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

Respuesta fisiológica y química de clones de Ulmus minor susceptibles y resistentes a la grafiosis tras la inoculación con Ophiostoma novo-ulmi

Los motivos por los que algunos genotipos de Ulmus minor Mill. resisten más que otros a la infección con el hongo patógeno Ophiostoma novo-ulmi son aun desconocida. Con el objetivo de evaluar si la resis- tencia a la enfermedad de la grafiosis está relacionada con la posesión de ciertos rasgos fisiológicos o quí- micos, se compararon clones de U. minor resistentes y susceptibles a la grafiosis, antes y después de la ino- culación con O. novo-ulmi . Se midieron el potencial hídrico, las tasas de respiración y fotosíntesis foliar, y la conductividad hidráulica de ramas terminales y su composición química mediante espectroscopía de infrarrojo (FT-IR). La inoculación con el hongo produjo un aumento en la proporción de vasos emboliza- dos, de modo que a los 21 días la conductividad hidráulica era solo un 20% de la conductividad máxima en los clones susceptibles. Como consecuencia, el potencial hídrico y la fotosíntesis disminuyeron entor- no a un 100-200% en relación a los controles en los clones susceptibles mientras que no hubo reducciones significativas en los resistentes. Además, los clones mostraron una composición química de sus ramas di- ferente. Por ejemplo, en los árboles inoculados con agua utilizados como control, el pico de absorción en la región del espectro infrarrojo relacionado con la suberina fue más alto en los clones resistentes que en los susceptibles.Estos resultados sugieren que el perfil químico más defensivo de los clones resistentes les permite mantener la funcionalidad fisiológica tras la inoculación con O. novo-ulmi prácticamente inalterada, en comparación con los clones más susceptibles

Can we favour growth of multi-centennial beech trees by reducing competition of their offspring?

Evaluación del efecto de reducir la competencia entre hayas en el crecimiento de hayas centenarias y de porvenir

Xylem and soil CO2 fluxes in a Quercus pyrenaica Willd. coppice: Root respiration increases with clonal size

Xylem and soil CO2 fluxes in coppiced oak forests increase with clonal size suggesting larger expenditures of energy for root respiration. An imbalance between root demand and shoot production of carbohydrates may contribute to the degradation of abandoned coppices

Ulmus laevis in the Iberian Peninsula: a review of its ecology and conservation

European white elm (Ulmus laevis Pallas) populations are scarce, small and fragmented in the Iberian Peninsula. Due to these characteristics the indigenous status of the species in the region has been questioned, whilst the species? role in Iberian riparian forest ecology has been neglected. Herein we review past studies regarding this species? distribution and ecology in the Iberian Peninsula, with special emphasis on the establishment of conservation priorities. We first present a collection of palaeogeographic, historic and genetic data suggesting that the Iberian Peninsula was a glacial refuge for U. laevis. Secondly, we analyse U. laevis distribution in relation to soil physico- chemical properties and water availability in Spain. Following this, we focus on the reproductive biology of the species, and investigate the effect of masting and empty seed production on predation and regeneration establishment. Finally, based on this knowledge, we propose conservation policies for U. laevis in the Iberian Peninsula

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

Carbon balance in two resprouting species suffering from massive xylem embolism.

Descripción de los procesos de mortalidad de las plantas cuando son expuestas a sequía con especial énfasis en los procesos hidráulico

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

Limitations to diffusion and biochemical factors affecting leaf carbon uptake were analyzed in young beech seedlings (Fagus sylvtica L.) growing in natural gaps of a beech-wood at the southern limit of the species. Half of the seedlings received periodic watering in addition to natural rainfall to reduce the severity of the summer drought. Plant water status was evaluated by measuring predawn water potential. Basic biochemical parameters were inferred from chlorophyll fluorescence and photosynthesis-CO2 curves (A-Cc) under saturating light. The curves were established on three dates during the summer months. The 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 moderate water stress, as the leaf predawn water potential (Ψpd) measured during the study was within the range –0.2 to –0.5 MPa. 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. In addition, it should be highlighted that 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 understanding of the functional mechanisms influencing the carbon fixation capacity of beech seedlings under natural conditions.Peer reviewe

Increased root investment can explain the higher survival of seedlings of ‘mesic’ Quercus suber than ‘xeric’ Quercus ilex in sandy soils during a summer drought

In Mediterranean-type ecosystems, drought is considered the main ecological filter for seedling establishment. The evergreen oaks Quercus ilex L. and Quercus suber L. are two of the most abundant tree species in the Mediterranean Basin. Despite their shared evergreen leaf habit and ability to resist low soil water potentials, traditionally it has been suggested that Q. ilex is better suited to resist dry conditions than Q. suber. In this study, we examined how seedlings of Q. ilex and Q. suber grown in sandy soils responded to different levels of water availability using natural dry conditions and supplemental watering. Specifically, we estimated survival and water status of seedlings and explored the role of acorn mass and belowground biomass in seedling performance. To our surprise, Q. suber was better able to survive the summer drought in our experiment than Q. ilex. Nearly 55% of the Q. suber seedlings remained alive after a 2-month period without rain or supplemental water, which represents almost 20% higher survival than Q. ilex over the same period. At the end of the dry period, the surviving seedlings of Q. suber had strikingly higher water potential, potential maximum quantum yield of photosystem II (F-v/F-m) and stomatal conductance (g(s)) than those of Q. ilex. Acorn mass was associated with the probability of survival under dry conditions; however, it did not explain the differences in survival or water status between the species. In contrast, Q. suber had a higher root ratio and root: shoot ratio than Q. ilex and these traits were positively associated with predawn leaf water potential, F-v/F-m, g(s) and survival. Taken together, our results suggest that the higher relative investment in roots by Q. suber when growing in a sandy acidic substrate allowed this species to maintain better physiological status and overall condition than Q. ilex, increasing its probability of survival in dry conditions.Peer reviewe