Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Three different methods for measuring xylem embolism due towater cavitation were compared—the acoustic method, thehydraulic method and the anatomical method. Young plants ofCeratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300kHz) acoustic emissions (AE) from 1-year-old twigs (acousticmethod). Xylem embolism was detected by measuring the loss ofhydraulic conductivity of twigs of the same age (hydraulic method).The blockage of single xylem conduits was detected by perfusingSafranin into the xylem of 1-year-old twigs of stressed plantsand measuring the number and the diameters of non-conductingxylem conduits, under the microscope (anatomical method). It was noted that: (a) the number of AE and the loss of conductivityincreased with the water stress applied; (b) a linear relationseemed to exist between the number of AE and the loss of conductivity,suggesting that the AE counted could be only (or mainly) producedin the xylem conduits; (c) the vulnerability of the xylem conduitsto embolism was a direct function of their diameter; and (d)the measured loss of conductivity was of the same order of magnitudeas the theoretical one. The three methods gave fairly similar results. Nonetheless,they are not alternative to one another in that: (a) the acousticmethod allows continuous recordings to be made but does notprovide information about the actual damage suffered by plants;(b) the hydraulic method is very informative but destructive;and (c) the anatomical method is very useful both in phytogcographicaland in genetic improvement studies. Ceratonia siliqua L., Carob tree, water stress, xylem embolism, acoustic method, hydraulic method, anatomical method     

Different Aspects of Cavitation Resistance in Ceratonia siliqua, a Drought-Avoiding Mediterranean Tree

Potted plants of Ceratonia siliqua L., growing in a greenhouse,were used to detect xylem cavitation (in terms of ultrasoundacoustic emissions AE) in internodes and node-to-petiole (N-P)junctions, after different periods of drought (9, 16 and 23d). Diurnal AE were only 100 in internodes of watered (W) plantsbut 320, 1250 and 2460 in 9-, 16- and 23-d stressed ones. InN-P junctions, AE were only 15 to 20% with respect to internodes. Stem perfusion with dye allowed measurement of the percentageof xylem conduit transverse area blocked by cavitation. Thiswas 2% in internodes of W-plants and 5.2, 13.8 and 40.4% inthose of 9-, 16- and 23-d stressed ones. In N-P junctions, 18.5%of the xylem conduit transverse area was blocked in the 23-dstressed plants only. The major resistance to cavitation exhibitedby the N-P junctions is interpreted in terms of their greaternumber of narrow xylem conduits. The percentage of blocked xylemconduits within a range of diameters showed that the narrowera xylem conduit, the less likely it was that cavitation wouldoccur. After rewatering, the release of the xylem blockage causedby cavitation occurred within 2 h. Our data suggest that C.siliqua can be considered to be a cavitation avoider, especiallyin its stem-to-leaf transition zones. Ceratonia siliqua L., Carob tree, cavitation avoidance, xylem architecture, ultrasonic acoustic emissions     

Three Different Methods for Measuring Xylem Cavitation and Embolism: A Comparison

Three different methods for measuring xylem embolism due towater cavitation were compared—the acoustic method, thehydraulic method and the anatomical method. Young plants ofCeratonia siliqua L. were water stressed for 9, 16 and 23 d. Xylem cavitation was detected by counting ultrasound (100–300kHz) acoustic emissions (AE) from 1-year-old twigs (acousticmethod). Xylem embolism was detected by measuring the loss ofhydraulic conductivity of twigs of the same age (hydraulic method).The blockage of single xylem conduits was detected by perfusingSafranin into the xylem of 1-year-old twigs of stressed plantsand measuring the number and the diameters of non-conductingxylem conduits, under the microscope (anatomical method). It was noted that: (a) the number of AE and the loss of conductivityincreased with the water stress applied; (b) a linear relationseemed to exist between the number of AE and the loss of conductivity,suggesting that the AE counted could be only (or mainly) producedin the xylem conduits; (c) the vulnerability of the xylem conduitsto embolism was a direct function of their diameter; and (d)the measured loss of conductivity was of the same order of magnitudeas the theoretical one. The three methods gave fairly similar results. Nonetheless,they are not alternative to one another in that: (a) the acousticmethod allows continuous recordings to be made but does notprovide information about the actual damage suffered by plants;(b) the hydraulic method is very informative but destructive;and (c) the anatomical method is very useful both in phytogeographicaland in genetic improvement studies. Ceratonia siliqua L, Carob tree, water stress, xylem embolism, acoustic method, hydraulic method, anatomical method     

Energy requirement for foliage formation is not constant along canopy light gradients in temperate deciduous trees

Foliage construction cost (glucose requirement for formation of a unit foliar biomass, G , kg glu kg⁻¹), chemical composition and morphology were examined along a light gradient across the canopies in five deciduous species, which ranked according to increasing shade-tolerance as Populus tremula < Fraxinus excelsior < Tilia cordata = Corylus avellana < Fagus sylvatica . Light conditions in the canopy were estimated by a hemispheric photographic technique, allowing ranking of sample locations according to long-term light input incident to the sampled leaves (relative irradiance). G and foliage carbon concentration increased with increasing relative irradiance in F. excelsior , T. cordata and C. avellana , but wereindependent of irradiance in F. sylvatica and P. tremula . However, if G of non-structural-carbohydrate-free dry mass was considered, it also increased with increasing relative irradiance in P. tremula . A positive correlation between the concentration of carbon-rich lignin and irradiance, probably a result of the acclimation to greater water stress at higher light, was the major reason for the light-dependence of G . Lignin concentrations were highest in more shade-tolerant species, resulting in greatest carbon concentrations in these species. Since carbon concentration and G are directly linked, the leaves of shade-tolerant species were also more expensive to construct. As the result of these effects, G increased faster with increasing leaf dry mass per area which was mainly determined by relative irradiance, in shade-tolerators. Given that shade-tolerant species had lower leaf dry mass per area at common irradiance and that this saturated at lower relative irradiance than leaf dry mass per area in the intolerant species, it was concluded that enhanced energy requirements for foliage construction might constrain species morphological plasticity and the upper limit of leaf dry mass per area attainable at high light.     

Drought Avoidance Strategy in Ceratonia siliqua L., a Mesomorphic-leaved Tree in the Xeric Mediterranean Area

We report measurements of diurnal changes in leaf relative watercontent (RWC), water potential (