Direct comparison of four methods to construct xylem vulnerability curves: Differences among techniques are linked to vessel network characteristics

During periods of dehydration, water transport through xylem conduits can become blocked by embolism formation. Xylem embolism compromises water supply to leaves and may lead to losses in productivity or plant death. Vulnerability curves (VCs) characterize plant losses in conductivity as xylem pressures decrease. VCs are widely used to characterize and predict plant water use at different levels of water availability. Several methodologies for constructing VCs exist and sometimes produce different results for the same plant material. We directly compared four VC construction methods on stems of black cottonwood (Populus trichocarpa), a model tree species: dehydration, centrifuge, X‐ray–computed microtomography (microCT), and optical. MicroCT VC was the most resistant, dehydration and centrifuge VCs were intermediate, and optical VC was the most vulnerable. Differences among VCs were not associated with how cavitation was induced but were related to how losses in conductivity were evaluated: measured hydraulically (dehydration and centrifuge) versus evaluated from visual information (microCT and optical). Understanding how and why methods differ in estimating vulnerability to xylem embolism is important for advancing knowledge in plant ecophysiology, interpreting literature data, and using accurate VCs in water flux models for predicting plant responses to drought.     

Bayesian analysis of Douglas-fir hydraulic architecture at multiple scales

We used a Bayesian hierarchical model to analyze the variation in xylem anatomy, hydraulic properties, and the relationship between anatomy and properties within Douglas-fir trees. The hierarchical scales in our study included fertilization treatments (fertilized and unfertilized), trees within the treatments, and positions within the trees. We measured tracheid diameter, tracheid length, percent latewood, number of pits per cell, density, and specific conductivity (K _s) on seven positions in each of 16 fertilized and 16 unfertilized trees: the trunk at cambial age 52 (breast height), 25, and 5; a branch at cambial age 20 and 7; and a root at cambial age 42 and 22. Vulnerability to embolism was also measured on the oldest trunk, branch, and root positions. For any measurement, there was little variation between treatments, however, there was great variation among positions. Tracheid diameter, tracheid length, number of pits per cell, K _s, and vulnerability to embolism decreased vertically from the roots to the branches. Correlations were evident between some positions for tracheid diameter, percent earlywood, pits per cell, and vulnerability to embolism, mostly in the fertilized treatment. We found evidence for large-scale relationships (among all observations from all trees) between density and tracheid diameter, K _s and diameter, vulnerability and diameter, K _s and pits per cell, and vulnerability and pits per cell. At a smaller scale of within position, however, usually only the branches and roots maintained the relationship.     

Xylem network connectivity and embolism spread in grapevine(Vitis vinifera L.)

Xylem networks are vulnerable to the formation and spread of gas embolisms that reduce water transport. Embolisms spread through interconduit pits, but the three-dimensional (3D) complexity and scale of xylem networks means that the functional implications of intervessel connections are not well understood. Here, xylem networks of grapevine (Vitis vinifera L.) were reconstructed from 3D high-resolution X-ray micro-computed tomography (microCT) images. Xylem network performance was then modeled to simulate loss of hydraulic conductivity under increasingly negative xylem sap pressure simulating drought stress conditions. We also considered the sensitivity of xylem network performance to changes in key network parameters. We found that the mean pit area per intervessel connection was constant across 10 networks from three, 1.5-m stem segments, but short (0.5 cm) segments fail to capture complete network connectivity. Simulations showed that network organization imparted additional resistance to embolism spread beyond the air-seeding threshold of pit membranes. Xylem network vulnerability to embolism spread was most sensitive to variation in the number and location of vessels that were initially embolized and pit membrane vulnerability. Our results show that xylem network organization can increase stem resistance to embolism spread by 40% (0.66 MPa) and challenge the notion that a single embolism can spread rapidly throughout an entire xylem network.

A complete digital reconstruction of a grapevine xylem network reveals that network connectivity imparts greater resistance to drought-induced embolism spread than pit membrane properties suggest.     

Xylem cavitation caused by drought and freezing stress in four co-occurring Juniperus species

Previous studies indicate that conifers are vulnerable to cavitation induced by drought but in many cases, not by freezing. Rarely have vulnerability to drought and freezing stress been studied together, even though both influence plant physiology and the abundance and distribution of plants in many regions of the world. We studied vulnerability to drought- and freezing-induced cavitation, along with wood density, conduit reinforcement, tracheid diameter, and hydraulic conductivity, in four Juniperus species that typically occupy different habitats, but uniquely co-occur at the same site in Arizona, AZ. We combined drought with a freeze-thaw cycle to create freezing-induced vulnerability curves. All four species demonstrated greater vulnerability to drought + freezing- than to drought-induced cavitation alone ( P  < 0.0001). Mean tracheid diameter was correlated with vulnerability to drought + freezing-induced cavitation (r = 0.512, P  = 0.01). The vulnerability to cavitation of each species followed expected rankings based on relative moisture within each species' natural distribution. Species with naturally drier distributions showed greater resistance to both drought- and drought + freezing-induced cavitation. Even conifer species with relatively small tracheid diameters can experience xylem embolism after a single freeze-thaw cycle when under drought stress.     

植物木质部栓塞测定技术的研究进展

气候变化引发干旱频度和强度的变化影响植物的生长发育和生态适应。干旱胁迫会引起木质部栓塞并造成水力失效,而如何准确量化木质部抗栓塞的能力对研究植物对干旱的响应过程尤为重要。通常可通过脆弱性曲线量化木质部抗栓塞的能力。目前已经研发出构建木质部栓塞脆弱性曲线的多种方法,但不同方法往往产生不一致的结果。深入理解这些方法的设计原理并在实际应用时比较各方法的异同,对合理解释相关文献数据及准确选择干旱预测模型等尤为重要。本文阐述了自然干燥法、离心法、注气法、声学测定法、同步加速器与X射线显微断层扫描法、光学可视化法及抽气法7种测定木质部栓塞脆弱性的方法,并总结了近年来各测定方法在具体研究中的运用情况及存在的争议。最后,对未来研究测定木质部栓塞脆弱性与实际运用相关方法的选择等提出了展望。     

Vulnerability to xylem embolism as a major correlate of the environmental distribution of rain forest species on a tropical island

Increases in drought‐induced tree mortality are being observed in tropical rain forests worldwide and are also likely to affect the geographical distribution of tropical vegetation. However, the mechanisms underlying the drought vulnerability and environmental distribution of tropical species have been little studied. We measured vulnerability to xylem embolism (P₅₀) of 13 woody species endemic to New Caledonia and with different xylem conduit morphologies. We examined the relation between P₅₀, along with other leaf and xylem functional traits, and a range of habitat variables. Selected species had P₅₀ values ranging between ?4.03 and ?2.00 MPa with most species falling in a narrow range of resistance to embolism above ?2.7 MPa. Embolism vulnerability was significantly correlated with elevation, mean annual temperature and percentage of species occurrences located in rain forest habitats. Xylem conduit type did not explain variation in P₅₀. Commonly used functional traits such as wood density and leaf traits were not related to embolism vulnerability. Xylem embolism vulnerability stands out among other commonly used functional traits as a major driver of species environmental distribution. Drought‐induced xylem embolism vulnerability behaves as a physiological trait closely associated with the habitat occupation of rain forest woody species.     

Hydraulic properties of Pinus halepensis,Pinus pinea and Tetraclinis articulata in a dune ecosystem of Eastern Spain

The hydraulic properties of Pinus pinea, Pinus halepensis and Tetraclinis articulata were studied in a coastal dune area from Eastern Spain. The measured variables include vulnerability to xylem embolism (vulnerability curves), hydraulic conductivity and carbon isotopic discrimination in leaves. Leaf water potentials were also monitored in the three studied populations during an extremely dry period. Our results showed that roots had always wider vessels and higher hydraulic conductivity than branches. Roots were also more vulnerable to xylem embolism and operated closer to their hydraulic limit (i.e., with narrower safety margins). Although it was not quantified, extensive root mortality was observed in the two pines during the study period, in agreement with the high values of xylem embolism (> 75%) predicted from vulnerability curves and the water potentials measured in the field. T. articulata was much more resistant to embolism than P. pinea and P. halepensis. Since T. articulata experienced also lower water potentials, safety margins from hydraulic failure were only slightly wider in this species than in the pines. Combining species and tissues, high resistance to xylem embolism was associated with low hydraulic conductivity and with high wood density. Both relationships imply a cost of having a resistant xylem. The study outlined very different water-use strategies for T. articulata and the pines. Whereas T. articulata had a conservative strategy that relied on the low vulnerability of its conducting system to drought-induced xylem embolism, the two pines showed regulatory mechanisms at different levels (i.e., embolism, root demography) that constrained the absorption of water when it became scarce. This revised version was published online in August 2006 with corrections to the Cover Date.     

木本植物木质部栓塞脆弱性研究新进展

木质部空穴化和栓塞是木本植物在干旱等条件下遭受水分胁迫时产生的木质部输水功能障碍, 在全球气候变化的大背景下, 栓塞脆弱性对干旱响应的研究已成为热点和重要内容。近年来有关木质部栓塞脆弱性与植物输水结构和耐旱性的关系已有大量研究并取得一定成果, 但是, 不同学者在不同地区对不同材料的研究结果存在很大不同。该文就近年来这一研究领域取得的成果及争议问题进行了概括和总结, 主要涉及木质部栓塞脆弱性(P₅₀)及脆弱曲线的建立方法、木质部栓塞脆弱性与木质部结构(导管直径、导管长度、纹孔膜、木质部密度、纤维及纤维管胞)间的关系和木质部栓塞脆弱性与耐旱性的关系, 并对未来工作进行展望, 提出在未来的工作中应对同一树种使用Cochard Cavitron离心机法、Sperry离心机技术与传统方法建立的脆弱曲线进行比较验证、计算P₅₀值、分析植物个体器官水平差异(根、茎、叶)、测定树种生理生态指标, 探索植物栓塞脆弱性与输水结构和耐旱性的关系, 从而评估不同类型植物在未来气候变化下的耐旱能力。     

A review of new research progress on the vulnerability of xylem embolism of woody plants

Xylem cavitation/embolism is the blockage of xylem conduits when woody plants suffer from water stress under drought and other environmental conditions, the study of embolism has become a hot and key topic under global climate change. Recent researches on the relationship between the vulnerability of xylem embolism and hydraulic architecture/drought tolerance have made some progress, however, scholars reached different conclusions based on results from different regions or different materials. This paper reviews the current achievements and controversial viewpoints, which includes indicator of xylem embolism vulnerability (P₅₀), method of vulnerability curve establishment, the relationship between embolism vulnerability and hydraulic architecture (vessel diameter, vessel length, pit area, wood density, fiber and fiber tracheid) and the relationship between embolism vulnerability and drought tolerance of woody plants. Future studies should use Cochard Cavitron centrifuge and Sperry centrifuge coupled with traditional methods to establish vulnerability curves, calculate P₅₀, analyze the difference among different organisms (root, stem, leaf), and measure physiological and ecological indexes. Future studies should be aimed to explore the relationship between the vulnerability of xylem embolism and hydraulic architecture/drought tolerance and to assess drought tolerance ability of different species under future climate change.     

Is desiccation tolerance and avoidance reflected in xylem and phloem anatomy of two coexisting arid‐zone coniferous trees?

Plants close their stomata during drought to avoid excessive water loss, but species differ in respect to the drought severity at which stomata close. The stomatal closure point is related to xylem anatomy and vulnerability to embolism, but it also has implications for phloem transport and possibly phloem anatomy to allow sugar transport at low water potentials. Desiccation‐tolerant plants that close their stomata at severe drought should have smaller xylem conduits and/or fewer and smaller interconduit pits to reduce vulnerability to embolism but more phloem tissue and larger phloem conduits compared with plants that avoid desiccation. These anatomical differences could be expected to increase in response to long‐term reduction in precipitation. To test these hypotheses, we used tridimensional synchroton X‐ray microtomograph and light microscope imaging of combined xylem and phloem tissues of 2 coniferous species: one‐seed juniper (Juniperus monosperma) and piñon pine (Pinus edulis) subjected to precipitation manipulation treatments. These species show different xylem vulnerability to embolism, contrasting desiccation tolerance, and stomatal closure points. Our results support the hypothesis that desiccation tolerant plants require higher phloem transport capacity than desiccation avoiding plants, but this can be gained through various anatomical adaptations in addition to changing conduit or tissue size.     

8种木本植物木质部栓塞变化与生理生态指标关系的研究Ⅰ.与植物木质部水势的关系

以自然状况下生长良好的耐旱树种刺槐(Robinia pseudoacacia L.)、元宝枫(Acer truncatum Bge.)、沙棘(Hippophae rhamnoides L.)、白榆(Ulmus pumila L.)、油松(Pinus tabulaeformis Carr.)、白皮松(Pinus bungeana Zucc.ex Endl.)及中生树种女贞(Ligustrum lucidum Ait.)、柳树(Salix matsudana Koidz. f. pendula Schneid.)为研究对象,用压力室法测定木质部水势,用冲洗法测定木质部栓塞程度,研究不同生长季节木质部栓塞与水势间的关系.结果表明针叶树油松、白皮松在各季节水势均较高,水势变化幅度较小,木质部不易发生栓塞,这与其木质部由管胞构成,对木质部栓塞不敏感,在干旱时采用高水势延迟脱水的耐旱策略有关.阔叶树刺槐、元宝枫、沙棘、白榆、女贞和柳树的木质部栓塞现象是其在每天正常生长过程中不可避免的 "平常事件",是它们适应干旱的一种方式.它们的木质部栓塞程度与水势表现出了相反的变化趋势,即同一树种在同一季节内水势值越低,木质部栓塞程度越大,但在不同树种及同一树种的不同季节不存在这种关系.由此可见,植物木质部栓塞对水势的敏感程度(即木质部栓塞脆弱性)主要由树种的木质部结构决定,同时受到树种特性、树木生长发育时期、外界环境因子的影响,木质部栓塞的脆弱性也具有季节变化特征.     

Embolism formation during freezing in the wood of Picea abies

Freeze-thaw events can cause embolism in plant xylem. According to classical theory, gas bubbles are formed during freezing and expand during thawing. Conifers have proved to be very resistant to freeze-thaw induced embolism, because bubbles in tracheids are small and redissolve during thawing. In contrast, increasing embolism rates upon consecutive freeze-thaw events were observed that cannot be explained by the classical mechanism. In this study, embolism formation during freeze-thaw events was analyzed via ultrasonic and Cryo-scanning electron microscope techniques. Twigs of Picea abies L. Karst. were subjected to up to 120 freeze-thaw cycles during which ultrasonic acoustic emissions, xylem temperature, and diameter variations were registered. In addition, the extent and cross-sectional pattern of embolism were analyzed with staining experiments and Cryo-scanning electron microscope observations. Embolism increased with the number of freeze-thaw events in twigs previously dehydrated to a water potential of -2.8 MPa. In these twigs, acoustic emissions were registered, while saturated twigs showed low, and totally dehydrated twigs showed no, acoustic activity. Acoustic emissions were detected only during the freezing process. This means that embolism was formed during freezing, which is in contradiction to the classical theory of freeze-thaw induced embolism. The clustered pattern of embolized tracheids in cross sections indicates that air spread from a dysfunctional tracheid to adjacent functional ones. We hypothesize that the low water potential of the growing ice front led to a decrease of the potential in nearby tracheids. This may result in freezing-induced air seeding.     

Poplar vulnerability to xylem cavitation acclimates to drier soil conditions

Xylem vulnerability to cavitation differs between tree species according to their drought resistance, more xerophilous species being more resistant to xylem cavitation. Variability in xylem vulnerability to cavitation is also found within species, especially between in situ populations. The origin of this variability has not been clearly identified. Here we analyzed the response of xylem hydraulic traits of Populus tremula×Populus alba trees to three different soil water regimes. Stem xylem vulnerability was scored as the xylem water potential causing 12, 50 and 88% loss of conductivity (P₁₂, P₅₀ and P₈₈). Vulnerability to cavitation was found to acclimate to growing conditions under different levels of soil water content, with P₅₀ values of ?1.82, ?2.03 and ?2.45 MPa in well‐watered, moderately water‐stressed and severely water‐stressed poplars, respectively. The value of P₁₂, the xylem tension at which cavitation begins, was correlated with the lowest value of midday leaf water potential (ψm) experienced by each plant, the difference between the two parameters being approximately 0.5 MPa, consistent with the absence of any difference in embolism level between the different water treatments. These results support the hypothesis that vulnerability to cavitation is a critical trait for resistance to drought. The decrease in vulnerability to cavitation under growing conditions of soil drought was correlated with decreased vessel diameter, increased vessel wall thickness and a stronger bordered pit field (t/b)². The links between these parameters are discussed.     

Rapid hydraulic recovery in Eucalyptus pauciflora after drought: linkages between stem hydraulics and leaf gas exchange

In woody plants, photosynthetic capacity is closely linked to rates at which the plant hydraulic system can supply water to the leaf surface. Drought‐induced embolism can cause sharp declines in xylem hydraulic conductivity that coincide with stomatal closure and reduced photosynthesis. Recovery of photosynthetic capacity after drought is dependent on restored xylem function, although few data exist to elucidate this coordination. We examined the dynamics of leaf gas exchange and xylem function in Eucalyptus pauciflora seedlings exposed to a cycle of severe water stress and recovery after re‐watering. Stomatal closure and leaf turgor loss occurred at water potentials that delayed the extensive spread of embolism through the stem xylem. Stem hydraulic conductance recovered to control levels within 6 h after re‐watering despite a severe drought treatment, suggesting an active mechanism embolism repair. However, stomatal conductance did not recover after 10 d of re‐watering, effecting tighter control of transpiration post drought. The dynamics of recovery suggest that a combination of hydraulic and non‐hydraulic factors influenced stomatal behaviour post drought.     

Static and dynamic bending has minor effects on xylem hydraulics of conifer branches (Picea abies,Pinus sylvestris)

The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought‐induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesized this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (?19.5 ± 2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco‐physiological importance. More importantly, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions.     

A new method for vulnerability analysis of small xylem areas reveals that compression wood of Norway spruce has lower hydraulic safety than opposite wood

Compression wood is formed at the underside of conifer twigs to keep branches at their equilibrium position. It differs from opposite wood anatomically and subsequently in its mechanical and hydraulic properties. The specific hydraulic conductivity (k_s) and vulnerability to drought‐induced embolism (loss of conductivity versus water potential ψ) in twigs of Norway spruce [Picea abies (L.) Karst.] were studied via cryo‐scanning electron microscope observations, dye experiments and a newly developed ‘Micro‐Sperry’ apparatus. This new technique enabled conductivity measurements in small xylem areas by insertion of syringe cannulas into twig samples. The hydraulic properties were related to anatomical parameters (tracheid diameter, wall thickness). Compression wood exhibited 79% lower k_s than opposite wood corresponding to smaller tracheid diameters. Vulnerability was higher in compression wood despite its narrower tracheids and thicker cell walls. The P₅₀ (ψ at 50% loss of conductivity) was ?3.6 MPa in opposite but only ?3.2 MPa in compression wood. Low hydraulic efficiency and low hydraulic safety indicate that compression wood has primarily a mechanical function.     

Over-accumulation of abscisic acid in transgenic tomato plants increases the risk of hydraulic failure

Climate change threatens food security, and plant science researchers have investigated methods of sustaining crop yield under drought. One approach has been to overproduce abscisic acid (ABA) to enhance water use efficiency. However, the concomitant effects of ABA overproduction on plant vascular system functioning are critical as it influences vulnerability to xylem hydraulic failure. We investigated these effects by comparing physiological and hydraulic responses to water deficit between a tomato (Solanum lycopersicum) wild type control (WT) and a transgenic line overproducing ABA (sp12). Under well-watered conditions, the sp12 line displayed similar growth rate and greater water use efficiency by operating at lower maximum stomatal conductance. X-ray microtomography revealed that sp12 was significantly more vulnerable to xylem embolism, resulting in a reduced hydraulic safety margin. We also observed a significant ontogenic effect on vulnerability to xylem embolism for both WT and sp12. This study demonstrates that the greater water use efficiency in the tomato ABA overproducing line is associated with higher vulnerability of the vascular system to embolism and a higher risk of hydraulic failure. Integrating hydraulic traits into breeding programmes represents a critical step for effectively managing a crop's ability to maintain hydraulic conductivity and productivity under water deficit.     

Analysis of freeze-thaw embolism in conifers. The interaction between cavitation pressure and tracheid size

Ice formation in the xylem sap produces air bubbles that under negative xylem pressures may expand and cause embolism in the xylem conduits. We used the centrifuge method to evaluate the relationship between freeze-thaw embolism and conduit diameter across a range of xylem pressures (Px) in the conifers Pinus contorta and Juniperus scopulorum. Vulnerability curves showing loss of conductivity (embolism) with Px down to -8 MPa were generated with versus without superimposing a freeze-thaw treatment. In both species, the freeze-thaw plus water-stress treatment caused more embolism than water stress alone. We estimated the critical conduit diameter (Df) above which a tracheid will embolize due to freezing and thawing and found that it decreased from 35 microm at a Px of -0.5 MPa to 6 microm at -8 MPa. Further analysis showed that the proportionality between diameter of the air bubble nucleating the cavitation and the diameter of the conduit (kL) declined with increasingly negative Px. This suggests that the bubbles causing cavitation are smaller in proportion to tracheid diameter in narrow tracheids than in wider ones. A possible reason for this is that the rate of dissolving increases with bubble pressure, which is inversely proportional to bubble diameter (La Place's law). Hence, smaller bubbles shrink faster than bigger ones. Last, we used the empirical relationship between Px and Df to model the freeze-thaw response in conifer species.     

Xylem vulnerability to cavitation can be accurately characterised in species with long vessels using a centrifuge method

Vulnerability to cavitation curves describe the decrease in xylem hydraulic conductivity as xylem pressure declines. Several techniques for constructing vulnerability curves use centrifugal force to induce negative xylem pressure in stem or root segments. Centrifuge vulnerability curves constructed for long‐vesselled species have been hypothesised to overestimate xylem vulnerability to cavitation due to increased vulnerability of vessels cut open at stem ends that extend to the middle or entirely through segments. We tested two key predictions of this hypothesis: (i) centrifugation induces greater embolism than dehydration in long‐vesselled species, and (ii) the proportion of open vessels changes centrifuge vulnerability curves. Centrifuge and dehydration vulnerability curves were compared for a long‐ and short‐vesselled species. The effect of open vessels was tested in four species by comparing centrifuge vulnerability curves for stems of two lengths. Centrifuge and dehydration vulnerability curves agreed well for the long‐ and short‐vesselled species. Centrifuge vulnerability curves constructed using two stem lengths were similar. Also, the distribution of embolism along the length of centrifuged stems matched the theoretical pressure profile induced by centrifugation. We conclude that vulnerability to cavitation can be accurately characterised with vulnerability curves constructed using a centrifuge technique, even in long‐vesselled species.     

Are needles of Pinus pinaster more vulnerable to xylem embolism than branches? New insights from X‐ray computed tomography

Plants can be highly segmented organisms with an independently redundant design of organs. In the context of plant hydraulics, leaves may be less embolism resistant than stems, allowing hydraulic failure to be restricted to distal organs that can be readily replaced. We quantified drought‐induced embolism in needles and stems of Pinus pinaster using high‐resolution computed tomography (HRCT). HRCT observations of needles were compared with the rehydration kinetics method to estimate the contribution of extra‐xylary pathways to declining hydraulic conductance. High‐resolution computed tomography images indicated that the pressure inducing 50% of embolized tracheids was similar between needle and stem xylem (P_{50 needle xylem} = ?3.62 MPa, P_{50 stem xylem} = ?3.88 MPa). Tracheids in both organs showed no difference in torus overlap of bordered pits. However, estimations of the pressure inducing 50% loss of hydraulic conductance at the whole needle level by the rehydration kinetics method were significantly higher (P_{50 needle} = ?1.71 MPa) than P_{50 needle xylem} derived from HRCT. The vulnerability segmentation hypothesis appears to be valid only when considering hydraulic failure at the entire needle level, including extra‐xylary pathways. Our findings suggest that native embolism in needles is limited and highlight the importance of imaging techniques for vulnerability curves.