Article

Different vulnerabilities of Quercus ilex L. to freeze- and summer drought-induced xylem embolism: an ecological interpretation

June 1993
Plant Cell and Environment 16(5):511-519

June 1993
16(5):511-519

DOI:10.1111/j.1365-3040.1993.tb00898.x

Authors:

Università degli Studi di Messina

Quercus ilex L. growing in the southern Mediterranean Basin region is exposed to xylem embolism induced by both winter freezing and summer drought. The distribution of the species in Sicily could be explained in terms of the different vulnerability to embolism of its xylem conduits. Naturally occurring climatic conditions were simulated by: (1) maintaining plants for 3h at ambient temperatures of 0, - 1-5, - 2 5, - 5 0 and - 11 °C; and (2) allowing plants to dry out to ratios of their minimum diurnal leaf water potentials (Yl) to that at the turgor loss point (Ytlp) of 0 6, 0 9,1 05, 1 20 and 1-33. The loss of hydraulic conductivity of one-year-old twigs reached 40% at - 1 5°C and at Yl/Ytlp = 1 05. Recovery from these strains was almost complete 24 h after the release of thermal stress or after one irrigation, respectively. More severe stresses reduced recovery consistently. The percentages of xylem conduits embolized following application of the two stresses, were positively related to xylem conduit diameter. The capability of the xylem conduits to recover from stress was positively related to the conduit diameter in plants subjected to summer drought, but not in the plants subjected to winter freezing stress. The ecological significance of the different vulnerabilities to embolism of xylem conduits under naturally occurring climatic conditions is discussed.

Significado funcional de la madera en el género Eucalyptus: relaciones entre microestructura y mecanismos de resistencia a estrés por sequía y heladas

Thesis

Full-text available

May 2021

Antonio José Barotto

En español: La capacidad de transporte de agua dentro de los árboles, a través del xilema, se relaciona funcionalmente con su capacidad de fijación de carbono y, por lo tanto, con su crecimiento y supervivencia. Este proceso se ve afectado, de manera más o menos reversible, por el fenómeno de cavitación, consistente en la ruptura de la columna de agua, debida fundamentalmente a dos procesos: el aumento de la tensión en el xilema durante procesos de sequía y los ciclos de congelamiento y descongelamiento del agua durante las heladas. La estructura anatómica de la madera juega un rol clave en la estrategia hidráulica de las plantas, con implicancias directas en el proceso de cavitación y, por lo tanto, en su fisiología y ecología, por lo que su estudio permite evaluar cómo varía el transporte de agua dentro del xilema en función del estrés abiótico. El estudio de las relaciones entre estructura y función hidráulica de la madera, a nivel inter- e intraespecífico, adquiere especial relevancia frente a un escenario de cambio climático, en el cual se prevé el aumento de sequías y extremos térmicos. El objetivo general de esta tesis fue conocer el valor funcional de la microestructura de la madera de Eucalyptus spp. en relación con ciertas variables descritas por la bibliografía referente al tema como claves para explicar la resistencia a sequía y heladas en especies leñosas. Este género, de gran importancia comercial a nivel mundial, se caracteriza por poseer una compleja anatomía de la madera, poco conocida en términos funcionales. En particular, uno de los objetivos que se plantearon fue analizar y comparar la estructura anatómica de cuatro especies de Eucalyptus, caracterizadas por poseer un amplio rango de variación en densidad de madera y requerimientos de hábitat. Se hipotetizó que existe una relación en la resistencia general al estrés abiótico que puede ser explicada por las características diferenciales de su madera (estudiada a nivel de ramas y fustes), las cuales determinan, en última instancia, los requerimientos ambientales de las diferentes especies. Otro objetivo particular se centró en relacionar la estructura anatómica de la madera con parámetros funcionales como conductividad hidráulica específica máxima, capacitancia y vulnerabilidad a la cavitación por frío y por sequía. Se hipotetizó que las tasas máximas de conductividad hidráulica se relacionan positivamente con el tamaño de los elementos conductivos, mientras que la seguridad hidráulica se relaciona con las características de los elementos celulares asociados a éstos (traqueidas vasicéntricas, fibrotraqueidas y parénquima). Los resultados hallados permitieron validar parcialmente estas hipótesis ya que, por un lado, la relación directa entre la resistencia a la cavitación por sequía medida en laboratorio y el desempeño a campo indicaría que este último está influenciado principalmente por las características anatómicas de la madera. Por otro lado, la relación inversa entre resistencia a la cavitación por congelamiento/ descongelamiento y la resistencia a las heladas indicaría que estos procesos se encuentran determinados por las características de otros órganos. Si bien la influencia significativa del tamaño de los vasos en el nivel de conductividad fue confirmada en los diferentes capítulos de esta tesis (vasos más grandes y mayor amplitud en la distribución de tamaños, presentan mayor eficiencia conductiva), el rol de las células acompañantes de los vasos en la seguridad del sistema fue parcialmente verificado. Así, en el caso de la cavitación por sequía, se encontró evidencia del rol de estos elementos en la protección del sistema de conducción, por un lado, aumentando la conectividad hidráulica entre vasos solitarios y, al mismo tiempo, limitando la propagación de aire (y, por ende, de embolismos) entre elementos conductivos cercanos. Por el contrario, en la cavitación por frío, los resultados indican que este proceso está directamente relacionado con el tamaño de los elementos conductivos, sin efectos significativos por parte de las células acompañantes. Por otro lado, los vasos más grandes no solo presentaron mayor conductividad sino también menor vulnerabilidad a la cavitación por tensión, lo cual sería explicado por la relación inversa entre el tamaño de los elementos conductivos y de sus punteaduras. Las relaciones entre anatomía y función de la madera se estudiaron a nivel interespecífico, pero también a nivel intraespecífico en dos de las especies, E. viminalis y E. globulus, a través del análisis de progenies con diferencias en densidad media. Varias de las relaciones observadas a nivel interespecífico se verificaron también dentro de las especies, aunque el menor rango de variación de los caracteres de madera en este nivel de organización resultó en cambios en el nivel de significancia y signo de algunas relaciones. El tercer objetivo particular fue determinar las relaciones existentes entre los espectros de absorción de infrarrojo cercano (NIR) de la madera de Eucalyptus y su anatomía y función, de manera de contribuir al desarrollo de metodologías de selección genética en base a caracteres adaptativos de fácil cuantificación. En este sentido, fue posible establecer calibraciones entre espectros NIR y las características anatómicas, físicas e hidráulicas de la madera de Eucalyptus y generar modelos de predicción con diferente grado de ajuste. Entre estos últimos se destacan aquellos desarrollados para los parámetros de la curva de cavitación que definen el potencial al cual se pierde el 12 y el 88% de la conductividad máxima y la pendiente entre estos dos puntos, que define la velocidad del proceso de cavitación. Estos resultados son los primeros de su tipo reportados para especies de Eucalyptus, en particular, y Angiospermas, en general. Los resultados de esta tesis permiten afirmar que la particular estructura anatómica de la madera del género Eucalyptus determina la existencia de complejas relaciones entre anatomía y función, las cuales regulan, en diferente grado según el estrés considerado, la capacidad de adaptación al ambiente de las especies de este género. En este sentido, se halló evidencia acerca de una falta de compromiso entre eficiencia y seguridad hidráulica frente a la cavitación por sequía, pero se observó una compensación entre ambos procesos en el caso de la cavitación por frío. El potencial compromiso funcional en la resistencia a ambos tipos de estrés, se evitaría mediante la separación espacial de los mecanismos de control de estos procesos, ubicándose en órganos diferentes. Esto, por un lado, explicaría las diferencias observadas en la resistencia al estrés por frío a campo y en laboratorio y, por otro, permitiría mejorar la resistencia a ambos tipos de estrés de manera simultánea. En este sentido, el establecimiento de modelos predictivos de características anatómicas, físicas e hidráulicas por métodos de fenotipado de alto rendimiento permitiría mejorar el proceso de selección de genotipos resistentes dentro de los programas de mejoramiento forestal. IN english: Water transport capacity within trees, through xylem, is functionally related to their carbon fixation capacity and, therefore, to their growth and survival. This process is affected, more or less reversibly, by the cavitation phenomenon, consisting of the water column breakage, mainly due to two processes: the increase in xylem tension during drought and the freezing/thawing cycles of water during frost. Wood anatomic structure plays a key role in the hydraulic strategy of plants, with direct implications in the cavitation process and, therefore, in their physiology and ecology, and its study allows to evaluate how water transport varies within xylem as a function of abiotic stress. The study of the relationships between wood structure and hydraulic function, at inter- and intraspecific level, becomes especially relevant in a climate change scenario, in which an increase in droughts and thermal extremes are expected. The general objective of this thesis was to understand the functional value of Eucalyptus spp. wood microstructure in relation to certain traits described by the reference literature as keys to explain the resistance to drought and frost in woody species. This genus, of great commercial importance worldwide, is characterized by having a complex wood anatomy, little known in functional terms. In particular, one of the objectives was to analyze and compare the anatomical structure of four Eucalyptus species, characterized by having a wide variation range of wood density and habitat requirements. It was hypothesized that there is a relationship in general resistance to abiotic stress that can be explained by wood differential characteristics (studied at branch and stem level), which ultimately determine the environmental requirements of the different species. Another particular objective was focused on the relationship between wood anatomical structure and functional parameters like maximum specific hydraulic conductivity, capacitance and vulnerability to cavitation due to frost and drought. It was hypothesized that maximum rates of hydraulic conductivity are positively related with the size of conductive elements, while hydraulic security is related to the characteristics of vessel related cellular elements (vasicentric tracheids, fibre tracheids and parenchyma). The results obtained in this work allows to partially validate the established hypotheses since, on the one hand, the direct relationship between drought cavitation resistance measured in laboratory and the field performance of species indicates that the latter is mainly influenced by wood characteristics. On the other hand, the inverse relationship between the resistance to freeze/thaw induced cavitation and frost tolerance indicates that these processes are determined by the attributes of different organs. Although the significative influence of vessel size on hydraulic conductivity was confirmed in the different chapters of this thesis (larger vessels and wider vessel size distribution has greater conductive efficiency), the role of vessel surrounding cells in conductive safety was partially verified. Thus, in the case of drought-induced cavitation, evidence about the role of these cells in xylem conductive safety was found, on the one hand, increasing the hydraulic connectivity between solitary vessels and, at the same time, limiting air propagation (and, therefore, embolisms) between nearby conductive elements. On the contrary, in freeze/thaw-induced cavitation, results indicate that this process is directly related to vessel size, without significant effects of the surrounding cells. Secondly, larger vessels not only showed greater conductivity but also lower vulnerability to drought-induced cavitation, which would be explained by the inverse relationship between vessel and pit sizes. The relationships between wood anatomy and function were studied at interspecific level, but also at intraspecific level in the case of two species, E. globulus and E. viminalis, analyzing progenies with differences in mean wood density. Several relationships observed between species were also verified within species, although the narrower range of variation of wood characteristics at this level of organization resulted in changes of the significance level and sign in some of them. The third particular objective was to determine the underlying relationships between near infrared absorption spectra (NIR) of Eucalyptus wood and its anatomy and function, in order to contribute to the development of genetic selection methodologies based on easy quantification characters. In this sense, it was possible to establish calibrations between NIR spectra and anatomical, physical and hydraulic properties of Eucalyptus wood, and to generate prediction models with different degrees of fit. Among the latter, those developed for the parameters of the cavitation curve that define the potential at which 12 and 88% of the maximum hydraulic conductivity is lost and the slope between these two points, which defines the speed of the cavitation process, stand out. These results are the first of their kind reported for Eucalyptus species, in particular, and Angiosperms, in general. The results of this thesis allow to affirm that the peculiar wood anatomical structure of Eucalyptus genus determines the existence of complex relationships between anatomy and function, which regulate, to a different degree according to the stress considered, this genus environmental adaptive capacity. In this sense, evidence was found about a lack of trade-off between hydraulic efficiency and safety in the case of drought-induced cavitation, but a compromise was observed between both processes in the case of frost-induced xylem cavitation. The potential trade-off in the resistance to both type of stress would be avoided through the spatial separation of the control mechanisms of these processes, being located in different organs. This, on the one hand, could explain the contrast between field and laboratory observations in the resistance to frost stress and, on the other hand, could allow to improve the resistance to both type of stress simultaneously. In this sense, the establishment of predictive models for anatomical, physical and hydraulic characteristics through high throughput phenotyping methods would allow to improve of the selection process for resistant genotypes in genetic improvement programs.

Acoustic Emissions to Measure Drought-Induced Cavitation in Plants

Article

Full-text available

Mar 2016

Acoustic emissions are frequently used in material sciences and engineering applications for structural health monitoring. It is known that plants also emit acoustic emissions, and their application in plant sciences is rapidly increasing, especially to investigate drought-induced plant stress. Vulnerability to drought-induced cavitation is a key trait of plant water relations, and contains valuable information about how plants may cope with drought stress. There is, however, no consensus in literature about how this is best measured. Here, we discuss detection of acoustic emissions as a measure for drought-induced cavitation. Past research and the current state of the art are reviewed. We also discuss how the acoustic emission technique can help solve some of the main issues regarding quantification of the degree of cavitation, and how it can contribute to our knowledge about plant behavior during drought stress. So far, crossbreeding in the field of material sciences proved very successful, and we therefore recommend continuing in this direction in future research.

Caractérisation physiologique de la réponse à la sècheresse de la Lavande et du Lavandin : impact de la culture inter-rang

Thesis

Full-text available

Jun 2020

Lia Lamacque

Les cultures françaises de Lavande et Lavandin sont soumises à un sévère dépérissement, résultant de l’interaction entre la maladie du Stolbur et des sécheresses de plus en plus intenses et fréquentes. L’amélioration de la résistance des lavanderaies est un défi pour sauvegarder cette filière à fort impact économique, touristique et social dans son territoire. Un projet associant des partenaires de la recherche et de la filière lavandicole vise à augmenter la résistance des cultures par des nouvelles pratiques. Dans ce cadre, les objectifs de la thèse ont été i) d’identifier des indicateurs physiologiques de l’état de stress, et en particulier un seuil physiologique de non-récupération, suite à des sécheresses sévères chez la Lavande et le Lavandin et ii) évaluer l’effet de la pratique agro-écologique de la culture en inter-rang sur la réponse du Lavandin à la sécheresse estivale. Par ailleurs, une étude sur les prévisions climatiques focalisée sur les départements de production a révélé une augmentation des températures estivales et automnales et une diminution des précipitations automnales à l’horizon proche (2021-2050), confortant l’intérêt de nos travaux pour la filière. Pour suivre en continu l’état physiologique des plants lors d’une sécheresse, des dendromètres de type PépiPIAF, qui mesurent les variations du diamètre des tiges, ont été utilisés sur ces espèces. Deux indices liés à l’intensité de la sécheresse et aux dégâts engendrés ont ainsi été identifiés : le pourcentage de perte de diamètre (PLD) et la perte de capacité de réhydratation (PLRC). Les plants ne récupéraient pas d’une sécheresse (PLRC = 100%) lorsque le PLD avait atteint une valeur maximale d’environ 21%. Ces résultats signifient que l’incapacité à récupérer survient lorsque les réservoirs élastiques d’eau sont vides et démontrent ainsi leur importance lors de sécheresses intenses. Lors des déshydratations, des mesures acoustiques et de fuites d’électrolytes ont montré que cette incapacité était associée à des dégâts cellulaires importants, et non à un haut niveau d’embolie. Ces deux indices développés en conditions contrôlées ont aussi permis de diagnostiquer l’état de stress de lavandins en champ. Les dendromètres sur les lavandins ont révélé une contrainte hydrique exercée par un couvert végétal en inter-rang pendant la période de croissance et de sécheresse estivale. Le stress hydrique fut plus précoce avec ce couvert, mais l’intensité de la sécheresse identique à celle avec un sol nu en inter-rang. Outre l’importance de ces travaux pour la recherche fondamentale, en particulier sur les mécanismes de mortalité des plantes, ces résultats ouvrent des perspectives sur l’anticipation des mortalités en lavanderaie, voire sur le pilotage de l’irrigation de ces cultures, pour un contrôle raisonné de la contrainte hydrique nécessaire à la production d’huiles essentielles, mais dommageables pour les plants selon son intensité et la période.

Seasonal coordination of leaf hydraulics and gas exchange in a wintergreen fern

Article

Full-text available

Sep 2020

Wintergreen fern Polystichum acrostichoides has fronds that are photosynthetically active year-round, despite diurnal and seasonal changes in soil moisture, air temperature and light availability. This species can fix much of its annual carbon during periods when the deciduous canopy is open. Yet, remaining photosynthetically active year-round requires the maintenance of photosynthetic and hydraulic systems that are vulnerable to freeze–thaw cycles. We aimed to determine the anatomical and physiological strategies P. acrostichoides uses to maintain positive carbon gain, and the coordination between the hydraulic and photosynthetic systems. We found that the first night below 0 °C led to 25 % loss of conductivity (PLC) in stipes, suggesting that winter-induced embolism occurred. Maximum photosynthetic rate and chlorophyll fluorescence declined during winter but recovered by spring, despite PLC remaining high; the remaining hydraulic capacity was sufficient to supply the leaves with water. The onset of colder temperatures coincided with the development of a necrotic hinge zone at the stipe base, allowing fronds to overwinter lying prostrate and maintain a favourable leaf temperature. Our conductivity data show that the hinge zone did not affect leaf hydraulics because of the flexibility of the vasculature. Collectively, these strategies help P. acrostichoides to survive in northeastern forests.

The Anatomy and Functioning of the Xylem in Oaks

Chapter

Full-text available

Dec 2017

Because of its economic and ecological importance, the genus Quercus has been relatively intensively studied for its anatomical and hydraulic characteristics, having often been testing ground for development of methods and hypotheses related to tree structure and function. However, despite long-withstanding interest, we are still far from having obtained a clear understanding of the hydraulic functioning of the species within this genus, the occurrence of trade-offs among various xylem properties and the prevalence of syndromes of characters under different environmental conditions. We conducted a review of the xylem anatomical literature of the genus Quercus, an undertaking that does not appear to have been carried out before. We also updated existing quantitative databases of vessel diameter and density, volumetric fractions of parenchyma, wood densityand xylem hydraulic properties, to synthesise the main patterns of variation in the hydraulic architecture and functioning of the genus. We found that ring-porous (deciduous) species have lower wood density, higher hydraulic conductivity, xylem that is more vulnerable to embolism and lower Huber values compared to diffuse-porous (evergreen) species. We also report systematic differences among taxonomic groups, with species of sections Quercus and Lobatae having smaller but more numerous vessels, lower wood density, more vulnerable xylem, higher conductivity and lower Huber values as opposed to species of section Cerris. Many of these trends appeared to map onto environmental differences across the three main biomes where Quercus species are found, i.e. the temperate, the Mediterranean/semi-arid and the tropical biomes. Although limited by the coverage of the empirical data, our compilation contributes to characterise the hydraulic architecture and functioning of the genus as a function of taxonomic grouping, biome, ring-porosity and leaf phenology. Future investigations can benefit by the identification of the main factors responsible for these patterns and their likely ecological significance.

Fonctionnement hydrique du hêtre : architecture hydraulique et sensibilité à la cavitation

Thesis

Jan 2000

Damien G Lemoine

A l'aide d'un fluxmètre haute pression (hpfm), nous avons déterminé la répartition des résistances hydrauliques dans les houppiers de hêtre. Nous avons observé un gradient de résistance dans les houppiers avec les plus fortes résistances dans les branches d'ombre. Ce gradient est fortement corrélé avec l'éclairement reçu par les branches au cours de leur croissance. C'est la structure morphologique (rameaux courts et rameaux longs) et anatomique (diamètre et densité des vaisseaux) des branches modulées par l'éclairement qui induisent ce gradient. Ainsi, nous avons montré que la taille réduite des vaisseaux et l'empilement des nu?ds dans les branches d'ombre augmentaient les résistances hydrauliques. L'architecture hydraulique est acclimatée aux conditions microclimatiques et permet de soutenir la demande évaporatoire en limitant les risques de dysfonctionnement (cavitation et embolie). Lorsqu'il y a modification des conditions de croissance (contrainte hydrique, modification de l'éclairement), nous avons montré que des mécanismes de régulation et d'acclimatation se mettent en place. La régulation stomatique permet une réponse rapide et à court terme en limitant fortement les flux d'eau, alors que des modifications anatomiques (modification de la taille des vaisseaux et de la densité) permettent à l'arbre de s'acclimater aux nouvelles conditions de croissance. Cependant le système conducteur du hêtre est une structure vulnérable. Au cours de l'année, nous avons observé des phases de développement de l'embolie. Chaque hiver, l'embolie se développe progressivement suite à l'alternance de périodes de gel et de dégel et au cours de l'été lorsque s'installe une contrainte hydrique précoce et intense (cf. 1998). Une fois les vaisseaux emboisés, la conductivité hydraulique est réduite et chez le hêtre, elle n'est restaurée qu'au printemps suivant par la formation d'un nouveau cerne.

Water uptake can occur through woody portions of roots and facilitates localized embolism repair in grapevine

Article

Full-text available

Feb 2018
NEW PHYTOL

• Water acquisition is thought to be limited to the unsuberized surface located close to root tips. However, there are recurring periods when the unsuberized surfaces are limited in woody roots systems, and radial water uptake across the bark of woody roots might play an important physiological role in hydraulic functioning. • Using X-ray micro-computed tomography (microCT) and hydraulic conductivity measurements (Lpr), we examined water uptake capacity of suberized woody roots in vivo and in excised samples. • Bark hydration in grapevine woody roots occurred quickly upon exposure to water (~4 h). Lpr measurements through the bark of woody roots showed that it is permeable to water and becomes more so upon wetting. After bark hydration, microCT analysis showed that absorbed water was utilized to remove embolism locally, where ~20% of root xylem vessels refilled completely within 15 h. Embolism removal did not occur in control roots without water. • Water uptake through the bark of woody roots likely plays an important role when unsuberized tissue is scarce/absent, and would be particularly relevant following large irrigation events or in late winter when soils are saturated, reestablishing hydraulic functionality before bud break.

Xylem function and leaf physiology in European beech saplings during and after moderate and severe drought stress

Article

Jun 2023

The extreme drought events in the last years caused high mortality amongst European beech (Fagus sylvatica L.) across Central Europe. Thus, knowledge of the response of beech to drought and its ability to recover its xylem and leaf functions after drought release is needed to better understand beech survival. In this study, changes in xylem function, leaf gas exchange, chlorophyll fluorescence and morphology of European beech saplings during drought and recovery phases were assessed. Beech saplings were exposed to three different watering intensities—well-watered (W), moderately drought stressed (M) and severely drought stressed (S) for 25 days, and then saplings were rewatered for 14 days. Reduced irrigation caused a drop in shoot water potential to −1.1 and −3.1 MPa in M and S saplings, respectively. Stomatal conductance in M and S saplings decreased to 15 and 5 per cent of that in W saplings, respectively, and it corresponded with a decrease in the photosynthesis rate and chlorophyll fluorescence parameters. Leaf water content and shoot functional xylem area were significantly affected by drought only in S saplings. Hence, these parameters could be used as sensitive indicators that distinguish plants at no risk of mortality from those at increasing risk under drought stress. In S saplings, some leaves also dried from the edges, leaving a green active central part. During the recovery phase, the leaf gas exchange and chlorophyll fluorescence parameters had recovered 4 days after rewatering in M saplings, whereas in S saplings, they were still lower after 2 weeks. Moreover, xylem function did not fully recover in S saplings till the end of the recovery phase. Hence, subsequent drought periods, even of lower intensity, could lead to tree mortality if tree functions have not fully recovered from the previous drought.

Anatomical variations related to water conduction in viviparous and non-viviparous seedlings of Echinocactus platyacanthus (Cactaceae)

Article

Oct 2022
FLORA

Vivipary is the germination of seeds within a fruit before they are shed from the parent plant. It occurs in a broad range of habitats and species, including cacti under harsh environmental conditions. Thus, an anatomical differentiation involving high water conduction is expected in viviparous cacti seedlings under water deficit stress. Wide-band tracheids (WBTs) have evolved under drought conditions for better water conduction. We have hypothesized that viviparous seedlings will develop larger and widest WBTs and vessel elements than non-viviparous seedlings with less water access. Thus, the length and diameter of WBTs and vessel elements in Echinocactus platyacanthus, a Mexican endemic cactus, were measured in: 1) non-viviparous seedlings (N-V; from fruits without germinated seeds inside), 2) non-viviparous seedlings from viviparous plant (N-V-V; from fruits without germinated seeds belonging to a plant with at least one fruit with germinated seeds), and 3) viviparous seedlings (V-V, from fruits that contained at least one germinated seed inside). These seedlings were grown under three osmotic potentials (0, -0.2, and -0.4 MPa) treatments. The longest WBT was found for V-V seedlings at 0 and -0.2 MPa. The vessel length was longest for V-V seedlings at -0.2 MPa, and the vessel diameter was biggest for N-V seedlings at -0.2 MPa. The vessel diameter/length ratio was lowest for V-V seedlings at -0.2 and -0.4 MPa. Our findings suggest that viviparous seedlings might have more efficient water conduction than non-viviparous ones, which may increase the possibilities of survivorship of wild E. platyacanthus populations and contributes to their natural regeneration in arid environments.

Association between xylem vasculature size and freezing survival in winter barley

Article

Aug 2021
J AGRON CROP SCI

Winter survival is a major yield-limiting factor in winter barley grown in the Upper Midwest, where winter temperatures regularly reach −20°C or lower. Here, we tested the hypothesis that improved freezing survival is associated with smaller xylem vessel diameters as a mechanism that minimizes physical damage arising from intracellular ice formation, using leaf vasculature as a proxy trait. A second goal was to test whether such anatomical differences could be captured non-destructively via gas exchange measurements. We first identified a group of 11 winter barley genotypes that exhibited differential field winter survival. We then conducted xylem diameter measurements on the first three leaves on all genotypes in two independent experiments based on 1,188 images, in addition to leaf gas exchange measurements. Freezing-tolerant genotypes consistently exhibited significantly smaller metaxylem vessel diameters irrespective of leaf rank, and this difference was not influenced by hardening, indicating that this trait is heritable. Additionally, genotypes with smaller vasculature tended to exhibit lower stomatal conductance and transpiration rates. Our data indicate that genotypes with leaf xylem diameters smaller than 30 μm are prime donor parents and could be identified using gas exchange measurements, pointing to new phenotyping approaches to accelerate breeding for freezing survival.

État sanitaire et croissance radiale des arbres : Analyse spatiale et temporelle des données du réseau systématique de suivi des dommages forestiers

Thesis

Dec 2020

Clara Tallieu

Depuis 30 ans, les mesures annuelles de déficit foliaire des arbres sur la partie française du réseau européen de suivi des dommages forestiers (ICP Forests, niveau 1), constituent la base du suivi de l’état de santé des forêts. Pourtant, l’utilisation du déficit foliaire comme indicateur de l’état de santé de l’arbre est régulièrement remise en cause pour des raisons méthodologiques mais aussi en raison du manque de connaissances sur le déterminisme du déficit foliaire et de son impact fonctionnel sur l’arbre. Dans ce contexte, au travers des notations de déficit foliaire de 9 essences (feuillues et résineuses) réparties sur plus de 300 placettes en France, nous avons 1) décrit et interprété les variations spatiales et interannuelles de déficit foliaire, en plus de 2) discuté de l’utilisation du déficit foliaire comme indicateur de l’état sanitaire des arbres à partir de l’analyse conjointe des variations interannuelles de déficit foliaire et de croissance radiale. L’analyse des variations géographiques du déficit foliaire a montré de multiples relations avec les facteurs édaphiques et climatiques, mais avec un pouvoir explicatif relativement modéré. L’analyse des variations interannuelles de déficit foliaire a permis de confirmer que les facteurs climatiques de l'année précédente contrôlent les variations interannuelles de déficit foliaire. Cependant, comparativement à la croissance radiale, le déficit foliaire présente une réponse au climat moins dynamique et peu cohérente entre arbres d’une même placette. L’analyse conjointe des deux signaux a montré l’existence d’un lien ténu entre la croissance et le déficit foliaire. Nous avons pu mettre en évidence une diminution de la croissance de l’arbre dans le cas de déficit foliaires importants lors d’années d’aléas climatiques extrêmes (sec ou froid). Cependant, l’introduction du déficit foliaire en tant que prédicteur de la croissance radiale n’a eu que peu ou pas d’effet significatif pour le hêtre et le sapin. Enfin, la mise en évidence de l’influence majeure de l’âge sur la notation du déficit foliaire empêche l’interprétation de déficit foliaire brut comme indicateur de la santé de l’arbre.

Information Technology in Water Harvesting

Chapter

Full-text available

Jan 2021

Harvesting water for future usage should be the prime concern of human beings. The variety of Internet of Things (IoT) technologies in water harvesting techniques will lead to a fruitful solution in determining the parameters associated with water harvesting anytime and anywhere. This technology helps the user to find the topographical conditions of the area, to determine the various parameters of the soil, the suitability of the soil for the specified crop, etc., which in turn helps to identify the type of artificial recharge techniques that can be applicable for that area for efficient water harvesting. This chapter briefly presents water harvesting methods. It describes IoT, followed by applications of IoT in water harvesting. The chapter covers the assessment of the available subsurface resources using IoT. Finally, IoT devices for efficient agricultural/irrigation usage are presented.

Application of Remote Sensing Techniques in Determining the Risk Taking Level of Different Seasons on Fire Generation in Terms of NDVI Index During the Year Case Study: Golestan Province, Iran

Article

Jan 2021

Knowledge of the nature of seasons and months in terms of the fire risk is very important in environmental planning, land management and forest resource management in order to achieve the sustainable development. One of the applications of remote sensing in this regard is the continuous monitoring of the zone to detect changes. Currently, the vegetation mapping is used to generate information for macro and micro planning. In order to monitor changes across the Golestan province forests through different seasons in 2000-2015, all images of MOD13Q1 MODIS were prepared during this period. Then, the images of the Normalized Difference Vegetation Index (NDVI) were prepared for the four seasons and twelve months of the year. The classification of the indices included lands covered with excellent, moderate, weak and very poor coverage was conducted in order to investigate the changes. Then, the comparison was then performed by LAND FIRE points and the validity of the classification results was evaluated. It was concluded that the seasons of the year from high risk to low risk were winter, summer, fall and spring, respectively. In the high-risk season, winter, January was the most dangerous month and in the low risk season, spring, may was the lowest month of the year.

Solutions to Managing Drought and Reducing Demands

Article

Jul 2020

Conserving and saving water during droughts need a special attitude and great attention. Because according to a variety of studies conducted, nowadays our demand and need for water far exceed the amount of water resources available in different areas. As a result, in order to cope with this crisis, it is necessary to use water-recycling systems, reduce demands, employ optimal equipment for water consumption and use other methods which will be discussed in this study.

The resistance and resilience of European beech seedlings to drought stress during the period of leaf development

Article

May 2020
TREE PHYSIOL

Spring drought is becoming a frequently occurring stress factor in temperate forests. However, the understanding of tree resistance and resilience to the spring drought remains insufficient. In this study, European beech seedlings at the early stage of leaf development were moderately and severely drought stressed for one month and then subjected to a two-week recovery period after rewatering. The study aimed to disentangle the complex relationships between leaf gas exchange, vascular anatomy, tree morphology, and patterns of biomass allocation. Stomatal conductance decreased by 80% and 85% upon moderate and severe drought stress, respectively, which brought along a decline in net photosynthesis. However, drought did not affect the indices of slow chlorophyll fluorescence, indicating no permanent damage to the light part of the photosynthetic apparatus. Stem hydraulic conductivity decreased by more than 92% at both drought levels. Consequently, the cambial activity of stressed seedlings declined, which led to lower stem biomass, reduced tree ring width, and a lower number of vessels in the current tree ring, these also with smaller dimensions. In contrast, the petiole structure was not affected, but at the cost of reduced leaf biomass. Root biomass was reduced only by severe drought. After rewatering, the recovery of gas exchange and re-growth of the current tree-ring were observed, all delayed by several days and by lower magnitudes in severely stressed seedlings. The reduced stem hydraulic conductivity inhibited the recovery of gas exchange, but xylem function started to recover by re-growth and refilling of embolised vessels. Despite the damage to conductive xylem, no mortality occurred. These results suggest the low resistance but high resilience of European beech to spring drought. Nevertheless, beech resilience could be weakened if the period between drought events is short as the recovery of severely stressed seedlings took longer time than 14 days.

Effect of Climate Change on Precipitation Patterns in an Arid Region Using GCM Models: Case Study of Isfahan-Borkhar Plain

Article

Full-text available

Jan 2020

Climate change has major implications for a wide range of natural processes and phenomena, with precipitation patterns particularly sensitive to changes in atmospheric forcing. The arid and semiarid regions of the world, such as Iran, have been affected by declining precipitation. The Isfahan-Borkhar plain in the central region of Iran is one of the areas that has been damaged due to the decrease in rainfall in recent years, and many agricultural lands in this area have already been laid. In this study, five general circulation models (GCM) (MIROC5, MIROC-ESM, MIROC-ESM-CHEM, MRI-CGCM3, and NorESM1-M) for the UN’s Fifth Assessment Report (AR5) on climate change were used to assess future changes to precipitation patterns for the Isfahan-Borkhar plain. These models were implemented using three emission scenarios: the representative concentration pathway (RCP)2.6, RCP4.5, and RCP8.5. The period for application of these models is from 2020 to 2044. The GCM models were weighted based on the comparison of their output in the historical period with observational data. Based on the weight assigned to each model, the models were combined and then downscaled using the LARS-WG model. The weighting results showed that the MIROC5 model was the most accurate model among all GCM models. The accuracy of this model in September was more than that of the other months. The results also showed that precipitation in all emission scenarios would decrease, which was higher in the RCP8.5 emission scenario than in other RCP’s and would have the highest drop in precipitation in August. As it is known, in the RCP2.6 and RCP4.5 emission scenarios, the highest precipitation reduction in winter is expected to be 7.2% and 17%, respectively. Also, for the RCP8.5 emission scenario, the highest precipitation in the spring would be 32.7%. The lowest seasonal precipitation reduction will occur in all emission scenarios in autumn, which will be 3%, 6.9%, and 14.4% in the RCP2.6, RCP4.5, and RCP8.5 emission scenarios, respectively.

Acoustic emission signal detection in drought-stressed trees: beyond counting hits

Book

Full-text available

Jan 2014

Oaks Under Mediterranean-Type Climates: Functional Response to Summer Aridity

Chapter

Dec 2017

Mediterranean-type climates are characterized by warm or hot summers, mild or cold winters and, especially, by the existence of a summer drought period driven by the low or even nule precipitation during this season. Mediterranean-type climates are represented in different areas of the world, both in the Northern and the Southern Hemisphere. Specifically, regarding the existence of Quercus under these climatic conditions, two main geographical areas should be considered, namely the Mediterranean Basin in the Palearctic and California (USA) and Baja California (Mexico) in the Nearctic. Despite the relatively low geographical extension of the areas occupied by oaks under this type of climate, it has deserved its own phytoclimatical entity since the first geobotanical synthesis at a global scale. Although evergreen and sclerophyllous oak species are widely assumed as a prototype of mediterranean oaks, both palaeoecological evidences and present biogeographical analysis confirm the co-existence of this oak type with winter-deciduous species of the same genus. In this chapter, the different advantages and disadvantages of both phenological patterns (evergreeness and winter-deciduousness) are presented. Moreover, the strategies for saving water through the overall leaf size reduction, the stomatal control of water losses or some xeromorphic traits for a further reduction of transpiration are also shown. Finally, the development of a high resistance to drought-induced cavitation, as a way for coping with low water potential during dry periods, is discussed.

Oaks under mediterranean-type climates: Functional responses to summer aridity

Chapter

Jan 2018

Diversification, adaptation, and community assembly of the American oaks (Quercus), a model clade for integrating ecology and evolution

Article

Full-text available

Oct 2018
NEW PHYTOL

Jeannine Cavender-Bares

Contents Summary 669 I. Model clades for the study and integration of ecology and evolution 670 II. Oaks: an important model clade 671 III. Insights from the history of the American oaks for understanding community assembly and ecosystem dominance 673 IV. Bridging the gap between micro‐ and macroevolutionary processes relevant to ecology 679 V. How do we reconcile evidence for adaptive evolution with niche conservatism and long‐term stasis? 682 VI. High plasticity and within‐population genetic variation contribute to population persistence 683 VII. Emerging technologies for tracking functional change 685 VIII. Conclusions 685 Acknowledgements 686 References 686 Summary Ecologists and evolutionary biologists are concerned with explaining the diversity and composition of the natural world and are aware of the inextricable linkages between ecological and evolutionary processes that maintain the Earth's life support systems. Yet examination of these linkages remains challenging due to the contrasting nature of focal systems and research approaches. Model clades provide a critical means to integrate ecology and evolution, as illustrated by the oaks (genus Quercus), an important model clade, given their ecological dominance, remarkable diversity, and growing phylogenetic, genomic, and ecological data resources. Studies of the clade reveal that their history of sympatric parallel adaptive radiation continues to influence community assembly today, highlighting questions on the nature and extent of coexistence mechanisms. Flexible phenology and hydraulic traits, despite evolutionary stasis, may have enabled adaptation to a wide range of environments within and across species, contributing to their high abundance and diversity. The oaks offer fundamental insights at the intersection of ecology and evolution on the role of diversification in community assembly processes, on the importance of flexibility in key functional traits in adapting to new environments, on factors contributing to persistence of long‐lived organisms, and on evolutionary legacies that influence ecosystem function.

Potassium Uptake and Transport in Apple Roots Under Drought Stress

Article

Full-text available

Oct 2018

As one of the most important mineral nutrient elements, potassium (K+) plays an important role in many plant physiological processes and determines both the yield and quality of crops. There are two typical gene families that regulate K+ transport in higher plants, including K+ channels and K+ transporters. However, little is known about how these channels and transporters divide their work in response to drought stress. In this study, the hydroponic experiment was conducted on Malus hupehensis. The K+ content was found to decrease in response to drought stress in M. hupehensis, the aboveground decreased by 34.15% and the underground decreased by 3.97%. Meanwhile, the root morphology change was detected by scanning the root system. Under conditions of drought, the genes encoding K+ transporters were upregulated including MdCHX1.3, MdCHX4.11, MdCHX4.8, MdCHX4.9, MdHKT1, and MdHAK3.2. The net influx of K+ was inhibited by 19.47% with the action of K+ channel inhibitors (CsCl), however a significant decrease (80.99%; P

Caractéristiques hydrauliques, régulation stomatique et efficience d'utilisation de l'eau de quatre espèces de conifères méditerranéens (Cedrus atlantica, Cupressus sempervirens, Pinus halepensis et Pinus nigra)

Thesis

Jun 2002

Fabienne Froux

Les objectifs de ce travail étaient l'analyse des caractéristiques hydrauliques, de la régulation stomatique et de l'efficience d'utilisation de l'eau (Wi) de 4 conifères méditerranéens présentant différents degrés de résistance à la sécheresse. Des plants de 3 ans, cultivés en serre, présentent une large gamme de conductivités hydrauliques et de vulnérabilité à la cavitation du xylème, allant d'une espèce vulnérable (P. nigra) à des espèces peu vulnérables (C. atlantica, C. sempervirens et P. halepensis). Pendant un dessèchement du sol, la fermeture totale des stomates intervient à un potentiel hydrique du xylème proche du seuil de cavitation dans les tiges, dépendant de l'espèce. Ces résultats confirment le rôle des stomates dans la limitation du développement de l'embolie. Entre espèces, des différences de [delta]13C et de Wi intrinsèque existent, le classement reste stable dans différentes conditions expérimentales mais aucune relation interspécifique n'a été montrée entre ces deux paramètres. Wi intrinsèque est faiblement corrélé à la conductance hydraulique spécifique des plants. D'après nos résultats, un modèle intégré de fonctionnement hydrique a été proposé.

Physiological Response of Garry Oak (Quercus garryana) Seedlings to Drought

Article

May 2017
NORTHWEST SCI

The purpose of this study was to determine physiological differences in drought response among Garry oak (Quercus garryana Douglas ex Hook. [Fagaceae]) seedlings from acorns collected at seven acorn collection sites in Washington state. Our objective was to aid in Garry oak restoration efforts by investigating potential differences in drought tolerance for seedlings grown from acorns collected at different sites. Acorns were collected from six sites east of the Cascades, and one site on Whidbey Island (Oak Harbor) west of the Cascades. Differences in morphological and photosynthetic characteristics observed for seedlings grown from acorns collected at these different sites became more pronounced after drought stress was induced by withholding water. Seedlings from acorns collected at the northernmost east-side site (Swauk Creek) were most susceptible to drought and had photosynthetic rates that were 35% lower under drought conditions than when well-watered. Seedlings from acorns collected at the site west of the cascades (Oak Harbor) were the least susceptible to drought and had assimilation rates under drought conditions that were similar to those when well-watered. Differences were also observed among seedlings from different sites in the occurrence of drought-induced loss of stem hydraulic conductivity and changes in leaf water potential and relative water content in response to drought. We conclude that seedlings grown from Garry oak trees at different sites across Washington State have distinct physiological responses to drought that may lead to differing survivorship when used in reforestation efforts and exposed to drought stress in the field. © 2017 by the Northwest Scientific Association. All rights reserved.

Embolism formation and removal in grapevines: A Molecular and Ecophysiological Perspective

Chapter

Mar 2016

Drought signalling among grapevine organs has a dual component: a hydraulic signal controlled by xylem physiology coexists with chemical signals (involving hormones, especially abscisic acid, ABA), transported via xylem, phloem and parenchyma pathways. Under water deficits, with high levels of tension developing, gas-filled xylem vessels may become disrupted by breakage of water columns, producing the so-called cavitation (or embolism) that drastically reduces hydraulic conductance. In grapevine, petioles and roots have been shown to be more vulnerable to xylem cavitation than shoots. When grapevines are re-watered following a drought period, either root or shoot and petioles recover 35–40% of hydraulic conductivity within 24 h, suggesting that a common and coordinated mechanism of recovery among plant organs occurs. To reintegrate vessel functionality, plants have developed different repair mechanisms, which involve active and energy-consuming processes in shoot conductive tissues, possibly involving the contribution of aquaporins. The role of ABA in xylem embolism repair during diurnal cycles is also apparent and discussed.

The role of climate change in the widespread mortality of holm oak in open woodlands of Southwestern Spain

Article

Jan 2016
Dendrochronologia

The role of climate change in the widespread mortality of Holm oak in open woodlands of Southwestern Spain

Article

Jun 2016
Dendrochronologia

Forest decline and increasing tree mortality are of global concern and the identification of the causes is necessary to develop preventive measures. Global warming is an emerging factor responsible for the increasing tree mortality in drought-prone ecosystems. In the southwestern Iberian Peninsula, Mediterranean holm oak open woodlands currently undergo large-scale population-level tree die-off. In this region, temperature and aridity have increased during recent decades, but the possible role of climate change in the current oak mortality has not been investigated.

Climatic events inducing die-off in Mediterranean shrublands: Are species’ responses related to their functional traits?

Article

Full-text available

Apr 2016
OECOLOGIA

Extreme climatic episodes, likely associated with climate change, often result in profound alterations of ecosystems and, particularly, in drastic events of vegetation die-off. Species attributes are expected to explain different biological responses to these environmental alterations. Here we explored how changes in plant cover and recruitment in response to an extreme climatic episode of drought and low temperatures were related to a set of functional traits (of leaves, roots and seeds) in Mediterranean shrubland species of south-west Spain. Remaining aerial green cover 2 years after the climatic event was positively related to specific leaf area (SLA), and negatively to leaf water potential, stable carbon isotope ratio and leaf proline content. However, plant cover resilience, i.e. the ability to attain pre-event values, was positively related to a syndrome of traits distinguished by a higher efficiency of water use and uptake. Thus, higher SLA and lower water-use efficiency characterized species that were able to maintain green biomass for a longer period of time but were less resilient in the medium term. There was a negative relationship between such syndromes and the number of emerging seedlings. Species with small seeds produced more seedlings per adult. Overall, recruitment was positively correlated with species die-off. This study demonstrates the relationship between plant traits and strong environmental pulses related to climate change, providing a functional interpretation of the recently reported episodes of climate-induced vegetation die-off. Our findings reveal the importance of selecting meaningful traits to interpret post-event resilience processes, particularly when combined with demographic attributes.

Approach to water cycle in forest ecosystems

Article

Dec 2005

Energy and water are essential in the functionalism of ecosystems, because solar energy, total radiation, drives the hydrological cycle through the movement of water from soil to atmosphere by means of evapotranspiration. This is the sum of evaporation from surfaces (soil and canopies) and direct water loss from plants, called transpiration. Ecosystems affect total radiation buy means of shortwave reflectance (albedo), which depends of rugosity of leaves and canopies. The great amount of absorbed energy is released as latent heat of vaporization (evapotranspiration) and sensible heat flux. The first one cools the surfaces and release water vapor to the atmosphere and the second one heats the air in the surfaces. The relationship between them is called Bowen’s ratio and characterized the relationship among water and energy in the different ecosystems. Rainfall is the more important source of water for the ecosystems and runoff and evapotranspiration cause the water losses in these.Water moves along a gradients from high to low potential energy, according to gradients of water potential, which determines the water’s continuum soil –plant– atmosphere. The water balance is affected by biotic and abiotic environmental stresses.

Cavitation and water fluxes driven by ice water potential in Juglans regia during freeze-thaw cycles

Article

Full-text available

Nov 2015
J EXP BOT

Freeze-thaw cycles induce major hydraulic changes due to liquid-to-ice transition within tree stems. The very low water potential at the ice-liquid interface is crucial as it may cause lysis of living cells as well as water fluxes and embolism in sap conduits, which impacts whole tree-water relations. We investigated water fluxes induced by ice formation during freeze-thaw cycles in Juglans regia L. stems using four non-invasive and complementary approaches: a microdendrometer, magnetic resonance imaging, X-ray microtomography, and ultrasonic acoustic emissions analysis. When the temperature dropped, ice nucleation occurred, probably in the cambium or pith areas, inducing high water potential gradients within the stem. The water was therefore redistributed within the stem toward the ice front. We could thus observe dehydration of the bark's living cells leading to drastic shrinkage of this tissue, as well as high tension within wood conduits reaching the cavitation threshold in sap vessels. Ultrasonic emissions, which were strictly emitted only during freezing, indicated cavitation events (i.e. bubble formation) following ice formation in the xylem sap. However, embolism formation (i.e. bubble expansion) in stems was observed only on thawing via X-ray microtomography for the first time on the same sample. Ultrasonic emissions were detected during freezing and were not directly related to embolism formation. These results provide new insights into the complex process and dynamics of water movements and ice formation during freeze-thaw cycles in tree stems.

Severity and duration of osmotic stress on partial root system: effects on root hydraulic conductance and root growth

Article

Full-text available

Jun 2016
PLANT GROWTH REGUL

Effects of severity and duration of osmotic stress on partial root system were investigated on root hydraulic conductance (Lp) and growth in each sub-root system. The maize seedlings were raised in nutrient solution with the roots divided equally into two containers. At 12 days after transplanting, half of root system was subjected to osmotic stress of −0.2, −0.4 and −0.6 MPa using PEG 6000 added in the solution, and no PEG 6000 solution was taken as control (CK). Lp and root growth in each sub-root system were measured at 0, 0.25, 0.5, 1, 3, 5, 7 and 9 days after treatment (DAT). Results show that compared to CK, −0.2 MPa treatment enhanced the hydraulic conductance per root area (Lpr) in non-stressed sub-root system by 12 % at 0.5 DAT. In −0.4 MPa treatment, Lpr in non-stressed sub-root system was significantly increased at 9 DAT. But in −0.6 MPa treatment, significant decrease of 12–40 % was observed in non-stressed sub-root system during 0.5–3 DAT if compared to CK, indicating that the threshold of osmotic stress for the compensatory effect of water uptake in non-stressed sub-root system was between −0.2 and −0.4 MPa. In addition, the root area growth rate in non-stressed sub-root system was significantly higher than that in CK during 0.25–0.5, 1–3 and 5–7 DAT for −0.2, −0.4 and −0.6 MPa treatments, respectively. Similar trend also was observed for root length growth rate, indicating that osmotic stress could still stimulate the compensatory effect of root growth other than water uptake under partial root system. Moreover, the occurrence of such compensatory effect delayed with the increasing osmotic stress. Meanwhile, −0.2 MPa treatment had no significant effect on maize shoot growth but −0.4 and −0.6 MPa treatments inhibited shoot biomass accumulation, which resulted in higher root/shoot ratio in −0.4 and −0.6 MPa treatments. Thus root plasticity in hydraulic conductance and root growth in different root zones varied largely depending on the severity and duration of osmotic stress under partial root system.

Understanding plant responses to drought: How important is woody tissue photosynthesis?

Article

Full-text available

May 2013

Within trees, it is known that a part of the respired CO2 is assimilated in chlorophyll-containing stem and branch tissues. However, the role of this woody tissue photosynthesis in tree functioning remains unclear, in particular under drought stress conditions. In this study, stem diameter and leaf photosynthesis were measured for one-year-old cutting-derived plants of Populus nigra 'Monviso' under both well-watered and drought stress conditions. Half of the plants were subjected to a stem and branch light-exclusion treatment to prevent woody tissue photosynthesis to occur, while the other trees served as controls. Drought stress was induced in both treatments by limiting the water supply. We found that under wellwatered conditions, light-exclusion resulted in reduced stem radial daily growth rate (DG) relative to DG observed for control trees. In response to drought, stem shrinkage of the light-excluded trees was more pronounced as compared to the control trees. Maximum leaf net photosynthesis (Amax) decreased more rapidly in light-excluded trees compared to the controls during drought stress. Our results are the first to report on the potentially significant role of woody tissue photosynthesis in tree drought stress tolerance. Moreover, our study implies that the impact of assimilation of respired CO2 on tree functioning extends beyond local stem processes and indicates that woody tissue photosynthesis is potentially a key factor in understanding plant responses to drought stress.

Embolism formation and removal in grapevines: a phenomenon affecting hydraulics and transpiration upon water stress

Chapter

Jan 2015

Vegetation and fire history of coastal north-eastern Sardinia (Italy) under changing Holocene climates and land use

Article

Full-text available

May 2016
VEG HIST ARCHAEOBOT

Little is known about the vegetation and fire history of Sardinia, and especially the long-term history of the thermo-Mediterranean belt that encompasses its entire coastal lowlands. A new sedimentary record from a coastal lake based on pollen, spores, macrofossils and microscopic charcoal analysis is used to reconstruct the vegetation and fire history in north-eastern Sardinia. During the mid-Holocene (c. 8,100–5,300 cal bp), the vegetation around Stagno di Sa Curcurica was characterised by dense Erica scoparia and E. arborea stands, which were favoured by high fire activity. Fire incidence declined and evergreen broadleaved forests of Quercus ilex expanded at the beginning of the late Holocene. We relate the observed vegetation and fire dynamics to climatic change, specifically moister and cooler summers and drier and milder winters after 5,300 cal bp. Agricultural activities occurred since the Neolithic and intensified after c. 7,000 cal bp. Around 2,750 cal bp, a further decline of fire incidence and Erica communities occurred, while Quercus ilex expanded and open-land communities became more abundant. This vegetation shift coincided with the historically documented beginning of Phoenician period, which was followed by Punic and Roman civilizations in Sardinia. The vegetational change at around 2,750 cal bp was possibly advantaged by a further shift to moister and cooler summers and drier and milder winters. Triggers for climate changes at 5,300 and 2,750 cal bp may have been gradual, orbitally-induced changes in summer and winter insolation, as well as centennial-scale atmospheric reorganizations. Open evergreen broadleaved forests persisted until the twentieth century, when they were partly substituted by widespread artificial pine plantations. Our results imply that highly flammable Erica vegetation, as reconstructed for the mid-Holocene, could re-emerge as a dominant vegetation type due to increasing drought and fire, as anticipated under global change conditions.

Acoustic Emission Signal Detection in Drought-Stressed Trees: Beyond Counting Hits

Conference Paper

Full-text available

Sep 2014

Tree survival and fitness under changing environmental conditions with increasing drought stress is currently of high interest. When trees experience water shortage, the whole water transport system experiences strong tensions, which involves a risk of air-embolism formation in sap-conducting conduits. The phenomenon, in which air bubbles are formed in water under tension, is called 'cavitation' and has been associated with the generation of acoustic emission signals. Cavitation reduces the hydraulic conductivity of the water transport system and hampers the hydraulic performance, which may eventually lead to tree mortality. Although the significant role of cavitation during drought stress has been widely accepted, the processes of embolism formation and repair are still poorly understood. Detection of cavitation by acoustic emission might be a powerful non-destructive method to investigate this phenomenon. It has been shown that the cumulative number of hits gives an indication of the degree of cavitation, but quantification in the field is still doubtful with this empirical method. Moreover, it is still not known which processes are generating the acoustic emission signals in drought-stressed trees. We used broadband sensors to collect acoustic emission signals in dehydrating branches and examined the waveforms to get more insight into the source mechanisms of the respective acoustic emission signals. A pattern recognition algorithm was applied to identify natural clusters in the signals and the obtained waveform types were interpreted in terms of possible source mechanism and source location. Occurrence of cavitation was validated using X-ray computed tomography.

Water fluxes and embolism formation during freeze-thaw cycle

Article

Full-text available

Nov 2013

Freeze–thaw cycles induce major hydraulic changes due to liquid-to-ice transition within tree stems. The very low water potential at the ice–liquid interface is crucial as it may cause lysis of living cells as well as water fluxes and embolism in sap conduits, which impacts whole tree–water relations. We investigated water fluxes induced by ice formation during freeze–thaw cycles in Juglans regia L. stems using four non-invasive and complementary approaches: a microdendrometer, magnetic resonance imaging, X-ray microtomography, and ultrasonic acoustic emissions analysis. When the temperature dropped, ice nucleation occurred, probably in the cambium or pith areas, inducing high water potential gradients within the stem. The water was therefore redistributed within the stem toward the ice front. We could thus observe dehydration of the bark's living cells leading to drastic shrinkage of this tissue, as well as high tension within wood conduits reaching the cavitation threshold in sap vessels. Ultrasonic emissions, which were strictly emitted only during freezing, indicated cavitation events (i.e. bubble formation) following ice formation in the xylem sap. However, embolism formation (i.e. bubble expansion) in stems was observed only on thawing via X-ray microtomography for the first time on the same sample. Ultrasonic emissions were detected during freezing and were not directly related to embolism formation. These results provide new insights into the complex process and dynamics of water movements and ice formation during freeze–thaw cycles in tree stems.

Talk is cheap: rediscovering sounds made by plants

Article

Jan 2024

Plants, Vital Players in the Terrestrial Water Cycle

Chapter

Aug 2022

Plant transpiration accounts for about half of all terrestrial evaporation. Plants need water for many vital functions including nutrient uptake, growth and leaf cooling. The regulation of plant water transport by stomata in the leaves leads to the loss of 97% of the water that is taken up via their roots, to the atmosphere. Measuring plant-water dynamics is essential to gain better insight into its roles in the terrestrial water cycle and plant productivity. It can be measured at different levels of integration, from the single cell micro-scale to the ecosystem macro-scale, on time scales from minutes to months. In this contribution, we give an overview of state-of-the-art techniques for plant-water dynamics measurement and highlight several promising innovations for future monitoring. Some of the techniques we will cover include: gas exchange for stomatal conductance and transpiration monitoring, lysimetry, thermometry, heat-based sap flow monitoring, reflectance monitoring including satellite remote sensing, ultrasound spectroscopy, dendrometry, accelometry, scintillometry, stable water isotope analysis and eddy covariance. To fully assess water transport within the soil-plant-atmosphere continuum, a variety of techniques are required to monitor environmental variables in combination with biological responses at different scales. Yet this is not sufficient: to truly account for spatial heterogeneity, a dense network sampling is needed.

Functional Attributes in Mediterranean-Type Ecosystems

Chapter

Jun 2007

Biophysical modelling of the Astroni Nature Reserve, Naples, Italy

Thesis

Jan 2000

Andrea Berardi

The aim of this thesis is to develop a computer model for predicting vegetation change within the Astroni crater, a State Nature Reserve near Naples, Italy. The Astroni crater presents a complex zonation of vegetation communities, including Mediterranean Quercus ilex woodlands, temperate deciduous oak woodlands and exotic plantations. It was hoped that the computer software developed, termed ASTROMOD, would allow the analysis of environmental and management scenarios in the crater, thus aiding the reserve's managers in effective decision making. ASTROMOD comprises a vegetation dynamics model developed for forest ecosystems, combined with models of environmental determinants. It successfully integrates a user-friendly interface, a geographical information system, a parameter database and a series of programming modules within Microsoft Excel. Simulations of vegetation dynamics using ASTROMOD were compared to actual vegetation communities in the Astroni crater. These data were gathered during a detailed vegetation survey using standard sampling techniques. The results show that the model is able to realistically simulate vegetation distribution. Similar results were also found when ASTROMOD simulations were compared to vegetation communities across temperate and Mediterranean bioclimates. However, ASTROMOD was limited in that simulations of species composition and demography were not significantly correlated with the Astroni survey data. The potential applications of vegetation change predictions by ASTROMOD are for avifauna conservation, fire management and climate change. The development of ASTROMOD is a significant achievement in terms of the user-friendliness and cost-effectiveness of software for nature reserve management decision support systems.

Functional Attributes in Mediterranean-Type Ecosystems

Chapter

Jun 2007

Ecosistemas mediterraneos : analisis funcional

Article

Jan 2001

Oaks and People: A Long Journey Together

Chapter

Dec 2017

Genus QuercusL. has been closely associated to humans throughout the history, with empirical evidences of such relationship before the appearance of Homo sapiens strictly speaking. Since then, mankind has obtained different basic resources from oaks, from acorns as food, charcoal for metal melting or wood as key material for different works. Such relation has been especially strong in some areas where oaks are considered as “tree of life” or “people’s species”. Moreover, the interest of scientists in the study of this genus has provided a lot of new discovers in different areas of the socalled plant sciences. Genus Quercus, comprising more than 400 species found throughout the Northern Hemisphere in a lot of contrasted habitats, have been the case study in many papers about taxonomy, palaeobotany, plant physiology or basic and applied ecology. This fact is summarized in this chapter, serving as a preface to this book.

Coordinated modifications in mesophyll conductance, photosynthetic potentials and leaf nitrogen contribute to explain the large variation in foliage net assimilation rates across Quercus ilex provenances

Article

May 2017
TREE PHYSIOL

Leaf dry mass per unit area (LMA) has been suggested to negatively affect the mesophyll conductance to CO2 (gm), the most limiting factor for photosynthesis per unit leaf area (AN) in many evergreens. Several anatomical traits (i.e., greater leaf thickness and thicker cell walls) constraining gm could explain the negative scaling of gm and AN with LMA across species. However, the Mediterranean sclerophyll Quercus ilex L. shows a major within-species variation in functional traits (greater LMA associated with higher nitrogen content and AN) that might contrast the worldwide trends. The objective of this study was to elucidate the existence of variations in other leaf anatomical parameters determining gm and/or biochemical traits improving the capacity of carboxylation (Vc,max) that could modulate the relationship of AN with LMA across this species. The results revealed that gm was the most limiting factor for AN in all the studied Q. ilex provenances from Spain and Italy. The within-species differences in gm can be partly attributed to the variation in several leaf anatomical traits, mainly cell-wall thickness (Tcw), chloroplast thickness (Tchl) and chloroplast exposed surface area facing intercellular air spaces (Sc/S). A positive scaling of gm and AN with Vc,max was also found, associated with an increased nitrogen content per area. A strong correlation of maximum photosynthetic electron transport (Jmax) with AN further indicated a coordination between the carboxylase activity and the electron transport chain. In conclusion, we have confirmed the strong ecotypic variation in the photosynthetic performance of individual provenances of Q. ilex. Thus, the within-species increases found in AN for Q. ilex with increasing foliage robustness can be explained by a synergistic effect among anatomical (at the subcellular and cellular level) and biochemical traits, which markedly improved gm and Vc,max.

Freezing Stress in Tree Xylem

Chapter

May 2016

Freezing in plant xylem is a complex process affecting living and dead components. This book chapter gives a brief overview of methods for analyzing freezing dynamics and tissue damage and focuses on the effects of freezing stress in the xylem symplast and apoplast. Survival strategies, such as supercooling, extracellular freezing, or avoidance of critical bubble formation/expansion in conduits are discussed, and insights from experimental and field studies available in the literature summarized. The final part deals with trees at the Alpine timberline, which are exposed to intense freezing as well as extreme drought stress every winter. Timberline trees are thus an interesting model system to study combined effects of drought and freezing stress in tree xylem and respective avoidance, tolerance, and repair strategies of plants.

Plant Water Relations

Chapter

Jan 1995

R. Lösch

An immense number of publications appeared during the review period 1975–1978 in the broad area of plant water relations. It is impossible to cover here in detail the different aspects of water biology, which range from biochemical and biophysical foundations to ecological and phytogeographical implications and which also touch on problems of applied botany. We attempt rather to report only general trends and major findings of recent research and to list representative papers, in order to gain an overview of a subject that is steadily increasing in its scope and importance.

Sap flow of three co-occurring Mediterranean woody species under varying atmospheric and soil water conditions

Article

Aug 2003

We studied the seasonal patterns of water use in three woody species co-occurring in a holm oak forest in north-eastem Spain. The three species studied, Quercus ilex L., Phillyrea latifolia L. and Arbutus unedo L., constitute more than 99% of the total basal area of the forest. The study period included the dry seasons of 1999 and 2000. Water use was estimated with Granier-type sap flux sensors. Standard meteorological variables, soil water content and leaf water potentials were also monitored. All monitored individuals reduced leaf-related sap flow (Q) during the summer, concurrent with an increase in soil moisture deficit (SMD). Despite similar maximum Q, between species, the decline in Q, with increasing SMD was species-dependent. The average reduction in Q, between early summer and the peak of the drought was 74% for A. unedo (n = 3),58% for P. latifolia (n = 3) and 87% for Q. ilex (n = 1). The relationship between canopy stomatal conductance (G(S)) and vapor pressure deficit (D) changed during the course of the drought, with progressively lower G, for any given D. Summertime reductions of Q, and G. were associated with between-species differences in vulnerability to xylem embolism, and with the corresponding degree of native embolism (lowest in P. latifolia and highest in Q. ilex). Our results, combined with previous studies in the same area, outlined differences among the species studied in manner of responding to water shortage, with P. latifolia able to maintain water transport at much lower water potentials than the other two species. In an accompanying experiment, A. unedo responded to an experimental reduction in water availability by reducing Q(1) during the summer. This species also modified its water use between years according to the different seasonal patterns of precipitation. These results are discussed in relation to the possible impacts that climate change will have on Q. ilex-dominated forests.

Xylem Cavitation and Freezing in Conifers

Chapter

Jan 2001

The productivity of plants depends on a continuous supply of water to the photosynthetic tissue. Without a water supply, the tissue could not access CO2 through open stomata without desiccation. Maintaining a water supply line requires, among other things, maintaining water as a liquid under pressures below vapour pressure. Water in this metastable condition is potentially vulnerable to the nucleation of the vapour phase, a process called ‘cavitation’. Once cavitation occurs, a vapour void expands to fill the xylem conduit and the conduit becomes ‘embolized’ as air diffuses in from surrounding tissue. The gas blockage is confined to a single conduit because the gas-water interface is trapped by meniscal forces in the mesh-like structure of the interconduit pit membranes. Extensive cavitation reduces the hydraulic conductance of the xylem and increases the water stress on the foliage under transpirational conditions.

Plant Responses to Drought Under Climate Change in Mediterranean-Type Ecosystems

Chapter

Jan 1995

The vegetation of Mediterranean-type ecosystems has adapted to a marked seasonality characterized by a mildly cold and rainy winter and a hot dry summer. However, it is drought in the hot summer that has more dramatically influenced evolution and plant life. Because of the peculiar climatic conditions, Mediterranean-type ecosystems have a great diversity of plant life forms dominated by C3 drought avoiders, ranging from winter annuals to deep-rooted perennials or summer-deciduous shrubs. The lack of water in the warmer part of the year does not allow C4 plants to compete successfully under natural conditions, even though they may be highly productive in irrigated agriculture.

Limitations on Stem Water Transport and Their Consequences

Chapter

Dec 1995

John Sperry

This chapter considers interactions between stem water transport, xylem structure, vegetative phenology, and stomatal regulation of gas exchange. The significance of stem water transport, detailed in the first part, is apparent in its influence on leaf water status and, ultimately, in how the leaf water status is linked to the regulation of gas exchange and other leaf-level processes affecting whole plant carbon gain. The importance of shoot k1 on leaf water status increases dramatically in response to drought and freezing stress because of physical limitations on xylem transport. The cavitation response of a plant unambiguously limits the xylem pressure range over which water transport is possible. The remainder of this chapter explains the mechanisms of cavitation in stems caused by freezing and water stress, and the implications of cavitation for adaptation to environmental stress. The role of cavitation in controlling water use may explain why many plants experience limited safety margins from failure of water transport. In particular, the occurrence of extensive xylem cavitation in stems and roots forces a new perspective on the stomatal regulation of water loss. The importance of cavitation for changing whole-plant hydraulic conductance, and the dependence of stomatal conductance on hydraulic conductance, reveals a link that can potentially explain variation in water use efficiency, drought survival, and signaling processes linking water stress to the stomatal reaction.

The Progression of Cavitation in Earlywood Vessels of Fraxinus mandshurica var japonica during Freezing and Thawing

Article

Full-text available

Nov 1999
PLANT PHYSIOL

Yasuhiro Utsumi

For an examination of the progression of cavitation in large-diameter earlywood vessels of a deciduous ring-porous tree, potted saplings of Fraxinus mandshurica var japonica Maxim. were frozen and then thawed. The changes in the amount and distribution of water in the lumina of the current year's earlywood vessels during the course of the freezing and thawing were visualized by cryo-scanning electron microscopy. When samples were frozen, most of the current year's earlywood vessels were filled with water. After the subsequent thawing, the percentage of cavitated current-year earlywood vessels gradually increased with time. All of the current year's earlywood vessels were cavitated within 24 h, and only limited amounts of water remained in the lumina of earlywood vessels. Similar cavitation of earlywood vessels was observed after thawing of frozen, excised stem pieces. In contrast, many vessels of the current year's latewood retained water in the lumina during freezing and thawing. These observations indicate that the cavita-tion of the current year's earlywood vessels is not produced during freezing but progresses during rewarming after freezing in F. mand-shurica var japonica.

The Measurement of the Turgor Pressure and the Water Relations of Plants by the Pressure-bomb Technique

Article

Full-text available

Feb 1972

The pressure-bomb technique as developed by Scholander and colleagues is reviewed. A theoretical analysis of the equilibrium water-relations of individual cells of a twig is derived taking due account of the fact that each cell has a unique solute concentration, fluid volume, shape, and unique mechanical constraint by virtue of its cell-wall structure and attachment to nearest neighbours. These equations combine to give a complete description of the whole twig in response to mechanical (air pressure) stress. Our theoretical analysis suggests that the ‘pressure-volume curve’ can be related quantitatively to meaningful bulk parameters of water relations: viz. the total osmolar content of the symplast Ns, the original volume of the symplast Vo, the volume expressed from the symplast Ve, the gas-pressure of the bomb P, and the volume-averaged turgor pressure (the sum of the products of the relative volume and turgor pressure of each cell). An empirical relation for the volume-averaged turgor pressure of twigs is found which fits all species examined; it also fits the turgor pressure relation for single (Nitella) cells.

Water stress induced cavitation and embolism in some woody plants

Article

Full-text available

Apr 2006
PHYSIOL PLANTARUM

A comparison was made of the relative vulnerability of xylem conduits to cavitation and embolism in three species [Thuja occidentalis L., Tsuga canadensis (L.) Carr. and Acer saccharum Marsh.]. Waterlogged samples of wood were air dehydrated while measuring relative water loss, loss of hydraulic conductance, cumulative acoustic emissions (= cavitations) and xylem water potential. Most cavitation events and loss of hydraulic conductance occurred while water potential declined from – 1 to –6 MPa. There were differences in vulnerability between species. Other people have hypothesized that large xylem conduits (e.g. vessels) should be more vulnerable to cavitations than small conduits (e.g. tracheids). Our findings are contrary to this hypothesis. Under water stress, the vessel bearing wood retained water better than tracheid bearing wood. However, within a species large conduits were more prone to cavitation than small conduits.

A method for measuring hydraulic conductivity and embolism in xylem

Article

Full-text available

Aug 1988
PLANT CELL ENVIRON

Abstract Hydraulic conductivity of the xylem is computed as the quotient of mass flow rate and pressure gradient. Measurements on excised plant stems can be difficult to interpret because of time-dependent reductions in flow rate, and because of variable degrees of embolism. Using Acer saccharum Marsh. stems, we found that certain perfusing solutions including dilute fixatives (e.g. 0.05% formaldehyde) and acids with pH below 3 (e.g. 10 mol m−3 oxalic) prevent long-term decline in conductivity. Xylem embolism can be quantified by expressing the initial conductivity as a percentage of the maximum obtained after flow-impeding air emboli have been removed by repeated high-pressure (175 kPa) flushes. Correlation between microbial contamination and declining conductivity suggests that long-term (> 4h) declines are caused by microbial growth within the vessels. Unpredictable trends in short-term (< 4h) measurements may be caused by movements of air emboli in vessels and/or participate matter.

Xylem dysfunction in Quercus: Vessel sizes, tyloses, cavitation and seasonal changes in embolism

Article

Full-text available

Dec 1990
TREE PHYSIOL

The seasonal progression of xylem dysfunction from tyloses and embolism induced both by cavitation and frost was studied in Quercus rubra L. and Quercus alba L. branches. Vessel lengths and diameters were measured in current-year rings of branches of various ages. Vessels in current-year shoots are about the same size as those in many diffuse porous trees, but vessels in older branches are two to six times larger in diameter and typically more than 10 times longer. Large Quercus vessels were more vulnerable to cavitation than small vessels. The small vessels in current-year shoots were more vulnerable to cavitation than vessels of comparable size in diffuse porous species. Earlywood vessels are completely blocked by tyloses within a year of their formation. Tylose growth starts in winter, but the vessels are not fully blocked until the next summer. Many latewood vessels, by contrast, remain free of complete blockage for several years. In Q. rubra, loss of hydraulic conductivity in current-year shoots due to cavitation reaches 20% by August and > 90% after the first hard frost. Both laboratory and field observations confirm that the role of frost in causing loss of hydraulic conduction by embolism is much more dramatic in Quercus than in conifers and diffuse porous hardwoods.

Cavitation Events in Thuja occidentalis L.? : Utrasonic Acoustic Emissions from the Sapwood Can Be Measured

Article

Full-text available

Sep 1983
PLANT PHYSIOL

Ultrasonic acoustic emissions (AE) in the frequency range of 0.1 to 1 megahertz appear to originate in the sapwood of Thuja occidentalis L. The AE are vibrations of an impulsive nature. The vibrations can be transduced to a voltage waveform and amplified. The vibrations of each AE event begin at a large amplitude which decays over 20 to 100 microseconds. Strong circumstantial evidence indicates that the ultrasonic AE result from cavitation events because: (a) they occur only when the xylem pressure potential Psi(xp) is more negative than a threshold level of about -1 megapascal; (b) the rate of AE events increases as Psi(xp) decreases and when the net rate of water loss increases; (c) the AE can be stopped by raising Psi(xp) above -1 megapascal. Ultrasonic AE have been measured in whole terminal shoots allowed to dry in the laboratory, in isolated pieces of sapwood as they dried in the laboratory, and in whole terminal shoots in a pressure bomb when Psi(xp) was decreased by lowering the gas pressure in the pressure bomb.

Spring Filling of Xylem Vessels in Wild Grapevine

Article

Full-text available

Mar 1987
PLANT PHYSIOL

Xylem vessels in grapevines Vitis labrusca L. and Vitis riparia Michx. growing in New England contained air over winter and yet filled with xylem sap and recovered their maximum hydraulic conductance during the month before leaf expansion in late May. During this period root pressures between 10 and 100 kilopascals were measured. Although some air in vessels apparently dissolved in ascending xylem sap, results indicated that some is pushed out of vessels and then out of the vine. Air in the vessel network distal to advancing xylem sap was compressed at about 3 kilopascals; independent measurements indicated this was sufficient to push air across vessel ends, and from vessels to the exterior through dead vine tips, inflorescence scars, and points on the bark. Once wetted, vessel ends previously air-permeable at 3 kilopascals remained sealed against air at pressures up to 2 and 3 megapascals. Permeability at 3 kilopascals was restored by dehydrating vines below -2.4 megapascals. We suggest that the decrease in permeability with hydration is due to formation of water films across pores in intervascular pit membranes; this water seal can maintain a pressure difference of roughly 2 megapascals, and prevents cavitation by aspirated air at xylem pressures less negative than -2.4 megapascals.

Do Woody Plants Operate Near the Point of Catastrophic Xylem Dysfunction Caused by Dynamic Water Stress? : Answers from a Model

Article

Full-text available

Dec 1988
PLANT PHYSIOL

We discuss the relationship between the dynamically changing tension gradients required to move water rapidly through the xylem conduits of plants and the proportion of conduits lost through embolism as a result of water tension. We consider the implications of this relationship to the water relations of trees. We have compiled quantitative data on the water relations, hydraulic architecture and vulnerability of embolism of four widely different species: Rhizophora mangle, Cassipourea elliptica, Acer saccharum, and Thuja occidentalis. Using these data, we modeled the dynamics of water flow and xylem blockage for these species. The model is specifically focused on the conditions required to generate ;runaway embolism,' whereby the blockage of xylem conduits through embolism leads to reduced hydraulic conductance causing increased tension in the remaining vessels and generating more tension in a vicious circle. The model predicted that all species operate near the point of catastrophic xylem failure due to dynamic water stress. The model supports Zimmermann's plant segmentation hypothesis. Zimmermann suggested that plants are designed hydraulically to sacrifice highly vulnerable minor branches and thus improve the water balance of remaining parts. The model results are discussed in terms of the morphology, hydraulic architecture, eco-physiology, and evolution of woody plants.

Drought resistance strategies and vulnerability to cavitation of some Mediterranean sclerophyllous trees

Chapter

May 1993

The prospect of future climate change has stimulated research into the physiological responses of plants to stress. Water is a key factor controlling the distribution and abundance of plants in nature and the efficient uptake and subsequent transport of water within the plant is critical in hot, dry regions. This book, based on a meeting which focused on the failure of the hydraulic pathway within the xylem, brings together contributions from a range of experts who have worked on the cavitation of water in the transport system. The phenomenon of cavitation, discovered only in the 1960s, is now becoming recognised as being widespread and, whilst its ecological significance is a matter for further research, many scientists consider than embolism in the xylem predisposes plants to further water stress. Cavitation and refilling may, therefore, hold the key to vegetational response to climatic warming and drying. This book will provide a valuable compendium of information for those working in the plant and environmental sciences as well as for those whose interests lie in the more applied disciplines of agriculture and forestry.

VASCULAR ANATOMY OF THE NODAL REGION IN POPULUS DELTOIDES BARTR

Article

Oct 1977

The ontogeny of vascular bundles in the nodal region of Populus deltoides Bartr. was examined to understand more thoroughly the structure-function relation between leaf and stem. Three vascular traces from the stem independently enter each leaf in the nodal region. At the base of each developing leaf a region was observed in which both bundle size and vascular development was reduced; this region was referred to as the constricted zone. The constricted zone was described quantitatively at 13 locations within the nodal region of a leaf at LPI 5 by determining the number of metaxylem vessels and the total metaxylem vessel area in each of the three leaf traces. A plot of these data showed a distinct minimum value for total metaxylem vessel area within the constricted zone of each trace; the location of this minimum value was referred to as the constriction plane. Each vascular bundle within the nodal region is composed of independent subsidiary bundles that originate within the constricted zone. These bundles provide a direct connection between the leaf lamina and the stem. The node was defined anatomically on the basis of the ontogenetic development of the subsidiary bundles. The node began at the initial exit point of the central trace from the vascular cylinder and extended distally to the constriction plane. This definition allowed us to quantify the limits of each node. The origin of the initiating layer and metacambium was also examined within the nodal region. These precursors of the cambium develop continuously and acropetally from the stem into the leaf. The developmental implications of the constricted zone and the metacambium within the nodal region are discussed with respect to wood formation.

Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Article

May 1991

M. A. LO GULLO

Three different methods for measuring xylem embolism due to water cavitation were compared—the acoustic method, the hydraulic method and the anatomical method. Young plants of Ceratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300 kHz) acoustic emissions (AE) from 1-year-old twigs (acoustic method). Xylem embolism was detected by measuring the loss of hydraulic conductivity of twigs of the same age (hydraulic method). The blockage of single xylem conduits was detected by perfusing Safranin into the xylem of 1-year-old twigs of stressed plants and measuring the number and the diameters of non-conducting xylem conduits, under the microscope (anatomical method). It was noted that: (a) the number of AE and the loss of conductivity increased with the water stress applied; (b) a linear relation seemed to exist between the number of AE and the loss of conductivity, suggesting that the AE counted could be only (or mainly) produced in the xylem conduits; (c) the vulnerability of the xylem conduits to embolism was a direct function of their diameter; and (d) the measured loss of conductivity was of the same order of magnitude as the theoretical one. The three methods gave fairly similar results. Nonetheless, they are not alternative to one another in that: (a) the acoustic method allows continuous recordings to be made but does not provide information about the actual damage suffered by plants; (b) the hydraulic method is very informative but destructive; and (c) the anatomical method is very useful both in phytogeographical and in genetic improvement studies.

Low Temperature Effects on Mediterranean Sclerophylls: An Unconventional Viewpoint

Article

Jan 1981

Walter Larcher

Mediterranean sclerophyllous trees and shrubs are considered to represent a life form which, by evolution and natural selection, has adapted to climates with summer drought and wet, mild winters. Obviously drought stress proves to be the climatic factor essentially responsible for the restriction of productivity, growth, and survival of evergreen woody plants in Mediterranean-type regions. In addition, low temperature effects in marginal districts, particularly in the northern and eastern parts of the Mediterranean basin and near to the altitudinal limit of the maquis vegetation, should not be neglected. Such effects are frost damage during severe winters, which are to be expected every 10–12 years (Morettini 1961), as well as reduced dry matter production and decreased vigour of the plants due to the depression of metabolic activities by suboptimal temperatures in December and January (Killian 1933, Larcher 1961a,b,1969a,b, Eckardt et al. 1975, Weinmann, Kreeb 1975). Recently the significance of low winter temperatures and episodic frost in limiting distribution range and causing alterations in the floristic composition of the maquis vegetation in Europe has been emphasized by Larcher (1980a) and Mitrakos (1980). Experimental data from previous investigations are evaluated here to illustrate the view that low temperatures, which were a major stress factor during Pleistocene, still exert a considerable influence on survival, reproduction and productivity of Mediterranean evergreen woody plants.

Winter low temperatures in mediterranean-type ecosystems

Article

Jan 1982

K. Mitrakos

Different Aspects of Cavitation Resistance in Ceratonia siliqua, a Drought-Avoiding Mediterranean Tree

Article

Sep 1989

Potted plants of Ceratonia siliqua L., growing in a greenhouse, were used to detect xylem cavitation (in terms of ultrasound acoustic emissions AE) in internodes and node-to-petiole (N-P) junctions, after different periods of drought (9, 16 and 23 d). Diurnal AE were only 100 in internodes of watered (W) plants but 320, 1250 and 2460 in 9-, 16- and 23-d stressed ones. In N-P junctions, AE were only 15 to 20% with respect to internodes. Stem perfusion with dye allowed measurement of the percentage of xylem conduit transverse area blocked by cavitation. This was 2% in internodes of W-plants and 5.2, 13.8 and 40.4% in those of 9-, 16- and 23-d stressed ones. In N-P junctions, 18.5% of the xylem conduit transverse area was blocked in the 23-d stressed plants only. The major resistance to cavitation exhibited by the N-P junctions is interpreted in terms of their greater number of narrow xylem conduits. The percentage of blocked xylem conduits within a range of diameters showed that the narrower a xylem conduit, the less likely it was that cavitation would occur. After rewatering, the release of the xylem blockage caused by cavitation occurred within 2 h. Our data suggest that C. siliqua can be considered to be a cavitation avoider, especially in its stem-to-leaf transition zones.

Xylem' Structure and Water Conduction in Conifer Trees, Dicot Trees, and Llanas

Article

Jan 1985

Frank W. Ewers

Coniferous trees, dicotyledonous trees, and dicotyledonous lianas (woody vines) form interesting morphological contrasts in their xylem structure and function. Lianas have among the largest (up to 8 metres or more) and widest (up to 500 µm) vessels in the plant kingdom. In conifers the water transport occurs through tracheids, which are relatively inefficient in transport. We can compare disparate growth forms in terms of leaf-specific. conductivity (LSC), which is hydraulic conductivity per surface area of leaves supplied by a stem. LSC is inversely proportional to localised pressure potential gradients. LSC is equal to the Huber value (sapwood area per leaf area supplied) times the specific conductivity (hydraulic conductivity per sapwood area). Lianas are similar to dicot trees and conifers in having hydraulic constrictions (low LSCs) at branch junctions. However, lianas generally have greater LSCs and specific conductivities but lower Huber values than do conifers. Dicot trees are intermediate in these values. The narrow but efficient stems of lianas are possible partly because lianas are not self-supporting; the mechanical requirements are reduced. Secondly, the wide and efficient vessels of lianas remain conductive for much longer than might be expected (two to several years, versus one year for similar wide vessels in dicots). Based upon experiments with glass capillary tubes and with living stem tissue, larger vessels are more susceptible to freezinginduced embolism than are small ones. However, in lianas, root pressures might serve to refill cavitated vessels on a daily or seasonal basis.

Xylem Cavitation in Nodes and Internodes of Whole Chorisia insignis H. B. et K. Plants Subjected to Water Stress: Relations Between Xylem Conduit Size and Cavitation

Article

Oct 1986

Measurements of cavitation occurring in xylem conduits of different stem parts in whole Chorisia insignis H.B. et. K. plants subjected to water stress are reported. Pre-stressed plants were shown to undergo cavitation over 10 times greater than watered ones. The most vulnerable parts of plants were one-year-old twigs where cavitation reached a peak of over 50 acoustic emissions (AE) min−1 while in two-year-old twigs AE min−1 were about one half this value. Stem zones were found where cavitation was typically very low even during water stress: these were one-year-old nodes and junctions where branches meet. Measurements of the inside diameters of xylem conduits and distribution of conduit ends in stem parts where AE were detected, showed that nodes have a significantly larger percentage of narrow xylem conduits than internodes. Similar ‘constricted zones’ were found in junctions with respect to two-year-old twigs. Here about 50 per cent of the xylem conduits were as narrow as 20 to 50 µm in diameter. The distribution of xylem conduit ends show about 3 per cent of them ending in the nodes and 1 per cent in the internodes of one-year-old twigs. About 11.6 per cent of xylem conduits end in the junctions and about a half in two-year-old internodes. Our data would give further experimental evidence to the functional concept of ‘plant segmentation’ into zones (internodes) more efficient in water conduction, i.e. with wider xylem conduits but more vulnerable to cavitation and others (nodes and junctions) with opposite characteristics.

Gas Penetration of Pit Membranes in the Xylem of Rhododendron as the Cause of Acoustically Detectable Sap Cavitation

Article

Jan 1985

The gas pressure required to force sap from Rhododendron stems was investigated. Sap was expressed from stems, and stem permeability to gas increased, at pressures of 1.3-3.5 MPa. We interpret the changing of permeability as a removal of water films in the pores of the pit membranes which normally limit the length of xylem conduits. Similar pressure differences exist across the pit membranes separating gas and sap-filled conduits when cavitation occurs in Rhododendron. It is suggested that cavitation in detached leaves and shoots of Rhododendron occurs when gas penetrates the pit membranes. The increase in the gas permeability of xylem subjected to high gas pressures was reversed by a soaking in water. It could not therefore have been a consequence of mechanical damage, caused when xylem conduits are subjected to high gas pressures, because such structural damage would be irreversible.

Vascular Anatomy of the Nodal Region in Populus deltoides Bartr

Article

Oct 1977

Water relations of two Sicilian species of Senecio (Groundsel) measured by the pressure bomb technique

Article

Oct 1983
NEW PHYTOL

S. Salleo

The possible role in drought resistance played by leaf water potential, osmotic potential, weight-averaged turgor pressure and bulk modulus of elasticity is studied in mature and young leaves of Senecio Candidus and S. ambiguus. Small water losses cause relatively large reductions in leaf water potential in, S. candidus without greatly altering its osmotic potential. This occurs because S. candidus develops thicker leaf cell walls with high values of leaf bulk elastic modulus. Recovery from water stress is very rapid in this species. Leaf growth is influenced by the structural pattern of the cell walls in that S. candidus leaves complete their expansion within a shorter period of time than those of S. ambiguus. The possible adaptive significance of changing the leaf bulk modulus of elasticity in mature and young leaves of the two species is discussed.

Xylem Structure and The Ascent of Sap

Book

Jan 1983

Mh Zimmerman

Characterization and propagation of acoustic emission signals in woody plants: Towards an improved acoustic emission counter

Article

Apr 2006
PLANT CELL ENVIRON

The physics of ultrasonic acoustic emissions (AEs) was investigated for AE transmission through wood and transducers. The physical properties measured were velocity, attenuation and frequency composition of AEs produced by two sources: cavitation events in xylem and pencil lead breaks. The authors also measured the relative sensitivity of various combinations of ultrasound transducers and amplifiers to aid in the selection of a measuring system optimized for cavitation detection in woody plants. Some of the authors' conclusions are: (1) Softwoods (Thuja, Pinus) attenuate AEs more rapidly than hardwoods (maple, birch). (2) The velocity of AEs in wood exceeds that measured by others in water so the main medium of AE transmission must be the cellulose. (3) The strongest frequencies of AEs are in the range of 100–300 kHz. (4) Cavitation-induced AEs tend to shift to higher frequency as wood dehydration progresses. (5) One cannot determine the locus of origin of AEs from its frequency composition. (6) The frequency composition of the acoustic emissions probably cannot be determined at all with the sensors used because of their tendency to ‘ring’. The data collected in this paper were used to aid in the design of an improved AE counter having a seven-fold increase in signal to noise ratio compared to counters previously used in our laboratory. The improved counter, model 4615 Drought Stress Monitor, is now commercially available from Physical Acoustics Corp., Princeton, NJ, U.S.A.

Changes in hydraulic conductivity upon freezing of the xylem of Populus x canadensis Moench ?robusta?

Article

Jun 1991

The impact of freezing stress on the hydraulic conductivity was studied in 4- to 6-year-old branches of Populus x canadensis Moench robusta under gravity flow conditions. In fresh branch segments, the hydraulic conductivity was approximately 3–610-2 1 h-1kPa-1m and the specific conductivity approximately 22 1 h-1kPa-1m-1. Depending on the gas content of the solutions fed to the xylem of the segments, their hydraulic conductivity was lowered by a freezing-thawing cycle by 20–50%. However, full recovery of hydraulic conductivity was found after about 2 days. Degassed solutions in contrast showed no impediment to flow after the same treatment. The results give evidence, firstly, that the harmful effect of freezing on functioning of water conducting elements is due to the formation of bubbles in xylem sap containing gas in solution, and secondly, that recovery from this impediment is possible in microporous vessels within a period of about 2 days.

Water Relations of Evergreen Sclerophylls. I. Seasonal Changes in the Water Relations of Eleven Species from the Same Environment

Article

Feb 1990

Leaf water relationships were studied in eleven evergreen sclerophyll species from a macchia near Athens, Greece. Water (ψ), solute (ψs) and turgor (ψp) potentials as well as relative water content (RWC) and stomatal conductance were measured during the course of a year. Relatively high values of water potential were measured initially in the young expanding leaves during the 60-90 d of the growth period. After this period a soil moisture deficit developed and leaves increased to full size. During the drought period leaf water potential and solute potential values, as well as stomatal conductance were low. The results show that during the dry season (Jun.-Aug.) all species are at or near zero turgor and this occurs in Arbutus, Myrtus and Nerium at around -1.5 MPa, in Ceratonia, Pistacia and Quercus at around -2.0 MPa, in Laurus, Olea and Phillyrea below -3·5 MPa. These values largely reflect differences in ψs at this time. Also, the seasonal variations in the water relations components reflect the responses of the different species to variation in water availability.

Water-stress-induced xylem embolism in three species of conifers

Article

Jun 1990
PLANT CELL ENVIRON

. The mechanism of water-stress-induced xylem embolism was studied in three species of conifers: Abies balsamea (L.) Mill., Picca rubens Sarg, and Juniperus virginiana L. Each species showed a characteristic relationship between xylem tension and the loss of hydraulic conductivity by air embolism. Abics balsamea and Picca rubens began to embolize at tensions between 2 and 3 MPa and were completely non-conducting between 3 and 4 MPa. Juniperus virginiana was least vulnerable, beginning to embolize at 4 and still retaining approximately 10% conductivity at 10 MPa. As with a previous study of the vessel-bearing Accr saccharum Marsh., a brief perfusion of branch segments with an oxalic acid and calcium solution (10 and 0.1 mol m−3. respectively) increased the vulnerability of the xylem to embolism; this was especially pronounced in Abies balsamea. In order to test whether embolism was caused by aspiration of air into functional tracheids from neighbouring embolized, ones (the ‘air-seeding’hypothesis), hydrated branch segments were injected with air at various pressures and measured for embolism. Results supported the air-seeding hypothesis because the relationship between injection pressure and embolism for both native and oxalic-calcium-treated segments was essentially the same as for embolism induced by xylem tension. Structural and experimental evidence suggested the air seeding occurred through inter-tracheid pit membranes when the thickened torus region of the membrane became displaced from its normal sealing position over the pit aperture. Thus, the embolism-inducing tension may be a function of pit membrane flexibility. This tension is of ecological significance because it reflects to some extent the range of xylem tensions to which a species is adapted.

Responses of Plants to Environmental Stresses

Article

Jan 1980

Jacob Levitt

Contenido: v. 1: Chilling, Freezing, and High temperature stresses. v. 2: Water, radiation, salt and other stresses Incluye bibliografía e índice

Water Relations of Plants

Article

Jan 1985
SOIL SCI

P.J. Kramer

Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Article

May 1991

Three different methods for measuring xylem embolism due to water cavitation were compared—the acoustic method, the hydraulic method and the anatomical method. Young plants of Ceratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300 kHz) acoustic emissions (AE) from 1-year-old twigs (acoustic method). Xylem embolism was detected by measuring the loss of hydraulic conductivity of twigs of the same age (hydraulic method). The blockage of single xylem conduits was detected by perfusing Safranin into the xylem of 1-year-old twigs of stressed plants and measuring the number and the diameters of non-conducting xylem conduits, under the microscope (anatomical method). It was noted that: ( a ) the number of AE and the loss of conductivity increased with the water stress applied; ( b ) a linear relation seemed to exist between the number of AE and the loss of conductivity, suggesting that the AE counted could be only (or mainly) produced in the xylem conduits; ( c ) the vulnerability of the xylem conduits to embolism was a direct function of their diameter; and ( d ) the measured loss of conductivity was of the same order of magnitude as the theoretical one. The three methods gave fairly similar results. Nonetheless, they are not alternative to one another in that: ( a ) the acoustic method allows continuous recordings to be made but does not provide information about the actual damage suffered by plants; ( b ) the hydraulic method is very informative but destructive; and ( c ) the anatomical method is very useful both in phytogcographical and in genetic improvement studies.

Freezing of Xylem Sap Without Cavitation

Article

Feb 1967
PLANT PHYSIOL

H T Hammel

Freezing of stem sections and entire twigs of hemlock (Tsuga canadensis) has been demonstrated to occur without increasing the resistance to the movement of water through the frozen part after rewarming. This was interpreted to mean that freezing did not produce cavitation in the xylem sap even though A) the sap was unquestionably frozen; B) it contained dissolved gases; and C) it was under tension before freezing and after. Freezing stem sections of some other evergreen gymnosperms during the summer again produced no evidence for cavitation of the xylem sap. On the other hand, freezing stem sections of some angiosperms invariably increased the resistance to sap flow leading to wilting and death in a few hours when the sap tension was at normal daytime values at the time of freezing. These results were interpreted to mean that the bordered pits on the tracheids of gymnosperms function to isolate the freezing sap in each tracheid so that the expansion of water upon freezing not only eliminates any existing tension but also develops positive pressure in the sap. Dissolved gases frozen out of solution may then be redissolved under this positive pressure as melting occurs. As the bubbles are reduced in size by this ice pressure developed in an isolated tracheid, further pressure is applied by the surface tension of the water against air. If the bubbles are redissolved or are reduced to sufficient small size by the time the tension returns to the sap as the last ice crystals melt, then the internal pressure from surface tension in any existing small bubbles may exceed the hydrostatic tension of the melted sap and the bubbles cannot expand and will continue to dissolve.

Sap Pressure in Vascular Plants: Negative hydrostatic pressure can be measured in plants

Article

May 1965

A method is described which permits measurement of sap pressure in the xylem of vascular plants. As long predicted, sap pressures during transpiration are normally negative, ranging from -4 or -5 atmospheres in a damp forest to -80 atmospheres in the desert. Mangroves and other halophytes maintain at all times a sap pressure of -35 to -60 atmospheres. Mistletoes have greater suction than their hosts, usually by 10 to 20 atmospheres. Diurnal cycles of 10 to 20 atmospheres are common. In tall conifers there is a hydrostatic pressure gradient that closely corresponds to the height and seems surprisingly little influenced by the intensity of transpiration. Sap extruded from the xylem by gas pressure on the leaves is practically pure water. At zero turgor this procedure gives a linear relation between the intracellular concentration and the tension of the xylem.

Water Relations of Plants Low temperature effects on mediterranean sclerophylls: an unconventional viewpoint

Jan 1981
259-266

P J Kramer

Kramer P.J. (1983) Water Relations of Plants. Academic Press Inc., New York, NY. Larcher W. (1981) Low temperature effects on mediterranean sclerophylls: an unconventional viewpoint. In Components of Productivity of Mediterranean Regions. Basic and Applied Aspects (eds N. Margaris & H.A. Mooney), pp. 259-266. Dr W.

Responses of Plants to Environmental Stresses Xylem architecture as the anatomical basis of drought resistance in the desert shrub Simmondsia chinensis (Link) Schneider

Jan 1980
255-267

Junk
Amsterdam
J Levitt

Junk, Amsterdam. Levitt J. (1980) Responses of Plants to Environmental Stresses. Academic Press, New York, NY. Lo Gullo M.A. (1989) Xylem architecture as the anatomical basis of drought resistance in the desert shrub Simmondsia chinensis (Link) Schneider. Giornale Botanico Italiano 123, 255-267.

Spring filling of xylem vessels in wild grapevine. Plant Physiology %i,A\A-A\l Freezing of conifer xylem sap and the cohesion-tension theory Water deficits in vascular disease

Jan 1968
225-331

J S Sperry
N M Holbrook
M H Zimmermann
M T Tyree

Sperry J.S., Holbrook N.M., Zimmermann M.H. & Tyree M.T. (1987) Spring filling of xylem vessels in wild grapevine. Plant Physiology %i,A\A-A\l. Sucoff E. (1969) Freezing of conifer xylem sap and the cohesion-tension theory. Physiologia Plantarum 22, 424—431. Talboys P.W. (1968) Water deficits in vascular disease. In Water Deficits and Plant Growth (ed. T.T. Kozlowski), pp. 225-331.

Desiccation tolerance and osmotic parameters in detached leaves of Quercus ilex L

Jan 1991
357

Kyriakopoulos E.

Kyriakopoulos E. & Richter H. (1991) Desiccation tolerance and osmotic parameters in detached leaves of Quercus ilex L. Acta Oecologia 12, 357-367.

Drought resistance strategies and vulnerability to cavitation of some Mediterranean sclero-phyllous trees Sap pressures in vascular plants

Jan 1965
99-113

S Salleo
M A Lo

Salleo S. & Lo Gullo M.A. (1993) Drought resistance strategies and vulnerability to cavitation of some Mediterranean sclero-phyllous trees. In Water Transport in Plants Under Stress Conditions (eds M. Borghetti, J. Grace &. A. Raschi), pp. 99-113. Cambridge University Press, Cambridge. Scholander P.F., Hammel H.T., Bradstreet E.D. & Hemmingsen E.A. (1965) Sap pressures in vascular plants. Science 148, 339-346.

Water Flow in Plants Winter low temperatures in mediterranean-type ecosystems

Jan 1979
95-102

J A Milburn

Milburn J.A. (1979) Water Flow in Plants. Longman, London. Mitrakos K. (1982) Winter low temperatures in mediterranean-type ecosystems. Ecologia Mediterranea T.VIII, 95-102.

Jan 1993
99

Salleo S.

Xylem architecture as the anatomical basis of drought resistance in the desert shrub Simmondsia chinensis (Link) Schneider

Jan 1989
255

Gullo M.A.

Different vulnerabilities of Quercus ilex L. to freeze- and summer drought-induced xylem embolism: an ecological interpretation

Abstract

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