Surface Density of the Spongy and Palisade Parenchyma Layers of Leaves Extracted From Wideband Ultrasonic Resonance Spectra

The wide band and air-coupled ultrasonic resonant spectroscopy together with a modified Simulated Annealing metaheuristic algorithm and a 1D layered acoustic-model are used to resolve the structure of plant leaves. In particular, this paper focuses on the extraction of the surface density of the different layers of tissue in leaves having a relatively simple structure. There are three main reasons to select the surface density as the focus of this study: (i) it is a parameter directly extracted by the proposed technique and it requires no further processing, (ii) it is relevant in order to study the dynamic of the water within the different tissues of the leaves and also to study the differential development of the different tissues, and (iii) unlike other parameters provided by this technique (like resonant frequency, impedance, ultrasonic elastic modulus, or ultrasonic damping), this parameter can be easier to understand as it is a direct measure of mass per unit surface. The selection of leaves with a simple structure is justified by the convenience of avoiding an unnecessary complication of the data extraction step. In this work, the technique was applied to determine the surface density of the palisade and spongy parenchyma layers of tissue of Ligustrum lucidum, Vitis vinifera, and Viburnum tinus leaves. The first species was used to study the variation of the surface density at full turgor with the thickness of the leaf, while the two other species were used to study the variation of the surface densities with the variation in the leaf relative water content. Consistency of the results with other conventional measurements (like overall surface density, and cross-section optical and cryo-SEM images) is discussed. The results obtained reveal the potential of this technique; moreover, the technique presents the additional advantage that can be applied in-vivo as it is completely non-invasive, non-destructive, fast, and equipment required is portable

Estudio dendroecológico del ataque de Epinotia subsequana Hw. (Lepidoptera: Tortricidae) sobre un abetar (Abies alba Mill.) del Pirineo aragonés (Diazas, Torla)

We found many narrow or missing annual tree-rings during the period from 1996 to 1998 in most of fir trees sampled in the Diazas forest (Torla; 42º 37’ 50’’ N, 0º 05’ 40’’ W, 1528 m a.s.l.). These tree-rings were synchronic with attacks in that area of the leaf miner Epinotia subsequana Hw. (Lepidoptera). This temporal coincidence motivated this dendroecological study. The radial growth in Diazas was compared with that observed in other 13 fir forests sampled across the Aragón Pyrenees and not affected by E. subsequana. During the 1996-98 period, the radial growth in Diazas was 12-22 % with respect to the mean growth in the rest of stands. The decrease of radial growth during these three years was the cause of the high frequency of missing rings. These were rarely found in others fir forests. This fact suggested that some local factor have caused the growth reduction. The lower radial growth was produced by the intense defoliations done by E. subsequana. The most pronounced reduction of growth was observed in 1997, one year after the maximum level of defoliation was reached (1996). This temporal lag may be due to the fact that the defoliation observed in 1996 reduced the reserves and growth potential to form the tree-ring in the next year. In fact, the radial growth did not increase notably until 3 years (1999) after the first intense growth reduction (1996) was observedLa presencia de anillos anuales de crecimiento estrechos o ausentes entre 1996 y 1998 en la mayoría de los árboles muestreados en el abetar de Diazas (Torla; 42  37’ 50’’ N, 0 05’ 40’’ W, 1528 m s.n.m.) y su coincidencia en el tiempo con ataques del lepidóptero minador Epinotia subsequana Hw. en la zona motivó el siguiente estudio dendroecológico. Se comparó el crecimiento radial del abetar de Diazas con el observado en otros 13 abetares muestreados a lo largo del Pirineo aragonés y no afectados por E. subsequana. Durante el período 1996-98, el crecimiento radial en Diazas fue de un 12-22 % respecto al crecimiento medio del resto de abetares. La reducción del crecimiento radial durante estos tres años también se manifestó en la elevada frecuencia de anillos ausentes, que raramente aparecían en el resto de abetares estudiados. Este hecho sugería que algún factor había actuado de forma local causando la reducción de crecimiento. El menor crecimiento radial fue producto de las intensas defoliaciones producidas por E. subsequana. La reducción más pronunciada del crecimiento radial se produjo en 1997, un año después de que la defoliación alcanzara niveles máximos (1996). Este desfase temporal puede deberse a que la defoliación observada en 1996 disminuyera las reservas y redujera así la capacidad de crecimiento para la producción del anillo del año posterior. De hecho, el crecimiento radial no aumentó de forma notable hasta tres años (1999) después de la primera reducción intensa de crecimiento (1996)

Un nuevo medidor de flujo de alta presión para la estimación de la resistencia hidráulica en brotes completos de plantas leñosas

A new high-pressure flowmeter has been developed and used to estimate hydraulic resistance in whole shoots of woody plants. It is based on the perfusion of pressurized water in the plant, and the simultaneous measurement of water flow (introduced volume of water per unit of time). This device was first calibrated, and then used to estimate the hydraulic resistance of stems and leaves in 1-yr seedlings of broadleaf Quercus species (Q. rubra, Q. cerris, Q. velutina, Q. petraea, Q. frainetto, Q. pyrenaica). The measured values are reliable and similar to those reported in the literature, but taking into account that this study dealt with seedlings. We have found significant differences between species and groups of species according to their hydraulic resistance values for stems and leaves. Those species whose seedlings showed lower leaf hydraulic resistance values can rehydrate their leaves more quickly and survive in environments with certain water stress (e.g., Q. pyrenaica). The high leaf hydraulic resistance of other species indicate that they can not resist these levels of water stress (e.g, Q. rubra). This study provided new insight to the importance of leaf hydraulic resistance as an adaptative trait to face water stress. Hydraulic resistance variability must be studied in depth as an additional mechanism within a wide array of morphological and ecophysiological adaptations that provide tree species a greater drought tolerance.Se ha desarrollado y utilizado un nuevo medidor de flujo de alta presión para plantas leñosas. Su principio de funcionamiento consiste en perfundir agua a presión a través de la planta y, simultáneamente, medir el flujo del líquido (volumen de agua introducida en la planta por unidad de tiempo). Este dispositivo ha sido primero calibrado y después empleado para estimar la resistencia hidráulica de tallos y hojas de plántulas de especies no esclerófilas del género Quercus (Q. rubra, Q. cerris, Q. velutina, Q. petraea, Q. frainetto, Q. pyrenaica). Los valores obtenidos son fiables y comparables a los de la literatura pero teniendo en cuenta que se han estudiado plántulas. Se han encontrado diferencias significativas entre especies y grupos de especies en cuanto a la resistencia hidráulica de hojas y tallos. Las especies cuyas plántulas muestran menor resistencia hidráulica de hojas pueden rehidratarlas de forma más rápida y así sobrevivir en medios con cierto estrés hídrico como los mediterráneos (p. ej. Q. pyrenaica). La elevada resistencia hidráulica de las hojas de otras especies indica que éstas no podrán soportar este estrés hídrico (p. ej. Q. rubra). Se ha puesto de manifiesto la importancia de la resistencia hidráulica foliar como adaptación frente al estrés hídrico. Debe profundizarse en el estudio de la variabilidad de la resistencia hidráulica como un mecanismo adicional dentro del amplio conjunto de adaptaciones morfológicas y ecofisiológicas que confieren a las especies arbóreas mayor tolerancia frente a la sequía

Drought and Forest Decline in the Iberian Peninsula: A Simple Explanation for a Complex Phenomenom?

Different episodes of forest decline have been reported in several areas of the Northern Hemisphere during the 20th century. The explanation of this process included anthropogenic (air pollution), biotic (pathogens) and climatic factors. Among the climatic factors, the effects of acute or chronic droughts have been the most common explanation for the massive dieback observed. In the Iberian Peninsula, besides the pathogenic explanation which gives a paramount relevance to the fungus Phytophtora cinnamomi in many situations, the role of an increment in aridity (chronic) or the consequences of severe droughts (acute) have been empirically supported. The evident synchronism between forest decline and abnormally adverse climatic conditions, in addition to the reversibility of the process when precipitation intensity increased, are two major arguments for supporting the climatic involvement in the phenomenon. Nevertheless, the two most affected species in the episodes of oak decline in the Iberian Peninsula were Quercus ilex and Q. suber, which are representatives of the so called Mediterranean woody flora and which have been considered as more drought resistant than the temperate oak species that co-occur in this territory. The climatic complexity ofthe Iberian Peninsula, the many mechanisms for coping with water stress that have been described within the sclerophyllous Mediterranean flora and the effects of human management partially explain this paradox. Other forest species have also been affected by massive decline. Pinus sylvestris and Abies alba, which have their southern distribution limit in the mountain ranges of the Iberian Peninsula, are two examples of this situation. Both cases, besides the inmediate effects of some climatic perturbations, need the incorporation of different predisposing factors – mainly historical aspects to obtain a complete image of the process

Non-contact ultrasonic resonant spectroscopy resolves the elastic properties of layered plant tissues

This paper describes the application of the wide-band non-contact ultrasonic resonant spectroscopy technique to layered plant tissues (leaves), a method to extract the properties of main component tissues: palisade parenchyma and spongy mesophyll, a verification of the obtained properties, and a discussion of the implications of the observed elastic anisotropy. Transmission coefficient spectra of Ligustrum lucidum leaves with the thickness in the range of 250-850 µm revealing several order thickness resonances have been measured. A leaf acoustic model based on a two-layered structure and a metaheuristic (simulated annealing algorithm) is used to solve the inverse problem. The extracted parameters of these two layers of tissue are consistent with cross-sectional cryo-SEM images and other independent measurements. The extracted resonant frequency and the impedance of each layer explain the origin of the observed resonances. Finally, the elastic modulus of each layer is extracted and analyzed. The presented technique is a unique tool to study (in vivo and in a completely non-invasive way) the ultrasonic, elastic, and viscoelastic properties of layered plant tissues which could lead to a better understanding of the relationship between the tissue microstructure and the tissue function with macroscopic properties and how this may affect water relations

Cuticular wax coverage and its transpiration barrier properties in Quercus coccifera L. leaves: does the environment matter?

Plants prevent uncontrolled water loss by synthesizing, depositing and maintaining a hydrophobic layer over their primary aerial organs-the plant cuticle. Quercus coccifera L. can plastically respond to environmental conditions at the cuticular level. When exposed to hot summer conditions with high vapour-pressure deficit (VPD) and intense solar radiation (Mediterranean atmospheric conditions; MED), this plant species accumulates leaf cuticular waxes even over the stomata, thereby decreasing transpirational water loss. However, under mild summer conditions with moderate VPD and regular solar radiation (temperate atmospheric conditions; TEM), this effect is sharply reduced. Despite the ecophysiological importance of the cuticular waxes of Q. coccifera, the wax composition and its contribution to avoiding uncontrolled dehydration remain unknown. Thus, we determined several leaf traits for plants exposed to both MED and TEM conditions. Further, we qualitatively and quantitatively investigated the cuticular lipid composition by gas chromatography. Finally, we measured the minimum leaf conductance (gmin) as an indicator of the efficacy of the cuticular transpiration barrier. The MED leaves were smaller, stiffer and contained a higher load of cuticular lipids than TEM leaves. The amounts of leaf cutin and cuticular waxes of MED plants were 1.4 times and 2.6 times higher than that found for TEM plants, respectively. In detail, MED plants produced higher amounts of all compound classes of cuticular waxes, except for the equivalence of alkanoic acids. Although MED leaves contained higher cutin and cuticular wax loads, the gmin was not different between the two habitats. Our findings suggest that the qualitative accumulation of equivalent cuticular waxes might compensate for the higher wax amount of MED plants, thereby contributing equally to the efficacy of the cuticular transpirational barrier of Q. coccifera. In conclusion, we showed that atmospheric conditions profoundly affect the cuticular lipid composition of Q. coccifera leaves, but do not alter its transpiration barrier properties

Cuticular wax coverage and its transpiration barrier properties in Quercus coccifera L. leaves: does the environment matter?

Plants prevent uncontrolled water loss by synthesizing, depositing and maintaining a hydrophobic layer over their primary aerial organs-the plant cuticle. Quercus coccifera L. can plastically respond to environmental conditions at the cuticular level. When exposed to hot summer conditions with high vapour-pressure deficit (VPD) and intense solar radiation (Mediterranean atmospheric conditions; MED), this plant species accumulates leaf cuticular waxes even over the stomata, thereby decreasing transpirational water loss. However, under mild summer conditions with moderate VPD and regular solar radiation (temperate atmospheric conditions; TEM), this effect is sharply reduced. Despite the ecophysiological importance of the cuticular waxes of Q. coccifera, the wax composition and its contribution to avoiding uncontrolled dehydration remain unknown. Thus, we determined several leaf traits for plants exposed to both MED and TEM conditions. Further, we qualitatively and quantitatively investigated the cuticular lipid composition by gas chromatography. Finally, we measured the minimum leaf conductance (gmin) as an indicator of the efficacy of the cuticular transpiration barrier. The MED leaves were smaller, stiffer and contained a higher load of cuticular lipids than TEM leaves. The amounts of leaf cutin and cuticular waxes of MED plants were 1.4 times and 2.6 times higher than that found for TEM plants, respectively. In detail, MED plants produced higher amounts of all compound classes of cuticular waxes, except for the equivalence of alkanoic acids. Although MED leaves contained higher cutin and cuticular wax loads, the gmin was not different between the two habitats. Our findings suggest that the qualitative accumulation of equivalent cuticular waxes might compensate for the higher wax amount of MED plants, thereby contributing equally to the efficacy of the cuticular transpirational barrier of Q. coccifera. In conclusion, we showed that atmospheric conditions profoundly affect the cuticular lipid composition of Q. coccifera leaves, but do not alter its transpiration barrier properties

Elevated atmospheric CO2 modifies responses to water-stress and flowering of Mediterranean desert truffle mycorrhizal shrubs

Predicted increases in atmospheric concentration of carbon dioxide (CO2) coupled with increased temperatures and drought are expected to strongly influence the development of most of the plant species in the world, especially in areas with high risk of desertification like the Mediterranean basin. Helianthemum almeriense is an ecologically important Mediterranean shrub with an added interest because it serves as the host for the Terfezia claveryi mycorrhizal fungus, which is a desert truffle with increasingly commercial interest. Although both plant and fungi are known to be well adapted to dry conditions, it is still uncertain how the increase in atmospheric CO2 will influence them. In this article we have addressed the physiological responses of H. almeriense × T. claveryi mycorrhizal plants to increases in atmospheric CO2 coupled with drought and high vapor pressure deficit. This work reports one of the few estimations of mesophyll conductance in a drought deciduous Mediterranean shrub and evaluates its role in photosynthesis limitation. High atmospheric CO2 concentrations help desert truffle mycorrhizal plants to cope with the adverse effects of progressive drought during Mediterranean springs by improving carbon net assimilation, intrinsic water use efficiency and dispersal of the species through increased flowering events

Wettability, polarity and water absorption of Quercus ilex leaves: effect of leaf side and age

Plant trichomes play important protective functions and may have a major influence on leaf surface wettability. With the aim of gaining insight into trichome structure, composition and function in relation to water-plant surface interactions, we analyzed the adaxial and abaxial leaf surface of Quercus ilex L. (holm oak) as model. By measuring the leaf water potential 24 h after the deposition of water drops on to abaxial and adaxial surfaces, evidence for water penetration through the upper leaf side was gained in young and mature leaves. The structure and chemical composition of the abaxial (always present) and adaxial (occurring only in young leaves) trichomes were analyzed by various microscopic and analytical procedures. The adaxial surfaces were wettable and had a high degree of water drop adhesion in contrast to the highly unwettable and water repellent abaxial holm oak leaf sides. The surface free energy, polarity and solubility parameter decreased with leaf age, with generally higher values determined for the abaxial sides. All holm oak leaf trichomes were covered with a cuticle. The abaxial trichomes were composed of 8% soluble waxes, 49% cutin, and 43% polysaccharides. For the adaxial side, it is concluded that trichomes and the scars after trichome shedding contribute to water uptake, while the abaxial leaf side is highly hydrophobic due to its high degree of pubescence and different trichome structure, composition and density. Results are interpreted in terms of water-plant surface interactions, plant surface physical-chemistry, and plant ecophysiology

Physico-chemical properties of plant cuticles and their functional and ecological significance

Most aerial plant surfaces are covered with a lipid-rich cuticle, which is a barrier for the bidirectional transport of substances between the plant and the surrounding environment. This review article provides an overview of the significance of the leaf cuticle as a barrier for the deposition and absorption of water and electrolytes. After providing insights into the physico-chemical properties of plant surfaces, the mechanisms of foliar absorption are revised with special emphasis on solutes. Due to the limited information and relative importance of the leaf cuticle of herbaceous and deciduous cultivated plants, an overview of the studies developed with Alpine conifers and treeline species is provided. The significance of foliar water uptake as a phenomenon of ecophysiological relevance in many areas of the world is also highlighted. Given the observed variability in structure and composition among, for example, plant species and organs, it is concluded that it is currently not possible to establish general permeability and wettability models that are valid for predicting liquid-surface interactions and the subsequent transport of water and electrolytes across plant surfaces.Este estudio ha sido parcialmente financiado por el Ministerio de Economía y Competitividad (RTA2015-00054-C02-01) y por el Gobierno de Aragón (grupo de investigación H38). El trabajo de DSK está respaldado por un contrato DOC INIA cofinanciado por el Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA) y el Fondo Social Europeo (FSE).Publishe