Xylem Vessel Diameter Research Articles

Hydraulic traits exert greater limitations on tree-level maximum sap flux density than photosynthetic ability: Global evidence

Transpiration is a key process that couples the land-atmosphere exchange of water and carbon, and its maximum water transport ability affects plant productivity. Functional traits significantly influence the maximum transpiration rate; however, which factor plays the dominant role remains unknown. SAPFLUXNET dataset, which includes sap flux density of diverse species worldwide, provides fundamental data to test the importance of photosynthetic and hydraulic traits on maximum tree-level sap flux density (Js_max). Here, we investigated variations in Js_max of 2194 trees across 129 species using data from the SAPFLUXNET dataset, and analysed the relationship of Js_max with photosynthetic and hydraulic traits. Our results indicated that Js_max was positively correlated with photosynthetic traits at both leaf and tree level. Regarding hydraulic traits, Js_max was positively related to xylem hydraulic conductivity (Ks), leaf-specific hydraulic conductivity (Kl), xylem pressure inducing 50 % loss of hydraulic conductivity (P50), xylem vessel diameter (Vdia), and leaf-to-sapwood area ratio (AlAs). Random forest model showed that 87 % of the variability in Js_max can be explained by functional traits, and hydraulic traits (e.g., P50 and sapwood area, As) exerted larger effects on Js_max than photosynthetic traits. Moreover, trees with a lower sapwood area or depth could increase their sap flux density to compensate for the reduced whole-tree transpiration. Js_max of the angiosperms was significantly higher than that of the gymnosperms. Mean annual total precipitation (MAP) were positively related to Js_max with a weak correlation coefficient. Furthermore, Js_max showed a significant phylogenetic signal with Blomberg's K below 0.2. Overall, tree species with acquisitive resource economics or more efficient hydraulic systems show higher water transport capacity, and the efficiency of xylem hydraulic system rather than the demand for carbon uptake predominantly determines water transport capacity.

Taller trees exhibit greater hydraulic vulnerability in southern Amazonian forests

Potential increases in drought frequency and vapour pressure deficit pose a risk to the future function of tropical trees. Previous studies have found that taller tropical trees show a stronger increase in mortality than shorter trees in response to dry anomalies, but the mechanisms behind this are unclear. Here we investigate whether canopy branches of taller tropical trees have different hydraulic traits compared to shorter conspecifics. We determined xylem resistance to embolism (P50), hydraulic safety margin (HSM), xylem functional traits and xylem theoretical hydraulic conductivity for canopy branches of four tree species across a range of tree heights (sapling to maximum tree height) in an ecotonal forest near the Amazonia-Cerrado transition. We found that canopy branches of taller trees within each species have lower HSM, suggesting that they are more susceptible to hydraulic failure under drought than smaller conspecifics. Height-related trends in HSM were driven by variation in P50 with height and not by variation in leaf water potential which did not vary with height. We find that canopy branches with greater xylem vessel diameters are generally more vulnerable to embolism, suggesting a potential role for a diameter-safety linkage in explaining observed patterns of decreasing HSM with height. However, we find no evidence of a branch-level trade-off between theoretical hydraulic conductivity and hydraulic vulnerability. The greater hydraulic vulnerability of larger trees provides a potential explanation for the higher drought-induced mortality observed in taller tropical trees. The consistency of the height-P50 relationship across species opens the door to a more accurate prediction of southern Amazon forest responses to future droughts. Whether the findings for forests in southern Amazonia can be generalized to other Amazonian regions remains an open question.

6-Benzylaminopurine mediated augmentation of cadmium phytostabilization potential in Strobilanthes alternata

This study unveiled the cadmium phytoremediation potential and its augmentation using 6-Benzylaminopurine in Strobilanthes alternata. Cadmium stress was provided by applying 250 mg/kg cadmium chloride in soil and 25 ppm of 6-BAP (25 ml) was administered to the plants as foliar spray. The results revealed high bioconcentration factor (BCF) (18.82 ± 0.54) and low translocation factor (TF) values (0.055 ± 0.002) for the plant based on which we strongly recommend S. alternata as a promising candidate for Cd phytoremediation. The phytostabilization potential of the plant was further enhanced by applying 6-BAP, which augmented its BCF to 22.09 ± 0.64 and reduced the TF to 0.038 ± 0.001. Cd toxicity caused a reduction of plant growth parameters, root volume, adaxial-abaxial stomatal indices, relative water content, tolerance index, moisture content, membrane stability index, and xylem vessel diameter in S. alternata. However, Cd + 6-BAP treated plants exhibited an increase of the same compared to Cd-treated plants. FTIR analysis of Cd + 6-BAP treated plants revealed increased deposition of hemicellulose, causing enhanced retention of Cd in the root xylem walls, which is largely responsible for increased phytostabilization of Cd. Therefore, 6-BAP application in S. alternata can be exploited to restore Cd-contaminated areas effectively.

UC Davis Controller Rootstocks for peach: their background and how they work

Unlike the situation with apples, until recently, there have been few commercially acceptable size-controlling rootstocks available for peach production. Nearly forty years ago a program was initiated to screen Prunus germplasm for ease of vegetative propagation, compatibility with peach and sizecontrolling potential. This initial research involved ~120 genotypes that were either various named Prunus species and cultivars or inter-specific Prunus hybrids. This collection was later narrowed down to nine selections that showed some promise for commercial production. After subsequent field trials two new rootstocks were released in 2004 (K146-43 and P30-135; Controller 5 and 9TM, respectively). Subsequently, a new breeding program was initiated based on the hypothesis that hybrids of two peach cultivars (Okinawa and Harrow Blood) would have the potential to reduce the scion vigor of peach and be resistant to root-knot nematodes. A seedling population of hybrids resulting for this cross were propagated and ‘O’Henry’ peach was grafted onto each individual genotype. Those that showed size-controlling potential were then put into a series of replicated field trials and evaluated for both size-controlling behavior and productivity characteristics. These trials resulted in the release of a series of new rootstocks (‘HBOK 27’, ‘HBOK 32’, ‘HBOK 10’, ‘HBOK 50’; Controller 6, 7, 8 and 9.5TM, respectively). Subsequent intensive research documented that a major mechanism involved in growth control of scions grafted on these rootstocks involves reduced hydraulic conductivity of these rootstocks during early spring growth caused by smaller sized xylem vessel diameters.

Xylem Hydraulic Conductance Role in Kiwifruit Decline Syndrome Occurrence

Kiwifruit decline syndrome (KiDS) has affected kiwifruit orchards for more than ten years in the Mediterranean area, severely compromising productivity and causing extensive uprooting. The affected plants go through an irreversible and fast wilting process. The problem has not been solved yet, and a single cause has not been identified. In this work, we carried out a survey on ten five-year-old healthy kiwifruit cv. Hayward plants cultivated in an area strongly affected by KiDS and characterised by a rising temperature and vapor pressure deficit (VPD). Five plants were located in a KiDS-affected orchard. Our goal was to assess the hydraulic conductance of asymptomatic plants in a KiDS-affected area where rising climate change stress is underway. Our hypothesis was that a rising temperature and VPD could impair xylem functionality, leading the plants to develop strategies of tolerance, such as vessel narrowing, or stress symptoms, such as cavitation or implosion, inducing a higher risk of KiDS onset. Hydraulic conductance was investigated using a physiological and morphological approach to detect trunk sap flow, trunk growth and daily diameter variations, leaf gas exchanges and temperature, stem water potential, and the root xylem vessel diameter and vulnerability to cavitation. A strong xylem vessel narrowing was observed in all plants, with the highest frequency in the 30–45 µm diameter class, which is an indicator of long-term adaptation to a rising VPD. In some plants, cavitation and implosion were also observed, which are indicative of a short-term stress response; this behaviour was detected in the plants in the KiDS-affected orchard, where a high leaf temperature (>39 °C), low stomatal conductance (<0.20 mol H2O m−2 s−1) and transpiration (<3 mmol H2O m−2 s−1), low stem water potential (<−1 MPa), high vulnerability to cavitation (3.7 μm mm−2), low trunk sap flow and high daily stem diameter variation confirmed the water stress status. The concurrence of climate stress and agronomic management in predisposing conditions favourable to KiDS onset are discussed, evidencing the role of soil preparation, propagation material and previous crop.

Evaluation of Five Chrysanthemum morifolium Cultivars against Leaf Blight Disease Caused by Alternaria alternata at Rooting and Seedling Growth Stages.

During the winter of 2018, leaf blight on florist's daisy (Chrysanthemum morifolium L.) was noticed in Egypt. The disease, which was identified as caused by Alternaria alternata, was widely spread and led to serious damage for the exportation sector of this crop. Therefore, a study was conducted to better understand what can be conducted to minimize the problem in the future. Isolates were gathered and evaluated on five chrysanthemum cultivars (i.e., 'Feeling Green Dark', 'Talitha', 'Chrystal Regan', 'Arctic queen', and 'Podolsk Purple') grown in a greenhouse. The objectives were to isolate and identify the phytopathogen and detect the resistant degree of these cultivars with emphasis on the early growth stages of the crop. The results showed that 'Podolsk Purple' was the most resistant cultivar against the different isolates during the rooting and seedling growth stages. 'Chrystal Regan' was very susceptible to the different isolates. In addition, the isolate from 'Feeling Green Dark' was the strongest, which negatively affected the chlorophyll content and its fluorescence parameters besides other measured vegetative and anatomical features. The findings indicated that the best anatomical characters of the stem and leaf, like the thickness of cuticle and cortex, stem diameter, xylem vessel diameter, and thickness of epidermis as well as lamina thickness were recorded in the 'Podolsk Purple' cultivar. This study highlighted that by using the right cultivars, chrysanthemum can be cultivated during the winter season under Egyptian conditions. These results can be a part of solution to overcome the leaf blight caused by A. alternata on chrysanthemum during the early growing stages.

Recovery of root hydraulic conductance and xylem vessel diameter following prolonged water deficit of maize

AbstractTo sustain crop growth following soil water deficit, it is essential to have rapid recovery of leaf gas exchange. One basis for rapid recovery would be the rapid return of root hydraulic conductance to predrought levels to support water transport to the plant shoot. In this study, transpiration and root hydraulic conductance were measured over a 9‐day recovery period following an initial water‐deficit treatment of three maize (Zea mays L.) cultivars. In addition, xylem vessel diameter was measured during the recovery period at different positions from the root tip. The initiation of recovery in the transpiration rate occurred in all three cultivars within 3 days after watering, although the root conductance and transpiration rate of one cultivar were much lower than the other two cultivars. Root conductance and vessel diameter increased more slowly than the recovery of transpiration. There was an indication that transpiration could have been limited by root hydraulic conductance only when its values were low during recovery. The relationship between hydraulic conductance and vessel diameter did not, however, indicate a Poiseuille's law relationship between the two variables. Overall, cultivar variability in recovery from water deficit of the transpiration rate and root hydraulic conductance indicates that the selection for rapid recovery of leaf gas exchange following water deficit could be an important component of genotype selection in maize breeding programs.

Divergences in stem and leaf traits between lianas and coexisting trees in a subtropical montane forest

Abstract Patterns in functional trait variation associated with the ecological strategies of lianas and trees in subtropical montane forests remain poorly understood due to lack of trait comparisons. Here, we filled this gap by investigating trait divergence between lianas and trees with different leaf habits for 13 traits of 33 species (7 deciduous and 4 evergreen liana species, and 10 deciduous and 12 evergreen tree species) in a subtropical montane forest in southwestern China. We found that lianas had significantly larger stem xylem vessel diameter, higher theoretical hydraulic conductivity, specific leaf area, leaf nitrogen, and phosphorus concentrations, but lower leaf dry-matter content and N/P ratio than sympatric trees, indicating that lianas employ an acquisitive ecological strategy, with a more efficient stem hydraulic system and more productive leaves. In contrast to trees, lianas exhibited a larger variation in vessel diameter, with a few wide and many narrow vessels in the xylem, indicating a greater vessel dimorphism. Growth form explained 48.7% of the total trait variation, while leaf habit only explained 3.8% of trait variation, without significant interaction between growth form and leaf habit. In addition, significant stem–leaf trait relationships were only found in trees, but not in lianas, indicating decoupling of stem hydraulic function and leaf traits in subtropical lianas. These results suggest that subtropical montane lianas and trees differ strikingly in stem and leaf functional traits. Further studies are warranted to strengthen our understanding of the mechanisms underlying the strong divergence in ecological strategies between lianas and trees in subtropical forest ecosystems.

Xylem Vessels Traits of Oil Palm Roots Influenced by Root Diameter and Soil Hydrological Regime

Oil palm has been widely studied regarding growth and development, water use, productivity, and other economically relevant functions. However, not much is known about the hydraulic conductivity of oil palm root systems and how xylem vessels perform their function to transport water from roots to shoots so far. This information is needed to describe oil palm strategies to maintain water status, especially in oil palms that grow under various soil hydrological regimes. To investigate the root hydraulic performance, we measured mean xylem vessel diameter (D), vessel density (VD), vessel lumen area (Alumen), and potential hydraulic conductivity (Kp) for oil palm root samples in seasonally flooded riparian and well-drained sites at Harapan Jambi Forest. The result showed that D, Alumen, and Kp increased with increasing root diameter at both plantation types. On the contrary, VD significantly decreased with increasing root diameter. Potential hydraulic conductivity (Kp) in riparian sites was smaller than in well-drained sites and significantly different in root diameter >2-5 and >5-10 mm and related to both plantation types. The low potential hydraulic conductivity of root xylem vessels and the narrowing of xylem vessel lumen that occurs in oil palm roots in the seasonally flooded riparian sites were presumed as adaptation mechanisms to maintain water supply from the roots to the shoot in oil palm plants in these sites.

Pipe Cavitation Parameters Reveal Bubble Embolism Dynamics in Maize Xylem Vessels across Water Potential Gradients

Maize, a crop of international relevance, frequently undergoes xylem embolism due to water shortage, negatively impacting growth, yield, and quality. Consequently, a refined comprehension of xylem embolism is vital for enhancing maize cultivation. Notwithstanding extensive research and the generation of analytical models for embolism mechanisms, prevalent models often disregard crop-specific hydraulic processes and the formation of embolisms via air bubbles in the xylem conduit. In this research, we present an inventive model applying pipe cavitation parameters to discern water potential and bubble formation in maize leaf xylem. The model integrates pivotal physiological traits of the maize–leaf count, leaf vein count, and diameter of xylem vessels—demonstrating robust correlations. Furthermore, we constructed Percent Loss of Conductivity (PLC) curve based on water potential and compared it with our model, offering interval data to observe embolization events triggered by air bubbles. Utilizing experimental data, our novel cavitation-parameter-based model effectively corresponds with observed bubble phenomena and appropriately characterizes water transport in plant xylem conduits. This method enabled us to observe the transition from bubble occurrence to cavitation embolism microscopically, which aligned with the embolism intervals provided by the model. This procedure reveals potential trends in bubble-induced embolism and deepens our knowledge of microscopic plant hydraulics and crop embolism. This work establishes a basis for understanding the generation of bubble embolisms in maize, assists in evaluating maize-plant water status for efficient water supply management throughout the growth cycle, and contributes towards potential water management strategies for maize.

Morphoanatomical Responses and Stomatal Conductance in Shaded and Sun-Exposed Broussonetia papyrifera Seedlings

Investigating invasive species’ morphoanatomical characteristics, such as leaf area and thickness of vascular tissues and storage cells, can reveal information about their adaptive ability and competitive advantage. Thus, we analyzed the variation in leaf, stem, and root morphoanatomical structure and stomatal conductance between shaded and sun-exposed seedlings of Broussonetia papyrifera to provide insights into management strategies to control its invasive ability. The variations in leaf area (LA), Leaf Mass per Area (LMA), stomatal density, thickness of palisade and spongy mesophyll tissues, thickness of xylem parenchyma cells, diameter of all xylem vessels in stem and roots and stomatal conductance were analyzed between shaded and sun-exposed seedlings. Results revealed that the LA and LMA of B. papyrifera were significantly larger in the sun-exposed than in the shaded condition. Seedlings exposed to sunlight also had thicker palisade mesophyll and xylem parenchyma cells. The diameter of xylem vessels in roots was also significantly higher in sun-exposed seedlings. Contrarily, a reverse pattern was observed in the diameter of stem xylem vessels (i.e., shaded > sun-exposed seedlings). Physiologically, a higher stomatal conductance was also observed in sun-exposed seedlings. In conclusion, we found significant variations in leaf, stem, and root morphoanatomy and stomatal conductance between shaded and sun-exposed seedlings of B. papyrifera. The findings of the present study may provide valuable implications for managing or controlling its invasibility in the introduced range. Keywords: freehand technique, invasive species, Moraceae, paper mulberry, stomatal conductance

Alterations in plant anatomy and higher lignin synthesis provides drought tolerance in cluster bean [Cyamopsis tetragonoloba (L.) Taub.

Four contrasting varieties of guar, RGC-1002 and RGC-1038, drought tolerant, while, Sarada and RGC-936, drought sensitive, were monitored in watered and drought. The water status, phenolics, plant anatomy and transcript level of genes related to anatomical traits were assessed. The study aimed to decipher the anatomical adaptations of guar plants in response to water stress. The physiological determinants, relative water content (RWC), water potential (ψ), and leaf membrane damage, declined under drought in all four varieties although, the decrement was lesser in the tolerant varieties. Furthermore, the tolerant cultivars subjected to water stress recorded higher accumulation of total phenolic content, anthocyanin and lignin, which efficiently scavenge the reactive oxygen species. The results suggest that the cultivars RGC-1002 and RGC-1038 are better able to resist drought-induced oxidative stress than Sarada and RGC-936. Moreover, leaf, petiole, stem and root anatomical traits viz. size of epidermal cell, parenchyma, width of cortex layer, and diameter of xylem vessels were narrowed in all the varieties although, the decrement was lesser in the tolerant varieties under drought. The expression analysis of genes revealed that drought-tolerant varieties showed enhanced mechanical support for water conduction by up-regulation of genes, Phenylalanine ammonia-lyase1 (PAL1), cinnamate-4-hydroxylase (C4H), 4-coumarate-CoA ligase (4CL), cinnamoyl-CoA reductase (CCR), caffeoyl-CoA O-methyltransferase (CCOMT), and cinnamyl-alcohol dehydrogenase (CAD6) in water stress conditions. The alterations in physio-anatomical, biochemical and gene expression traits in tolerant guar varieties enabled them to maintain steady nutrient transport while reducing the risk of embolisms and increasing water-flow resistance for better survival in water stressed conditions.

Botanical and physiological parameters response of black bean (Phaseolus vulgaris L.) cultivars under increasing boron concentrations

Argentina is one of the five leading exporters of common bean (Phaseolus vulgaris L.) worldwide. Although common bean has been characterized as sensitive to boron toxicity, its production is often subjected to high boron concentrations. The aim of this study was to provide detailed information on the impact of increasing boron concentrations (0.5–8.0 mg L−1) on germination, growth, and root anatomy of two black bean cultivars (Leales 24 and Uirapurú) frequently produced in Argentina. Standard germination assays and pot greenhouse experiments were conducted. Radicles obtained in germination assays were used to make cross sections, which were analyzed under the microscope to identify anatomical alterations. Increasing boron concentrations had no effect on germination variables. In contrast, most of the growth variables analyzed (height, leaf area, fresh and dry weight, and water content) showed a steady decrease for boron concentrations above 1.0 mg L−1. Tissue boron concentrations showed an increase when boron concentrations increased. At the microscopic level, there seemed to be a decreasing trend in xylem vessel diameter. Our results suggest that boron concentrations above 1.0 and 2.0 mg L−1 may cause considerable growth and yield decreases in Uirapurú and Leales 24, respectively, thus affecting Argentinian bean production. Additionally, our results suggest that Leales 24 is moderately sensitive to boron toxicity and is best adapted for production in areas with higher boron concentrations. These findings highlight the importance of evaluating boron concentrations in soils and irrigation water in agricultural areas, and selecting cultivars best adapted to local conditions as tools for obtaining higher yields.

Hydraulic conductance and xylem vessel diameter of young maize roots subjected to sustained water‐deficit

AbstractWater deficit can have large impacts on plants, including likely alteration of root hydraulic conductance and root xylem vessel diameter, which can decrease crop productivity. No results, however, exist to assess possible linkages between these two variables as critical components contributing to plant water status. This linkage was investigated in three maize (Zea mays L.) cultivars. A stable water‐deficit treatment was established and maintained in pots by allowing soil drying to the point where transpiration rate was held constant at about 0.5 of well‐watered pots. Initially, the root hydraulic conductance of the water‐deficit plants was equivalent to that of well‐watered plants. Subsequently, however, hydraulic conductance decreased substantially. The results for xylem vessel diameter at 5 cm from the root tip exhibited a pattern similar to the decrease in root hydraulic conductance. A graph of root hydraulic conductance versus xylem vessel diameter at 5 cm showed a curvilinear response with lessening in the increase in hydraulic conductance with increasing xylem vessel diameter. The results indicate a possible link between root conductance and xylem diameter but the conductance is much less sensitive to vessel diameter than the fourth power of the radius predicted by Poiseuille's law. The association between conductance and xylem vessel diameter may reflect interaction of radial and axial water flux through the root system as indexed by vessel radius in the zone near the root tip.

Petal Morphology Is Correlated with Floral Longevity in Paeonia suffruticosa

Floral longevity (FL) is an important floral functional trait which is critical for flowering plants. FL shows great diversity among angiosperms; however, there is limited information on the mechanisms that influence differences in floral longevity, especially the relationship between petal anatomical traits and floral longevity. We aimed to examine (1) the relationships between petal anatomical traits and FL in tree peony cultivars and (2) the petal anatomical characteristics of longer FL cultivars. Eleven traits of six tree peony cultivars with different FL were investigated, including six water conservation traits (petal thickness, cuticle thickness, number of cell layers, mesophyll thickness, adaxial epidermis thickness and abaxial epidermis thickness), three water supply traits (vein density, number of xlylem vessels and xylem vessel diameter), petal fresh mass and petal dry mass across cultivars. There are significant differences in traits related to water conservation and water supply ability of tree peonies with different FL. Tree peony cultivars with long FL were characterized by the thicker Mesophyll, cuticles, adaxial and abaxial epidermis of the petals. There was a positive correlation between FL and vessel number and vessel diameter. These results suggest that the ability to retain water in flowers is associated with floral longevity. Petal traits related to water conservation and supply, including vein densities, mesophyll thickness, and epidermis thickness, are beneficial for prolonging the flower longevity in tree peonies.

Vessel dimorphism and wood traits in lianas and trees among three contrasting environments.

Determining how xylem vessel diameters vary among plants and across environments gives insights into different water-use strategies among species and ultimately their distributions. Here, we tested the vessel dimorphism hypothesis that the simultaneous occurrence of many narrow and a few wide vessels gives lianas an advantage over trees in seasonally dry environments. We measured the diameters of 13,958 vessels from 15 liana species and 10,430 vessels from 16 tree species in a tropical seasonal rainforest, savanna, and subtropical evergreen broadleaved forest. We compared differences in mean and hydraulically weighted vessel diameter (MVD and Dh ), vessel density (VD), theoretical hydraulic conductivity (Kt ), vessel area fraction (VAF), and wood density (WD) between lianas and trees and among three sites. Nine liana species and four tree species had dimorphic vessels. From the tropical seasonal rainforest to the savanna, liana MVD, Dh and Kt decreased, and VD and WD increased, while only tree WD increased. From the tropical seasonal rainforest to the subtropical forest, six wood traits remained unchanged for lianas, while tree MVD, Dh and Kt decreased and VD increased. Trait space for lianas and trees were more similar in the savanna and more divergent in the subtropical forest compared to the tropical seasonal rainforest. These results suggest that lianas tend to possess greater vessel dimorphism, which may explain how lianas grow well during seasonal drought, influencing their unique distribution across tropical rainfall gradients.

The effect of salinity on anatomical characteristics of two halophyte species from Turkey

ABSTRACT Anatomical adaptations of vegetative organs of Salicornia perennans Willd. and Suaeda prostrata Pall. subsp. prostrata distributed throughout the Kizilirmak Delta, Samsun were investigated in this study. To examine root, stem, and leaf anatomical modifications, the examined halophytic taxa were collected from the natural salt-affected soils of the study area. Some anatomical differences were detected in the roots, stems, and leaves of the taxa exposed to salinity. High salinity significantly increased the thickness of the periderm and cortex and the width of the aeriferous cavities in the root cortex of Salicornia perennans. The number of xylem vessels increased at higher salinity levels, whereas the diameters of xylem vessels decreased in the roots of Salicornia perennans. The diameters of xylem vessels decreased in the roots of Suaeda prostrata subsp. prostrata. Stem anatomical characteristics such as the thickness of the cuticle, palisade tissue, water-storing parenchyma, and the length and width of lignified cells, were increased by high salinity. Similarly, the thickness of the cortex in the stem of Suaeda prostrata subsp. prostrata was increased at the high salinity level. In addition, many tracheoblasts specific to Salicornia perennans were observed in the palisade tissue. In the leaves of Suaeda prostrata subsp. prostrata, the thickness of palisade tissue, and the succulence were significantly increased with a further increase in salt concentrations. Furthermore, stomata dimensions and stomata indices of both investigated taxa were considerably decreased under high salinity.

Effects of water and salt stresses on plant growth and xylem hydraulic properties of tomato.

Xylem is the main tissue for water transport in plants, and the changes of hydraulic properties in which would affect plant water relations and fruit water accumulation. It remains unclear regarding the responses of xylem anatomy and hydraulic properties to water and salt stresses in tomato plants and their relationships with plant growth and fruit water content. We conducted a pot experiment in a greenhouse to investigate the responses of plant growth, fruit water content, and xylem hydraulic properties of a cherry tomato (Hong Baoshi) and a medium-fruited tomato (Beifan 501). There were three treatments, control with a soil water content (θ) of 75%-95% of field capacity (FC) and an initial electrical conductivity (EC) of 0.398 dS·m-1; water stress with θ of 75%-95% of FC (before flowering) and 45%-65% of FC (from flowering until maturity) and an EC of 0.398 dS·m-1; and salt stress with θ of 75%-95% of FC and an EC of 1.680 dS·m-1. Results showed that water and salt stresses decreased the cross-sectional stem area and xylem vessel diameter by 22.0%-40.7% and 10.0%-18.3%, respectively, and reduced the specific hydraulic conductivity of stem and the hydraulic conductivity of peduncle by 8.8%-41.1% and 12.9%-28.4%, respectively. Those changes inhibited plant growth and reduced aboveground fresh weight, fruit size, fresh weight and water content, with a more pronounced negative effect in the medium-fruited tomato. More-over, fruit water content was positively correlated with the specific hydraulic conductivity of stem and peduncle. In conclusion, water and salt stresses would inhibit plant growht, fruit fresh weight, and consequently tomato yield, due to their negative effects on xylem hydraulic properties of the tomato plant. Medium-fruited tomatoes are more susceptible to water and salt stresses than cherry tomatoes.

The limiting effect of genome size on xylem vessel diameter is shifted by environmental pressures in seed plants.

Current and previous studies have extensively studied the physiological and ecological consequences of genome size (GS) on plants because of the limiting effect of GS on cell size. However, it is still obscure whether such limiting effect could be shifted by environmental pressures, or not. Here, we compiled a global dataset comprised of GS, xylem vessel diameter (V dia), xylem hydraulic conductivity (K S), P 50 (xylem water potential at the loss of 50% maximum K S), and climate factors of 251 phylogeny and habitat divergent species from 59 families. The results showed that GS could limit the V dia of the species from the same family sampled in the similar climate conditions. But the expected positive relationship between GS and V dia became uncertain and even negative across different environmental conditions. V dia was strongly positively coordinated with mean annual temperature (MAT), mean annual precipitation (MAP), and potential evapotranspiration (PET). Furthermore, V dia as the anatomic foundation of plant hydraulic performance was strongly positively coordinated with K S and negatively coordinated with -P 50. The strong environmental selection on K S and P 50 explained the concerted regulation of V dia by environmental factors. The findings revealed the combined regulation of GS and environmental pressures on xylem cell size and thus affected plant eco-physiological performance. The shifted cell size limiting effect of GS by environmental factors manifests plants great plasticity under changed environmental conditions.

The impact of xylem geometry on olive cultivar resistance to Xylella fastidiosa: An image‐based study

AbstractXylella fastidiosa is a xylem‐limited plant pathogen infecting many crops globally and is the cause of the recent olive disease epidemic in Italy. One strategy proposed to mitigate losses is to replant susceptible crops with resistant varieties. Several genetic, biochemical and biophysical traits are associated to X. fastidiosa disease resistance. However, mechanisms underpinning resistance are poorly understood. We hypothesize that the susceptibility of olive cultivars to infection will correlate to xylem vessel diameters, with narrower vessels being resistant to air embolisms and having slower flow rates limiting pathogen spread. To test this, we scanned stems from four olive cultivars of varying susceptibility to X. fastidiosa using X‐ray computed tomography. Scans were processed by a bespoke methodology that segmented vessels, facilitating diameter measurements. Though significant differences were not found comparing stem‐average vessel section diameters among cultivars, they were found when comparing diameter distributions. Moreover, the measurements indicated that although vessel diameter distributions may play a role regarding the resistance of Leccino, it is unlikely they do for FS17. Considering Young–Laplace and Hagen–Poiseuille equations, we inferred differences in embolism susceptibility and hydraulic conductivity of the vasculature. Our results suggest susceptible cultivars, having a greater proportion of larger vessels, are more vulnerable to air embolisms. In addition, results suggest that under certain pressure conditions, functional vasculature in susceptible cultivars could be subject to greater stresses than in resistant cultivars. These results support investigation into xylem morphological screening to help inform olive replanting. Furthermore, our framework could test the relevance of xylem geometry to disease resistance in other crops.