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

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

Hydraulic traits are associated with the distribution range of two closely related Mediterranean firs, Abies alba Mill. and Abies pinsapo Boiss

Abies alba and Abies pinsapo are two closely related fir species that occur in the Iberian Peninsula under very different environmental conditions. Abies alba proliferates in the humid European mountains, including the Spanish Pyrenees. In contrast, A. pinsapo is a relict species that occurs in some restricted areas of the Mediterranean mountain ranges in Spain and Morocco, which experience intense summer drought periods. To cope with the high atmospheric evaporative demand during summer, A. pinsapo may either have a high resistance to xylem cavitation or develop a very efficient conducting system to reduce the soil-to-leaf water potential gradient. To investigate such hypotheses, we measured (i) the xylem vulnerability to cavitation for different populations, and (ii) several anatomical and hydraulic parameters indicating xylem sufficiency for supplying water to the shoot in two contrasting populations of both species. Our results show that the resistance to cavitation was not different between species or populations. However, hydraulic conductivity (Kh), specific hydraulic conductivity (K s), leaf-specific conductivity (LSC) and whole-shoot hydraulic conductance (K shoot) were higher in A. pinsapo, indicating a higher efficiency of water transport, which should contribute to maintaining its xylem tension below the threshold for rapidly increasing cavitation. The higher K s in A. pinsapo was largely a result of its wider tracheids, suggesting that this species may be much more vulnerable to freeze-thaw-induced cavitation than A. alba. This is consistent with the absence of A. pinsapo in northern mountain ranges with cooler winters. These physiological differences could partly explain the niche segregation and the geographical separation of these two firs.Este estudio fue parcialmente financiado por el proyecto CAIXA GA-­LC­-­002/2010 (Departamento de Ciencia, Tecnología y Universidad, Gobierno de Aragón) y por el proyecto AGL2010-21153-C02-02 (Ministerio de Ciencia e Innovación). También se agradece el apoyo financiero del Gobierno de Aragón (grupo de investigación A54).Publishe

Deciduous and evergreen oaks show contrasting adaptive responses in leaf mass per area across environments

Increases in leaf mass per area (LMA) are commonly observed in response to environmental stresses and are achieved through increases in leaf thickness and/or leaf density. Here, we investigated how the two underlying components of LMA differ in relation to species native climates and phylogeny, across deciduous and evergreen species. Using a phylogenetic approach, we quantified anatomical, compositional and climatic variables from 40 deciduous and 45 evergreen Quercus species from across the Northern Hemisphere growing in a common garden. Deciduous species from shorter growing seasons tended to have leaves with lower LMA and leaf thickness than those from longer growing seasons, while the opposite pattern was found for evergreens. For both habits, LMA and thickness increased in arid environments. However, this shift was associated with increased leaf density in evergreens but reduced density in deciduous species. Deciduous and evergreen oaks showed fundamental leaf morphological differences that revealed a diverse adaptive response. While LMA in deciduous species may have diversified in tight coordination with thickness mainly modulated by aridity, diversification of LMA within evergreens appears to be dependent on the infrageneric group, with diversification in leaf thickness modulated by both aridity and cold, while diversification in leaf density is only modulated by aridity

Cambios en el perfil terpénico y en el crecimiento secundario en poblaciones en decaimiento de Pinus sylvestris L. bajo influencia mediterránea en respuesta a factores locales

The terpenoid profile could give information about the water status in Scots pine, especially for trees growing in the same geographical area but under contrasting local environmental conditions. Terpenes were analyzed by gas chromatography-mass spectrometry in needles, twigs and wood of ten affected and ten unaffected Scots pines in the southern “Sistema Ibérico” range (Teruel, Spain), where forest decline has been recently reported. Soil depth and secondary growth was also studied in both types of trees. Needles and twigs total resin acids were significantly higher in affected trees. The pimarane type resin acids were also higher in the twigs of affected trees. Secondary growth was lower in affected trees and it showed higher climate sensitivity. The use of the terpenoid profile may be used as an additional tool for the estimation of the water status, especially for situations inducing moderate but relatively prolonged stress conditions.El perfil terpénico podría dar información sobre el estado hídrico en el pino albar, especialmente cuando se comparen especímenes de una zona geográfica concreta afectados por factores ambientales locales. Los terpenos de acículas, brotes del año y madera fueron analizados en diez ejemplares afectados y otros tantos no afectados por el decaimiento mediante cromatografía de masas acoplada a espectrometría de masas. La serie de crecimiento secundario en ambos tipos de ejemplares fue también estudiada. La concentración total de ácidos resínicos aumentó de modo significativo en los árboles afectados tanto en brotes del año como en acículas. La cantidad de ácidos de tipo pimarano también aumentó en los brotes de los árboles afectados. La profundidad del suelo y el crecimiento secundario era menor en este tipo de ejemplares, que muestran una mayor sensibilidad en términos dendrocronológicos. El perfíl terpénico podría utilizarse como una herramienta adicional a la estimación del estado hídrico, especialmente cuando el árbol está afectado por condiciones de estrés moderadas pero prolongadas en el tiempo

Hydraulic and photosynthetic limitations prevail over root non-structural carbohydrate reserves as drivers of resprouting in two Mediterranean oaks

Resprouting is an ancestral trait in angiosperms that confers resilience after perturbations. As climate change increases stress, resprouting vigor is declining in many forest regions, but the underlying mechanism is poorly understood. Resprouting in woody plants is thought to be primarily limited by the availability of non-structural carbohydrate reserves (NSC), but hydraulic limitations could also be important. We conducted a multifactorial experiment with two levels of light (ambient, 2–3% of ambient) and three levels of water stress (0, 50 and 80 percent losses of hydraulic conductivity, PLC) on two Mediterranean oaks (Quercus ilex and Q. faginea) under a rain-out shelter (n = 360). The proportion of resprouting individuals after canopy clipping declined markedly as PLC increased for both species. NSC concentrations affected the response of Q. ilex, the species with higher leaf construction costs, and its effect depended on the PLC. The growth of resprouting individuals was largely dependent on photosynthetic rates for both species, while stored NSC availability and hydraulic limitations played minor and non-significant roles, respectively. Contrary to conventional wisdom, our results indicate that resprouting in oaks may be primarily driven by complex interactions between hydraulics and carbon sources, whereas stored NSC play a significant but secondary role

Leaf anatomical properties in relation to differences in mesophyll conductance to CO2 and photosynthesis in two related Mediterranean Abies species

Abies alba and Abies pinsapo are closely related species with the same ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit (rbcL) but contrasting hydraulic traits and mesophyll structure occurring in the Iberian Peninsula under contrasting conditions. As photosynthesis and hydraulic capacities often co-scale, we hypothesize that these species differ in mesophyll conductance to CO2 (gm). gm and key anatomical traits were measured in both species. Drought-adapted population of A.pinsapo has higher photosynthesis than the more mesic population of A.alba, in agreement with its higher hydraulic capacity. However, A.alba exhibits the largest stomatal conductance (gs), and so water use efficiency (WUE) is much higher in A.pinsapo. The differences in photosynthesis were explained by differences in gm, indicating a correlation between hydraulic capacity and gm. We report a case where gm is the main factor limiting photosynthesis in one species (A.alba) when compared with the other one (A.pinsapo). The results also highlight the discrepancy between gm estimates based on anatomical measurements and those based on gas exchange methods, probably due to the very large resistance exerted by cell walls and the stroma in both species. Thus, the cell wall and chloroplast properties in relation to CO2 diffusion constitute a near-future research priority. © 2012 Blackwell Publishing Ltd.Este estudio ha sido parcialmente financiado por el proyecto GA-LC-002/2010 de la CAIXA (Departamento de Ciencia, Tecnología y Universidad, Gobierno de Aragón) y por los proyectos AGL2010-21153-C02-02 y BFU2011-23294 (Ministerio de Ciencia e Innovación, España). También se agradece el apoyo financiero del Gobierno de Aragón (grupo de investigación A54). El trabajo de José Javier Peguero-Pina cuenta con el apoyo de un contrato postdoctoral 'Juan de la Cierva'-MICIIN.Publishe

The Application of leaf ultrasonic resonance to vitis vinifera L. suggests the existence of a diurnal osmotic adjustment subjected to photosynthesis

The main objective of this study was to apply the air-coupled broad-band ultrasonic spectroscopy in attached transpiring leaves of Vitis vinifera L. to monitor changes in leaf water potential (9) through the measurements of the standardized value of the resonant frequency associated with the maximum transmitance (f/fo). With this purpose, the response of grapevine to a drought stress period was investigated in terms of leaf water status, ultrasounds, gas exchange and sugar accumulation. Two strong correlations were obtained between f/fo and 9 measured at predawn (pd) and at midday (md) with different slopes. This fact implied the existence of two values of 9 for a given value of f/fo, which was taken as a sign that the ultrasonic technique was not directly related to the overall 9, but only to one of its components: the turgor pressure (P). The difference in 9 at constant f/fo (d) was found to be dependent on net CO2 assimilation (A) and might be used as a rough estimator of photosynthetic activity. It was then, the other main component of 9, osmotic potential (p), the one that may have lowered the values of md 9 with respect to pd 9 by the accumulation of sugars associated to net CO2 assimilation. This phenomenon suggests the existence of a diurnal osmotic adjustment in this species associated to sugars production in well-watered plants