The distribution of mechanical stresses in the cell wall of wood induced by capillary tension in the lumen water - an approximate analysis

Hunter, A. J.

doi:10.1007/s002260100098

Cited by 7 publications

(9 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Further work is required to understand the glass transition kinetics of in situ lignin, hemicelluloses, and cellulose, and how these control conduit wall geometry in response to mechanical stresses induced by the sap tension of transpiring trees (e.g. Innes, 1995; Hunter, 2001; Alméras & Gril, 2007).…”

Section: Discussionmentioning

confidence: 99%

Moving beyond the cambium necrosis hypothesis of post‐fire tree mortality: cavitation and deformation of xylem in forest fires

2012

View full text Add to dashboard Cite

Summary• It is widely assumed that post-fire tree mortality results from necrosis of phloem and vascular cambium in stems, despite strong evidence that reduced xylem conductivity also plays an important role.• In this study, experiments with Populus balsamifera were used to demonstrate two mechanisms by which heat reduces the hydraulic conductivity of xylem: air seed cavitation and conduit wall deformation. Heat effects on air seed cavitation were quantified using air injection experiments that isolate potential temperature-dependent changes in sap surface tension and pit membrane pore diameters. Heat effects on conduit wall structure were demonstrated using air conductivity measurements and light microscopy.• Heating increased vulnerability to cavitation because sap surface tension varies inversely with temperature. Heating did not affect cavitation via changes in pit membrane pore diameters, but did cause significant reductions in xylem air conductivity that were associated with deformation of conduit walls (probably resulting from thermal softening of viscoelastic cell wall polymers).• Additional work is required to understand the relative roles of cavitation and deformation in the reduction of xylem conductivity, and how reduced xylem conductivity in roots, stems, and branches correlates and interacts with foliage and root necroses to cause tree mortality. Future research should also examine how heat necrosis of ray parenchyma cells affects refilling of embolisms that occur during and after the fire event.

show abstract

Section: Discussionmentioning

confidence: 99%

Moving beyond the cambium necrosis hypothesis of post‐fire tree mortality: cavitation and deformation of xylem in forest fires

2012

View full text Add to dashboard Cite

show abstract

“…The reversibility of implosion means that implosion and resultant tears in the pit membrane or microfracture of the lignified cell walls might not be visible with conventional light microscopy and would be difficult to distinguish from artifacts with electron microscopy. However, some authors consider checks that are often seen in wood to be damage caused by negative pressure (Hunter, 2001;Donaldson, 2002).…”

Section: Discussionmentioning

confidence: 99%

Do Xylem Fibers Affect Vessel Cavitation Resistance?

et al. 2005

View full text Add to dashboard Cite

Possible mechanical and hydraulic costs to increased cavitation resistance were examined among six co-occurring species of chaparral shrubs in southern California. We measured cavitation resistance (xylem pressure at 50% loss of hydraulic conductivity), seasonal low pressure potential (P min ), xylem conductive efficiency (specific conductivity), mechanical strength of stems (modulus of elasticity and modulus of rupture), and xylem density. At the cellular level, we measured vessel and fiber wall thickness and lumen diameter, transverse fiber wall and total lumen area, and estimated vessel implosion resistance using (t/b) h 2 , where t is the thickness of adjoining vessel walls and b is the vessel lumen diameter. Increased cavitation resistance was correlated with increased mechanical strength (r 2 5 0.74 and 0.76 for modulus of elasticity and modulus of rupture, respectively), xylem density (r 2 5 0.88), and P min (r 2 5 0.96). In contrast, cavitation resistance and P min were not correlated with decreased specific conductivity, suggesting no tradeoff between these traits. At the cellular level, increased cavitation resistance was correlated with increased (t/b) h 2 (r 2 5 0.95), increased transverse fiber wall area (r 2 5 0.89), and decreased fiber lumen area (r 2 5 0.76). To our knowledge, the correlation between cavitation resistance and fiber wall area has not been shown previously and suggests a mechanical role for fibers in cavitation resistance. Fiber efficacy in prevention of vessel implosion, defined as inward bending or collapse of vessels, is discussed.Among vascular plants, water is transported through xylem under negative pressure. Xylem must withstand both the mechanical stresses associated with negative pressure as well as the risk of air entering the hydraulic pathway. Failure to do so may lead to cavitation of water columns and blockage of water transport. Failure may occur when gas is pulled into water-filled xylem conduits from gas-filled cells or intercellular spaces through pores in the xylem pit membrane in a process referred to as air-seeding (Zimmermann, 1983;Baas et al., 2004). Failure may also occur when negative pressures overcome the ability of the xylem conduit walls to resist implosion (i.e. inward bending or collapse; Carlquist, 1975;Hacke et al., 2001a;Donaldson, 2002;Cochard et al., 2004;Brodribb and Holbrook, 2005). Implosion may trigger cavitation or, in leaves, may restrict hydraulic transport by reducing conduit diameter (Brodribb and Holbrook, 2005). In addition to negative pressures, freezing can lead to failure when sap in the xylem freezes and the gas dissolved in the sap comes out of solution. This can lead to cavitation upon thawing if the bubbles do not go back into solution but instead expand (Yang and Tyree, 1992). The result of cavitation is embolism or gas blockage, which reduces hydraulic transport and can result in reduced stomatal conductance (Pratt et al., 2005), reduced photosynthesis (Brodribb and Feild, 2000), and dieback of branchlets (Rood et al., 2000;Da...

show abstract

“…6). Xylem cells arranged in matrices of 6rectangular cells would be likely to be more resistant to collapse due to the reinforced geometry of the xylem (Hunter, 2001) as well as the probable exclusion of air from around many cells. This perhaps explains why collapse was not observed in the leaf vein of P. grayi.…”

Section: Discussionmentioning

confidence: 99%

Water Stress Deforms Tracheids Peripheral to the Leaf Vein of a Tropical Conifer

2005

View full text Add to dashboard Cite

Just as a soggy paper straw is prone to yielding under the applied suction of a thirsty drinker, the xylem tracheids in leaves seem prone to collapse as water potential declines, impeding their function. Here we describe the collapse, under tension, of lignified cells peripheral to the leaf vein of a broad-leaved rainforest conifer, Podocarpus grayi de Laub. Leaves of Podocarpus are characterized by an array of cylindrical tracheids aligned perpendicular to the leaf vein, apparently involved in the distribution of water radially through the mesophyll. During leaf desiccation the majority of these tracheids collapsed from circular to flat over the water potential range 21.5 to 22.8 MPa. An increase in the percentage of tracheids collapsed during imposed water stress was mirrored by declining leaf hydraulic conductivity (K leaf ), implying a direct effect on water transport efficiency. Stomata responded to water stress by closing at 22.0 MPa when 45% of cells were collapsed and K leaf had declined by 25%. This was still substantially before the initial indications of cavitation-induced loss of hydraulic conductance in the leaf vein, at 23 MPa. Plants droughted until 49% of tracheids had collapsed were found to fully recover tracheid shape and leaf function 1 week after rewatering. A simple mechanical model of tracheid collapse, derived from the theoretical buckling pressure for pipes, accurately predicted the collapse dynamics observed in P. grayi, substantiating estimates of cell wall elasticity and measured leaf water potential. The possible adaptive advantages of collapsible vascular tissue are discussed.Leaves employ the strong cohesive properties of water to do the work of pulling water from the soil to prevent leaf desiccation during gas exchange (Dixon and Joly, 1895). Of course this mode of water transport does not come without attendant costs, the most profound of which is the generation of hydraulic tension or negative pressure in the plumbing of vascular plants. The magnitude of this tension is generally large due to subzero soil water potential and substantial resistances to hydraulic flow through the vascular system of plants (Jeje and Zimmermann, 1979;Pockman et al., 1995). As such, it is common to measure hydraulic tensions (negative water potentials) of the order of 22 MPa in plants exposed to moderate water stress. In nonliving xylem cells conducting dilute sap, such tension will exert a large mechanical force on cell walls wherever they are bordered by air spaces. To place this force into perspective, if it were possible to reproduce a tension of 22 MPa inside a stainless steel tube it would be capable of crushing a pipe of 60 mm radius and 2 mm wall thickness.To resist megapascals of crushing pressure across the cell wall, xylem conduits have evolved thick secondary walls incorporating lignin as a means of fortifying their tangential elastic modulus against collapse (Raven, 1977). However, given that both lignin and celluloses are costly to synthesize, it is likely that plants minimize xylem wal...

show abstract

The distribution of mechanical stresses in the cell wall of wood induced by capillary tension in the lumen water - an approximate analysis

Cited by 7 publications

References 0 publications

Moving beyond the cambium necrosis hypothesis of post‐fire tree mortality: cavitation and deformation of xylem in forest fires

Moving beyond the cambium necrosis hypothesis of post‐fire tree mortality: cavitation and deformation of xylem in forest fires

Do Xylem Fibers Affect Vessel Cavitation Resistance?

Water Stress Deforms Tracheids Peripheral to the Leaf Vein of a Tropical Conifer

Contact Info

Product

Resources

About