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

Características funcionales que influyen en la respuesta a la sequía de las especies del género Quercus: variación inter- e intra-específica

El género Quercus sp. tiene una amplia distribución geográfica a lo largo de todo el Hemisferio Norte, y está presente desde zonas templado-frías de Europa o Norte-América, hasta zonas tropicales de América del Sur. En términos de macro-evolución son muchas las especies de este género que han desarrollado mecanismos de resistencia al estrés hídrico en combinación con caracteres funcionales y morfológicos que evitan la deshidratación de los tejidos aéreos, y que en último término hacen de este grupo de especies organismos muy efectivos en ambientes caracterizados por una fuerte restricción hídrica esporádica o estacional. La falta de agua, sobre todo en fases como la regeneración, interactúa con la disponibilidad lumínica, y de cuyo resultado se establece una compleja modulación de la expresión de los rasgos funcionales. Además, y desde un punto de vista micro-evolutivo, es elemento característico de muchas especies de Quercus un alto grado de variación genética intraespecífica en la respuesta a sequía. Esta diversidad en la respuesta se establece bajo distintos órdenes jerárquicos de variación genética, y desde diferencias poblacionales hasta líneas maternas o individuos dentro de una misma población. Así, muchas especies albergan unos niveles relativamente altos de variabilidad intraespecífica en respuesta a la falta de agua. En este trabajo se revisan diferentes mecanismos de tolerancia y evitación de la sequía que explican el éxito de numerosas especies del género Quercus en ambientes con importantes limitaciones hídricas. El análisis se hace extensible a los estudios de la variación intra-específica, para finalizar con una breve visión de algunos posibles patrones de respuesta esperables en un futuro caracterizado por ambientes hídricamente más estresantes en amplias zonas del mundo, y en particular en el área mediterránea

Species-specific water use by forest tree species: from the tree to the stand

Forests play a critical role in the hydrological cycle making the study of water use by trees and forest stands of prime importance in the global change context .Very negative effects of increasing and more intense droughts on forest vegetation have been described over the last decades. Symptoms of disease and decline have been associated with changed precipitation patterns in many forests particularly in European temperate and Mediterranean regions. Intra- and inter-specific differences in both physiology and morphology exert a large but not well understood influence on the water balance of forest ecosystems, further affecting their vulnerability to drought. Stand structure and composition influences rainfall interception, runoff and water fluxes of the whole ecosystem. Both expanding plantations of renovated interest for biofuel industry and natural and semi-natural forests must be managed in a sustainable way on the basis of their water consumption. We review the role of key drivers on forest water use such as species composition, tree canopy status of each of them and species specific sensitivity to soil water scarcity. Specifically we discuss the role of these factors for natural forest, but with references also to forest plantations. Water scarcity is expected to be one of the largest societal problems worldwide in the near future, so water use by natural and planted forest ecosystems has become a central subject in current research agendas.This work was supported by the INIA and Ministry of Economy and Competitiveness (grants SUM2008-00004-C03-01 and AGL2011-25365).Peer reviewe

Evaluación precoz de la resistencia a la sequía inducida con polietilénglicol en cultivos hidropónicos de especies forestales

El estadio juvenil supone una de las fases más críticas para todas las plantas. Uno de los factores que inciden de manera determinante en la supervivencia durante las primeras etapas de desarrollo en áreas con clima mediterráneo es la sequía. Con objeto de profundizar en el conocimiento del comportamiento adaptativo de los distintos materiales de base de pinos mediterráneos, se han puesto a punto técnicas para la evaluación precoz bajo condiciones de estrés hídrico en cultivo hidropónico utilizando PEG-8000. En el presente estudio se evaluó la respuesta de dos procedencias de Pinus canariensis y una de Pinus pinaster a tres tratamientos: control, estrés moderado (-1 MPa) y estrés fuerte (-2 Mpa). Se encontraron diferencias significativas en el reparto de biomasa entre las plantas no sometidas a estrés y las plantas estresadas, destinando estas últimas mayor porcentaje de biomasa a las raíces que al sistema aéreo. El potencial osmótico de Pinus pinaster se mantuvo más elevado durante todo el tratamiento que en las dos procedencias de Pinus canariensis, indicando mayor capacidad de ajuste osmótico de las procedencias canarias en condiciones prolongadas de estrés hídrico. Las diferencias en contenido hídrico relativo se detectaron sólo los últimos días del ensayo. Las plántulas de pino canario de ambas procedencias sometidas al mayor nivel de estrés absorbieron su médula, presentando tallos huecos en la cosecha final

Differences in the leaf functional traits of six beech (Fagus sylvatica L.) populations are reflected in their response to water limitation

Patterns of intraspecific variation in functional traits have been widely studied across plant species to find out what general suites of traits provide functional advantage under specific environmental conditions. Much less is known about this variation within tree species and, in particular, about its relationship with performance variables such as photosynthetic rates under water deficit. Nevertheless, this knowledge is fundamental to understand the adaptive potential of drought sensitive tree species to increased aridity as predicted in the context of climate change. Intraspecific variation in photosynthetic performance and other leaf functional traits in response to water availability were examined in a glasshouse experiment using seedlings of six European beech populations. The physiological response of seedlings to a “water stress” treatment was compared to a “control” treatment along an experimental cycle of progressive soil water deficit and recovery. We found evidence of intraspecific variation in beech's photosynthetic performance and other leaf functional traits in response to water availability. We also detected intraspecific variation in leaf-level tolerance of water deficit and phenotypic plasticity to water availability suggesting a pattern shaped by both regional and local scale effects. The Swedish population was particularly sensitive to water deficit, being the only population showing impaired photochemical efficiency under the experimental water deficit. Leaf-level tolerance of water deficit was related to PNUE, but not to other functional traits, such as WUE, SLA or leaf nitrogen content, that have been described to vary across species in adaptation to drought tolerance. Our results support the idea that general trends for variation in functional traits across species do not necessarily reflect a similar pattern when observed at the intraspecific level. The observed functional variation between beech populations reaffirms the importance of local adaptation to water deficit in the context of climate changePeer ReviewedClimate changeGas exchangeIntraspecific variabilityNitrogen contentPhotochemical efficiencyPhotosynthesisSpecific leaf areaStomatal conductanceWater-use efficiencyWater stressPublishe

Dehydrins in maritime pine (Pinus pinaster) and their expression related to drought stress response

Maritime pine (Pinus pinaster) is an important commercial species throughout its Atlantic distribution. With the anticipated increase in desiccation of its habitat as a result of climate change, the selection of genotypes with increased survival and growth capability under these conditions for breeding programs is of great interest for this species. We aimed to study the response to a realistic drought stress under controlled conditions, looked for a method to measure dehydration resistance, and analyzed dehydrin expression in drought-resistant and drought-sensitive clones from different ecotypes. We report here the sequence characteristics and the expression patterns of five dehydrins from P. pinaster, along with the physiological characterization of drought stress responses in different genotypes (clonally replicated plants), originating from a broad geographical distribution across France and Spain (provenances). In total, we distinguished five different dehydrin genes in silico, grouped into two types—K2 and SKn. Three of the dehydrin genes had several sequence variants, differing by multiple or single amino acid substitutions. Only two of the dehydrins (PpinDhn3 and PpinDhn4) showed an increase in transcription with increased drought stress which was dependent on provenance and genotype, suggesting their involvement in drought resistance. The other dehydrins showed decreased expression trends with increased severity of the drought stress. The lack of close association between the drought stress and expression patterns of these dehydrin genes suggest that they could have other functions and not be involved in drought resistance. Our results suggest large differences in function between different dehydrin genes

Stomatal and non-stomatal limitations on leaf carbon assimilation in beech (Fagus sylvatica L.) seedlings enduring moderate water stress under natural conditions

Seasonal variation and the differential effect of drought on photosynthetic parameters involved in carbon assimilation in forest species have been poorly studied under natural conditions. Limitations to diffusion and biochemical factors affecting leaf carbon uptake were analyzed in young beech seedlings (Fagus sylvatica L.) growing in natural gaps of a beech-wood at the southern limit of the species. Half of the seedling received periodic watering in addition to natural rainfall to reduce the severity of the summer drought which is typical in the area. Plant water status was evaluated by measuring predawn water potential. Basic biochemical parameters were inferred from photosynthesis-CO2 curves (A-Cc) under saturating light and chlorophyll fluorescence. The curves were established on three dates during the summer months Main variables studied included: stomatal and mesophyll conductance to CO2 (gs and gm respectively), maximum velocity of carboxylation (Vcmax) and maximum electron transport capacity (Jmax). The gm was estimated by two methodologies: the curve-fitting and J constant methods. Seedlings withstood a moderate water stress as the leaf predawn water potential (Ψpd) measured during the study was within the range –0.2 to –0.5 MPa. A mild drought caused gs and gm to decrease only slightly in response to Ψpd. However both diffusional parameters explained most of the limitations to CO2 uptake. Furthermore, non-stomatal limitations were also important limiting net photosynthesis as water stress increased. In addition, it should be highlighted that the biochemical limitations, prompted by Vcmax and Jmax, were related mainly to ontogenic factors, without any clear relationship with drought under the moderate water stress experienced by beech seedlings through the study. The results may help to further understand of the functional mechanisms influencing carbon fixation capacity of beech seedlings. This capacity may influence the total carbon balance of beech seedlings, and feed forward to their growth and survival under drought-prone environments such as those in the south of Europe.Peer reviewe

Obtaining Requirements for Designing a Tool to Support Distributed Development

Abstract: The Distributed Software Development involves various challenges, many of which are related to the lack of trust experienced by team members since they often do not know each other personally. Other problems which are already considered to be classic are related to communication, coordination and collaboration. Bearing in mind that providing information about co-workers may increase both the team spirit and the team members' confidence in each other, we have carried out surveys to discover what information might be useful in attaining this objective, and to reduce those problems related to the three 'c's. The results of the questionnaires have been analyzed from different points of view, first by differentiating the respondents' roles and then by analyzing their specific use in communication, coordination and control activities. The results of this analysis have allowed us to obtain the requirements needed to design a tool with which to support global software development. The implementation of this tool is also described in this paper