The relevance of seed size in modulating leaf physiology and early plant performance in two tree species

he size of seeds and the microsite of seed dispersal may affect the early establishment of seedlings through different physiological processes. Here, we examined the effects of seed size and light availability on seedling growth and survival, and whether such effects were mediated by water use efficiency. Acorns of Quercus petraea and the more drought-tolerant Quercus pyrenaica were sowed within and around a tree canopy gap in a sub-Mediterranean forest stand. We monitored seedling emergence and measured predawn leaf water potential (Ψpd), leaf nitrogen per unit area (Na), leaf mass per area, leaf carbon isotope composition (δ13C) and plant growth at the end of the first summer. Survival was measured on the next year. Path analysis revealed a consistent pattern in both species of higher δ13C as Ψpd decreased and higher δ13C as seedlings emerged later in the season, indicating an increase in 13C as the growing season is shorter and drier. There was a direct positive effect of seed size on δ13C in Q. petraea that was absent in Q. pyrenaica. Leaf δ13C had no effect on growth but the probability of surviving until the second year was higher for those seedlings of Q. pyrenaica that had lower δ13C on the first year. In conclusion, leaf δ13C is affected by seed size, seedling emergence time and the availability of light and water, however, leaf δ13C is irrelevant for first year growth, which is directly dependent on the amount of seed reserves.

Effect of sugar beet pulp fibre fractions on growth performance, fecal digestibility and digestive physiology in rabbits around weaning

The present study investigated the effect of the different fibre components of sugar beet pulp (SBP) on growth performance and some digestive traits. Four semi-synthetic diets were formulated with similar NDF (33% DM) and protein (16% DM) level. Control diet was formulated to contain the lowest level of soluble fibre (3% DM) and SBP diet the highest (9%). The soluble (pectins) and insoluble fractions of SBP were studied in other two diets (Pectin and InsSBP diets). A total of 136 weanling rabbits (25 d of age) was housed individually, randomly assigned to 4 experimental groups, and fed ad libitum with the experimental diets during 10 days after weaning. The type of diet did not affect growth rate and stomach pH. Animals fed with SBP diet showed higher DM and NDF digestibility (4 and 83%, respectively), gain:feed ratio (13%), cecal and total tract weight (13 and 9%) and ileal viscosity (148%) than rabbits fed the Control diet, but lower cecal pH (9%). Pectin diet increased ileal viscosity and decreased the weight of stomach content with respect to SBP diet. Rabbits fed InsSBP diet showed similar results to SBP diet but lower ileal viscosity and cecal pH than those fed Pectin diet. In conclusion, SBP and their soluble and insoluble fractions are well digested in young rabbits. However the soluble and insoluble fibre of SBP produce different effects in the gastrointestinal tract.

Molecular physiology of nickel and cobalt homeostasis in Rhizobium leguminosarum.

Transition metals such as Fe, Cu, Mn, Ni, or Co are essential nutrients, as they are constitutive elements of a significant fraction of cell proteins. Such metals are present in the active site of many enzymes, and also participate as structural elements in different proteins. From a chemical point of view, metals have a defined order of affinity for binding, designated as the Irving-Williams series (Irving and Williams, 1948) Mg2+ menor que Mn2+ menor que Fe2+ menor que Co2+ menor que Ni2+ menor que Cu2+mayor queZn2+ Since cells contain a high number of different proteins harbouring different metal ions, a simplistic model in which proteins are synthesized and metals imported into a ?cytoplasmic soup? cannot explain the final product that we find in the cell. Instead we need to envisage a complex model in which specific ligands are present in definite amounts to leave the right amounts of available metals and protein binding sites, so specific pairs can bind appropriately. A critical control on the amount of ligands and metal present is exerted through specific metal-responsive regulators able to induce the synthesis of the right amount of ligands (essentially metal binding proteins), import and efflux proteins. These systems are adapted to establish the metal-protein equilibria compatible with the formation of the right metalloprotein complexes. Understanding this complex network of interactions is central to the understanding of metal metabolism for the synthesis of metalloenzymes, a key topic in the Rhizobium-legume symbiosis. In the case of the Rhizobium leguminosarum bv viciae (Rlv) UPM791 -Pisum sativum symbiotic system, the concentration of nickel in the plant nutrient solution is a limiting factor for hydrogenase expression, and provision of high amounts of this element to the plant nutrient solution is required to ensure optimal levels of enzyme synthesis (Brito et al., 1994).

Fish physiology put into practice: A robotic fish model

Underwater creatures are capable of high performance movements in water. Thus, underwaterrobot design based on the mechanism of fish locomotion appears to be a promising approach.Over the past few years, researches have been developing underwater robots based on underwatercreatures swimming mechanism.

Caracterización morfofisiológica de semillas de especies leñosas distribuidas en dos zonas secas presentes en el Sur del Ecuador

Sudamérica es una de las zonas con mayor cantidad de bosque seco tropical a nivel mundial. No obstante, estos bosques han sido poco conocidos y la mayoría de estudios han estado orientados hacia los bosques húmedos tropicales. Los bosques secos se han reducido drásticamente y siguen muy amenazados, corriendo el riesgo de desaparecer en los próximos años. Por ello, es fundamental, generar investigación aplicada para la conservación inmediata de los ecosistemas secos tropicales. En Ecuador, la situación no es diferente y las zonas secas catalogadas como biodiversas están en constante amenaza. Los pocos estudios realizados en Ecuador sobre zonas secas, han permitido mejorar nuestro conocimiento referente a la diversidad y abundancia de las especies, relaciones planta-planta y síndromes de dispersión. No existen estudios sobre caracteres morfológicos en frutos y semillas de las especies leñosas de bosque seco. Sin embargo, nuestra comprensión de la dinámica y estructura de las comunidades ecológicas de zonas secas poco estudiadas, puede mejorar rápidamente mediante el estudio y enfoque de rasgos morfofisiológicos funcionales. El objetivo general del presente estudio fue aportar al conocimiento de la ecología y biología de semillas de zonas secas tropicales mediante el análisis y evaluación de rasgos morfofisiológicos de frutos y semillas de una comunidad de especies leñosas. El estudio se realizó en una zona de bosque y matorral seco, ubicados al sur occidente del Ecuador, a una altitud comprendida entre los 250 a 1 200 m s.n.m. caracterizada por una marcada estacionalidad ambiental, con lluvias desde diciembre a abril y una estación seca de mayo a noviembre. Precipitación media anual de 500 mm con una temperatura media anual de 20° a 26 °C. La zona de estudio forma parte de la región Tumbesina compartida entre el sur del Ecuador y el norte del Perú con gran diversidad de especies vegetales endémicas. Para el estudio se colectaron frutos con semillas maduras previamente a su dispersión de entre ocho y diez individuos de 80 especies entre árboles y arbustos más representativos de los bosques secos ecuatorianos. De los frutos colectados se utilizó una muestra al azar de 50 frutos y semillas por especie para los diferentes análisis. Se midió y evaluó 18 rasgos morfológicos y fisiológicos cuantitativos y cualitativos de frutos, semillas y de la especie. Se realizaron diferentes análisis de asociación y correlación entre los rasgos evaluados, con cinco variables ambientales registradas de las 109 parcelas establecidas en el área de estudio, además analizamos el tipo de dormición y comparamos la respuesta germinativa a la deshidratación relacionada con dos comunidades secas, matorral y bosque seco. Los resultados mostraron que las especies presentan gran heterogeneidad en rasgos continuos de las semillas. La variabilidad fue más evidente en rasgos como tamaño, volumen, masa y número de semillas por fruto. Sin embargo, una alta proporción de las especies tiende a producir una semilla por fruto. Además, la mayoría de las especies de bosque seco se caracterizan por no poseer algún tipo de apéndices o areola en sus semillas, forma ovalada y sin endospermo. La reserva nutritiva de las semillas se encuentra especialmente en los cotiledones de los embriones. Se encontraron seis tipos diferentes de embriones y la mayoría de las especies presentó embriones gruesos e invertidos. La dispersión de semillas está dominada por zoocoria en un 38 %, con relación a anemocoria (22 %) y autocoria (19 %). Sin embargo, encontramos que el 70 % de las especies posee frutos secos. Los análisis de dormición en las semillas de bosque seco, mostraron que el 60 % de las especies de bosque seco presentaron semillas con algún tipo de latencia, menor a la encontrada en especies de bosque deciduo tropical y sabanas, sin embargo, la dormición de las especies de bosque seco fue mayor al porcentaje de especies con dormición de bosque semiperenne y selva lluviosa tropical. La dormición física constituyó el 35 % de las especies de bosque seco, seguido del 12 % con dormición fisiológica, mientras que solamente una especie tuvo dormición morfológica. Encontramos que la dormición de las semillas de las especies en estudio se relaciona significativamente con el tipo y función del embrión y con el endospermo. Existieron relaciones significativas entre los rasgos morfológicos de los frutos, semillas, embriones y atributos de los individuos de 46 especies, aunque en algunos casos con coeficientes de correlación bajos. Hubo pocas relaciones entre los rasgo morfológicos de las semillas con las variables ambientales registradas. Solamente el tipo de testa y la presencia de apéndices en las semillas mostraron relación con el pH y la temperatura media del suelo. No obstante usando el modelo fouth corner-RLQ, no se encontraron asociaciones claras ni significativas entre rasgos morfológicos de semillas y frutos con variables ambientales. Al medir el efecto de la deshidratación en las semillas de los dos hábitats secos tropicales: bosque y matorral seco, los resultados determinaron que tanto las semillas de las especies leñosas de ambientes más áridos (matorral seco) están en gran medida pre-adaptadas a la desecación que las especies de ambientes menos áridos (bosque seco). Los tratamientos de deshidratación ejercieron un efecto negativo en los porcentajes de germinación en todas las especies, excepto para C. platanifolia. Los resultados más sorprendentes se registraron para Senna alata que mostró germinación extremadamente baja o incluso sin germinación a contenidos de humedad de la semillas de 0,10 g H2O g de peso seco. Las curvas de germinación difirieron significativamente entre los tratamientos de deshidratación en cada especie. Aportar al conocimiento la fisiología de la deshidratación y los límites de tolerancia de las semillas de bosque y matorral seco ayudará a entender mejor el papel de este rasgo en la ecología de las semillas y dinámica de las comunidades áridas tropicales. El estudio demostró, que la adaptación ecológica de las semillas de las especies leñosas de bosque seco a factores ambientales extremos, puede verse reflejada en una red de interacciones y correlaciones complejas entre los propios rasgos morfológicos y fisiológicos continuos y cuantitativos, sobre todo en rasgos internos de las semillas, quienes ejercerían una mayor influencia en toda la red de interacciones. Si bien, los rasgos de las semillas no mostraron fuertes relaciones con las variables ambientales, posiblemente las asociaciones presentes entre rasgos morfológicos pudiesen predecir en cambio interacciones entre especies y comportamientos y procesos relacionados con la tolerancia a la deshidratación y dormición de las semillas. ABSTRACT South America is one of the areas with the largest number of tropical dry forest in the world. However, these forests have been poorly understood and most studies have been directed to tropical rainforests. Dry forests have been drastically reduced and are very threatened, risking desaparecerer in the next years. It is therefore essential, generate applied research for conservation of tropical dry ecosystems. In Ecuador the situation is no different and dry areas classified as biodiverse are under constant threat. The few studies made in Ecuador on drylands have improved our knowledge concerning the diversity and abundance of species, plant-plant relationships and dispersion syndromes. Morphological studies on fruits and seeds of woody dry forest species do not exist. However, our understanding of the dynamics and structure of ecological communities dryland little studied, may improve quickly through the study and functional approach morphophysiological traits. The overall objective of this study was to contribute to the knowledge of the ecology and biology of tropical dry seeds through analysis and evaluation of morphophysiological traits of fruits and seeds of a community of woody species. The study was conducted in an area of dry scrub forest, located at the southwest of Ecuador, at an altitude between 250 to 1200 m asl. Environmental characterized by a marked seasonality, with rainfall from December to April and a dry season from May to November. Annual rainfall of 500 mm with an average annual temperature of 20° to 26 °C. The study area is part of the shared Tumbesina region between southern Ecuador and northern Peru with a great diversity of endemic plant species. For the study, we collected fruit and seed madure of eight and ten individuos of 80 species of trees and shrub most representated of the Ecuador dry forest. We selected a sample of 50 fruits and seeds for different analysis. We measure and evaluate 18 morphological and physiological traits of fruits, seeds and species. We perform analysis and correlation between traits associated with five environmental variables taken from the 109 plots established in the study area also analyze and compare the germination response to dehydration related to two dry communities, scrub and dry forest. The results showed that the species have great heterogeneity in continuous seed traits. Variability was more evident in features such as size, volume, mass, and number of seeds per fruit. However, a high proportion of species tends to produce a seed per fruit. In addition, most of the species of dry forest is characterized by not having some sort of ppendices or areola in its seeds, oval form and without endosperm. The nutrient reserves of seeds are especially in the cotyledons of the embryos. Six different embryos were found and most of the species presented thick and inverted embryos. Seed dispersal zoochory is dominated by 38 %, relative to anemochory (22 %) and autochory (19 %). However, we found that 70 % of the species has dried fruits. The analysis of dormancy from tropical dry forest, showed that 60 % of species showed seed dormancy, down from species found in tropical deciduous forest and savanna, however dormancy dry forest species was higher than the percentage of forest species dormancy semi-evergreen and tropical rain forest. Physical dormancy corresponds to 35 % of species, followed by 12 % with physiological dormancy, while only one species had morphological dormancy. We found that dormancy of the seeds was significantly related to the type and function of the embryo and the endospemo. There were significant relationships between morphological traits of fruits, seeds, embryos and attributes of individuals of 46 species, although in some cases with low correlation coefficients. There was little relationship between the morphologic traits of the seeds with the registered environmental variables. Only the type of tesla and the presence of appendages on the seeds showed relation to pH and the mean soil temperature. However, using the fourth corner-RLQ model, neither clear nor significant between morphological traits of seeds and fruits associations with environmental variables were found. The effect of dehydration on seeds of two tropical dry forest habitats was evident in dry scrub. The results determined that both the seeds of woody species forest and dry scrub are pre-adapted to drier conditions. Dehydration treatments exerted a negative effect on germination percentage in all species, except for C. platanifolia. However, all species germinated in treatments of extreme dryness, but in low percentages. The most striking results were recorded for Senna alata showed no germination when its moisture content was 0.10 g H2O g dry weight. Germination curves differ significantly between the treatments of dehydration in each species. Contribute to the knowledge of physiology and dehydration tolerance limits seeds dry scrub forest and help you better understand the role of this trait in seed ecology and dynamics of tropical arid communities. The study showed that the ecological adaptation of seeds of woody species of dry forest to extreme environmental factors may be reflected in a complex web of interactions and correlations between morphological and physiological traits continuous and quantitative themselves, especially in internal seed traits, who exerted a major influence on the entire network of interactions. While the seed traits showed strong relationships with environmental variables possibly present associations between morphological traits could predict interactions between species and change behaviors related to desiccation tolerance and seed dormancy processes.