Efecto de borde en la distribución de líquenes y el contenido de clorofilas en fragmentos de Polylepis quadrijuga (Rosaceae) en el páramo de La Rusia (Boyacá-Colombia) / Edge effect on lichen's distribution and chlorophyll content, in fragments of Polylepis quadrijuga (Rosaceae) in Páramo de la Rusia (Boyacá-Colombia)

Resumen:La fragmentación de los ecosistemas es uno de los fenómenos antrópicos de mayor impacto global, y el efecto borde provoca que solo el interior de los fragmentos conserve sus características bióticas y abióticas originales. Los líquenes son organismos especialmente susceptibles a la variabilidad ambiental, lo que podría ser útil para la bio-indicación del efecto borde. En este trabajo se evaluó el efecto borde en dos fragmentos de Polylepis quadrijuga en el Páramo de la Rusia (Boyacá-Colombia), para determinar si existe un efecto borde sobre la distribución de los líquenes asociados a P. quadrijuga y su contenido de clorofilas. Se utilizaron tres transectos de 70 m a través del gradiente matriz-borde-interior en cada fragmento. Se escogieron nueve forofitos por transecto para medir variables ambientales: radiación fotosintéticamente activa, humedad relativa y temperatura del aire, y variables biológicas: riqueza y cobertura de cada especie. Además, fueron elegidas las especies que estaban presentes en las tres zonas del gradiente para cuantificar el contenido de clorofilas a y b, y determinar si hay cambios en la relación de clorofilas a/b que podrían sugerir plasticidad fisiológica como respuesta al efecto borde. Nuestros resultados mostraron que el fragmento 2 tenía una mayor exposición al borde debido a su alta relación perímetro/área, lo que causa una homogenización ambiental y pérdida de biodiversidad con relación con el fragmento 1. En general, se encontraron 55 especies que se distribuyen diferencialmente en relación con los fragmentos y el gradiente matriz-borde-interior. El interior del fragmento 1 fue la zona más conservada, que alberga una composición diferente en más de un 40 % a la composición de cualquier otra zona. Se clasificaron los líquenes de acuerdo con sus hábitos: gelatinosos, fruticosos, costrosos o foliosos, pero no se encontró ninguna relación entre la distribución por hábito y el efecto borde. Seis especies de amplia distribución mostraron cambios en el contenido de clorofila a lo largo del gradiente matriz-borde-interior, lo que es una evidencia de la plasticidad fisiológica al efecto borde. También fue posible diferenciar entre especies con preferencia por ambientes de alta temperatura y especies con preferencia a lugares más húmedos y suficientemente irradiados. Se concluye que algunas especies podrían tener un importante potencial como bio-indicadores de la fragmentación en ambientes de páramo.

Abstract:The ecosystems fragmentation is one of the anthropic phenomena with highest impact at global level and the edge effect causes that only the interior of fragments conserves their original biotic and abiotic characteristics. Lichens are organisms especially susceptible to environmental variability, what could be useful for bio-indication of edge effect. In this work, we evaluated the edge effect in two fragments of Polylepis quadrijuga in the Páramo de la Rusia (Boyacá-Colombia) to determine if there is an edge effect on distribution of lichens associated to P. quadrijuga and their chlorophyll content. We used three transects of 70 m across the matrix-edge-interior gradient in each fragment. We chose nine phorophytes per transect to measure the environmental variables: photosynthetically active radiation, relative humidity and air temperature, and the biological variables: richness and cover per species. Besides, we employed the species that were present in all the three zones of the gradient to quantify the content of chlorophylls a and b, and determine if there are changes in the ratio of chlorophylls a/b that could suggest physiological plasticity as a response to the edge effect. Our results showed that fragment 2 had a higher edge exposition because of its high relation perimeter/area, allowing to an environmental homogenization and lose of biodiversity in relation with fragment 1. Overall, we found 55 differentially distributed species in relation with the fragments and the matrix-edge-interior gradient. The interior of fragment 1 was the most conserved zone, harboring a composition different in more than 40 % to the composition of any other zone. We classified the lichens according with their habits: gelatinous, fruticose, crusty or foliose, but we did not find any relationship between the habit distribution and the edge effect. Six species of wide distribution showed changes in the chlorophyll content along the matrix- edge-interior gradient, what is an evidence of physiological plasticity to edge effect. It was also possible to distinguish between species with preference to warmer environment and species with preference to more humid and sufficiently irradiated places. We concluded that some species of lichens could have an important potential as bio-indicators of fragmentation in the páramo. Rev. Biol. Trop. 64 (4): 1683-1697. Epub 2016 December 01.

Influence of rootstocks on growth, yield, fruit quality and leaf mineral element contents of pear cv. 'Santa Maria' in semi-arid conditions

BACKGROUND: Rootstocks play an essential role to determining orchard performance of fruit trees. Pyrus communisand Cydonia oblonga are widely used rootstocks for European pear cultivars. The lack of rootstocks adapted to different soil conditions and different grafted cultivars is widely acknowledged in pear culture. Cydonia rootstocks (clonal) and Pyrus rootstocks (seedling or clonal) have their advantages and disadvantages. In each case, site-specific environmental characteristics, specific cultivar response and production objectives must be considered before choosing the best rootstock. In this study, the influence of three Quince (BA 29, Quince A = MA, Quince C = MC) and a local European pear seedling rootstocks on the scion yield, some fruit quality characteristics and leaf macro (N, P, K, Ca and Mg) and micro element (Fe, Zn, Cu, Mn and B) content of 'Santa Maria' pear (Pyrus communis L.) were investigated. RESULTS: Trees on seedling rootstock had the highest annual yield, highest cumulative yield (kg tree(-1)), largest trunk cross-sectional area (TCSA), lowest yield efficiency and lowest cumulative yield (ton ha(-1)) in the 10th year after planting. The rootstocks had no significant effect on average fruit weight and fruit volume. Significantly higher fruit firmness was obtained on BA 29 and Quince A. The effect of rootstocks on the mineral element accumulation (N, K, Ca, Mg, Fe, Zn, Cu, Mn and B) was significant. Leaf analysis showed that rootstocks used had different mineral uptake efficiencies throughout the early season. CONCLUSION: The results showed that the rootstocks strongly affected fruit yield, fruit quality and leaf mineral element uptake of 'Santa Maria' pear cultivar. Pear seedling and BA 29 rootstock found to be more prominent in terms of several characteristics for 'Santa Maria' pear cultivar that is grown in highly calcareous soil in semi-arid climate conditions. We determined the highest N, P (although insignificant), K, Ca, Mg, Fe and Cu mineral element concentrations on the pear seedling and BA 29 rootstocks. According to the results, we recommend the seedling rootstock for normal density plantings (400 trees ha(-1)) and BA 29 rootstock for high-density plantings (800 trees ha(-1)) for 'Santa Maria' pear cultivar in semi-arid conditions.

Variabilidad ambiental y respuestas fisiológicas de Polylepis cuadrijuga (Rosaceae) en un ambiente fragmentado en el Páramo de la Rusia (Colombia) / Environmental variability and physiological responses from Polylepis cuadrijuga (Rosaceae) in a fragmented environment in the Páramo de la Rusia (Colombia)

Polylepis cuadrijuga is an endemic woody species from the Colombian Eastern range, being the only tree species with capacity to live on mountainous environments beyond 4 000m of altitude. Grazing and agriculture have transformed at least 30% of the Guantiva-La Rusia region, turning continuous extensions of high Andean forest in a fragmented landscape, and P. cuadrijuga remnants have become smaller and more isolated. The aim of this study was to establish the environmental differences between a matrix of grazing pastures and the interior of fragments, to evaluate the physiological responses of P. cuadrijuga and determining the edge effect. Air temperature and humidity, soil water holding capacity and photosynthetic active radiation, were measured along two 50X2m transects from the matrix toward the center of fragment. Six trees inside the transects were chosen in each one of three sites (matrix, edge and interior) to measure the index chlorophyll content and to sample leaves to assess the leaf area, leaf biomass, specific leaf area, anatomy, health condition and pubescence. Results showed significantly differences between the matrix and the interior and intermediate conditions in the edge. Radiation, temperature and air desiccation were higher in the matrix than in the interior, submitting P. cuadrijuga trees to a stressing environment, where they presented stratification of epidermis and palisade parenchyma, and a higher leaf area, leaf thickness, chlorophyll content and pubescence than in the interior of fragments. All these physiological traits allow avoiding the photoxidation and damages by freezing or desiccation to which trees are exposed in a grazing pasture matrix. Nevertheless, there was a higher frequency of healthy leaves in the interior of fragments, showing that high irradiations and extreme air temperature and humidity reach adversely affect to P. cuadrijuga. Individuals in the edge had ecophysiological traits similar to the matrix ones, which confirm an edge effect that could penetrate 17m inside the fragments. We conclude that P. cuadrijuga is a plastic species, able to overcome the stress conditions from anthropogenic transformations, species able to be used in high Andean forest restoration programs.

Polylepis cuadrijuga es una especie leñosa endémica de la cordillera oriental de Colombia, donde la agricultura y el pastoreo han generado la fragmentación de sus bosques. Para determinar si existe un efecto borde en fragmentos ubicados en el Páramo de la Rusia, se establecieron diferencias ambientales y se evaluó las respuestas ecofisiológicas de P. cuadrijuga entre matriz de pastura, borde e interior de los fragmentos, a través de la medición de temperatura ambiental, humedad relativa, capacidad de retención de agua del suelo y radiación fotosintéticamente activa, a lo largo de dos transectos de 50m desde la matriz hacia el interior. En cada sitio se escogieron seis árboles para evaluar el contenido de clorofila, área foliar, biomasa foliar, área foliar específica, anatomía foliar, sanidad y pubescencia. En matriz fue mayor la temperatura y la radiación, condiciones relacionadas con la disminución del AFE y el aumento del contenido de clorofilas, evidenciado por la presencia de un parénquima en empalizada biestratificado. Características ecofisiológicas similares a las expuestas en borde, confirman un efecto de borde que podría penetra unos 17m en el interior de los fragmentos. Se concluye que P. cuadrijuga es una especie plástica, capaz de enfrentar condiciones de estrés generadas por actividades antropogénicas.