Detection of cavitation events upon freezing and thawing of water in stems using ultrasound techniques (original) (raw)
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
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.
Field measurements of xylem cavitation: are acoustic emissions useful?
Journal of Experimental Botany, 1996
Cavitation of water columns within the xylem is deleterious for plant water relations as it results in embolism, so reducing hydraulic conductivity. This cavitation can be detected as it is accompanied by the production of acoustic emissions, which can be detected urtrasonically and logged automatically over periods of days. The acoustic emission technique is useful to determine the threshold water potential at which damage to the water-conducting system of the plant is initiated. It can reveal which environmental variables are deleterious to the plant water relations, and which parts of the plant are most sensitive to cavitation. Species comparisons, and comparisons of the same species in different environments can be made, to obtain indications of drought tolerance. However, acoustic emissions have only a limited use in determining the proportion of embolism in a conducting stem, and other methods are needed to find the percentage reduction in hydraulic conductivity.
Plant, Cell and Environment, 1997
Water transport from the roots to leaves in chaparral shrubs of California occurs through xylem vessels and tracheids. The formation of gas bubbles in xylem can block water transport (gas embolism), leading to shoot dieback. Two environmental factors that cause gas embolism formation in xylem conduits are drought and freezing air temperatures. We compared the differential vulnerabilities of Rhus laurina and Ceanothus megacarpus, co-dominant shrub species in the coastal regions of the Santa Monica Mountains of southern California, to both water stress-induced and freezing-induced embolism of their xylem. Rhus laurina has relatively large xylem vessel diameters, a deep root system, and a large basal burl from which it vigorously resprouts after wildfire or freezing injury. In contrast, Ceanothus megacarpus has smalldiameter vessels, a shallow root system, no basal burl and is a non-sprouter after shoot removal by wildfire. We found that R. laurina became 50% embolized at a water stress of-3 MPa and 100% embolized by a freeze-tbaw cycle at all hydration levels. In contrast, C. megacarpus became 50% embolized at a water stress of-9 MPa and 100% embolized by freeze-tbaw events only at water potentials lower tban-3 MPa. Reducing tbaw rates from 0-8 °C min~^ to 0 08 °C min"^ (tbe normal tbaw rate measured in situ) bad no effect on embolism formation in R. laurina but significantly reduced embolism occurrence in well-bydrated C. megacarpus (embolism reduced from 74 to 35%). Tbese results were consistent witb tbe tbeory of gas bubble formation and dissolution in xylem sap. Tbey also agree witb field observations of differential sboot dieback in tbese two species after a natural freeze-tbaw event in tbe Santa Monica Mountains.
2007
Changes in hydraulic conductivity (K h) were measured monthly in stems of Laurus nobilis between July 2005 and June 2006 and in March and June 2006 in stems of Prunus laurocerasus and Phillyrea latifolia. Percent enhancement of K h (DK h) was recorded as KCl injected into stems compared with deionized water. Stems of L. nobilis perfused with increasing [KCl] saturated the hydraulic effect at 50 mM KCl, while P. laurocerasus and Ph. latifolia showed saturation at 17 and less than 5 mM KCl, respectively. Impressive seasonal changes in DK h were recorded in L. nobilis, from 1120% in February to 120% during the growth period. DK h was negatively correlated to minimum air temperatures and was highest during winter frost. Negative correlation also existed between DK h and conduit lengths as detected during transition of plants from activity to winter rest and from winter to spring. In the winter, the thermal effect was prevailing. High cavitation-induced K h loss coincided with high DK h. Similar but much smaller seasonal effects on DK h were recorded in the other two species where, however, also smaller seasonal changes in conduit lengths were recorded. We conclude that (1) the K 1-induced effect on K h was because of interference of the cation with pectins of intervessel pit membranes (increasingly crossed by the ionic solution in stems with shorter conduits); (2) winter frost might have an effect on DK h and (3) seasonal changes in DK h because of possible change in pectic composition may represent a mechanism to regulate water flows in planta.
Plant water relations and control of cell elongation at low water potentials
Journal of Plant Research, 1998
Recent developments in water status measurement techniques using the psychrometer, the pressure probe, the osmometer and pressure chamber are reviewed, and the process of cell elongation from the viewpoint of plant-water relations is discussed for plants subjected to various environmental stress conditions. Under water-deficient conditions, cell elongation of higher plants can be inhibited by interruption of water flow from the xylem to the surrounding elongating cells. The process of growth inhibition at low water potentials could be reversed by increasing the xylem water potential by means of pressure application in the root region, allowing water to flow from the xylem to the surrounding cells. This finding confirmed that a water potential field associated with growth process,i.e., the growth-induced water potential, is an important regulating factor for cell elongation other than metabolic factors. The concept of the growth-induced water potential was found to be applicable for growth retardation caused by cold stress, heat stress, nutrient deficiency and salinity stress conditions. In the present review, the fact that the cell elongation rate is primarily associated with how much water can be absorbed by elongating cells under water-deficiency, nutrient deficiency, salt stress, cold stress and heat stress conditions is suggested.
Annals of Forest Science, 2002
We studied the xylem hydraulic traits and anatomy of four diverse Mediterranean conifers to determine how these species protect themselves against catastrophic xylem failure. Cedrus atlantica, Cupressus sempervirens, Pinus nigra and P. halepensis seedlings were grown for two years in pots in a greenhouse under well-watered conditions. Measurements were conducted in April and September. The vulnerability to cavitation was lower in April in the two pines and cedar whereas the conductivity was lower in the two pines and cypress. There were also large species differences in vulnerability to cavitation in September: loss of 50% conductivity occurred at-2.8 MPa in P. nigra,-3.8 MPa in C. atlantica,-4.8 MPa in C. sempervirens and-4.9 MPa in P. halepensis. Leaf specific hydraulic conductivity was much higher in Cupressus sempervirens and P. nigra than in Cedrus atlantica and P. halepensis. No trade-off between xylem safety (low vulnerability) and efficiency (high hydraulic conductivity) was found among the four species. Specific conductivity was directly related to "hydraulic mean" tracheid lumen diameter, while xylem vulnerability appeared to be independent of tracheid size. xylem embolism / hydraulic conductivity /xylem anatomy / Mediterranean conifers Résumé-Efficience hydraulique et vulnérabilité de plantules de quatre espèces de conifères méditerranéens (Cedrus atlantica, Cupressus sempervirens, Pinus halepensis et Pinus nigra). Nous avons étudié les caractéristiques hydrauliques et l'anatomie du xylème de quatre espèces de conifères méditerranéens afin de déterminer comment ces espèces se protègent contre un dysfonctionnement catastrophique du xylème. Des plants de Cedrus atlantica, Cupressus sempervirens, Pinus halepensis et P. nigra ont été cultivés en serre pendant deux ans en conditions d'alimentation en eau non limitante. Les mesures ont été effectuées en avril et septembre. La vulnérabilité à la cavitation a été plus faible en avril chez les deux pins et le cèdre tandis que la conductivité hydraulique a été plus faible chez les deux pins et le cyprès. D'importantes différences de vulnérabilité à la cavitation ont également été observées entre les espèces en septembre : la perte de 50 % de conductivité est intervenue à-2,8 MPa chez P. nigra,-3,8 MPa chez C. atlantica,-4,8 MPa chez C. sempervirens et-4,9 MPa chez P. halepensis. La conductivité spécifique foliaire a été plus élevée chez C. sempervirens et P. nigra que chez C. atlantica et P. halepensis. Aucun compromis n'a été mis en évidence entre la protection du système conducteur (faible vulnérabilité à la cavitation) et l'efficacité de la circulation de la sève (forte conductivité hydraulique) entre les 4 espèces. La conductivité hydraulique spécifique est positivement corrélée avec le diamètre « hydraulique moyen » des lumières des trachéides alors que la vulnérabilité du xylème semble être indépendante de la taille des trachéides. embolie / conductivité hydraulique / anatomie du xylème / conifères méditerranéens
Spatiotemporal Coupling of Vessel Cavitation and Discharge of Stored Xylem Water in a Tree Sapling
Plant Physiology, 2019
Water discharge from stem internal storage compartments is thought to minimize the risk of vessel cavitation. Based on this concept, one would expect that water storage compartments involved in the buffering of xylem tensions empty before the onset of vessel cavitation under drought stress, and potentially refill after soil saturation. However, scant in vivo data exist that elucidate this localized spatiotemporal coupling. In this study on intact saplings of American chestnut (Castanea dentata), x-ray computed microtomography (microCT) showed that the xylem matrix surrounding vessels releases stored water and becomes air-filled either concurrent to or after vessel cavitation under progressive drought stress. Among annual growth rings, the xylem matrix of the current year remained largely water-filled even under severe drought stress. In comparison, microtomography images collected on excised stems showed that applied pressures of much greater than 0 MPa were required to induce water...