embolism resistance
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Author(s):  
Yanjun Song ◽  
Lourens Poorter ◽  
Angelina Horsting ◽  
Sylvain Delzon ◽  
Frank Sterck

Abstract Conifers face increased drought mortality risks because of drought-induced embolism in their vascular system. Variation in embolism resistance may result from species differences in pit structure and function, as pits control the air seeding between water transporting conduits. This study quantifies variation in embolism resistance and hydraulic conductivity for 28 conifer species grown in a 50-year-old common garden experiment and assesses the underlying mechanisms. Conifer species with a small pit aperture, high pit aperture resistance and large valve effect were more resistant to embolism, as they all may reduce air seeding. Surprisingly, hydraulic conductivity was only negatively correlated with tracheid cell wall thickness. Embolism resistance and its underlying pit traits related to pit size and sealing were stronger phylogenetically controlled than hydraulic conductivity and anatomical tracheid traits. Conifers differed in hydraulic safety and hydraulic efficiency, but there was no trade-off between safety and efficiency because they are driven by different xylem anatomical traits that are under different phylogenetic control.


2021 ◽  
Vol 78 (4) ◽  
Author(s):  
Sébastien Levionnois ◽  
Camille Ziegler ◽  
Patrick Heuret ◽  
Steven Jansen ◽  
Clément Stahl ◽  
...  

Abstract Key message Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stem. However, although it has been intensively investigated these past decades, the extent to which vulnerability segmentation promotes drought resistance is not well understood. Based on a trait-based model, this study theoretically supports that vulnerability segmentation enhances shoot desiccation time across 18 Neotropical tree species. Context Leaf-stem vulnerability segmentation predicts lower xylem embolism resistance in leaves than stems thereby preserving expensive organs such as branches or the trunk. Although vulnerability segmentation has been intensively investigated these past decades to test its consistency across species, the extent to which vulnerability segmentation promotes drought resistance is not well understood. Aims We investigated the theoretical impact of the degree of vulnerability segmentation on shoot desiccation time estimated with a simple trait-based model. Methods We combined data from 18 tropical rainforest canopy tree species on embolism resistance of stem xylem (flow-centrifugation technique) and leaves (optical visualisation method). Measured water loss under minimum leaf and bark conductance, leaf and stem capacitance, and leaf-to-bark area ratio allowed us to calculate a theoretical shoot desiccation time (tcrit). Results Large degrees of vulnerability segmentation strongly enhanced the theoretical shoot desiccation time, suggesting vulnerability segmentation to be an efficient drought resistance mechanism for half of the studied species. The difference between leaf and bark area, rather than the minimum leaf and bark conductance, determined the drastic reduction of total transpiration by segmentation during severe drought. Conclusion Our study strongly suggests that vulnerability segmentation is an important drought resistance mechanism that should be better taken into account when investigating plant drought resistance and modelling vegetation. We discuss future directions for improving model assumptions with empirical measures, such as changes in total shoot transpiration after leaf xylem embolism.


2021 ◽  
Vol 118 (33) ◽  
pp. e2104336118
Author(s):  
R. B. Pratt ◽  
A. L. Jacobsen ◽  
M. I. Percolla ◽  
M. E. De Guzman ◽  
C. A. Traugh ◽  
...  

The xylem in plants is specialized to transport water, mechanically support the plant body, and store water and carbohydrates. Balancing these functions leads to trade-offs that are linked to xylem structure. We proposed a multivariate hypothesis regarding the main xylem functions and tested it using structural equation modeling. We sampled 29 native shrub species from field sites in semiarid Southern California. We quantified xylem water transport (embolism resistance and transport efficiency), mechanical strength, storage of water (capacitance) and starch, minimum hydrostatic pressures (Pmin), and proportions of fibers, vessels, and parenchyma, which were treated as a latent variable representing “cellular trade-offs.” We found that xylem functions (transport, mechanical support, water storage, and starch storage) were independent, a result driven by Pmin. Pmin was strongly and directly or indirectly associated with all xylem functions as a hub trait. More negative Pmin was associated with increased embolism resistance and tissue strength and reduced capacitance and starch storage. We found strong support for a trade-off between embolism resistance and transport efficiency. Tissue strength was not directly associated with embolism resistance or transport efficiency, and any associations were indirect involving Pmin. With Pmin removed from the model, cellular trade-offs were central and related to all other traits. We conclude that xylem traits are broadly governed by functional trade-offs and that the Pmin experienced by plants in the field exerts a strong influence over these relationships. Angiosperm xylem contains different cell types that contribute to different functions and that underpin trade-offs.


Author(s):  
Rodrigo Avila ◽  
Xinyi Guan ◽  
Cade Kane ◽  
Amanda Cardoso ◽  
Timothy Batz ◽  
...  

Xylem embolism resistance varies across species influencing drought tolerance, yet little is known about the determinants of the embolism resistance of an individual conduit. Here we conducted an experiment using the optical vulnerability method to test whether individual conduits have a specific water potential threshold for embolism formation and whether pre-existing embolism in neighbouring conduits alters this threshold. Observations were made on a diverse sample of angiosperm and conifer species through a cycle of dehydration, rehydration and subsequent dehydration to death. Upon rehydration after the formation of embolism, no refilling was observed. When little pre-existing embolism was present, xylem conduits had a conserved, individual, embolism resistance threshold that varied across the population of conduits. The consequence of a variable conduit-specific embolism threshold is that a small degree of pre-existing embolism in the xylem results in an apparently more resistant xylem in a subsequent dehydration, particularly in angiosperms with vessels. While our results suggest that pit membranes separating xylem conduits are critical for maintaining a conserved individual embolism threshold for given conduit when little pre-exisiting embolism is present, as the percentage of embolized conduits increases, gas movement, local pressure differences, and connectivity between conduits increasingly contribute to embolism spread.


2021 ◽  
Vol 12 ◽  
Author(s):  
Christophe L. Trabi ◽  
Luciano Pereira ◽  
Xinyi Guan ◽  
Marcela T. Miranda ◽  
Paulo R. L. Bittencourt ◽  
...  

The Pneumatron device measures gas diffusion kinetics in the xylem of plants. The device provides an easy, low-cost, and powerful tool for research on plant water relations and gas exchange. Here, we describe in detail how to construct and operate this device to estimate embolism resistance of angiosperm xylem, and how to analyse pneumatic data. Simple and more elaborated ways of constructing a Pneumatron are shown, either using wires, a breadboard, or a printed circuit board. The instrument is based on an open-source hardware and software system, which allows users to operate it in an automated or semi-automated way. A step-by-step manual and a troubleshooting section are provided. An excel spreadsheet and an R-script are also presented for fast and easy data analysis. This manual aims at helping users to avoid common mistakes, such as unstable measurements of the minimum and maximum amount of gas discharged from xylem tissue, which has major consequences for estimating embolism resistance. Major advantages of the Pneumatron device include its automated and accurate measurements of gas diffusion rates, including highly precise measurements of the gas volume in intact, embolised conduits. It is currently unclear if the method can also be applied to woody monocots, gymnosperm species that possess torus-margo pit membranes, or to herbaceous species.


IAWA Journal ◽  
2021 ◽  
pp. 1-19
Author(s):  
Shohei Yamagishi ◽  
Kengo Shigetomi ◽  
Syunya Fujiyasu ◽  
Dan Aoki ◽  
Tetsuro Uno ◽  
...  

Abstract Intervessel pit membranes are recognized as key structures for influencing water flow/embolism resistance. The mechanisms remain largely unclear owing to difficulties in examining them intact in nature. This study investigates ethanol-extractable pit membrane incrustations (PMIs), which were previously reported in certain angiosperms and may affect their water conduction. The presence of PMIs was determined for 40 angiosperms by field-emission scanning electron microscopy (FE-SEM). Candidate components of PMIs were determined by chemical analyses of wood extracts, and their distributions in the xylem were examined by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Cryo-TOF-SIMS and cryo-FE-SEM were also performed to clarify the native distribution of PMIs. PMIs were observed in 11 species. Some of them were categorized as fat trees, which are known to store abundant lipids. Tilia japonica sapwood displaying PMIs contained large amounts of lipids, which were distributed in the dried xylem tissue, consistent with the distribution of the PMIs. In the frozen samples of T. japonica, however, the distributions were restricted to the parenchyma. In conclusion, PMIs consist of an artifactual coating of lipids originated from the parenchyma in dried samples at room temperature. Researchers performing surface analyses of plant cell walls should take strong precautions against such self-coating by these intrinsic chemicals.


2021 ◽  
Author(s):  
Rodrigo T. Avila ◽  
Amanda A. Cardoso ◽  
Timothy A. Batz ◽  
Cade N. Kane ◽  
Fábio M. DaMatta ◽  
...  
Keyword(s):  

IAWA Journal ◽  
2021 ◽  
pp. 1-20
Author(s):  
Marta I. Percolla ◽  
Jaycie C. Fickle ◽  
F. Daniela Rodríguez-Zaccaro ◽  
R. Brandon Pratt ◽  
Anna L. Jacobsen

Abstract Many plant lineages, including oaks (Quercus spp.), have both vessels and tracheids as hydraulically conductive cells within their xylem. The structure of these co-occurring conduit types and their contribution to plant hydraulic function have been relatively little studied. We hypothesized that vasicentric tracheids contribute to hydraulic function under conditions of low water availability. We predicted that within a species, oaks growing at drier and warmer low elevation sites would have more tracheids and be more embolism resistant compared to those growing at moister and colder higher elevation sites. We also predicted that across species, lower elevation oaks would have increased tracheid abundance within their xylem. Five oak species differed in many xylem traits, including vessel diameter and length, tracheid size and abundance, embolism resistance, and hydraulic conductivity. Tracheids were most abundant in the xylem of the highest elevation species at sites that receive winter snow and freezing temperatures. Vessels were relatively vulnerable to embolism as confirmed with multiple methods, including centrifuge vulnerability curves, micro-CT scans of native stem samples, and single vessel air injection. Theoretical conductivity calculations indicated that tracheids account for 5.7–15.5% of conductivity in hydrated stems, with tracheids likely increasing in importance as large diameter vulnerable vessels embolize. The occurrence of both vessels and vasicentric tracheids in the xylem of oaks may enable them to function within highly seasonal climates. Tracheids, though often overlooked, may be particularly important in maintaining conductivity throughout much of the year when water potentials decline from seasonal maximums and following freeze-thaw events.


2021 ◽  
Vol 230 (5) ◽  
pp. 1829-1843 ◽  
Author(s):  
Lucian Kaack ◽  
Matthias Weber ◽  
Emilie Isasa ◽  
Zohreh Karimi ◽  
Shan Li ◽  
...  

Water ◽  
2021 ◽  
Vol 13 (6) ◽  
pp. 850
Author(s):  
Xin Jiang ◽  
Brendan Choat ◽  
Yong-Jiang Zhang ◽  
Xin-Yi Guan ◽  
Wen Shi ◽  
...  

Mangroves growing in tropical and subtropical intertidal zones face challenges from warming and altered rainfall patterns associated with global climate change. Intraspecific variation in hydraulic traits may allow a mangrove species to acclimate to novel climatic conditions, yet little is known regarding the potential for adaptive plasticity in these traits. In this study, we aimed to quantify the variation in plant hydraulic traits of two widespread mangrove species growing across a latitudinal gradient. We investigated the xylem hydraulic structure and function of Avicennia marina and Aegiceras corniculatum, across three sites spanning a latitudinal gradient of 17.45° in eastern Australia. We found that both species were highly resistant to xylem embolism and that there was significant intraspecific variation in hydraulic traits between sites. The highest embolism resistance and sapwood-specific hydraulic conductivity (KS) were found at the lowest latitude site that had the highest mean annual temperature and precipitation. A. marina showed no differences in vessel size and density among sites. It has other special features such as successive cambia enhancing its ability to adapt to a large environmental gradient. In contrast, A. corniculatum showed higher vessel densities at lower latitudes. There was a significant and positive correlation (R2 = 0.72, p < 0.05) between KS and embolism resistance across species and sites, suggesting the absence of a tradeoff between hydraulic efficiency and safety. Both embolism resistance and KS were negatively correlated with wood density but positively with vessel wall reinforcement. This study reveals that these two widespread mangrove species were adapted to warmer climates by enhancing both hydraulic efficiency and safety.


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