más balanceados de micronutrientes en el suelo. Los bancos de semillas, que albergan propágulos que soportan la temporada seca para germinar en condiciones más favorables, fueron más diversos y abundantes en la sabana arbolada, mostrando que este ecosistema tiene mayores opciones de recuperación ecológica que la sabana de pastizal. El estudio demuestra la importancia de la cobertura arbórea en la llanura inundable, especialmente en la autorregulación ecosistémica durante temporadas climáticas desfavorables. Se recomienda la implementación de sistemas de producción ganadera que involucren el componente forestal, y la conservación de los remanentes de bosque.Palabras clave: Bosque de galería, bosque del piedemonte, Orinoquía, pastizal, regulación climática, sabana arbolada, suelo.
ABSTRACT. Introduction: Thanks to filtration by foliage, urban trees have a crucial role in air depuration. However, the exposure to pollutants could reduce their health and physiological performance, mainly because of low access to light and clogging of stomata by particulate matter. Objective: The accumulation of particulate matter on leaves (PMAL) and physiological traits of five urban tree species (Croton bogotanus Cuatrec., Eugenia myrtifolia Sims., Ficus soatensis Dugand, Schinus mole L., and Sambucus nigra L.) were quantified in sixty points in Bogotá, with the aims to (1) build a model explaining the PMAL based on traffic variables, (2) establishing the effect of vehicle pollution on physiological and phytosanitary variables, and (3) to evaluate the susceptibility of seedlings and trees to vehicle pollution. Methods: The physiological parameters: photochemical efficiency, stomatal conductance, chlorophyll content, leaf area, and specific leaf mass were measured and correlated with phytosanitary condition, PMAL and traffic variables: number of lanes, vehicular flow and tree-to-avenue distance. Additionally, tree physiological responses were measured in control, residential streets (RS), low traffic avenues (LTA), and high traffic avenues (HTA), and these last were compared with physiology of seedlings planted by three months in HTA. Results: PMAL was strongly associated with physiological responses. Ficus soatensis and C. bogotanus were the species with the maximum and the minimum PMAL. The exposure to traffic increased the photochemical efficiency and specific leaf mass, which could be related to the enrichment of nitrogen and atmospheric CO2. The stomatal conductance followed a bell pattern of low gas exchange in control sites, high values in RS and LTA, and decreasing again in HTA, which suggests an optimization in CO2 fixation at intermediate levels of pollution and susceptibility to stomatal clogging by extreme vehicle emissions. The chlorophyll a/b ratio, leaf area, and specific leaf mass were significantly related to the severity of leaf symptoms, and S. molle was the species with the healthiest leaves in HTA. Seedlings were more susceptible to pollution than trees, and fruits size and seedlings growth were affected by vehicular pollution. Conclusions: Ficus soatensis optimizes particle filtration and C. bogotanus is ideal for planting in HTA, although only as saplings. By contrast, the fast-growing E. myrtifolia and S. nigra seedlings should not be planted in HTA because of susceptibility of pigment contents, leaf area, and stomatal conductance to pollutants. Finally, because of its persistent high stomatal conductance and its low leaf symptoms, S. molle is the species with the best adaptation to vehicle pollution. A complete analysis of interactions among traffic, physiology, and health will help to improve the urban forestry planning.
Background Some studies have indicated that the Horned Larks (Eremophila alpestris) should be considered as a species complex. Recently it split into four species or clades and seven subclades based on genetic, morphological, and biogeographic data. However, other aspects like song divergence have not been studied and several subspecies have not been evaluated, leading to important information gaps in this group of birds. In this work, we aimed to assess the differences in song traits and playback response between the Nearctic subclade and the Neotropical or Colombian subspecies E. a. peregrina. Methods We compared six song traits between these groups and performed field playback experiments, to test the response of the Neotropical larks to both songs. We tested the difference in the variables for separate as well as by principal component analysis (PCA). Results We found significant differences (p < 0.05) in the individual song traits and the PCA analysis between the two groups. Further, the PCA analysis showed a clearer divergence of the Neotropical songs in comparison to the Nearctic songs of different locations within North America. Similarly, the playback analysis showed a significantly lower response of E. a. peregrina to the songs of the Nearctic larks. Conclusions Besides this song divergence, there are important ecological and biogeographic differences between the Neotropical and Nearctic Horned Larks, that indicate an unclear relationship between these two groups. Thus, further morphological and genetic studies are required to clarify the taxonomy of the Neotropical Horned Lark and define if they share the same evolutionary history as the other subspecies of the Nearctic subclade.
Efecto de las giberelinas y arsénico en la germinación de A. acuminata 45 45 ¿La giberelina aumenta la aclimatación de plántulas de Alnus acuminata al arsénico? Does gibberellin increase the acclimation of seedlings of Alnus acuminata to arsenic?
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