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.

Effects of different water management options and fertilizer supply on photosynthesis, fluorescence parameters and water use efficiency of Prunella vulgaris seedlings

BACKGROUND: Prunella vulgaris L. is a medical plant cultivated in sloping, sun-shaded areas in China. Recently, owing to air-environmental stress, especially drought stress strongly inhibits plant growth and development, the appropriate fertilizer supply can alleviate these effects. However, these is little information about their effects on P. vulgaris growing in arid and semi-arid areas with limited water and fertilizer supply. RESULTS: In this study, water stress decreased the photosynthetic pigment contents, inhibited photosynthetic efficiency, induced photodamage in photosystem 2 (PS2), and decreased leaf instantaneous WUE (WUEi). The decreased net photosynthetic rate (Pn) under medium drought stress compared with the control might result from stomatal limitations. However, fertilizer supply improved photosynthetic capacity by increasing the photosynthetic pigment contents and enhancing photosynthetic efficiency under water deficit. Moreover, medium fertilization also increased WUEi under the two water conditions, but fertilizer supply did little to alleviate the PS2 photodamage caused by drought stress. Hence, drought stress was the primary limitation in the photosynthetic process of P. vulgaris seedlings, while the photosynthetic characteristics of the seedlings exhibited positive responses to fertilizer supply. CONCLUSIONS: Appropriate fertilizer supply is recommended to improve photosynthetic efficiency, enhance WUEi and alleviate photodamage under drought stress.

Origin of the subepidermal tissue in Piper L. leaves / Origem do tecido subepidérmico em folhas de Piper L.

Studies on the anatomy of Piper leaves demonstrate the presence of a subepidermal tissue distinct from the adjacent epidermis, which cells show thin walls and hyaline contents. Some authors consider such cells a hypodermal tissue, while others refer to them as components of a multiple epidermis. In this study, the nature of this subepidermal tissue was investigated through the analysis of leaf ontogeny in three Piper species. The analysis showed that the referred tissue originates from the ground meristem and, thus, should be considered a hypodermis. The studied species suggests that the role of the hypodermis would be to protect the photosynthetic apparatus from excess light, regulating the intensity of light reaching the chlorophyll parenchyma.

Os estudos de anatomia foliar de espécies de Piper revelam a presença de um tecido subepidérmico distinto da epiderme e cujas células apresentam paredes finas e conteúdo hialino. Estas células são referenciadas por alguns autores como um tecido hipodérmico e por outros, como sendo constituintes de uma epiderme múltipla. Nesse estudo verificou-se a natureza deste tecido subepidérmico a partir da análise da ontogênese foliar de três espécies de Piper. A análise revelou que o referido tecido tem origem do meristema fundamental e, portanto, deve ser denominado de hipoderme. Para as espécies avaliadas, sugere-se que a hipoderme teria função de, proteger o aparato fotossintético do excesso de luminosidade, regulando a intensidade luminosa que atinge o parênquima clorofiliano.

Photochemical efficiency of adult and young leaves of the neotropical understory shrub Psychotria limonensis (Rubiaceae)in response to changes in the light environment

We explored the short-term adjustment in photochemical efficiency (Fv /Fm )in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae)in response to rapid changes in the light environment.Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula,Barro Colorado Natural Monument (Republic of Panama),during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade,BA leaves experienced the opposite transfer,and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions).Adult and young leaves did not differ in overall photochemical efficiency.Instead,differences were found among light environments,for which leaves transferred from shade to sun showed the lowest F v /F m ratios.There was no relationship between photochemical efficiency and leaf temperature.In P.limonensis,understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage.The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species

Se exploró el ajuste a corto plazo en la eficiencia fotosintética (Fv /Fm )en hojas jovenes y adultas del arbusto del sotobosque neotropical Psychotria limonensis Krause (Rubiaceae)en respuesta a cambios rápidos de luz ambiental. Las hojas fueron recolectadas de 20 plantas individuales bajo condiciones de sol y sombra en Peninsula Gigante, Monumento Natural Barro Colorado (Panamá),durante la estación lluviosa de 1996.Las hojas fueron distribuidas en una secuencia cuatro tratamientos de luz (AB las hojas fueron expandidas bajo el sol y fueron transferidas a la sombra,BA las hojas experimentaron la transferencia contraria,y las hojas controles AA y BB que fueron expandidas y mantenidas bajo condiciones de sol o de sombra).Las hojas adultas o jóvenes no difieren en la eficiencia fotoquímica general.Por el contrario,se encontró diferencias entre los ambientes de luz (iluminados), para los cuales las hojas transferidas de la sombra al sol mostraron las menores tasas Fv /Fm .No hubo relación entre la eficiencia fotoquímica y la temperatura de las hojas. En P.limonensis ,las plantas son suceptibles a la foto -inhibición independientemente del estado ontogenético de la hoja. El enfoque utilizado en este experimento permitió la rápida exploración de esta capacidad y demostró que puede ser utilizado en otras especies poco estudiadas del sotobosque