Water relations in silver birch during springtime: How is sap pressurised?

Hölttä, Teemu; Carrasco, Maria del Rosario Domínguez; Salmon, Yann; Aalto, Juho; Vanhatalo, Anni; Bäck, Jaana; Lintunen, Anna

doi:10.1111/plb.12838

Cited by 29 publications

(20 citation statements)

References 76 publications

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“…This shrinkage would result from cell volume change due to water release and/or cell wall shrinkage due to adhesive forces between water and the surfaces of the water transporting conduits (Rosner, Karlsson, Konnerth, & Hansmann, 2009). Indeed, daily sapwood shrinkage has been observed in several angiosperm trees (Hölttä et al, 2018;Lintunen, Lindfors, Nikinmaa, & Hölttä, 2017;F. C. Scholz et al, 2008;Sevanto, Hölttä, & Holbrook, 2011), although F. C. Scholz et al (2008) found no correlation between WD and diurnal sapwood shrinkage across six species.…”

Section: Day Capacitance and Its Structural Correlatesmentioning

confidence: 99%

Wood day capacitance is related to water content, wood density, and anatomy across 30 temperate tree species

Ziemiñska

Rosa

Gleason

et al. 2020

Plant Cell & Environment

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Water released from wood during transpiration (capacitance) can meaningfully affect daily water use and drought response. To provide context for better understanding of capacitance mechanisms, we investigated links between capacitance and wood anatomy. On twigs of 30 temperate angiosperm tree species, we measured day capacitance (between predawn and midday), water content, wood density, and anatomical traits, that is, vessel dimensions, tissue fractions, and vessel-tissue contact fractions (fraction of vessel circumference in contact with other tissues). Across all species, wood density (WD) and predawn lumen volumetric water content (VWC L-pd) together were the strongest predictors of day capacitance (r 2 adj = .44). Vessel-tissue contact fractions explained an additional 10% of the variation in day capacitance. Regression models were not improved by including tissue lumen fractions. Among diffuse-porous species, VWC L-pd and vessel-ray contact fraction together were the best predictors of day capacitance, whereas among semi/ring-porous species, VWC L-pd , WD and vessel-fibre contact fraction were the best predictors. At predawn, wood was less than fully saturated for all species (lumen relative water content = 0.52 ± 0.17). Our findings imply that day capacitance depends on the amount of stored water, tissue connectivity and the bulk wood properties arising from WD (e.g., elasticity), rather than the fraction of any particular tissue.

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Section: Day Capacitance and Its Structural Correlatesmentioning

confidence: 99%

Wood day capacitance is related to water content, wood density, and anatomy across 30 temperate tree species

Ziemiñska

Rosa

Gleason

et al. 2020

Plant Cell & Environment

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“…Springtime stem pressure in Betula pendula is most strongly correlated with temperature, peaking at mid‐day. Xylem sap osmotic pressure in one study was small compared with total xylem pressure and showed little diurnal variation (Hölttä et al ., 2018), but vertical gradients of sugar concentrations were found in birch sap during leaf emergence (Westhoff et al ., 2008), leaving it open to whether osmotic forces play a role for positive pressure in birch. In walnut, xylem pressure was closely correlated with soil temperature and xylem sap osmolarity, and the pressure appeared to originate mainly in the roots (Améglio et al ., 2001).…”

Section: Seasonal Root and Stem Pressure Before Leaf‐out In Deciduousmentioning

confidence: 99%

“…Positive pressure in xylem, which we define as above atmospheric pressure, can potentially occur in roots, stems, rhizomes, and even in leaves, but in the published literature it is generally referred to as ‘root pressure’ even if the source of the pressure is undetermined. For a long time, positive pressure in xylem has been viewed as relative unimportant compared with transpiration‐driven water transport under negative pressure via the cohesion–tension mechanism (Askenasy, 1895; Dixon & Joly, 1895), but there is a resurgence of interest in the topic (Knipfer et al ., 2015; Yang et al ., 2015; Gleason et al ., 2017; Hölttä et al ., 2018). While general reviews of the subject are available (Kramer & Boyer, 1995; Singh, 2016b), the purpose of this review is to discuss positive xylem pressure with a critical assessment of what is known about underlying mechanisms and explore by model calculations what conditions are required for root pressure to occur.…”

Section: Introductionmentioning

confidence: 99%

“…Cut and bleeding stems or roots have also been most commonly used for pressure measurements. Less destructive and continuous methods included pressure probes designed for short‐term measurements of individual cells or vessels (Steudle & Jeschke, 1983; Balling & Zimmermann, 1990; Tomos & Leigh, 1999) or probes inserted into xylem of intact plants (Cochard et al ., 1994; Saha et al ., 2009; Hölttä et al ., 2018), including very small probes that minimally disturb the system (Clearwater et al ., 2007; Charrier et al ., 2017) (Fig. 2c).…”

Section: Introductionmentioning

confidence: 99%

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Positive pressure in xylem and its role in hydraulic function

2021

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Summary Although transpiration‐driven transport of xylem sap is well known to operate under absolute negative pressure, many terrestrial, vascular plants show positive xylem pressure above atmospheric pressure on a seasonal or daily basis, or during early developmental stages. The actual location and mechanisms behind positive xylem pressure remain largely unknown, both in plants that show seasonal xylem pressure before leaf flushing, and those that show a diurnal periodicity of bleeding and guttation. Available evidence shows that positive xylem pressure can be driven based on purely physical forces, osmotic exudation into xylem conduits, or hydraulic pressure in parenchyma cells associated with conduits. The latter two mechanisms may not be mutually exclusive and can be understood based on a similar modelling scenario. Given the renewed interest in positive xylem pressure, this review aims to provide a constructive way forward by discussing similarities and differences of mechanistic models, evaluating available evidence for hydraulic functions, such as rehydration of tissues, refilling of water stores, and embolism repair under positive pressure, and providing recommendations for future research, including methods that avoid or minimise cutting artefacts.

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“…xylem sap pressurization [167,168]. The concentrations of the main sugars (glucose 2.5-4.7 and fructose 2.3-4.5 5-8 g L −1 ) of birch sap (Betula pendula Roth.…”

Section: Effects Of Climate Change On Efn-dependent Communitiesmentioning

confidence: 99%

Functional Role of Extrafloral Nectar in Boreal Forest Ecosystems under Climate Change

Holopainen

Blande

Sorvari

2020

Forests

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Carbohydrate-rich extrafloral nectar (EFN) is produced in nectaries on the leaves, stipules, and stems of plants and provides a significant energy source for ants and other plant mutualists outside of the flowering period. Our review of literature on EFN indicates that only a few forest plant species in cool boreal environments bear EFN-producing nectaries and that EFN production in many boreal and subarctic plant species is poorly studied. Boreal forest, the world’s largest land biome, is dominated by coniferous trees, which, like most gymnosperms, do not produce EFN. Notably, common deciduous tree species that can be dominant in boreal forest stands, such as Betula and Alnus species, do not produce EFN, while Prunus and Populus species are the most important EFN-producing tree species. EFN together with aphid honeydew is known to play a main role in shaping ant communities. Ants are considered to be keystone species in mixed and conifer-dominated boreal and mountain forests because they transfer a significant amount of carbon from the canopy to the soil. Our review suggests that in boreal forests aphid honeydew is a more important carbohydrate source for ants than in many warmer ecosystems and that EFN-bearing plant species might not have a competitive advantage against herbivores. However, this hypothesis needs to be tested in the future. Warming of northern ecosystems under climate change might drastically promote the invasion of many EFN-producing plants and the associated insect species that consume EFN as their major carbohydrate source. This may result in substantial changes in the diet preferences of ant communities, the preventative roles of ants against insect pest outbreaks, and the ecosystem services they provide. However, wood ants have adapted to using tree sap that leaks from bark cracks in spring, which may mitigate the effects of improved EFN availability.

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Water relations in silver birch during springtime: How is sap pressurised?

Cited by 29 publications

References 76 publications

Wood day capacitance is related to water content, wood density, and anatomy across 30 temperate tree species

Wood day capacitance is related to water content, wood density, and anatomy across 30 temperate tree species

Positive pressure in xylem and its role in hydraulic function

Functional Role of Extrafloral Nectar in Boreal Forest Ecosystems under Climate Change

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