Detection of cavitation events upon freezing and thawing of water in stems using ultrasound techniques (original) (raw)
Related papers
Tree physiology, 2017
Stems and leaves of Olea europaea L. (olive) avoid freezing damage by substantial supercooling during the winter season. Physiological changes during acclimation to low temperatures were studied in five olive cultivars. Water relations and hydraulic traits, ice nucleation temperature (INT) and temperatures resulting in 50% damage (LT50) were determined. All cultivars showed a gradual decrease in INT and LT50 from the dry and warm summer to the wet and cold winter in Patagonia, Argentina. During acclimation to low temperatures there was an increase in leaf cell wall rigidity and stomatal conductance (gs), as well as a decrease in leaf apoplastic water content, leaf water potential (Ψ), sap flow and stem hydraulic conductivity (ks). More negative Ψ as a consequence of high gs and detrimental effects of low temperatures on root activity resulted in a substantial loss of ks due to embolism formation. Seasonal stem INT decrease from summer to winter was directly related to the xylem resi...
PLANT PHYSIOLOGY, 2014
Freeze-thaw events can affect plant hydraulics by inducing embolism. This study analyzed the effect of temperature during the freezing process on hydraulic conductivity and ultrasonic emissions (UE). Stems of 10 angiosperms were dehydrated to a water potential at 12% percentage loss of hydraulic conductivity (PLC) and exposed to freeze-thaw cycles. The minimal temperature of the frost cycle correlated positively with induced PLC, whereby species with wider conduits (hydraulic diameter) showed higher freezethaw-induced PLC. Ultrasonic activity started with the onset of freezing and increased with decreasing subzero temperatures, whereas no UE were recorded during thawing. The temperature at which 50% of UE were reached varied between 29.1°C and 231.0°C across species. These findings indicate that temperatures during freezing are of relevance for bubble formation and air seeding. We suggest that species-specific cavitation thresholds are reached during freezing due to the temperature-dependent decrease of water potential in the ice, while bubble expansion and the resulting PLC occur during thawing. UE analysis can be used to monitor the cavitation process and estimate freeze-thaw-induced PLC. Ball MC, Canny MJ, Huang CX, Egerton JJG, Wolfe J (2006) Freeze/thawinduced embolism depends on nadir temperature: the heterogeneous hydration hypothesis. Plant Cell Environ 29: 729-745
AE Events Issued from the Stem of Plants under Long Term Water Stress
Journal of Environment and Engineering, 2007
Environmental changes due to global warming greatly influence ecological systems including those of plants. Diagnostic technologies using non-destructive inspection methods to evaluate environmental stress are few. Acoustic emission (AE) is applied to plants under water stress and the damage is measured. Cavitation phenomena are created by negative pressure in plants because of the lack of water in vessels or tracheids. Since shock waves due to cavitations create AE, the water stress state of plants can be monitored in real time by measuring AE. In this paper, AE events due to cavitation were measured in the drought-treated Ginkgo biloba L., Ficus spp., and Lycopersicon. In all plants examined, AE events increased during drought. In a short-term drought experiment, AE events were stopped by supplying water, but not in a long-term drought experiment. In Ginkgo biloba L. and Ficus spp, a temporary decrease of AE events was observed during drought. Plants adjust their internal water balance through certain self-defense mechanisms.
IX International Workshop on Sap Flow, 2013
The interesting species-specific relationship between maximum daily shrinkage (MDS) and stem water potential ( stem) was investigated in order to understand the mechanisms involved. Vulnerability curves of Vitis, Citrus, Olea and Prunus were analysed and the air entry stem in the xylem (P e) was calculated. The water relations parameters of the living tissue of the bark were also studied by building P-V curves. A strong linear correlation was obtained between the stem at which MDS occurs ( MDS) and P e in the studied species. Furthermore, P-V curves showed that, the species with the highest resistance to cavitation, i.e., Prunus, had the lowest osmotic pressure and the largest bulk elastic modulus. The conclusions of this study reinforce the idea of a tight correlation among plant capacitance, transpiration and maintenance of water status of the plant. These results illustrate the importance of studying the integration of long-distance transport systems in plants.
Xylem' Structure and Water Conduction in Conifer Trees, Dicot Trees, and Llanas
Iawa Journal, 1985
Coniferous trees, dicotyledonous trees, and dicotyledonous lianas (woody vines) form interesting morphological contrasts in their xylem structure and function. Lianas have among the largest (up to 8 metres or more) and widest (up to 500 j.L1ll) vessels in the plant kingdom. In conifers the water transport occurs through tracheids, which are relatively inefficient in transport. We can compare disparate growth forms in terms of leaf-specific. conductivity (LSC), which is hydraulic conductivity per surface area of leaves supplied by a stem. LSC is inversely proportional to localised pressure potential gradients. LSC is equal to the Huber value (sapwood area per leaf area supplied) times the specific conductivity (hydraulic conductivity per sapwood area). Lianas are similar to dicot trees and conifers in having hydraulic constrictions (low LSCs) at branch junctions. However, lianas generally have greater LSCs and specific conductivities but lower Huber values than do conifers. Dicot trees are intermediate in these values. The narrow but efficient stems of lianas are possible partly because lianas are not self-supporting; the mechanical requirements are reduced. Secondly, the wide and efficient vessels of lianas remain conductive for much longer than might be expected (two to several years, versus one year for similar wide vessels in dicots). Based upon experiments with glass capillary tubes and with living stem tissue, larger vessels are more susceptible to freezinginduced embolism than are small ones. However, in lianas, root pressures might serve to refill cavitated vessels on a daily or seasonal basis.
Journal of Experimental Botany, 1995
The vulnerability of xylem vessels to water stressinduced cavitation was studied by measuring hydraulic conductivity and ultrasound acoustic emissions [AEs) in Fagus sylvatica L. f. purpurea (Ait.) Schneid. and Populus balsamifera L.. The occurrence of xylem embolism in summer was investigated in relation to leaf water potential and stomatal conductance. Populus was extremely vulnerable to cavitation, losing functional vessels due to embolism at water potentials lower than-0.7 MPa. Fagus experienced embolism when water potential fell below-1.9 MPa. Midday water potentials often approached these threshold values. When evaporative demand increased rapidly on sunny days, water loss became limited by low stomatal conductance. Thus water potentials fell only slightly below the threshold values inducing cavitation. Despite the differences in vulnerability, both species tolerated a similar embolism rate of about 10% in the summer. There was no embolism reversal during prolonged periods of rain. AEs were predictive of loss in hydraulic conductivity, indicating that AEs were mainly confined to vessels. Finally, vessel length distribution, vessel diameter (tangential axis), vessel density, and vessel wall thickness had been determined for both species investigated. Populus had longer and wider vessels than Fagus, whereas vessel wall thickness was similar in both species.
The Relationship between Xylem Conduit Diameter and Cavitation Caused by Freezing
American Journal of Botany, 1999
The centrifuge method for measuring the resistance of xylem to cavitation by water stress was modified to also account for any additional cavitation that might occur from a freeze-thaw cycle. A strong correlation was found between cavitation by freezing and mean conduit diameter. On the one extreme, a tracheid-bearing conifer and diffuse-porous angiosperms with small-diameter vessels (mean diameter Ͻ30 m) showed no freezing-induced cavitation under modest water stress (xylem pressure ϭ Ϫ0.5 MPa), whereas species with larger diameter vessels (mean Ͼ40 m) were nearly completely cavitated under the same conditions. Species with intermediate mean diameters (30-40 m) showed partial cavitation by freezing. These results are consistent with a critical diameter of 44 m at or above which cavitation would occur by a freeze-thaw cycle at Ϫ0.5 MPa. As expected, vulnerability to cavitation by freezing was correlated with the hydraulic conductivity per stem transverse area. The results confirm and extend previous reports that small-diameter conduits are relatively resistant to cavitation by freezing. It appears that the centrifuge method, modified to include freeze-thaw cycles, may be useful in separating the interactive effects of xylem pressure and freezing on cavitation.
Plant physiology
Cavitation resistance is a key parameter to understand tree drought tolerance but little is known about the mechanisms of air entry into xylem conduits. For conifers three mechanisms have been proposed: (1) a rupture of pit margo microfibrils, (2) a displacement of the pit torus from its normal sealing position over the pit aperture, and (3) a rupture of an air-water menisci in a pore of the pit margo. In this article, we report experimental results on three coniferous species suggesting additional mechanisms. First, when xylem segments were injected with a fluid at a pressure sufficient to aspirate pit tori and well above the pressure for cavitation induction we failed to detect the increase in sample conductance that should have been caused by torus displacement from blocking the pit aperture or by membrane rupture. Second, by injecting xylem samples with different surfactant solutions, we found a linear relation between sample vulnerability to cavitation and fluid surface tension. This suggests that cavitation in conifers could also be provoked by the capillary failure of an air-water meniscus in coherence with the prediction of Young-Laplace's equation. Within the bordered pit membrane, the exact position of this capillary seeding is unknown. The possible Achilles' heel could be the seal between tori and pit walls or holes in the torus. The mechanism of water-stress-induced cavitation in conifers could then be relatively similar to the one currently proposed for angiosperms.
Effects of desiccation and freezing on vitality and field performance of broadleaved tree species
Annals of Forest Science, 2001
Seedlings of Acer pseudoplatanus L., Fraxinus ornus L. and Castanea sativa Miller., were exposed to desiccating conditions (15 °C, 50% RH, air movement 0.3 m s -1 , photosynthetic active radiation 350 µmol m -2 s -1 ) and freezing (-5°C, darkness). The effect of stress factors on seedling quality was assessed using root electrolyte leakage, water potential and moisture content of fine roots. After treatments, seedlings were outplanted in a field site. The effects of desiccation and freezing on planting stock quality and field performance varied and depended upon the length of exposure and species. Root electrolyte leakage values were significantly related to field performance rates of seedlings exposed to both stress factors. Root moisture content and root water potential were related to survival only in the case of desiccation treatment.