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Changes in vapour pressure deficit can lead to the depletion and replenishment of stem water pools to buffer water potential variations in the xylem. Yet, the precise velocity at which stem water pools track environmental cues remains poorly explored. Nine eucalyptus seedlings grown in a glasshouse experienced high-frequency environmental oscillations and their stem radial variations (ΔR) were monitored at a 30-s temporal resolution in upper and lower stem locations and on the bark and xylem. The stem ΔR response to vapour pressure deficit changes was nearly instantaneous (<1 min), while temperature lagged behind stem ΔR. No temporal differences in the stem ΔR response were observed between locations. Punctual gravimetric measurements confirmed the synchrony between transpiration and stem ΔR dynamics. These results indicate (i) that stem-stored water can respond to the atmospheric evaporative demand much faster than commonly assumed and (ii) that the origin of the water released to the transpiration stream seems critical in determining time lags in stem water pool dynamics. Near-zero time lags may be explained by the high elasticity of eucalyptus woody tissues and the predominant water use from the xylem, circumventing the hydraulic radial barriers to water flow from/to the outer tissues., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Seasonality in temperate regions is prominent during the era of increased climatic variability. A hydraulic trait that can adjust to seasonally changing climatic conditions is crucial for tree safety. However, little attention has been paid to the intraspecific seasonality of drought-related traits and hydraulic safety of keystone forest trees. We examined seasonal variations in the key morphological and physiological traits as well as multiple hydraulic safety margins (SMs) at the branch and leaf levels in oriental cork oak (Quercus variabilis Bl.), which is predominant in Chinese temperate forests. Pneumatic measurements indicated that, as seasons progressed, the water potential at which 50% of branch embolisms occur (P50&#95;branch) decreased from -3.34 to -4.23 MPa, with a coefficient of variation (CV) of 9.08%. Sapwood capacitance ranged from 48.19 to 248.08 kg m-3 MPa-1, peaking in autumn and reaching minimum in winter (CV 60.58%). Rehydration kinetics confirmed higher leaf embolism vulnerability (P50&#95;leaf) in spring and autumn than those in summer, with values ranging from -1.06 to -3.02 MPa (CV 39.85%). All leaf pressure-volume (PV) traits shifted with growth, with CVs ranging from 6.95% to 46.69%. Sapwood density had significant negative correlations with P50&#95;branch and hydraulic capacitance for elastic water storage, whereas leaf mass per area was linearly associated with PV traits but not with P50&#95;leaf. Furthermore, the branch typical SMs (difference between branch midday water potential and P50&#95;branch) were consistently >1.84 MPa, and vulnerability segmentation was prevalent throughout, implying a plausible hydraulic foundation for the dominance of Q. variabilis. Diverse hydraulic response patterns existed across seasons, leading to positive SMs mediated by the aforementioned physiological traits. Although Q. variabilis exhibits a high level of hydraulic safety, its susceptibility to sudden summer droughts may increase due to global climate change., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Water-use strategies play a crucial role in the adaptive capabilities of mangroves to the saline intertidal conditions, yet the intricacies of daily water-use patterns in mangrove species, which are pivotal for maintaining water balance, remain poorly understood. In this comprehensive study, we aimed to clarify the water use strategies of three co-occurring mangrove species, Avicennia marina, Aegiceras corniculatum and Kandelia obovata, through stem sap flow monitoring, leaf gas exchange and stem diameter change measurements. Our findings revealed that the daily sap flow density of Avicennia and Aegiceras reached the peak about 1 h earlier than that of Kandelia. When transpiration was strong, Kandelia and Aegiceras used stem storage to meet water demand, while Avicennia synchronized stem water storage. These three mangrove species adopted cross-peak water used and unique stem water storage to regulate their water balance. In Kandelia, the daily sap flow in per sapwood area was significantly lower, while water-use efficiency was significantly higher than those of Avicennia and Aegiceras, indicating that Kandelia adopted a more conservative and efficient water-use strategy. Sap flow in Avicennia was the most sensitive to environmental changes, while Kandelia limited water dissipation by tightly controlling stomata. Meteorological factors (photosynthetically active radiation, vapor pressure deficit and air temperature) were the main driving factors of sap flow. The increase of soil temperature can promote the water use of mangrove species, while the increase of salinity resulted in more conservative water use. Our results highlight the diversity of daily water-use strategies among the three co-occurring mangrove species, pinpointing Kandelia as the most adaptive at navigating the changing conditions of intertidal habitats in the future climate. In conclusion, our findings provide a mesoscale perspective on water-use characteristics of mangroves and also provides theoretical basis for mangroves afforestation and ecological restoration., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Tropical montane evergreen broad-leaved forests cover the majority of forest areas and have high carbon storage in Xishuangbanna, southwest China. However, stem radial growth dynamics and their correlations with climate factors have never been analyzed in this forest type. By combining bi-weekly microcoring and high-resolution dendrometer measurements, we monitored xylogenesis and stem radius variations of the deciduous species Betula alnoides Buch.-Ham. ex D. Don and the evergreen species Schima wallichii (DC.) Korth. We analyzed the relationships between weekly climate variables prior to sampling and the enlarging zone width or wall-thickening zone width, as well as weekly radial increments and climate factors during two consecutive years (2020 to 2021) showing contrasting hydrothermal conditions in the pre-monsoon season. In the year 2020, which was characterized by a warmer and drier pre-monsoon season, the onset of xylogenesis and radial increments of B. alnoides and S. wallichii were delayed by three months and one month, respectively, compared with the year 2021. In 2020, xylem formation and radial increments were significantly reduced for B. alnoides, but not for S. wallichii. The thickness of enlarging zone and wall-thickening zone in S. wallichii were positively correlated with relative humidity, and minimum and mean air temperature, but were negatively correlated with vapor pressure deficit during 2020 to 2021. The radial increments of both species showed significant positive correlations with precipitation and relative humidity, and negative correlations with vapor pressure deficit and maximum air temperature during two years. Our findings reveal that drier pre-monsoon conditions strongly delay growth initiation and reduce stem radial growth, providing deep insights to understand tree growth and carbon sequestration potential in tropical forests under a predicted increase in frequent drought events., (© The Author(s) 2024. Published by Oxford University Press.)

Microcomputed tomography (µCT) is a nondestructive X-ray imaging method used in plant physiology to visualize in situ plant tissues that enables assessments of embolized xylem vessels. Whereas evidence for X-ray-induced cellular damage has been reported, the impact on plant physiological processes such as carbon (C) uptake, transport, and use is unknown. Yet, these damages could be particularly relevant for studies that track embolism and C fluxes over time. We examined the physiological consequences of µCT scanning for xylem embolism over 3 mo by monitoring net photosynthesis (Anet), diameter growth, chlorophyll (Chl) concentration, and foliar nonstructural carbohydrate (NSC) content in 4 deciduous tree species: hedge maple (Acer campestre), ash (Fraxinus excelsior), European hornbeam (Carpinus betulus), and sessile oak (Quercus petraea). C transport from the canopy to the roots was also assessed through 13C labeling. Our results show that monthly X-ray application did not impact foliar Anet, Chl, NSC content, and C transport. Although X-ray effects did not vary between species, the most pronounced impact was observed in sessile oak, marked by stopped growth and stem deformations around the irradiated area. The absence of adverse impacts on plant physiology for all the tested treatments indicates that laboratory-based µCT systems can be used with different beam energy levels and doses without threatening the integrity of plant physiology within the range of tested parameters. However, the impacts of repetitive µCT on the stem radial growth at the irradiated zone leading to deformations in sessile oak might have lasting implications for studies tracking plant embolism in the longer-term., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists.)

Green stem photosynthesis has been shown to be relatively inefficient but can occasionally contribute significantly to the carbon budget of desert plants. Although the possession of green photosynthetic stems is a common trait, little is known about their photosynthetic characteristics in non-desert species. Dianthus caryophyllus is a semi-woody species with prominent green stems, which show similar photosynthetic anatomy with leaves. In the present study, we used a combination of gas exchange and chlorophyll fluorescence measurements, some of which were taken under varying O 2 and CO 2 partial pressures, to investigate whether the apparent anatomical similarities between the species' leaves and stems translate into similar photosynthetic physiology and capacity for CO 2 assimilation. Both organs displayed high photosynthetic electron transport rates (ETR) and similar values of steady-state non-photochemical quenching (NPQ), albeit leaves could attain them faster. The analysis of OJIP transients showed that the quantum efficiencies and energy fluxes along the photosynthetic electron transport chain are largely similar between leaves and stems. Stems displayed higher total conductance to CO 2 diffusion, similar biochemical properties, significantly higher photosynthetic rates and lower water use efficiency than leaves. Leaf ETR was more sensitive to sub-ambient O 2 and super-ambient CO 2 partial pressures, while leaves also displayed a higher relative rate of Rubisco oxygenation. We conclude that the highly responsive NPQ and the enhanced photorespiration and WUE in leaves represent photoprotective and water-conserving adaptations to the high incident light intensities they experience naturally, at the expense of higher CO 2 assimilation rates, which the vertically orientated stems can readily attain., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

Reserves of non-structural carbohydrates (NSC) stored in living cells are essential for drought tolerance of trees. However, little is known about the phenotypic plasticity of living storage compartments (SC) and their interactions with NSC reserves under changing water availability. Here, we examined adjustments of SC and NSC reserves in stems and roots of seedlings of two temperate tree species, Acer negundo L. and Betula pendula Roth., cultivated under different substrate water availability. We found that relative contents of soluble NSC, starch and total NSC increased with decreasing water availability in stems of both species, and similar tendencies were also observed in roots of A. negundo. In the roots of B. pendula, soluble NSC contents decreased along with the decreasing water availability, possibly due to phloem decoupling or NSC translocation to shoots. Despite the contrast in organ responses, NSC contents (namely starch) positively correlated with proportions of total organ SC. Individual types of SC showed markedly distinct plasticity upon decreasing water availability, suggesting that water availability changes the partitioning of organ storage capacity. We found an increasing contribution of parenchyma-rich bark to the total organ NSC storage capacity under decreasing water availability. However, xylem SC showed substantially greater plasticity than those in bark. Axial storage cells, namely living fibers in A. negundo, responded more sensitively to decreasing water availability than radial parenchyma. Our results demonstrate that drought-induced changes in carbon balance affect the organ storage capacity provided by living cells, whose proportions are sensitively coordinated along with changing NSC reserves., (© 2024 The Author(s). Physiologia Plantarum published by John Wiley & Sons Ltd on behalf of Scandinavian Plant Physiology Society.)

In wheat (Triticum aestivum ), canopy architecture, culm diameter and stem strength are the key providers of lodging tolerance. To better understand the lodging phenomenon and determine the best linked trait to lodging, a study of lodging resistance was conducted in both artificially-induced and natural lodging conditions. Various morphological, phenological and biochemical traits, such as acid detergent fibre, acid detergent lignin, cellulose and activity of lignin-synthesising enzymes (phenylalanine ammonia lyase and tyrosine ammonia lyase) were recorded. Anatomical features were also examined by light microscopy, using the Wiesner reaction. Genotype C306 demonstrated the highest susceptibility to lodging compared to other varieties due to its limited production of lignin-synthesising enzymes, as well as its taller plant height and narrower culms. The dwarf mutants (DM6 and DM7) have a stronger resistance against lodging because they have thick stems and a short plant canopy structure. The most suitable donors for lodging are semidwarf varieties (HD2967, DPW621-50, DBW88) because they have higher production of lignin and lignin-synthesising enzymes. Grey correlation analysis also confirmed the ability of these three genotypes to tolerate lodging. The genotypes studied were comprehensively ranked. The study also includes an effort towards the standardisation of lodging methodology under artificial conditions.

The water relation strategy is a key issue in climate change. Given the difficulty of determining water relations strategy, there is a need for simple traits with a solid theoretical basis to estimate it. Traits associated with resource allocation patterns along a 'fast-slow' plant economics spectrum are particularly compelling, reflecting trade-offs between growth rate and carbon allocation. Avocado (Persea americana ), fig tree (Ficus carica ), mandarin (Citrus reticulata ), olive (Olea europaea ), pomegranate (Punica granatum ), and grapevine (Vitis vinifera ) were characterised in terms of iso-anisohydric strategy through stomatal behaviour, water potential at the turgor loss point (TLP), and hydroscape area. Additionally, the association of these metrics with leaf mass per area (LMA) and wood density (WDen) was explored. We observed high coordination between LMA and WDen, and both traits were related to metrics of water relation strategy. More anisohydric species tended to invest more carbon per unit leaf area or unit stem volume, which has implications for hydraulic efficiency and water stress tolerance. WDen and TLP were the most powerful traits in estimating the water relation strategy for six fruit species. These traits are easy to measure, time-cost efficient, and appear central to coordinating multiple traits and behaviours along the water relations strategies.

Stem water content serves as a pivotal parameter that reflects the plant vitality and maintains their internal water balance. Given the insufficient comprehension regarding the stem water content characteristics and its influencing factors during different stages of the overwintering period, the study focused on Acer truncatum Bunge and developed an Internet of Things (IoT)-based ecological information monitoring system. The system incorporated a proprietary stem water content sensor, allowing non-invasive, in-situ and real time acquisition of stem water content while monitoring diverse environmental parameters. We conducted a detailed elucidation of stem water content variation characteristics and their responses to diverse environmental factors. The results showed: (1) During the overwintering period, stem water content exhibited diurnal variations characterized by " daytime ascent and nighttime descent" across the three stages, exhibiting differences in the moment when the stem water content reaches extremal values and daily fluctuations ranges. Stem water content exhibited minimal fluctuations during deciduous and bud-breaking stages but experienced significant freezing-thawing alternations during the dormant stage, leading to an increased daily fluctuation range. (2) The Pearson correlation coefficients between environmental parameters and stem water content varied dynamically across stages. Path analysis revealed that during the deciduous stage, stem temperature and saturation vapor pressure deficit were dominant factors influencing stem water content; during dormant stage, air temperature and saturation vapor pressure deficit directly impacted stem water content; during the bud-breaking stage, the primary parameters affecting stem water content were saturation vapor pressure deficit and stem temperature. The study provides valuable insights into unveiling the water transport patterns within tree stems tissue and their environmental adaptation mechanisms during the overwintering period, aiding in the scientific development of winter management strategies to protect trees from severe cold and freezing damage, while fostering healthy growth in the subsequent year., (© 2024. The Author(s) under exclusive licence to The Botanical Society of Japan.)

Plant cells withstand mechanical stress originating from turgor pressure by robustly maintaining the mechanical properties of the cell wall. This applies at the organ scale as well; many plant stems act as pressurized cylinders, where the epidermis is under tension and inner tissues are under compression. The clavata3 de-etiolated3 (clv3-8 det3-1) double mutant of Arabidopsis thaliana displays cracks in its stems because of a conflict between the mechanical properties of the weak epidermis and over-proliferation of inner stem tissues. In this work, we conducted three-point bending tests on various Arabidopsis thaliana mutants, including those displaying the stem cracking phenotype, to examine the differences in their mechanical properties. The clv3-8 det3-1 double mutant exhibited reduced stem stiffness, consistent with reduced differentiation due to the clv3-8 mutation. Yet, in clv3-8, stem cross-sectional area was increased associating with the increase in vascular bundle number, and stem cross-sections displayed various shapes. To uncouple the contribution of geometry and cell-wall differentiation to the mechanical properties of the whole stems, we tested the contribution of lignified fibers to stem stiffness. In order to suppress lignin deposition in stems genetically, we generated multiple higher-order mutants by crossing clv3-8 and/or det3-1 with nst1-1 nst3-1, in which lignin deposition is suppressed. Stem stiffness was reduced markedly in all nst1-1 nst3-1 mutant backgrounds. Overall, our results suggest that stem stiffness relies on the presence of differentiated, lignified, fiber tissue as well as on the alignment or spatial distribution of vascular bundles within the stem organ., (© 2024. The Author(s) under exclusive licence to The Botanical Society of Japan.)

Stem CO2 efflux is an important component of the carbon balance in forests. The efflux is considered to principally reflect the net result of two dominating and opposing processes: stem respiration and stem photosynthesis. In addition, transport of CO2 in xylem sap is thought to play an appreciable role in affecting the net flux. This work presents an approach to partition stem CO2 efflux among these processes using sap-flux data and CO2-exchange measurements from dark and transparent chambers placed on mature Scots pine (Pinus sylvestris) trees. Seasonal changes and monthly parameters describing the studied processes were determined. Respiration contributed most to stem net CO2 flux, reaching up to 79% (considering the sum of the absolute values of stem respiration, stem photosynthesis, and flux from CO2 transported in xylem sap to be 100%) in June, when stem growth was greatest. The contribution of photosynthesis accounted for up to 13% of the stem net CO2 flux, increasing over the monitoring period. CO2 transported axially with sap flow decreased towards the end of the growing season. At a reference temperature, respiration decreased starting around midsummer, while its temperature sensitivity increased during the summer. A decline was observed for photosynthetic quantum yield around midsummer together with a decrease in light-saturation point. The proposed approach facilitates modeling net stem CO2 flux at a range of time scales., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Experimental Biology.)

The stems of some herbaceous species can undergo basal secondary growth, leading to a continuum in the degree of woodiness along the stem. Whether the formation of secondary growth in the stem base results in differences in embolism resistance between the base and the upper portions of stems is unknown. We assessed the embolism resistance of leaves and the basal and upper portions of stems simultaneously within the same individuals of two divergent herbaceous species that undergo secondary growth in the mature stem bases. The species were Solanum lycopersicum (tomato) and Senecio minimus (fireweed). Basal stem in mature plants of both species displayed advanced secondary growth and greater resistance to embolism than the upper stem. This also resulted in significant vulnerability segmentation between the basal stem and the leaves in both species. Greater embolism resistance in the woodier stem base was found alongside decreases in the pith-to-xylem ratio, increases in the proportion of secondary xylem, and increases in lignin content. We show that there can be considerable variation in embolism resistance across the stem in herbs and that this variation is linked to the degree of secondary growth present. A gradient in embolism resistance across the stem in herbaceous plants could be an adaptation to ensure reproduction or basal resprouting during episodes of drought late in the lifecycle., (© 2024 The Authors. Plant, Cell & Environment published by John Wiley & Sons Ltd.)

Resolving the position of roots in the whole-plant hierarchy of drought-induced xylem embolism resistance is fundamental for predicting when species become isolated from soil water resources. Published research generally suggests that roots are the most vulnerable organ of the plant vascular system, although estimates vary significantly. However, our knowledge of root embolism excludes the fine roots (< 2 mm diameter) that form the bulk of total absorptive surface area of the root network for water and nutrient uptake. We measured fine root and stem xylem vulnerability in 10 vascular plant species from the major land plant clades (five angiosperms, three conifers, a fern and lycophyte), using standardised in situ methods (Optical Methods and MicroCT). Mean fine root embolism resistance across the network matched or exceeded stems in all study species. In six of these species (one fern, one lycophyte, three conifers and one angiosperm), fine roots were significantly more embolism resistant than stems. No clear relationship was found between root xylem conduit diameter and vulnerability. These results provide insight into the resistance of the plant hydraulic pathway at the site of water and nutrient uptake, and challenge the long-standing assumption that fine roots are more vulnerable than stems., (© 2024 The Author(s). New Phytologist © 2024 New Phytologist Foundation.)

Herbivory is a fundamental ecological force in the evolution of plant physiological, morphological, and chemical attributes. In this study, we explored how browsing pressure by local deer populations affected leaf form and function in two California native tree species, Quercus agrifolia (coast live oak) and Umbellularia californica (California bay laurel). Specifically, we investigated how leaf and stem vascular attributes differed between browsed and non-browsed zones of each species. Browsing significantly altered traits such as leaf to phloem ratios and leaf area, but we observed few meaningful differences in leaf and stem anatomy between browsed and non-browsed material. We discuss these results in the context of leaf and stem adaptations to herbivory and water use efficiency and explore future research considerations for investigating leaf and stem vascular trait development with herbivore presence., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Leonard et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Green leafy vegetables are an essential component of Chinese leafy vegetables. Due to their crisp stems and tender leaves, orderly harvester generally causes significant mechanical clamping damage. The physical and mechanical properties of green leafy vegetables are one of the important basis to design the orderly harvester. At the same time, they provide important parameters for the simulation and optimization of harvester. So, this paper measured the physical characteristic parameters of roots and stems of green leafy vegetables. Then, based on the TMS-Pro texture analyzer, the elasticity modulus of the roots and stems of green leafy vegetables were measured. The static friction coefficient, dynamic friction coefficient, and restitution coefficient of green leafy vegetables root-root, stem-stem, root-steel, and stem-steel were measured separately using a combination method of inclined plane and high-speed photography. Uniaxial compression creep experiments were carried out on whole and single leaf of green leafy vegetables using the TA.XT plus C universal testing machine. The constitutive equation of the four-element Burgers model was used to fit the deformation curve of the sample with time during the constant-pressure loading stage. The fitting determination coefficients R2 were all higher than 0.996, which verified the reasonable validity of the selected model. The above experimental results provide a parameter basis and theoretical support for the design and discrete element simulation optimization of orderly harvester critical components of green leafy vegetables., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Jin et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Water transport, mechanical support and storage are the vital functions provided by the xylem. These functions are carried out by different cells, exhibiting significant anatomical variation not only within species but also within individual trees. In this study, we used a comprehensive dataset to investigate the consistency of predicted hydraulic vessel diameter widening values in relation to the distance from the tree apex, represented by the relationship Dh ∝ Lβ (where Dh is the hydraulic vessel diameter, L the distance from the stem apex and β the scaling exponent). Our analysis involved 10 Fagus sylvatica L. trees sampled at two distinct sites in the Italian Apennines. Our results strongly emphasize that vessel diameter follows a predictable pattern with the distance from the stem apex and β ~ 0.20 remains consistent across cambial age and climates. This finding supports the hypothesis that trees do not alter their axial configuration represented by scaling of vessel diameter to compensate for hydraulic limitations imposed by tree height during growth. The study further indicates that within-tree variability significantly contributes to the overall variance of the vessel diameter-stem length exponent. Understanding the factors that contribute to the intraindividual variability in the widening exponent is essential, particularly in relation to interspecific responses and adaptations to drought stress., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Vulnerability curves (VCs) have been measured extensively to describe the differences in plant vulnerability to cavitation. Although the roles of hydraulic conductivity (Ks,max) and hydraulic safety (P50, embolism resistance), both of which are parameters of VCs ('sigmoidal' type), in tree demography have been evaluated across different forests, the direct linkages between VCs and tree demography are rarely explored. In this study, we combined measured VCs and plot data of 16 tree species in Panamanian seasonal tropical forests to investigate the connections between VCs and tree mortality, recruitment and growth. We found that the mortality and recruitment rates of evergreen species were most significantly positively correlated with P50. However, the mortality and recruitment rates of deciduous species only exhibited significant positive correlations with parameter a, which describes the steepness of VCs and indicates the sensitivity of conductivity loss with water potential decline, but is often neglected. These differences among evergreen and deciduous species may contribute to the poor performance of existing quantitative relationships (such as the fitting relationships for all 16 species) in capturing tree mortality and recruitment dynamics. Additionally, evergreen species presented a significant positive relationship between relative growth rate (RGR) and Ks,max, while deciduous species did not display such relationship. The RGR of both evergreen and deciduous species also displayed no significant correlations with P50 and a. Further analysis demonstrated that species with steeper VCs tended to have high mortality and recruitment rates, while species with flatter VCs were usually those with low mortality and recruitment rates. Our results highlight the important role of parameter a in tree demography, especially for deciduous species. Given that VC is a key component of plant hydraulic models, integrating measured VC rather than optimizing its parameters will help improve the ability to simulate and predict forest response to water availability., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The seasonal plasticity of resistance to xylem embolism has been demonstrated in leaves of some tree species, but is controversial in stems. In this study, we investigated the seasonality of stem xylem resistance to embolism in six temperate woody species (four deciduous and two evergreen tree species) that were grown at the same site. The xylem conduit anatomy, the concentrations, and ratios of the main cation in the xylem sap, as well as the content of nonstructural carbohydrates (including soluble sugars and starch) were measured in each species under each season to reveal the potential mechanisms of seasonal change in embolism resistance. The stem of all species showed increasing resistance to embolism as seasons progressed, with more vulnerable xylem in spring, but no significant adjustment in the other three seasons. The seasonal plasticity of stem embolism resistance was greater in deciduous species than in evergreen. On a seasonal scale, conduit diameter and conduit implosion resistance, the ratios of K + /Ca 2+ and K + /Na + , and starch content were generally not correlated with embolism resistance, suggesting that these are probably not the main drivers of seasonal plasticity of stem embolism resistance. The seasonality of embolism resistance provides critical information for better understanding plant hydraulics in response to seasonal environments, especially under climate change., (© 2024 Scandinavian Plant Physiology Society.)

The plasticity of the xylem and its associated hydraulic properties play crucial roles in plant acclimation to environmental changes, with vessel diameter (D v ) being the most functionally prominent trait. While the effects of external environmental factors on xylem formation and D v are not fully understood, the endogenous hormones indole-3-acetic acid (IAA) and abscisic acid (ABA) are known to play significant signalling roles under stress conditions. This study investigates how these hormones impact D v under various environmental changes. Experiments were conducted in maize plants subjected to drought, soil salinity, and high CO 2 concentration treatments. We found that drought and soil salinity significantly reduced D v at the same stem internode, while an elevated CO 2 concentration can mitigate this decrease in D v . Remarkably, significant negative correlations were observed between D v and the contents of IAA and ABA when considering the different treatments. Moreover, appropriate foliar application of either IAA or ABA on well-watered and stressed plants led to a decrease in D v , while the application of corresponding inhibitors resulted in an increase in D v . This finding underscores the causal relationship between D v and the levels of both IAA and ABA, offering a promising approach to manipulating xylem vessel size., (© 2024 Scandinavian Plant Physiology Society.)

Aerosols could significantly influence ecosystem carbon and water fluxes, potentially altering their interconnected dynamics, typically characterized by water-use efficiency (WUE). However, our understanding of the underlying ecophysiological mechanisms remains limited due to insufficient field observations. We conducted 4-yr measurements of leaf photosynthesis and transpiration, as well as 3-yr measurements of stem growth (SG) and sap flow of poplar trees exposed to natural aerosol fluctuation, to elucidate aerosol's impact on plant WUE. We found that aerosol improved sun leaf WUE mainly because a sharp decline in photosynthetically active radiation (PAR) inhibited its transpiration, while photosynthesis was less affected, as the negative effect induced by declined PAR was offset by the positive effect induced by low leaf vapor pressure deficit (VPD leaf ). Conversely, diffuse radiation fertilization (DRF) effect stimulated shade leaf photosynthesis with minimal impact on transpiration, leading to an improved WUE. The responses were further verified by a strong DRF on SG and a decrease in sap flow due to the suppresses in total radiation and VPD. Our field observations indicate that, contrary to the commonly assumed coupling response, carbon uptake and water use exhibited dissimilar reactions to aerosol pollution, ultimately enhancing WUE at the leaf and canopy level., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

It is well established that solar irradiance greatly influences tree metabolism and growth through photosynthesis, but its effects acting through individual climate metrics have not yet been well quantified. Understanding these effects is crucial for assessing the impacts of climate change on forest ecosystems. To describe the effects of solar irradiance on tree growth, we installed 110 automatic dendrometers in two old-growth mountain forest reserves in Central Europe, performed detailed terrestrial and aerial laser scanning to obtain precise tree profiles, and used these to simulate the sum of solar irradiance received by each tree on a daily basis. Generalized linear mixed-effect models were applied to simulate the probability of growth and the growth intensity over seven growing seasons. Our results demonstrated various contrasting effects of solar irradiance on the growth of canopy trees. On the one hand, the highest daily growth rates corresponded with the highest solar irradiance potentials (i.e. the longest photoperiod). Intense solar irradiance significantly decreased tree growth, through an increase in the vapor pressure deficit. These effects were consistent for all species but had different magnitude. Tree growth is the most effective on long rainy/cloudy days with low solar irradiance., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

A key process in forest management planning is the estimation of tree volume and, more specifically, merchantable volume. The ability to predict the cumulative stem volume relative to any upper stem diameter on standing trees or stands is essential for forest inventories and the management of forest resources. In the 1980s, the Hellenic Public Power Corporation (HPPC) started the rehabilitation of lignite post-mining areas in Greece by planting mainly black locust (Robinia pseudoacacia, L.). Today, these plantations occupy an area of approximately 2570 ha, but the stem volume has not yet been estimated. Therefore, we aimed to estimate the over- and under-bark stem volume using taper function models for 30 destructively sampled trees. Of the nineteen calibrated fixed-effects models, Kozak's (2004) equation performed best for both the over-bark and under-bark datasets, followed by Lee's (2003) and Muhairwe's (1999) equations. Two fixed effect models were compared with fitted coefficients from Poland and the United States confirming that the local model fits were better suited, as the foreign model coefficients caused an increase in root mean square error (RMSE) for stem diameter predictions of 13% and 218%, respectively. The addition of random effects on a single-stem basis for two coefficients of Kozak's (2004) equation improved the model fit significantly at 86% of the over-bark fixed effect RMSE and 69% for the under-bark model. Integrated taper functions were found to slightly outperform three volume equations for predictions of single stem volume over and under bark. Ultimately it was shown that these models can be used to precisely predict stem diameters and total stem volume for the population average as well as for specific trees of the black locust plantations in the study area., (© 2024. The Author(s).)

Understanding the capacity of temperate trees to acclimate to limited soil water has become essential in the face of increasing drought risk due to climate change. We documented seasonal - or phenological - patterns in acclimation to water deficit stress in stems and leaves of tree species spanning the angiosperm phylogeny. Over 3 yr of field observations carried out in two US arboreta, we measured stem vulnerability to embolism (36 individuals of 7 Species) and turgor loss point (119 individuals of 27 species) over the growing season. We also conducted a growth chamber experiment on 20 individuals of one species to assess the mechanistic relationship between soil water restriction and acclimation. In three-quarters of species measured, plants became less vulnerable to embolism and/or loss of turgor over the growing season. We were able to stimulate this acclimatory effect by withholding water in the growth chamber experiment. Temperate angiosperms are capable of acclimation to soil water deficit stress, showing maximum vulnerability to soil water deficits following budbreak and becoming more resilient to damage over the course of the growing season or in response to simulated drought. The species-specific tempo and extent of this acclimatory potential constitutes preadaptive climate change resilience., (© 2024 The Authors. New Phytologist © 2024 New Phytologist Foundation.)

Background: Variations in hydraulic conductivity may arise from species-specific differences in the anatomical structure and function of the xylem, reflecting a spectrum of plant strategies along a slow-fast resource economy continuum. Spruce (Picea spp.), a widely distributed and highly adaptable tree species, is crucial in preventing soil erosion and enabling climate regulation. However, a comprehensive understanding of the variability in anatomical traits of stems and their underlying drivers in the Picea genus is currently lacking especially in a common garden., Results: We assessed 19 stem economic properties and hydraulic characteristics of 17 Picea species grown in a common garden in Tianshui, Gansu Province, China. Significant interspecific differences in growth and anatomical characteristics were observed among the species. Specifically, xylem hydraulic conductivity (K s ) and hydraulic diameter exhibited a significant negative correlation with the thickness to span ratio (TSR), cell wall ratio, and tracheid density and a significant positive correlation with fiber length, and size of the radial tracheid. PCA revealed that the first two axes accounted for 64.40% of the variance, with PC1 reflecting the trade-off between hydraulic efficiency and mechanical support and PC2 representing the trade-off between high embolism resistance and strong pit flexibility. Regression analysis and structural equation modelling further confirmed that tracheid size positively influenced K s , whereas the traits DWT, D&#95;r, and TSR have influenced K s indirectly. All traits failed to show significant phylogenetic associations. Pearson's correlation analysis demonstrated strong correlations between most traits and longitude, with the notable influence of the mean temperature during the driest quarter, annual precipitation, precipitation during the wettest quarter, and aridity index., Conclusions: Our results showed that xylem anatomical traits demonstrated considerable variability across phylogenies, consistent with the pattern of parallel sympatric radiation evolution and global diversity in spruce. By integrating the anatomical structure of the stem xylem as well as environmental factors of origin and evolutionary relationships, our findings provide novel insights into the ecological adaptations of the Picea genus., (© 2024. The Author(s).)

Background and Aims: Plant water status is important for fruit development, because many fleshy fruits contain large amounts of water. However, there is no information on vascular flows of Persea americana 'Hass' avocado. The aims of this research were to explore the impact of drought stress on the water relationships of the 'Hass' avocado plant and its fruit growth., Methods: Well-watered and water-stressed 'Hass' avocado plants were compared. Over 4 weeks, water flows through the shoot and fruit pedicel were monitored using external sap flow gauges. Fruit diameter was monitored using linear transducers, and stomatal conductance (gs), photosynthesis (A) and leaf and stem water potentials (Ѱleaf and Ѱstem) were measured to assess the response of the plants to water supply., Key Results: In well-watered conditions, the average water inflow to the shoot was 72 g day-1. Fruit water inflow was 2.72 g day-1, but there was water loss of 0.37 g day-1 caused by the outflow (loss back into the tree) through the vascular tissues and 1.06 g day-1 from the fruit skin. Overall, fruit volume increased by 1.4 cm3 day-1. In contrast, water flow into fruit of water-stressed plants decreased to 1.88 g day-1, with the outflow increasing to 0.61 g day-1. As a result, increases in fruit volume were reduced to 0.4 cm3 day-1. The values of A, gs and sap flow to shoots were also reduced during drought conditions. Changes in the hourly time-courses of pedicel sap flow, fruit volume and stem water potential during drought suggest that the stomatal response prevented larger increases in outflow from the fruit. Following re-watering, a substantial recovery in growth rate was observed., Conclusions: In summary, a reduction in growth of avocado fruit was observed with induced water deficit, but the isohydric stomatal behaviour of the leaves helped to minimize negative changes in water balance. Also, there was substantial recovery after re-watering, hence the short-term water stress did not decrease avocado fruit size. Negative impacts might appear if the drought treatment were prolonged., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Studying the response of physiological and xylem anatomical traits under cadmium stress is helpful to understand plants' response to heavy metal stress. Here, seedlings of Pinus thunbergii Parl. were treated with 50, 100 and 150 mg kg-1 Cd2+ for 28 days. Cadmium and nonstructural carbohydrate content of leaves, stems and roots, root Cd2+ flux, cadmium distribution pattern in stem xylem and phloem, stem xylem hydraulic traits, cell wall component fractions of stems and roots, phytohormonal content such as abscisic acid, gibberellic acid 3, molecule -indole-3-acetic acid, and jasmonic acid from both leaves and roots, as well as xylem anatomical traits from both stems and roots were measured. Root Cd2+ flux increased from 50 to 100 mmol L-1 Cd2+ stress, however it decreased at 150 mmol L-1 Cd2+. Cellulose and hemicellulose in leaves, stems and roots did not change significantly under cadmium stress, while pectin decreased significantly. The nonstructural carbohydrate content of both leaves and stems showed significant changes under cadmium stress while the root nonstructural carbohydrate content was not affected. In both leaves and roots, the abscisic acid content significantly increased under cadmium stress, while the gibberellic acid 3, indole-3-acetic acid and jasmonic acid methylester content significantly decreased. Both xylem specific hydraulic conductivity and xylem water potential decreased with cadmium stress, however tracheid diameter and double wall thickness of the stems and roots were not affected. High cadmium intensity was found in both the stem xylem and phloem in all cadmium stressed treatments. Our study highlighted the in situ observation of cadmium distribution in both the xylem and phloem, and demonstrated the instant response of physiological traits such as xylem water potential, xylem specific hydraulic conductivity, root Cd2+ flux, nonstructural carbohydrate content, as well as phytohormonal content under cadmium stress, and the less affected traits such as xylem anatomical traits, cellulose and hemicellulose., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Background: Water stress seriously affects the survival of plants in natural ecosystems. Plant resistance to water stress relies on adaptive strategies, which are mainly based on plant anatomy with following relevant functions: (1) increase in water uptake and storage; (2) reduction of water loss; and (3) mechanical reinforcement of tissues. We measured 15 leaf-stem anatomical traits of five dominant shrub species from 12 community plots in the eastern Qaidam Basin to explore adaptive strategies based on plant leaf-stem anatomy at species and community levels. and their relationship with environmental stresses were tested., Results: Results showed that the combination of leaf-stem anatomical traits formed three types of adaptive strategies with the drought tolerance of leaf and stem taken as two coordinate axes. Three types of water stress were caused by environmental factors in the eastern Qaidam Basin, and the established adaptive strategy triangle could be well explained by these environmental stresses. The interpretation of the strategic triangle was as follows: (1) exploitative plant strategy, in which leaf and stem adopt the hydraulic efficiency strategy and safety strategy, respectively. This strategy is mostly applied to plants in sandy desert (i.e., Nitraria tangutorum, and Artemisia sphaerocephala) which is mainly influenced by drought stress; (2) stable plant strategy, in which both leaf/assimilation branches and stem adopt hydraulic safety strategy. This strategy is mostly applied to plants in salty desert (i.e., Kalidium foliatum and Haloxylon ammodendron) which aridity has little effect on them; and (3) opportunistic plant strategy, in which leaf and stem adopt hydraulic safety strategy and water transport efficiency strategy. This strategy is mostly applied to plants in multiple habitats (i.e., Sympegma regelii) which is mainly affected by coldness stress., Conclusion: The proposed adaptive strategy system could provide a basis for elucidating the ecological adaptation mechanism of desert woody plants and the scientific management of natural vegetation in the Qinghai-Tibet Plateau., (© 2024. The Author(s).)

Cultivating drought-tolerant tea varieties enhances both yield and quality of tea plants in northern China. However, the mechanisms underlying their drought tolerance remain largely unknown. Here we identified a key regulator called CsREV, which differentially regulates xylem patterns between leaves and stems, thereby conferring drought tolerance in tea plants. When drought occurs, upregulation of CsREV activates the CsVND7a-dependent xylem vessel differentiation. However, when drought persists, the vessel differentiation is hindered as CsVND7a is downregulated by CsTCP4a. This, combined with the CsREV-promoted secondary-cell-wall thickness of xylem vessel, leads to the enhanced curling of leaves, a characteristic closely associated with plant drought tolerance. Notably, this inhibitory effect of CsTCP4a on CsVND7a expression is absent in stems, allowing stem xylem vessels to continuously differentiate. Overall, the CsREV-CsTCP4-CsVND7 module is differentially utilized to shape the xylem patterns in leaves and stems, potentially balancing water transportation and utilization to improve tea plant drought tolerance., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Xylem embolism is a significant factor in tree mortality. Restoration of hydraulic conductivity after massive embolization of the vascular system requires the application of positive pressure to the vessels and/or the creation of new conductive elements. Some species generate positive pressure from the root system to propagate pressure in distal, aboveground organs in spring, whereas other species generate positive pressure locally at the stem level during winter. We provide a mechanistic explanation for winter stem pressure build-up in the walnut tree. We have developed a physical model that accounts for temperature fluctuations and phase transitions. This model is based on the exchange of water and sugars between living cells and vessels. Our computations demonstrate that vessel pressurization can be attributed to the transfer of water between vessels across the parenchyma rays, which is facilitated by a radial imbalance in sugar concentration. The ability to dispose of soluble sugars in living cells, and to transport them between living cells and up to the vessels, is identified as the main drivers of stem pressure build-up in the walnut tree., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com.)

Female plants not only flower but also produce resource-rich seeds, fruits, and cones. Thus, it is generally considered that female plants allocate more resources to sexual reproduction than male plants and that this allocation difference can explain vegetative dimorphism, such as greater leaf size in females. We found significant sexual vegetative differences in the dioecious and serotinous species, Aulax umbellata and A. cancellata. Plant height, annual branch length and canopy spread were greater in males whereas leaf size, branch thickness and branch number were greater in females. Sex ratios and basal stem area were, however, equal in the sexes. Equal sex ratios imply equal allocation to sexual reproduction and equal stem areas imply equal resource use and biomass, and thus allocation to vegetative growth. Given equal allocation to reproduction and resource use, we suggest that the vegetative dimorphism is driven by intra-male-competition to be more visually conspicuous to pollinators. This implies that plant architecture is both a vegetative and a reproductive trait., (© 2022. The Author(s).)

Background: The stalk rind is one of the important factors affecting maize stalk strength that is closely related to stalk lodging. However, the mechanism of rind development in maize is still largely unknown., Results: In this study, we analyzed the mechanical, anatomical, and biochemical properties of the third basal internode in one maize non-stiff-stalk (NSS) line and two stiff-stalk (SS) lines. Compared with the NSS line, the two SS lines had a significantly higher rind penetrometer resistance, thicker rind, and higher dry matter, hemicellulose, cellulose, and lignin weights per unit length. RNA-seq analysis was used to compare transcriptomes of the third basal internode of the two SS lines and the NSS line at the ninth leaf and tasseling stages. Gene Ontology (GO) enrichment analysis revealed that genes involved in hydrolase activity (hydrolyzing O-glycosyl compounds) and cytoskeleton organization were significantly up-regulated in the two SS lines at the ninth leaf stage and that microtubule process-related genes were significantly up-regulated in the two SS lines at the tasseling stage. Moreover, the two SS lines had enhanced expression of cell wall metabolism-related genes at the tasseling stage., Conclusions: The synthesis of cell wall polysaccharides and the cytoskeleton might play important roles in internode development. Our results can be applied for screening lodging-resistant inbred lines and breeding lodging-resistant cultivars in maize., (© 2022. The Author(s).)

Reproductive success largely defines the fitness of plant species. Understanding how heat and drought affect plant reproduction is thus key to predicting future plant fitness under rising global temperatures. Recent work suggests reproductive tissues are highly vulnerable to water stress in perennial plants where reproductive sacrifice could preserve plant survival. However, most crop species are annuals where such a strategy would theoretically reduce fitness. We examined the reproductive strategy of tomato (Solanum lycopersicum var. Rheinlands Ruhm) to determine whether water supply to fruits is prioritized above vegetative tissues during drought. Using optical methods, we mapped xylem cavitation and tissue shrinkage in vegetative and reproductive organs during dehydration to determine the priority of water flow under acute water stress. Stems and peduncles of tomato showed significantly greater xylem cavitation resistance than leaves. This maintenance of intact water supply enabled tomato fruit to continue to expand during acute water stress, utilizing xylem water made available by tissue collapse and early cavitation of leaves. Here, tomato plants prioritize water supply to reproductive tissues, maintaining fruit development under drought conditions. These results emphasize the critical role of water transport in shaping life history and suggest a broad relevance of hydraulic prioritization in plant ecology., (© 2021 John Wiley & Sons Ltd.)

Tree stems have been identified as sources of volatile organic compounds (VOCs) that play important roles in tree defence and atmospheric chemistry. Yet, we lack understanding on the magnitude and environmental drivers of stem VOC emissions in various forest ecosystems. Due to the increasing importance of extreme drought, we studied drought effects on the VOC emissions from mature Scots pine (Pinus sylvestris L.) stems. We measured monoterpenes, acetone, acetaldehyde and methanol emissions with custom-made stem chambers, online PTR-MS and adsorbent sampling in a drought-prone forest over the hot-dry summer of 2018 and compared the emission rates and dynamics between trees in naturally dry conditions and under long-term irrigation (drought release). The pine stems were significant monoterpene sources. The stem monoterpene emissions potentially originated from resin, based on their similar monoterpene spectra. The emission dynamics of all VOCs followed temperature at a daily scale, but monoterpene and acetaldehyde emission rates decreased nonlinearly with drought over the summer. Despite the dry conditions, large peaks of monoterpene, acetaldehyde and acetone emissions occurred in late summer potentially due to abiotic or biotic stressors. Our results highlight the potential importance of stem emissions in the ecosystem VOC budget, encouraging further studies in diverse environments., (© 2021 John Wiley & Sons Ltd.)

Background: Arabinogalactan-proteins (AGPs) are structurally complex hydroxyproline-rich cell wall glycoproteins ubiquitous in the plant kingdom. AGPs biosynthesis involves a series of post-translational modifications including the addition of type II arabinogalactans to non-contiguous Hyp residues. To date, eight Hyp-galactosyltransferases (Hyp-GALTs; GALT2-GALT9) belonging to CAZy GT31, are known to catalyze the addition of the first galactose residues to AGP protein backbones and enable subsequent AGP glycosylation. The extent of genetic redundancy, however, remains to be elucidated for the Hyp-GALT gene family., Results: To examine their gene redundancy and functions, we generated various multiple gene knock-outs, including a triple mutant (galt5 galt8 galt9), two quadruple mutants (galt2 galt5 galt7 galt8, galt2 galt5 galt7 galt9), and one quintuple mutant (galt2 galt5 galt7 galt8 galt9), and comprehensively examined their biochemical and physiological phenotypes. The key findings include: AGP precipitations with β-Yariv reagent showed that GALT2, GALT5, GALT7, GALT8 and GALT9 act redundantly with respect to AGP glycosylation in cauline and rosette leaves, while the activity of GALT7, GALT8 and GALT9 dominate in the stem, silique and flowers. Monosaccharide composition analysis showed that galactose was decreased in the silique and root AGPs of the Hyp-GALT mutants. TEM analysis of 25789 quintuple mutant stems indicated cell wall defects coincident with the observed developmental and growth impairment in these Hyp-GALT mutants. Correlated with expression patterns, galt2, galt5, galt7, galt8, and galt9 display equal additive effects on insensitivity to β-Yariv-induced growth inhibition, silique length, plant height, and pollen viability. Interestingly, galt7, galt8, and galt9 contributed more to primary root growth and root tip swelling under salt stress, whereas galt2 and galt5 played more important roles in seed morphology, germination defects and seed set. Pollen defects likely contributed to the reduced seed set in these mutants., Conclusion: Additive and pleiotropic effects of GALT2, GALT5, GALT7, GALT8 and GALT9 on vegetative and reproductive growth phenotypes were teased apart via generation of different combinations of Hyp-GALT knock-out mutants. Taken together, the generation of higher order Hyp-GALT mutants demonstrate the functional importance of AG polysaccharides decorating the AGPs with respect to various aspects of plant growth and development., (© 2021. The Author(s).)

Herbaceous peony (Paeonia lactiflora Pall.) is a popular high-end cut flower, but stem bending caused by low stem strength severely decreases its quality. To enhance stem strength, the regulatory effects of exogenous silicon were investigated in P. lactiflora. The results showed that silicon application enhanced stem strength by increasing the thickness of secondary cell walls and the layers of thickened secondary cells. Moreover, more lignin accumulated, particularly G-lignin and S-lignin, and the activities of lignin biosynthetic enzymes increased with silicon application. In addition, based on transcriptome analysis, silicon application induced the expression of genes participating in lignin biosynthesis pathway. Among them, hydroxycinnamoyl-CoA: shikimate hydroxycinnamoyl transferase gene (HCT1) was isolated from P. lactiflora and found to be mainly localized in the cytoplasm of cells. Overexpression of PlHCT1 increased the layers of thickened secondary cells and lignin accumulation in tobacco, resulting in enhanced stem strength and demonstrably straight stems. Finally, silicon content, lignin content and PlHCT1 expression in P. lactiflora cultivars with high stem strengths were totally higher than those in cultivars with low stem strengths. These results indicated that silicon application enhanced stem strength by promoting lignin accumulation in P. lactiflora, which has prospects for stem quality improvement in general., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Xylem tracheids are the channels for water transport in conifer. Tracheid flow resistance is composed of tracheid lumen resistance and pit resistance. The single tracheid structure parameters in the stem and root of Sabina chinensis were obtained by dissociation and slicing, combined with numerical simulation to analyze the tracheid flow resistance characteristics. The results showed that the tracheid lumen resistance was determined by the tracheid width and tracheid length. The pit resistance was determined by the number of pits and single pit resistance. The single pit resistance was composed of four elements: the secondary cell wall, the border, the margo and the torus. The margo contributed a relatively large fraction of flow resistance, while the torus, the border and the secondary cell wall formed a small fraction. The size and position of the pores in the margo had a significant effect on the fluid velocity. The number of pits were proportional to tracheid length. The power curve, S-curve and inverse curve were fitted the scatter plot of total pit resistance, total resistance, total resistivity, which was found that there were the negative correlation between them. The three scatter plot values were larger in the stem than in the root, indicating that the tracheid structure in the root was more conducive to water transport than the stem. The ratio of tracheid lumen resistance to pit resistance mainly was less than 0.6 in the stem and less than 1 in the root, indicating that the pit resistance was dominant in the total resistance of the stem and root., Competing Interests: no.

The enucleated vascular elements of the xylem and the phloem offer an excellent system to test the effect of ploidy on plant function because variation in vascular geometry has a direct influence on transport efficiency. However, evaluations of conduit sizes in polyploid plants have remained elusive, most remarkably in woody species. We used a combination of molecular, physiological and microscopy techniques to model the hydraulic resistance between source and sinks in tetraploid and diploid mango trees. Tetraploids exhibited larger chloroplasts, mesophyll cells and stomatal guard cells, resulting in higher leaf elastic modulus and lower dehydration rates, despite the high water potentials of both ploidies in the field. Both the xylem and the phloem displayed a scaling of conduits with ploidy, revealing attenuated hydraulic resistance in tetraploids. Conspicuous wall hygroscopic moieties in the cells involved in transpiration and transport indicate a role in volumetric adjustments as a result of turgor change in both ploidies. In autotetraploids, the enlargement of organelles, cells and tissues, which are critical for water and photoassimilate transport at long distances, point to major physiological novelties associated with whole-genome duplication., (© 2021 The Authors. The Plant Journal published by Society for Experimental Biology and John Wiley & Sons Ltd.)

Soil salinity is a global concern and often the primary factor contributing to land degradation, limiting crop growth and production. Alfalfa (Medicago sativa L.) is a low input high value forage legume with a wide adaptation. Examining the tissue-specific responses to salt stress will be important to understanding physiological changes of alfalfa. The responses of two alfalfa cultivars (salt tolerant 'Halo', salt intolerant 'Vernal') were studied for 12 weeks in five gradients of salt stress in a sand based hydroponic system in the greenhouse. The accumulation and localization of elements and organic compounds in different tissues of alfalfa under salt stress were evaluated using synchrotron beamlines. The pattern of chlorine accumulation for 'Halo' was: root > stem ~ leaf at 8 dSm -1 , and root ~ leaf > stem at 12 dSm -1 , potentially preventing toxic ion accumulation in leaf tissues. In contrast, for 'Vernal', it was leaf > stem ~ root at 8 dSm -1 and leaf > root ~ stem at 12 dSm -1 . The distribution of chlorine in 'Halo' was relatively uniform in the leaf surface and vascular bundles of the stem. Amide concentration in the leaf and stem tissues was greater for 'Halo' than 'Vernal' at all salt gradients. This study determined that low ion accumulation in the shoot was a common strategy in salt tolerant alfalfa up to 8 dSm -1 of salt stress, which was then replaced by shoot tissue tolerance at 12 dSm -1 ., (Copyright © 2021 The Author(s). Published by Elsevier GmbH.. All rights reserved.)

Xylella fastidiosa (Xf) is the xylem-dwelling bacterial agent associated with Pierce's disease (PD), which leads to significant declines in productivity in agriculturally important species like grapevine (Vitis vinifera). Xf spreads through the xylem network by digesting the pit membranes (PMs) between adjacent vessels, thereby potentially changing the hydraulic properties of the stem. However, the effects of Xf on water transport vary depending on the plant host and the infection stage, presenting diverse outcomes. Here, we investigated the effects of polygalacturonase, an enzyme known to be secreted by Xf when it produces biofilm on the PM surface, on stem hydraulic conductivity, and PM integrity. Experiments were performed on six grapevine genotypes with varying levels of PD resistance, with the expectation that PM resistance to degradation by polygalacturonase may play a role in PD resistance. Our objective was to study a single component of this pathosystem in isolation to better understand the mechanisms behind reported changes in hydraulics, thereby excluding the biological response of the plant to the presence of Xf in the vascular system. PM damage only occurred in stems perfused with polygalacturonase. Although the damaged PM area was small (2%-9% of the total pit aperture area), membrane digestion led to significant changes in the median air-seeding thresholds, and most importantly, shifted frequency distribution. Finally, enzyme perfusion also resulted in a universal reduction in stem hydraulic conductivity, suggesting the development of tyloses may not be the only contributing factor to reduced hydraulic conductivity in infected grapevine., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Biological invasion is a hot topic in ecological research. Most studies on the physiological mechanisms of plants focus on leaves, but few studies focus on stems. To study the tolerance of invasive plant (Sphagneticola trilobata L.) to low temperature, relevant physiological indicators (including anthocyanin and chlorophyll) in different organs (leaves and stems) were analyzed, using a native species (Sphagneticola calendulacea L.) as the control. The results showed that, upon exposure to low temperature for 15 days, the stems of two Sphagneticola species were markedly reddened, their anthocyanin content increased, chlorophyll and chlorophyll fluorescence parameters decreased, and the accumulation of reactive oxygen species in the stem increased. The percentage increases of antioxidants and total antioxidant capacities in stems were significantly higher in S. trilobata than in S. calendulacea. This showed that S. trilobata had higher cold tolerance in stems while leaves were opposite. To further verify the higher cold tolerance of the stem of S. trilobata, a defoliation experiment was designed. We found that the defoliated stem of S. trilobata reduced anthocyanin accumulation and increased chlorophyll content, while alleviating membrane lipid damage and electrical conductivity, and the defoliated stem still showed an increase in stem diameter and biomass under low temperature. The discovery of the physiological and adaptive mechanisms of the stem of S. trilobata to low temperature will provide a theoretical basis for explaining how S. trilobata maintains its annual growth in South China. This is of great significance for predicting the future spread of cloned and propagated invasive plants., (© 2020. Springer Nature B.V.)

Drought at flowering and grain filling greatly reduces maize (Zea mays) yield. Climate change is causing earlier and longer-lasting periods of drought, which affect the growth of multiple maize organs throughout development. To study how long periods of water deficit impact the dynamic nature of growth, and to determine how these relate to reproductive drought, we employed a high-throughput phenotyping platform featuring precise irrigation, imaging systems, and image-based biomass estimations. Prolonged drought resulted in a reduction of growth rate of individual organs-though an extension of growth duration partially compensated for this-culminating in lower biomass and delayed flowering. However, long periods of drought did not affect the highly organized succession of maximal growth rates of the distinct organs, i.e. leaves, stems, and ears. Two drought treatments negatively affected distinct seed yield components: Prolonged drought mainly reduced the number of spikelets, and drought during the reproductive period increased the anthesis-silking interval. The identification of these divergent biomass and yield components, which were affected by the shift in duration and intensity of drought, will facilitate trait-specific breeding toward future climate-resilient crops., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

Background: Branch angle is a pivotal component of tea plant architecture. Tea plant architecture not only affects tea quality and yield but also influences the efficiency of automatic tea plant pruning. However, the molecular mechanism controlling the branch angle, which is an important aspect of plant architecture, is poorly understood in tea plants., Results: In the present study, three CsLAZY genes were identified from tea plant genome data through sequence homology analysis. Phylogenetic tree displayed that the CsLAZY genes had high sequence similarity with LAZY genes from other plant species, especially those in woody plants. The expression patterns of the three CsLAZYs were surveyed in eight tissues. We further verified the expression levels of the key CsLAZY1 transcript in different tissues among eight tea cultivars and found that CsLAZY1 was highly expressed in stem. Subcellular localization analysis showed that the CsLAZY1 protein was localized in the plasma membrane. CsLAZY1 was transferred into Arabidopsis thaliana to investigate its potential role in regulating shoot development. Remarkably, the CsLAZY1 overexpressed plants responded more effectively than the wild-type plants to a gravity inversion treatment under light and dark conditions. The results indicate that CsLAZY1 plays an important role in regulating shoot gravitropism in tea plants., Conclusions: The results provide important evidence for understanding the functions of CsLAZY1 in regulating shoot gravitropism and influencing the stem branch angle in tea plants. This report identifies CsLAZY1 as a promising gene resource for the improvement of tea plant architecture.

Background: Electrical impedance tomography (EIT) has rarely been applied in plant science, particularly to study plant resistance to abiotic and biotic stresses. In this study, we evaluated the freezing resistance of floribunda roses (Rosa Floribunda) during frost dehardening using the EIT technique to identify a new method for rapid and non-destructive measurement of plant freezing resistance., Results: The current was the excitation source, the boundary voltage value was measured, and then the boundary voltage reconstructed value was formed. Using an imaging algorithm, the two-dimensional (2D) distribution of impedance or impedance variation was reconstructed. The EIT reconstructed values decreased obviously with the decline in freezing temperatures. The EIT reconstructed values of stems had the best fit to the logistic equation, and subsequently, the semi-lethal temperatures were calculated. The freezing resistance results evaluated using EIT reconstructed values were linearly correlated with the results of the traditional electrolyte leakage (EL) method (r = 0.93, P < 0.01)., Conclusions: In conclusion, after freezing tests, the reconstructed values of EIT images could be used to quantitatively evaluate the freezing resistance of floribunda rose stems. The present study provides a reference for the further application of the EIT technique for non-destructive and rapid detection of plant freezing resistance.

Plants constantly experience fluctuating internal and external mechanical cues, ranging from nanoscale deformation of wall components, cell growth variability, nutating stems, and fluttering leaves to stem flexion under tree weight and wind drag. Developing plants use such fluctuations to monitor and channel their own shape and growth through a form of proprioception. Fluctuations in mechanical cues may also be actively enhanced, producing oscillating behaviors in tissues. For example, proprioception through leaf nastic movements may promote organ flattening. We propose that fluctuation-enhanced proprioception allows plant organs to sense their own shapes and behave like active materials with adaptable outputs to face variable environments, whether internal or external. Because certain shapes are more amenable to fluctuations, proprioception may also help plant shapes to reach self-organized criticality to support such adaptability., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

The mode of action of 1 -naphthylphthalamic acid (NPA) to induce conspicuous local stem swelling in the area of its application to the growing internode in intact Bryophyllum calycinum was studied based on the aspects of histological observation and comprehensive analyses of plant hormones. Histological analyses revealed that NPA induced an increase in cell size and numerous cell divisions in the cortex and pith, respectively, compared to untreated stem. In the area of NPA application, vascular tissues had significantly wider cambial zones consisting of 5-6 cell layers, whereas phloem and xylem seemed not to be affected. This indicates that stem swelling in the area of NPA application is caused by stimulation of cell division and cell enlargement mainly in the cambial zone, cortex, and pith. Comprehensive analyses of plant hormones revealed that NPA substantially increased endogenous levels of indole-3-acetic acid (IAA) in the swelling area. NPA also increased endogenous levels of cytokinins, jasmonic acid, and its precursor, 12-oxo-phytodienoic acid, but did not increase abscisic acid and gibberellin levels. It was shown, using radiolabeled 14 C-IAA, that NPA applied to the middle of internode segments had little effect on polar auxin transport, while 2,3,5-triiodobenzoic acid substantially inhibited it. These results strongly suggest that NPA induces changes in endogenous levels of plant hormones, such as IAA, cytokinins, and jasmonic acid, and their hormonal crosstalk results in a conspicuous local stem swelling. The possible different mode of action of NPA from other polar auxin transport inhibitors in succulent plants is extensively discussed.

Knowing the key hydraulic traits of different genotypes at early seedling stages can potentially provide crucial information and save time for breeding programs. In the current study we investigated: (1) how root, stem and whole plant conductivities are linked to xylem traits, and (2) how the integrated hydraulic system impacts leaf water potential, gas exchange, chlorophyll a fluorescence and the growth of three coffee cultivars (clones of Coffea canephora Pierre ex Froehner cv. Conilon) with known differences in drought tolerance. The Conilon clones CL 14, CL 5 V and CL 109A, classified as tolerant, moderately tolerant, and sensitive to drought respectively, were grown under non-limiting soil-water supply but high atmospheric demand (i.e., high VPD air ). CL 14 and CL 5 V displayed higher root and stem hydraulic conductance and conductivity, and higher whole plant conductivity than CL 109A, and these differences were associated with higher root growth traits. In addition, CL 109A exhibited a non-significant trend towards wider vessels. Collectively, these responses likely contributed to reduce leaf water potential in CL 109A, and in turn, reduced leaf gas exchange, especially during elevated VPD air . Even when grown under well-watered conditions, the elevated VPD air observed during this study resulted in key differences in the hydraulic traits between the cultivars corresponding to differences in plant water status, gas exchange, and photochemical activity. Together these results suggest that coffee hydraulic traits, even when grown under non-water stress conditions, can be considered in breeding programs targeting more productive and efficient genotypes under drought and high atmospheric demand., (Copyright © 2020. Published by Elsevier GmbH.)

An increasing number of microRNAs (miRNAs) and miRNA-related sequences produced during miRNA biogenesis, comprising the isomiRome, have been recently highlighted in different species as critical mediators of environmental stress responses. Conifers have some of the largest known genomes but an extensive characterization of the isomiRome from any conifer species has been lacking. We provide here a comprehensive overview of the Pinus pinaster isomiRome expressed in roots, stem and needles under well-watered and drought conditions. From the 13,441 unique small RNA sequences identified, 2,980 were annotated as canonical miRNAs or miRNA* and the remaining were classified as isomiRNA or miRNA-like sequences. A survey of their expression patterns highlighted roots as the most responsive organ under drought, where specific sequences of which a 24-nt novel miRNA stood out, were strongly down-regulated. Given the putative roles of the miRNA-targeted transcripts validated specifically in root tissues, some of the miRNAs, conserved and novel, are shortlisted as potential regulators of drought response. These results provide a valuable resource for comparative studies between gymnosperms and angiosperms. Furthermore, it evidences high transferability of the isomiRome between pine species being a useful basis for further molecular regulation and physiological studies, and especially those focused on adaptation to drought conditions., (© 2020 John Wiley & Sons Ltd.)

Understanding tree physiological responses to fire is needed to accurately model post-fire carbon processes and inform management decisions. Given trees can die immediately or at extended time periods after fire, we combined two experiments to assess the short- (one-day) and long-term (21-months) fire effects on Pinus ponderosa sapling water transport. Native percentage loss of conductivity (nPLC), vulnerability to cavitation and xylem anatomy were assessed in unburned and burned saplings at lethal and non-lethal fire intensities. Fire did not cause any impact on nPLC and xylem cell wall structure in either experiment. However, surviving saplings evaluated 21-months post-fire were more vulnerable to cavitation. Our anatomical analysis in the long-term experiment showed that new xylem growth adjacent to fire scars had irregular-shaped tracheids and many parenchyma cells. Given conduit cell wall deformation was not observed in the long-term experiment, we suggest that the irregularity of newly grown xylem cells nearby fire wounds may be responsible for decreasing resistance to embolism in burned plants. Our findings suggest that hydraulic failure is not the main short-term physiological driver of mortality for Pinus ponderosa saplings. However, the decrease in embolism resistance in fire-wounded saplings could contribute to sapling mortality in the years following fire., (© 2020 John Wiley & Sons Ltd.)