Xylem Anatomical Characteristics Research Articles

Anatomical Characteristics of the Xylem of Populus euphratica at Different Groundwater Burial Depths in the Lower Tarim River (China) and Its Response to Temperature Extremes

The anatomical characteristics of xylem and their relationship with temperature during the year can be studied at the cellular scale by using micro-coring technology and the wood anatomy method. In this study, we used Populus euphratica Oliv. trees with different groundwater burial depths in the lower Tarim River as the research subjects. Micro-core samples of Populus euphratica were collected near two sampling sites, TY1 and TY2, which have different groundwater burial depths. We analyzed the differences in xylem anatomical characteristics and their relationship with extreme temperatures under these varying groundwater conditions using wood anatomy methods. The results showed that the anatomical parameters at TY1, with a higher groundwater table, were greater than those at TY2, which had a lower groundwater table. Specifically, the conduit density, total conduit area, average conduit area and maximum conduit area of Populus euphratica xylem were significantly and positively correlated with both maximum and minimum temperatures. The principal components of xylem parameters at TY1, with the higher water table, were significantly and positively correlated with both maximum and minimum air temperatures. In contrast, the principal components of xylem parameters at TY2, with the lower water table, were not significantly correlated with either maximum or minimum air temperatures. The sensitivity analysis indicated that the sensitive maximum air temperature for the principal component parameter index change of Populus euphratica xylem was 34.1 °C, and the sensitive minimum air temperature was 16.1 °C. Therefore, different moisture conditions affected the sensitivity of xylem parameter growth to temperature, with the temperature threshold for Populus euphratica xylem growth being between 16.1 °C and 34.1 °C.

Xylem plasticity of root, stem, and branch in Cunninghamia lanceolata under drought stress: implications for whole-plant hydraulic integrity.

A better understanding of xylem hydraulic characteristics in trees is critical to elucidate the mechanisms of forest decline and tree mortality from water deficit. As well as temperate forests and forests growing in arid regions, subtropical and tropical forests are also predicted to experience an increased frequency and intensity of climate change-induced drought in the near future. In this study, 1-year-old Cunninghamia lanceolata seedlings (a typical subtropical species in southern China) were selected for a continuous controlled drought pot experiment of 45 days duration. The experimental treatments were non-drought (control), light drought, moderate drought and severe drought stress, which were 80%, 60%, 50%, and 40%, respectively of soil field maximum moisture capacity. The hydraulic conductivity, specific conductivity and water potential of roots, stems, and branches of C. lanceolata all decreased with the prolonging of drought in the different drought intensities. The relative decrease in these hydraulic values were greater in roots than in stems and branches, indicating that roots are more sensitive to drought. Root tracheid diameters normally reduce to ensure security of water transport with prolonged drought, whilst the tracheid diameters of stems and branches expand initially to ensure water transport and then decrease to reduce the risk of embolism with continuing drought duration. The pit membrane diameter of roots, stems and branches generally increased to different extents during the 15-45 days drought duration, which is conducive to enhanced radial water transport ability. The tracheid density and pit density of stems generally decreased during drought stress, which decreased water transport efficiency and increased embolism occurrence. Correlation analysis indicated that anatomical plasticity greatly influenced the hydraulic properties, whilst the relationships varied among different organs. In roots, tracheid diameter decreased and tracheid density increased to enhance water transport security; stems and branches may increase tracheid diameter and pit membrane diameter to increase hydraulic conductivity ability, but may increase the occurrence of xylem embolism. In summary, under drought stress, the xylem anatomical characteristics of C. lanceolata organs were highly plastic to regulate water transport vertically and radially to maintain the trade-off between hydraulic conductivity efficiency and safety.

The Impact of Urbanization on Tree Growth and Xylem Anatomical Characteristics.

In the context of the intensification of global urbanization, how urbanization (urban heat island effect and air pollution) affects urban tree growth is not fully understood. In this paper, the radial growth and xylem anatomical characteristics of three different tree species (Quercus mongolica, Fraxinus mandshurica, and Pinus sylvestris var. mongolica) in urban and rural areas of Harbin were compared by means of tree-ring anatomy. The results showed that there were significant differences in the growth of both broadleaf trees and conifers between urban and rural areas. The vessel number, cumulative area of vessels, and theoretical hydraulic conductivity of all tree species in rural areas were higher than those in urban areas, indicating that urbanization may have the effect of slowing down growth. However, broadleaf trees in urban areas had higher vessel density and a greater percentage of a conductive area within xylem and theoretical xylem-specific hydraulic conductivity. The thickness of cell walls and cell wall reinforcement index of P. sylvestris var. mongolica were strongly reduced by air pollution, implying that it may be more sensitive to urbanization. Compared to Q. mongolica, F. mandshurica showed less sensitivity to urbanization. Warming and drying climate in Harbin may be an important factor affecting tree growth.

Hydraulic traits and photosynthesis are coordinated with trunk sapwood capacitance in tropical tree species.

Water stored in trunk sapwood is vital for the canopy to maintain its physiological function under high transpiration demands. Little is known regarding the anatomical properties that contribute to the hydraulic capacitance of tree trunks and whether trunk capacitance is correlated with the hydraulic and gas exchange traits of canopy branches. We examined sapwood capacitance, xylem anatomical characteristics of tree trunks, embolism resistance, the minimal xylem water potential of canopy branches, leaf photosynthesis and stomatal conductance in 22 species from a tropical seasonal rainforest and savanna. The results showed that the mean trunk sapwood capacitance did not differ between the two biomes. Capacitance was closely related to the fiber lumen fraction and fiber wall reinforcement and not to the axial and ray parenchyma fractions. Additionally, it was positively correlated with the theoretical hydraulic conductivity of a trunk and the specific hydraulic conductivity of branches, and showed a trade-off with branch embolism resistance. Species with a high trunk sapwood capacitance maintained less negative canopy water potentials in the dry season, but higher leaf photosynthetic rates and stomatal conductance in the wet season. This study provides a functional link among trunk sapwood capacitance, xylem anatomy, canopy hydraulics and photosynthesis in tropical trees.

Spatial Heterogeneity of Root Water Conduction Strategies of Zygophyllaceae Plants in Arid Regions of China.

Simple SummaryDesert plants are the main body of species diversity in desert ecosystems and often employ different strategies to adapt to their surrounding environment. In this study, the water conduction strategies of Zygophyllaceae plants along the drought gradient were discussed by dissecting the roots of Zygophyllaceae plants based on their vessel characteristic parameters. The results show that: (1) With the aggravation of drought stress, the water use strategy of Zygophyllaceae plants’ roots changed from safety priority to efficiency priority. (2) The root age of Zygophyllaceae plants increased with temperature, and the growth rate showed a downward trend. (3) Altitude mainly influenced plant growth by affecting the temperature and precipitation of arid habitats. The root xylem anatomical characteristics and life history strategies of Zygophyllaceae plants elaborated in the present study may provide a scientific basis for the ecological restoration of vegetation in arid and semi-arid areas of China.Desert plants are the main component of species diversity in desert ecosystems, and studying the anatomy and function of desert plant xylem is of great significance for understanding climate sensitivity and adaptation mechanisms to arid ecosystems. In this study, 11 sampling points were selected in the region starting from the Loess Plateau to the Jungar Basin, the taproot anatomy materials of 9 samples of Zygophyllaceae plants were collected, and the water conduction strategies and spatial distribution characteristics of these species were analyzed. The age, growth rate, vessel number, vessel fraction, vessel area within a fixed measurement range (TVA), MVA, water conductivity (TKp, MKp) and vessel diameter ranged between 1 and 27 years, 43.67 and 678.10 μm/year, 20 and 1952, 4.43 and 26.58%, 8009.62 and 192069.12 μm², 27.63 and 2164.33 μm², 0.417 and 364.97 kg m−1 MPa−1 s−1, 0.000624 and 7.60 kg m−1 Mpa−1 s−1, and 5.57 and 73.87 μm, respectively. The number of root vessels (R = 0.27, p > 0.05) of Zygophyllaceae plants decreased with the decrease in precipitation, and the average vessel area (R = −0.28, p > 0.05) and hydraulic diameter (R = −0.29, p > 0.05) showed an upward trend. This shows that the water hydraulic efficiency priority strategy may be adopted in the root system of Zygophyllaceae plants in severe drought stress condition, and the water hydraulic safety priority strategy may be used in mild drought stress conditions. With the increase in temperature, the root age of Zygophyllaceae plants showed an increasing trend, and the growth rate showed a downward trend, indicating that the radial growth of the roots of Zygophyllaceae plants is mainly affected by temperature. Altitude influences plant growth by affecting temperature and precipitation in arid habitats. The findings of the present study on root xylem anatomical characteristics and life history strategies provides a scientific basis for the ecological restoration of vegetation in arid and semi-arid areas of China.

The intraspecific relationship between wood density, vessel diameter and other traits across environmental gradients

Abstract Wood density (WD), a key trait in the trait‐based approach of plant ecology, represents a carbon investment trait that varies across species and reflects a trade‐off between metabolism and longevity. Across species, WD has been found to vary with phylogeny, moisture, temperature and xylem anatomy (e.g. vessel diameter). However, we know little about WD variation at the intraspecific level. Here, we examined how ecologically important functional traits vary in relation to WD in three generalist, exceptionally wide‐niche breadth tree species from southern Chile, making use of broad precipitation and temperature gradients. We collected branches from Embothrium coccineum and Nothofagus antarctica across a wide W–E precipitation gradient (2,500–600 mm of annual precipitation) and from N. pumilio across an elevational gradient (from low to treeline elevation). For each individual, we determined WD, several xylem anatomical features, for example, mean vessel diameter (MVD), hydraulic diameter (Dh), hydraulic conductivity (Kt), mean vessel area (MVA), vessel size distribution (MVA/VD) and other traits including concentrations of non‐structural carbohydrates (NSCs), secondary growth, leaf traits, water‐use efficiency (iWUE) and growth rate (AI). We quantified the correlation between WD and other traits and evaluated whether WD‐trait relationships differed across species using linear mixed‐effects models. We found consistent and significant negative relationships between WD and several xylem anatomy traits, including Dh, Kt, MVA and MVD. Contrary to our expectations, WD was not related to leaf traits, NSCs, iWUE and AI. Wood density had a significantly negative relationship to MVA/VD (and to a lesser extent, MVD) for both E. coccineum and N. antarctica (the precipitation gradient), while these relationships were positive for N. pumilio (the temperature gradient). Few of the WD and other trait relationships examined at the intraspecific level in this study paralleled those found across species. At the intraspecific level, WD proved to be much more related to xylem anatomical traits than to other traits. Importantly, in some cases, WD‐xylem anatomical trait relationships showed opposite trends depending on the environmental gradient. We must be cautious when using interspecific studies as the basis for inferring trait‐based responses to environmental change across other organisation levels. Read the free Plain Language Summary for this article on the Journal blog.

Xylem anatomical characteristics of Fraxinus mandshurica and relationship with climate in different slope positions

With global climate warming, warming and drying in Northeast China are becoming more and more serious. To understand the effects of drought on the radial growth of Fraxinus mandshurica at different slope positions in Xiaoxing'an Mountains, we analyzed the responses of xylem anatomical characteristics of F. mandshurica to moisture change at different slope positions by wood anatomi-cal method. The results showed that F. mandshurica on the upper and lower slope positions were the same in the changes of xylem anatomical parameters. The abundance of vessels showed a linear distribution, the maximum vessel area and total vessel area showed a logarithmic distribution, while the average vessel area showed a partial normal distribution. There were significant differences in many anatomical parameters among different slope positions. The abundance and area of vessels on the lower slope positions were larger than those on the upper slope positions. Most of the anatomical parameters were significantly positively correlated with daily accumulated temperature, though there were some differences between them. The total vessel area of F. mandshurica on the upper slope positions was positively correlated with the daily mean temperature, while the number and total area of vessels were positively correlated with the relative humidity. The correlation on the upper slope positions was stronger than that on the lower slope positions. The minimum vessel area was negatively correlated with daily accumulated temperature and relative humidity on the upper slope positions, while the total vessel area was positively correlated with relative humidity on lower slope positions. The warming and drying climate would reduce the area and number of vessels in F. mandshurica, but would not affect the distribution of vessels, while the distribution of vessels on the upper and lower slope positions was generally the same. The current climate warming and drying do not limit but promote the radial growth of F. mandshurica.

Xylem features detrending methods matter: A case study on earlywood vessels of Fraxinus mandshurica

Xylem anatomy can provide valuable information about tree allometry and ecophysiological performance. It has unique advantages in the study of global climate change and forest adaptation compared to traditional ring-width or density proxy parameters. Developing appropriate detrended sequences of xylem features is necessary to carry out a series of further studies. However, the differences between detrending methods and their effects for xylem features are still unclear, presenting a challenge to the choice of proper detrending methods. In this study, we used the earlywood vessel features of Fraxinus mandshurica as an example and compared the differences in four common detrending methods (Spline, CSS: cubic smoothing spline, NEP: negative exponential curve, and RCS: regional curve standardization) to highlight the importance of the detrending methods in dendroanatomical studies. The results show that detrending methods significantly affect the long-term growth trends and climate signals recorded in xylem anatomical features. Among them, NEP has good performance in terms of ring width and vessel number, which is not suitable for other vessel features because of its deterministic nature. Spline and CSS are relatively conservative methods, in which are not easy to make mistakes, but the problem of overfitting (lack of climate signals) deserves attention. Multiple RCS may be a promising detrending method with quantitative wood anatomy technology development if sufficient samples are available. Our results highlight the importance of selecting detrending methods for xylem feature identification and emphasize the importance of testing various detrending methods rather than arbitrarily choosing a standard method. The detrending method should be selected based on the purpose, such as the balance between climate signals and thorough detrended effects. We recommend applying multiple methods to test the growth trends in xylem features before selecting a detrending method. More interdisciplinary studies involving ecophysiology, wood anatomy, and dendrochronology will help to distil the valuable information in xylem features accurately.

Different response of earlywood vessel features of Fraxinus mandshurica to rapid warming in warm-dry and cold-wet areas

Xylem anatomical features are constantly adapting to changing environmental conditions, and are directly related to the key functions and physiological processes of trees. However, little is known about the responses of xylem to recent rapid warming in many areas. Based on the anatomical features of the xylem of Fraxinus mandshurica Rupr. from 14 sites in two contrasting areas (warm-dry and cold-wet) of northeast China, the plasticity response and adaptation strategies of radial growth, earlywood vessels (EWV), and hydraulic features of F. mandshurica to climate change were studied. Results showed that, compared with the cold-wet area, F. mandshurica in warm-dry area had wider rings, larger vessel area, higher number of vessels (VN), larger hydraulic diameters (Dh) and higher theoretical tree-ring hydraulic conductivity (Kh). On the contrary, the vessel density (VD), percentage of EWV (PC) and xylem-specific theoretical hydraulic conductivity (Ks) in warm-dry area was lower than those in cold-wet area. In these two areas, the RW, mean vessel area (MVA), total vessel area (TVA), VN, Dh, and Kh were significantly positively correlated with temperature, and negatively correlated with winter moisture. However, the PC, VD, and Ks were inversely related to climate factors in the two areas. F. mandshurica can adjust the density and proportion of EWV by changing the configuration of earlywood and latewood to cope with the interannual climate change and balance the hydraulic efficiency and safety. Rapid warming significantly increased the growing season length and hydraulic efficiency of F. mandshurica in warm-dry and cold-wet areas, thus maximizing carbon fixation. This provides a potential physiological explanation for the growth increase and range expansion of the main broadleaf tree species in temperate zone of northeast China in recent years. F. mandshurica in warm-dry areas benefits greatly from continuous climate warming, but the risk of hydraulic failure may increase.

Macroscopic and Microscopic Modifications of Wood after Debarking of Trees in the South Cameroon

Wounding of trees by debarking has been reported to form a callus tissue. This work aims to investigate macroscopic and microscopic modifications of wood after the removal of barks in Alstonia boonei, Scorodophloeus zenkeri, and Garcinia lucida. Species that are not yet barking were wounded to conducting experimental debarking. The wound was rectangular with 30 cm vertically with a lateral extent of 10 cm. Every three months, there was a follow-up for fifteen months during which the macroscopic and microscopic phenomena were observed and recorded. Microsections of 15–20 μm thickness were taken on a piece of wood from the regenerated and intact wood, with a sledge microtome. Staining of cell walls was done with safranin and fast green to increase contrast in an anatomical slide. Analyzes of the variability of xylem anatomical features were done by semi-automatic measurements using the SpectrumSee digital image analysis software. The speed of recovery of the bark of these three species is 9.04 cm/year for A. boonei, 5.9 cm/year for S. zenkeri, and 3.85 cm/year for G. lucida. The recovery of A. boonei’s bark is the fastest, and it just takes 15 months to heal its wound. Densities of vessels were 8, 38, and 17 per mm², respectively, for the wood of A. boonei, S. zenkeri, and G. lucida before barking. These values increased for A. boonei (26) and G. lucida (20) except for S. zenkeri (25). In all species, the diameter of the vessels has decreased in the regenerated wood. Management practices that enhance the monitoring of sustainable harvesting levels of species and promote alternative plants for the same uses should be considered as part of conservation strategies.

Stem hydraulic architecture of Malus sieversii in degraded wild fruit forest in Ili valley, China

To reveal mechanisms underlying the dieback of Malus sieversii in degraded wild fruit forest in Ili valley of China, we compared the differences in stem hydraulic architecture, water transport effectiveness and safety, as well as their influencing factors among three growth classes of dead branches ratios, including Class Ⅰ (<20%), Class Ⅱ (40%-60%) and Class Ⅲ (>80%), respectively. With the increases in degradation degree of Xinjiang wild fruit forest, sapwood-specific hydraulic conductivity and leaf-specific hydraulic conductivity decreased, without significant differences among the three growth classes. Branch embolism at dusk and hydraulic safety significantly increased. The xylem water potential at 50% loss of hydraulic conductivity was -1.87, -1.35 and -0.53 MPa for Class Ⅰ, Ⅱ and Ⅲ, respectively. Predawn and midday leaf water potential and the hydraulic safety margin exhibited an order of Ⅰ>Ⅱ>Ⅲ. Xylem anatomical cha-racteristics and branch and leaf traits related to hydraulics were significantly different among the three growth classes. Results from correlation analysis revealed a weak tradeoff between xylem-specific hydraulic efficiency and xylem safety of M. sieversii. Stem hydraulic architecture of M. sieversii altered with the decline of Xinjiang wild apple forest. With increasing degrees of degradation, the severity of xylem embolisms aggravated, resistance to cavitation embolisms reduced, and the risk of water imbalance increased.

Long-Term Impacts of Defoliator Outbreaks on Larch Xylem Structure and Tree-Ring Biomass.

Defoliator insects are a major disturbance agent in many forests worldwide. During outbreaks, they can strongly reduce photosynthetic carbon uptake and impact tree growth. In the Alps, larch budmoth (Zeiraphera diniana) outbreaks affect European larch (Larix decidua) radial growth over several years. However, immediate and legacy effects on xylem formation, structure, and functionality are still largely unknown. In this study, we aimed at assessing the impact of budmoth defoliations on larch xylem anatomical features and tree-ring structure. Analyses were performed in the Lötschental (Swiss Alps) within (1,900 m a.s.l.) and above (2,200 m a.s.l.) the optimum elevational range of larch budmoth. We investigated variability of xylem anatomical traits along century-long tree-ring series of larch (host) and Norway spruce (non-host) trees. We identified eight outbreaks affecting larch xylem anatomy during the 20th century, particularly at 1,900 m a.s.l. Tracheid number always showed a higher percent reduction than properties of individual cells. Cell lumen size was slightly reduced in the first 2–3 years of outbreaks, especially in the early part of the ring. The more carbon-demanding cell wall was thinned along the entire ring, but more evidently in the last part. Theoretical tree-ring hydraulic conductivity was reduced for several years (up to 6), mostly due to cell number decrease. Reduced cell wall area and cell number resulted in a strong reduction of the tree-ring biomass, especially in the first year of outbreak. Our study shows that, under carbon source limitations caused by natural defoliation, cell division is more impacted than wall thickening and cell enlargement (the least affected process). Consequences on both xylem hydraulic properties and tree-ring biomass should be considered when assessing long-term defoliator effects on xylem functioning, forest dynamics, and terrestrial carbon cycle.

Which matters more for wood traits in Pinus halepensis Mill., provenance or climate?

Intra-annual wood density fluctuations are valuable indicators of the role of the local climate and provenance origins on tree growth. These intra-ring wood features were the most informative about local adaptation and phenotypic plasticity of Pinus halepensis Mill. in a provenance trial. This highlights the importance of taking provenance into account when selecting forest reproductive material to mitigate the effects of climate change. It is essential to disentangle the influence of climate from the effect of provenance on inter- and intra-annual wood traits to identify populations’ responses to climate changes. This will be even more relevant in the drought-prone Mediterranean region, where species have high genetic differentiation among populations. We investigated the effects of provenance and climate driving Pinus halepensis Mill. wood traits, as imprinted phenotypic adaptations to the Mediterranean climate. Inter- and intra-annual wood trait variation (ring-, early-, and latewood width, wood density) was studied by microdensitometry in 8 provenances from Spain, France, Greece, and Italy in a common-garden experiment. We related wood traits and density fluctuations with inter-annual climate variations at the trial site and the provenance origin. Provenances showed distinct responses to climate regarding tree growth, wood density, and intra-annual fluctuations. Density fluctuations in latewood were more frequent than in earlywood. Climate at the provenance origin was a more important force for density fluctuations than climatic variations at the planting site, with different trends between coastal and inland provenances, and higher frequency of latewood fluctuations in provenances from arid and semiarid sites. Differences in P. halepensis wood density fluctuations confirmed the imprinted origin provenance control in response to climate variations and indicated a relation with local adaptation of these xylem anatomical features. Moreover, the position of these fluctuations in rings reflected the high plasticity of P. halepensis to cope with high intra-seasonal variability of climatic conditions. This underlines the importance of considering tree-ring features for the selection of provenances in reforestation material for conservation and silvicultural programs.

Relationships of growth, stable carbon isotope composition and anatomical properties of leaf and xylem in seven mulberry cultivars: a hint towards drought tolerance.

The fast growth of mulberry depends on high water consumption, but considerable variations in drought tolerance exist across different cultivars. Physiological and anatomical mechanisms are important to plant survival under drought. However, few research efforts have been made to reveal the relationships of these two aspects in relation to drought tolerance. In this study, growth rates, leaf functional physiology and anatomical characteristics of leaf and xylem of 1-year-old saplings of seven mulberry cultivars at a common garden were compared. Their relationships were also explored. Growth, leaf physiology and anatomy were significantly different among the tested cultivars. Foliar stable carbon isotope composition (δ13 C) was negatively correlated with growth rates, and closely related to several leaf and xylem anatomical traits. Particularly, leaf thickness, predicted hydraulic conductivity and vessel element length jointly contributed 77% of the variability in δ13 C. Cultivar Wupu had small stomata, intermediate leaf thickness, the smallest hydraulically weighted vessel diameter and highest vessel number, and higher δ13 C; Yunguo1 had high abaxial stomatal density, low specific leaf area, moderate hydraulic conductivity and δ13 C; these are beneficial features to reduce leaf water loss and drought-induced xylem embolism in arid areas. Cultivar Liaolu11 had contrasting physiological and anatomical traits compared with the previous two cultivars, suggesting that it might be sensitive to drought. Our findings indicate that growth and δ13 C are closely associated with both leaf and xylem anatomical characteristics in mulberry, which provides fundamental information to assist evaluation of drought tolerance in mulberry cultivars and in other woody trees.

Anatomical features of Fagaceae wood statistically extracted by computer vision approaches: Some relationships with evolution.

The anatomical structure of wood is complex and contains considerable information about its specific species, physical properties, growth environment, and other factors. While conventional wood anatomy has been established by systematizing the xylem anatomical features, which enables wood identification generally up to genus level, it is difficult to describe all the information comprehensively. This study apply two computer vision approaches to optical micrographs: the scale-invariant feature transform algorithm and connected-component labelling. They extract the shape and pore size information, respectively, statistically from the whole micrographs. Both approaches enable the efficient detection of specific features of 18 species from the family Fagaceae. Although the methods ignore the positional information, which is important for the conventional wood anatomy, the simple information on the shape or size of the elements is enough to describe the species-specificity of wood. In addition, according to the dendrograms calculated from the numerical distances of the features, the closeness of some taxonomic groups is inconsistent with the types of porosity, which is one of the typical classification systems for wood anatomy, but consistent with the evolution based on molecular phylogeny; for example, ring-porous group Cerris and radial-porous group Ilex are nested in the same cluster. We analyse which part of the wood structure gave the taxon-specific information, indicating that the latewood zone of group Cerris is similar to the whole zone of group Ilex. Computer vision approaches provide statistical information that uncovers new aspects of wood anatomy that have been overlooked by conventional visual inspection.

Assessment of Pierce's disease susceptibility in Vitis vinifera cultivars with different pedigrees

Pierce's disease (PD) of grapevine is caused by the bacterium Xylella fastidiosa. In this study, an integrated approach was applied to assess PD susceptibility among different Vitis vinifera cultivars that incorporated disease severity, bacterial pathogen abundance and loss of stem xylem hydraulic conductivity. It was hypothesized that levels of PD susceptibility in V. vinifera can be attributed in part to the host anatomical features that are shaped by its pedigree background. Two popular wine grape cultivars were initially selected from the occidentalis group, Merlot and Cabernet Sauvignon, and one from the orientalis group, Thompson Seedless. The more recently bred table grape cultivar Scarlet Royal, that has mixed pedigree parentage, was also included. PD susceptibility was compared to the known PD resistant b43‐17 V. arizonica/candicans wild grape species from North America. The data indicated that Thompson Seedless was ranked as the most susceptible to PD because it significantly exhibited the most severe disease symptoms at 12 weeks post‐inoculation and hosted the highest X. fastidiosa titre of the cultivars, and lost over 90% of its stem hydraulic conductivity. In contrast, the other three cultivars displayed less susceptibility to PD. The way in which the xylem anatomy could impact PD susceptibility in V. vinifera cultivars is discussed, together with how grape pedigrees and their cognate centre of domestication may have influenced xylem anatomical features. This work provides a reference framework to further test the hypothesis that V. vinifera cultivars with wide xylem vessels may be more prone to PD decline.

Coordination and trade-offs between leaf and stem hydraulic traits and stomatal regulation along a spectrum of isohydry to anisohydry.

The degree of plant iso/anisohydry, a widely used framework for classifying species-specific hydraulic strategies, integrates multiple components of the whole-plant hydraulic pathway. However, little is known about how it associates with coordination of functional and structural traits within and across different organs. We examined stem and leaf hydraulic capacitance and conductivity/conductance, stem xylem anatomical features, stomatal regulation of daily minimum leaf and stem water potential (Ψ), and the kinetics of stomatal responses to vapour pressure deficit (VPD) in six diverse woody species differing markedly in their degree of iso/anisohydry. At the stem level, more anisohydric species had higher wood density and lower native capacitance and conductivity. Like stems, leaves of more anisohydric species had lower hydraulic conductance; however, unlike stems, their leaves had higher native capacitance at their daily minimum values of leaf Ψ. Moreover, rates of VPD-induced stomatal closure were related to intrinsic rather than native leaf capacitance and were not associated with species' degree of iso/anisohydry. Our results suggest a trade-off between hydraulic storage and efficiency in the leaf, but a coordination between hydraulic storage and efficiency in the stem along a spectrum of plant iso/anisohydry.

Impact of extreme drought on tree-ring width and vessel anatomical features of Chukrasia tabularis

Multiple sources of evidence suggest an increasing frequency of extreme climatic events during the past century. In Bangladesh, a country strongly influenced by the South Asian monsoon climate, the years 1999 and 2006 were the most severe droughts among the ten drought events identified over the last four decades. We investigated the impact of these two drought events on radial growth and xylem anatomical features of the brevi-deciduous tree species Chukrasia tabularis in a moist tropical forest in Bangladesh. Tree radial growth declined by 54% during the 1999 and 48.7% during the 2006 droughts, respectively. Among the wood anatomical features, the number of vessels (NV) showed the highest sensitivity to drought, with a 45% decrease in the 1999 drought year, followed by total vessel area (TVA) and mean vessel area (MVA). On the other hand, Vessel density (VD) increased by 13% during the 1999 drought but the increase in VD was very low in the drought year 2006. The decreasing vessel area and increasing vessel density indicate xylem hydraulic adaptation of C. tabularis to minimize drought induced cavitation risk and to avoid hydraulic failure. The significant correlations between the Standardized Precipitation Evapotranspiration Index (SPEI) and time series of tree-ring width and vessel variables imply that decline in radial growth and changes in vessel features in C. tabularis are likely to be caused by drought induced water stress. Our analyses suggest that radial growth and wood anatomical features of C. tabularis are highly sensitive to extreme drought events in South Asian moist tropical forests and can be used to reconstruct past droughts and to model tree response to drought stress under future climate conditions.

Divergent hydraulic strategies to cope with freezing in co-occurring temperate tree species with special reference toroot and stem pressure generation.

Some temperate tree species mitigate the negative impacts of frost-induced xylem cavitation by restoring impaired hydraulic function via positive pressures, and may therefore be more resistant to frost fatigue (the phenomenon that post-freezing xylem becomes more susceptible to hydraulic dysfunction) than nonpressure-generating species. We test this hypothesis and investigate underlying anatomical/physiological mechanisms. Using a common garden experiment, we studied key hydraulic traits and detailed xylem anatomical characteristics of 18 sympatric tree species. These species belong to three functional groups, that is, one generating both root and stem pressures (RSP), one generating only root pressure (RP), and one unable to generate such pressures (NP). The three functional groups diverged substantially in hydraulic efficiency, resistance to drought-induced cavitation, and frost fatigue resistance. Most notably, RSP and RP were more resistant to frost fatigue than NP, but this was at the cost of reduced hydraulic conductivity for RSP and reduced resistance to drought-induced cavitation for RP. Our results show that, in environments with strong frost stress: these groups diverge in hydraulic functioning following multiple trade-offs between hydraulic efficiency, resistance to drought and resistance to frost fatigue; and how differences in anatomical characteristics drive such divergence across species.

Anatomical and morphological changes in scion of some olive grafting combinations under water deficit

Effects of water stress deficit were studied on xylem anatomical fea- tures and some growth parameters among six olive grafting combinations; Amygdalifolia/Arbequina (Am/Ar), Amygdalifolia/Koroneiki (Am/Ko), Amygdalifolia/Zard (Am/Z), Conservallia/Koroneiki (Co/Ko), Conservallia/Zard (Co/Z) and Conservallia/Arbequina (Co/Ar) of about three-year-old olive trees ( Olea europaea L.) under greenhouse conditions. To realize this, a factorial experiment was conducted in a completely randomized design (CRD). The results showed that rootstocks exhibited significant effects on scions xylem anatomical physiognomies, such as vessel lumen area (VLA) and vessel diame- ter (VD) and additionally on some growth indices including main stem length (SL), lateral shoot number (LSN) and graft union-cross sectional area (GU-CSA). Xylem anatomical characteristics including VLA, porosity, vessel frequency (VF) and VD of scions decreased when they were grafted onto Arbequina and Koroneiki rootstocks, but increased onto Zard rootstock. All growth parameters showed a decrease under drought stress, while this reduction was more pro- nounced for Zard rootstock than the other rootstocks. However, Co/Z showed the highest VF and the lowest vulnerability index (VI) and exhibited a better performance at the end of recovery.