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100 results for “Xylem”
Topography strongly affects drought stress and xylem embolism resistance in woody plants from a karst forest in Southwest China
<p>1. Xylem resistance to drought-induced embolism is an important trait determining plant distribution. In the karst hills of Southwest China, with a relatively small variation in altitude, soil depth and water availability strongly decrease from the foot towards the top, and woody plant species display distinct spatial distribution.</p> <p>2. For testing the hypothesis that embolism resistance of leaf and stem xylem reflects the spatial distribution across species along a topographical gradient of the karst hills, we measured the xylem water potential in the dry season, vulnerability to drought-induced embolism in stems and leaves, and relevant anatomical traits in 17 evergreen species with a different topographical distribution.</p> <p>3. We found that from the foot towards the hill top, plant water potential sharply decreased, and both stem and leaf xylem showed increasing resistance to hydraulic dysfunction and drought-resistant anatomical characteristics, but non-significant variation in specific hydraulic conductivity. Also, hydraulic safety margins increased with relative altitude and thus increasing water deficit, which underlies the local distribution of the species, but does not come at the cost of hydraulic efficiency.</p> <p>4. Our results demonstrate that plant hydraulic safety largely shape the niche differentiation and hence community assembly in highly heterogeneous and water-limited landscapes.</p>
Data from: Axial xylem architecture of Larix decidua exposed to CO2 enrichment and soil warming at the treeline
1. Trees continuously adjust their axial xylem structure to meet changing needs imposed by ontogenetic and environmental changes. These axial structure-function responses need to be coordinated among competing biophysical constraints to avoid failure of the xylem system. Here, we investigated if ontogeny or experimental manipulation of CO2 and soil temperature influence these structure-function responses. 2. We performed detailed xylem cell anatomical quantification along the axis of 40-year-old Larix decidua trees planted at the Swiss treeline and exposed to a combination of elevated CO2 (+200 ppm) and soil warming (+4 °C) between 2001 and 2012. We assessed how mean hydraulic tracheid diameter (Dh), the cell wall reinforcement ((t/b)2), tracheid wall thickness (CWT) and the percent area of ray parenchyma (PERPAR) – proxies for hydraulic efficiency, hydraulic safety, biomechanical support and metabolic xylem functions, respectively – co-vary along the tree axis. 3. Dh increased from the stem apex to base, strictly following a power function (R2=0.81), independent from ontogeny and experimental treatments. In contrast, axial trends of (t/b)2 and CWT were either influenced by treatment and/or ontogeny, or showed no axial trend (PERPAR). Additionally, we found that a larger Dh only at the stem apex promoted primary and secondary growth. 4. Our approach of analyzing xylem anatomical traits along the tree axis and across tree-rings provides novel insights into xylem functional architecture and allows reconstructing xylem function over time. We conclude that the maintenance of hydraulic efficiency during ontogeny is very robust, as the conduit diameter undergoes a strong apical control, and plays a fundamental role for assimilation and tree growth. Instead, the other functional traits more plastically vary with ontogeny and environmental changes.
Data from: Variation of xylem vessel diameters across a climate gradient: insight from a reciprocal transplant experiment with a widespread boreal tree
Xylem vessel diameters represent an important plant hydraulic trait to ensure sufficient water supply from the roots to the leaves. The ability to adjust the hydraulic pathway to environmental cues is key in order to satisfy transpirational demands and maximize growth and survival. We evaluated the variability of vessel diameters in trembling aspen in a reciprocal transplant experiment. We tested six provenances from three ecological regions of North America planted at four test sites in western Canada. All test sites were established at the same time with the same provenances arranged in a randomized complete block design. Vessel diameter showed a strong interaction of population and test site suggesting a high degree of phenotypic plasticity in this trait. Gaussian kernel density estimates support plastic as well as genetic contributions in vessel diameter control trending from bimodal distributions at the most northern test site towards unimodal distributions at the warmest and mildest test site. Furthermore, we used test site-specific climate data in form of a 2-year, 5-year and 10-year average of 21 directly and derived climatic variables and found that average site-specific vessel diameters correlated strongly with summer moisture availability. A previously found negative relationship with vessel diameter and tree height in central Alberta was also found at two other boreal test sites but reversed at a wetter and milder sub-boreal test site. In summary, vessel diameters were highly plastic in response to different environments and varied with summer moisture availability. The variability of vessel diameter and tree height correlations suggests that vessel diameter alone cannot serve as a reliable proxy for long-term growth performance beyond boreal environments. Instead, selecting aspen populations with a high degree of plasticity in this trait appears to be the safest option for assisted migration and seed transfer programmes under climate change.
Water potential gradient, root conduit size and root xylem hydraulic conductivity determine the extent of hydraulic redistribution in temperate trees
1. Hydraulic redistribution (HR) of soil water through plant roots is widely described, however its extent, especially in temperate trees, remains unclear. Here, we quantified redistributed water of five temperate tree species. We hypothesized that both, HR within a plant and into the soil increases with higher water-potential gradients, larger root conduit diameters and root-xylem hydraulic conductivities. 2. Saplings of conifer (<i>Picea abies</i>, <i>Pseudotsuga menziesii</i>), diffuse-porous (<i>Acer pseudoplatanus</i>) and ring-porous species (<i>Castanea sativa</i>, <i>Quercus robur</i>) were planted in split-root systems, where one plant had its roots split between two pots with different water-potential gradients (0.23 to 4.20 MPa). Hydraulic redistribution was quantified via deuterium labeling. 3. On average, species redistributed 0.39 ± 0.14 ml water overnight (0.08 ± 0.01 ml g<sup>-1</sup> root mass). Higher pre-dawn water-potential gradients, xylem hydraulic conductivities and larger conduit diameters significantly increased HR. Hydraulic conductivity had the greatest influence on HR, within the plants (0.03 ± 0.01 ml g<sup>-1</sup>) and into the soil (0.06 ± 0.01 ml g<sup>-1</sup>). 4. Additional factors as soil-root contact should be considered, especially when calculating water transfer into the soil. Nevertheless, trees maintaining high xylem hydraulic conductivity showed higher HR amounts, potentially making them valuable 'silvicultural tools' to improve plant water-status.
Causes and factors of cryogenic extraction biases on isotopes of xylem water
<p>Rehydration experiment on plant materials</p>
Supplementary material for Progressive enrichment in 18O and 2H in xylem water along sap flow paths in Fagus sylvatica trees
<p>Database related to the results that are presented in the manuscript Montemagno et al. that will be submitted as research paper in the journal Ecohydrology:</p> <p><strong>Progressive enrichment in <sup>18</sup>O and <sup>2</sup>H in xylem water along sap flow paths in <em>Fagus sylvatica </em></strong></p> <p>Alessandro Montemagno<sup>1,3</sup>, Richard F. Keim<sup>2</sup>, Veneranda López-Días<sup>1</sup>, Victor Bense<sup>3</sup>, Adriaan J. Teuling<sup>3</sup>, Christophe Hissler<sup>1</sup></p> <p><sup>1</sup>CATchment and ecohydrology research group (CAT/ENVISION/ERIN), Luxembourg Institute of Science and Technology, Belvaux, 4408, Luxembourg</p> <p><sup>2</sup> School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA 70803 USA</p> <p><sup>3 </sup>Department of Environmental Sciences, Hydrology and Quantitative Water Management Group, Wageningen University and Research, Droevendaalsesteeg 4, Wageningen, 6708 PB, The Netherlands</p> <p><em>Correspondence: </em>Alessandro Montemagno (<a href="mailto:alessandro.montemagno@outlook.com">alessandro.montemagno@outlook.com</a>), Christophe Hissler (<a href="mailto:christophe.hissler@list.lu">christophe.hissler@list.lu</a>)</p>
Data used in the paper "Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought"
<p>Data used in the paper "Optimal balancing of xylem efficiency and safety explains plant vulnerability to drought"</p>
Data from: Environmental conditions and vascular cambium regulate carbon allocation to xylem growth in deciduous oaks
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Data from: No role for xylem embolism or carbohydrate shortage in temperate trees during the severe 2015 drought
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Data from: Variation of xylem vessel diameters across a climate gradient: insight from a reciprocal transplant experiment with a widespread boreal tree
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Data from: Axial xylem architecture of Larix decidua exposed to CO2 enrichment and soil warming at the treeline
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Data from: The chromatin-modifying protein HUB2 is involved in the regulation of lignin composition in xylem vessels
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Water potential gradient, root conduit size and root xylem hydraulic conductivity determine the extent of hydraulic redistribution in temperate trees
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Topography strongly affects drought stress and xylem embolism resistance in woody plants from a karst forest in Southwest China
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Data from: Xylem vessel traits predict the leaf phenology of native and non-native understory species of temperate deciduous forests
Non-native understorey woody species have been shown to extend leaf display and inhabit vacant phenological niches in early spring and late autumn when growing with native counterparts in temperate deciduous forests across the world. Despite the potential competitive advantages, extended leaf duration also subjects non-native species to possible hydraulic risks associated with maintaining leaves during periods of increased frost probability. It remains unclear how non-native species are able to maintain xylem function within this context. Leaf phenology in temperate deciduous trees has been shown to be a function of xylem anatomy, with earlier bud break associated with smaller xylem vessels due to the presumed resistance of smaller vessels to freezing-induced cavitation. We examined relationships between leaf phenology and xylem vessel traits across 82 native and non-native understorey deciduous woody species common to eastern U.S. deciduous forests. We hypothesized that non-native species possess xylem vessel traits associated with maximum hydraulic safety during frost-prone spring and autumn leaf display without compromising rapid growth rate. Larger metaxylem vessels in non-native species were associated with both faster spring growth and delayed autumn leaf fall compared to native species. Non-native species also had smaller latewood vessel diameter, latewood vessel area percentage and a higher proportion of solitary vessels in the entire secondary xylem cross section compared to natives, potentially increasing their resistance to freezing- and/or drought-induced cavitation in autumn, thus allowing for delayed autumn leaf fall. Native and non-native species exhibited similar dates of spring bud break and leaf emergence, consistent with similar xylem vessel size and vessel area percentage within metaxylem and earlywood. Within both groups, species with earlier bud and leaf emergence had a higher total percentage of vessel area within metaxylem and earlywood. This suggests understorey species need sufficient water to support their early spring growth at the risk of freezing-induced cavitation. Our study suggests xylem vessel properties, along with cross-sectional spatial xylem vessel distribution, reflect the capacity of non-native plants to thrive in a new environment and deepen our understanding of the physiological mechanisms of successful invasions of non-native understorey woody plant species.
Data from: Physiological regulation and efficient xylem water transport regulate diurnal water and carbon balances of tropical lianas
Tropical lianas deploy most of their leaves towards the top of the forest canopy, whereas trees exhibit a more stratified crown. Forest canopies are often exposed to hot and windy conditions, and how lianas cope with the extremely high transpirational demands under these environments remains unknown. We investigated stem hydraulic properties, leaf drought tolerance, diurnal changes in leaf and stem water potentials (Ψleaf and Ψstem), stomatal conductance (gs), photosynthetic rate, sap flow and stem native percentage loss of conductivity (PLC) for four liana species in a tropical forest in southwest China. Five co-occurring tree species were also selected for comparison. Lianas reached maximal transpiration at a relatively lower vapour pressure deficit (<1 kPa) than did co-occurring trees, suggesting vigorous photosynthesis during the morning. However, liana gs declined markedly over the day, with low gs at midday and afternoon. Lianas generally had higher stem sapwood-specific conductivity and maximum sap flux density but were less tolerant to drought-induced cavitation than were evergreen trees. Both lianas and trees lost leaf turgor in the top canopy at midday, but lianas lost leaf turgor earlier (∼2 h) than trees. Seven of eight species exhibited midday increases in PLC when xylem tensions were released to −0·3 to −0·5 MPa for PLC measurements. On average, lianas experienced high PLC (35·9%), along with a greater degree of disequilibrium between leaf and stem water potentials than trees (ΔΨstem–leaf: 1·37 MPa vs. 0·75 MPa) during the day. Earlier stomatal closure and efficient water transport may help lianas maintain higher Ψstem than trees despite having similar Ψleaf. Our results provide evidence that physiological regulation and efficient water transport mediate daily water relations in tropical lianas and may explain how lianas operate efficiently in tropical seasonal forests. Further studies involving a broader range of species are needed to confirm our findings.
Data from: An inconvenient truth about xylem resistance to embolism in the model species for refilling Laurus nobilis L.
Direct, non-invasive X-ray microtomography and optical technique observations applied in stems and leaves of intact seedlings revealed that laurel is highly resistant to drought-induced xylem embolism. Contrary to what has been brought forward, daily cycles of embolism formation and refilling are unlikely to occur in this species and to explain how it copes with drought. There has been considerable controversy regarding xylem embolism resistance for long-vesselled angiosperm species and particularly for the model species for refilling (Laurus nobilis L.). The purpose of this study was to resolve the hydraulic properties of this species by documenting vulnerability curves of different organs in intact plants. Here, we applied a direct, non-invasive method to visualize xylem embolism in stems and leaves of intact laurel seedlings up to 2-m tall using X-ray microtomography (microCT) observations and the optical vulnerability technique. These approaches were coupled with complementary centrifugation measurements performed on 1-m long branches sampled from adult trees and compared with additional microCT analyses carried out on 80-cm cut branches. Direct observations of embolism spread during desiccation of intact laurels revealed that 50% loss of xylem conductivity (Ψ50) was reached at − 7.9 ± 0.5 and − 8.4 ± 0.3 MPa in stems and leaves, respectively, while the minimum xylem water potentials measured in the field were − 4.2 MPa during a moderate drought season. Those findings reveal that embolism formation is not routine in Laurus nobilis contrary to what has been previously reported. These Ψ50 values were close to those based on the flow-centrifuge technique (− 9.2 ± 0.2 MPa), but at odds with microCT observations of cut branches (− 4.0 ± 0.5 MPa). In summary, independent methods converge toward the same conclusion that laurel is highly resistant to xylem embolism regardless its development stage. Under typical growth conditions without extreme drought events, this species maintains positive hydraulic safety margin, while daily cycles of embolism formation and refilling are unlikely to occur in this species.
Data from: An ignored anatomical variable: pore shape shows a nonrandom variation pattern in xylem cross section
Anatomical characteristics of vessels have a profound impact on the hydraulic conductivity of the xylem. However, pore shape, the cross-section shape of a vessel, has been ignored in previous hydraulic architecture studies. In this study, we examined whether pore shape tended to be circular, and whether this variation tendency might be affected by water flow path-length and cambial age. The circularity pores in <i>Betula platyphylla</i> Roth and Quercus mongolica (only earlywood) were analyzed from the pith to the bark along the water flow path. It was found that although there were very few pores with absolutely circular shape, solitary pores did tend to be regularly circular. The pore shape of sequentially formed vessels in the xylem was influenced by cambial age and flow path-length. Pore shape tended to be more circular as flow path-length increased or cambial age decreased. Moreover, circular pore shape is an important morphogenetic mechanism for hydraulic architecture development, which can also expand the understanding of structure-function relationships for the xylem.
Data from: Divergence in strategies for coping with winter embolism among co-occurring temperate tree species: the role of positive xylem pressure, wood type and tree stature
1. In temperate ecosystems, freeze-thaw events are an important environmental stress that can induce severe xylem embolism (i.e. clogging of conduits by air bubbles) in overwintering organs of trees. However, no comparative studies of different adaptive strategies among sympatric tree species for coping with winter embolism have examined the potential role of the presence or absence of embolism refilling by positive xylem pressure. 2. We evaluated the degree of winter embolism and hydraulic architecture traits in 22 deciduous angiosperm tree species typical of temperate forest sites in NE China. Co-occurring trees growing in a local botanical garden were used to minimize variation caused by differences in proximal environmental conditions and to ensure that interspecific variation reflected genetic differences between species. 3. Four functional groups with potentially different strategies for coping with winter embolism were compared: positive xylem pressure generating species (PXP) that are all diffuse-porous, except a semi-ring-porous species, large (LDP) and small (SDP) statured diffuse-porous tree species that are unable to generate positive xylem pressure, and ring-porous species (RP). 4. The PXP group exhibited nearly full recovery from winter embolism in contrast to the other three groups, which showed persistent and relatively high degrees of hydraulic dysfunction during the subsequent growing season. The absence of a functional trade-off between hydraulic efficiency and safety against freeze-thaw induced embolism in the PXP group and the presence of a trade-off in the other three groups, suggests that the ability to generate root or stem pressure for embolism refilling may partially free some temperate tree species from adaptive constraints imposed by winter embolism formation. 5. Efficient winter embolism reversal by positive pressure in PXP species did not distinguish them from their non-xylem pressure-generating LDP counterparts in terms of various measures of xylem hydraulic efficiency during the growing season. Divergence in the ability to refill winter embolism through generation of positive xylem pressure implies a series of functional trade-offs that may partially explain the co-existence of these two types of temperate tree species.
Linkages among stem xylem transport, biomechanics and storage in lianas and trees across three contrasting environments
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