Xylem sap composition of beech (Fagus sylvatica L.) trees: seasonal changes in the axial distribution of sulfur compounds

During different phases of the annual growth cycle, xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by the water displacement technique. Irrespective of the height of the trunk, both sulfate and reduced sulfur compounds were detected in the xylem sap throughout the year. Sulfate was the predominant sulfur compound in all samples analyzed. Its concentration in the xylem sap varied between 10 and 350 micro mol l(-1), with highest concentrations in April, shortly before bud break. In contrast to other tree species, cysteine and not glutathione was the predominant thiol transported in the xylem sap of beech trees. The cysteine concentration ranged between 0.1 and 1 micro mol l(-1). As observed for sulfate, maximum cysteine concentrations were found in April. Apparently, both sulfate and cysteine transport contribute to the sulfur supply of the developing leaves. Seasonal changes in the axial distribution of cysteine and sulfate differed, indicating differences in the source-sink relations of these sulfur compounds. High, but uniform, xylem sap sulfate concentrations in April may originate from balanced sulfate uptake by the roots, whereas high cysteine concentrations in April, increasing with increasing height of the trunk, may originate in part from protein breakdown in the trunk. Reversal of the axial distribution of xylem sap cysteine in late summer-early fall to higher concentrations in the lower part of the trunk than in the upper part of the trunk suggests that the upper part of the trunk becomes a sink for cysteine as a result of the synthesis of storage proteins at this time of the year.     

Drought tolerance,xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of canopy trees of three temperate deciduous angiosperms

Patterns of water relations, xylem sap abscisic acid concentration ([ABA]) and stomatal aperture were characterized and compared in drought-sensitive black walnut (Juglans nigra L.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.) trees co-occurring in a second-growth forest in Missouri, USA. There were strong correlations among reduction in predawn leaf water potential, increased xylem sap [ABA] and stomatal closure in all species. Stomatal conductance was more closely correlated with xylem sap ABA concentration than with ABA flux or xylem sap pH and cation concentrations. In isohydric black walnut, increased concentrations of ABA in the xylem sap appeared to be primarily of root origin, causing stomatal closure in response to soil drying. In anisohydric sugar maple and white oak, however, there were reductions in midday leaf water potential associated with stomatal closure, making it uncertain whether drought-induced xylem sap ABA was of leaf or root origin. The role of root-originated xylem sap ABA in these species as a signal to the shoot of the water status of the roots is, therefore, less certain.     

Role of organic acids in aluminum accumulation and plant growth in Melastoma malabathricum

Melastoma malabathricum L. (melastoma) is an Al-accumulating woody plant that grows in tropical Southeast Asia in acid soils with high aluminum (Al) concentrations and low nutrient concentrations. Because oxalate serves as a ligand for Al accumulation in melastoma leaves and citrate is the ligand associated with Al translocation from roots to shoots, we investigated the role of organic acids in the adaptation of melastoma to growth on these soils. Phosphorus starvation increased oxalate concentration in the rhizosphere, enabling melastoma to solubilize insoluble aluminum phosphate in the rhizosphere. Increased availability of P and Al in the rhizosphere enhanced growth. In the xylem sap, the concentration of citrate increased with increasing Al concentration. In contrast, the concentrations of malate, succinate and alpha-ketoglutarate in the xylem sap decreased with increasing Al concentration, suggesting that tricarboxylic acid cycle enzymes were affected by Al treatment.     

Drought tolerance,xylem sap abscisic acid and stomatal conductance during soil drying: a comparison of young plants of four temperate deciduous angiosperms

Patterns of water relations, xylem sap abscisic acid (ABA) concentration ([ABA]) and stomatal aperture were compared in drought-sensitive black walnut (Juglans nigra L.) and black willow (Salix nigra Marsh.), less drought-sensitive sugar maple (Acer saccharum Marsh.) and drought-tolerant white oak (Quercus alba L.). Strong correlations among reduction in predawn water potential, increase in xylem sap [ABA] and stomatal closure were observed in all species. Stomatal response was more highly correlated with xylem [ABA] than with ABA flux. Xylem sap pH and ion concentrations appeared not to play a major role in the stomatal response of these species. Stomata were more sensitive to relative changes in [ABA] in drought-sensitive black walnut and black willow than in sugar maple and white oak. In the early stages of drought, increased [ABA] in the xylem sap of black walnut and black willow was probably of root origin and provided a signal to the shoot of the water status of the roots. In sugar maple and white oak, leaf water potential declined with the onset of stomatal closure, so that stomatal closure also may have occurred in response to the change in leaf water potential.     

Stomatal and leaf growth responses to partial drying of root tips in willow

Root tips of intact willow (Salix dasyclados Wimm., Clone 81-090) plants were partially dried by exposure to ambient greenhouse air and then kept in water-vapor-saturated air for up to 3 days. The drying treatment increased abscisic acid (ABA) concentrations in both the root tips subjected to drying and in the xylem sap, while it reduced leaf stomatal conductance and leaf extension rate. Despite the decrease in stomatal conductance, leaf water potentials were unaffected by the root drying treatment, indicating that the treatment reduced hydraulic conductivity between roots and foliage. After roots subjected to drying were returned to a nutrient solution or excised, ABA concentrations in the remaining roots and in the xylem sap, stomatal conductance of mature leaves and extension rate of unfolding leaves all returned to values observed in control plants. The 4-fold increase in xylem sap ABA concentration following the root drying treatment was not solely the result of reduced sap flow, and thus may be considered a potential cause, not merely a consequence, of the observed reduction in stomatal conductance.     

Soluble N compound profiles and concentrations in European beech (Fagus sylvatica L.) are influenced by local climate and thinning

We assessed seasonal changes of total soluble nonprotein nitrogen compounds (TSNN) in adult European beech trees (Fagus sylvatica, L.) growing under different local climate during the growing season immediately following a thinning treatment and 3 years later. In both years, samples of leaves, xylem sap and phloem exudates from beech trees growing in thinned and unthinned (control) stands on a dry, warm SW exposed and a cooler, moist NE exposed site were collected in May, July and September. In May of both years, asparagine (Asn) and glutamine (Gln) were most abundant in leaves and xylem, respectively, whereas arginine (Arg) dominated in the phloem. In July, TSNN concentrations decreased in all tissues and sites, but differences in water availability between aspects were reflected in TSNN concentrations. In September, differences in the increase of Arg concentration in the phloem were related to differences in the onset of senescence between treatments. Thinning treatment increased amino compound concentrations of beech tissues in July on both aspects, particularly at the NE thinned site. It is supposed that, the N balance of adult beech is favoured by both, the thinning treatments as well as the cool-moist climate prevailing at the NE aspect.     

Contrasting distribution and seasonal dynamics of carbohydrate reserves in stem wood of adult ring-porous sessile oak and diffuse-porous beech trees

We tested the hypothesis that broad-leaved forest species with contrasting wood anatomy and hydraulic system (ring-porous versus diffuse-porous) also differ in distribution and seasonal dynamics of carbohydrate reserves in stem wood. Total nonstructural carbohydrate (TNC) reserves (starch and sugars) were measured enzymatically in the 10 youngest stem xylem rings of adult oak (Quercus petraea (Matt.) Liebl.) and beech (Fagus sylvatica L.) trees during an annual cycle. Radial distribution of carbohydrates was investigated according to ring age. On all dates, oak trees had twofold higher TNC concentration than beech trees (41 versus 23 mg g(DM)(-1)), with starch accounting for the high TNC concentration in oak. Seasonal dynamics of TNC concentration were significantly (P < 0.05) more pronounced in oak (20-64 mg TNC g(DM)(-1)) than in beech (17-34 mg TNC g(DM)(-1)). A marked decrease in TNC concentration was observed in oak trees during bud burst and early wood growth, whereas seasonal fluctuations in TNC concentrations in beech trees were small. The radial distribution of TNC based on ring age differed between species: TNC was restricted to the sapwood rings in oak, whereas in beech, it was distributed throughout the wood from the outermost sapwood ring to the pith. Although the high TNC concentrations in the outermost rings accounted for most of the observed seasonal pattern, all of the 10 youngest xylem rings analyzed participated in the seasonal dynamics of TNC in beech trees. The innermost sapwood rings of oak trees had low TNC concentrations. Stem growth and accumulation of carbon reserves occurred concomitantly during the first part of the season, when there was no soil water deficit. When soil water content was depleted, stem growth ceased in both species, whereas TNC accumulation was negligibly affected and continued until leaf fall. The contrasting dynamics and distribution of carbohydrate reserves in oak and beech are discussed with reference to differences in phenology, early spring growth and hydraulic properties between ring-porous trees and diffuse-porous trees.     

Seasonal changes in the axial distribution of peroxidase activity in the xylem sap of beech (Fagus sylvatica L.) trees

Xylem sap was collected from trunk segments of adult beech (Fagus sylvatica L.) trees by water displacement. Peroxidase activity was analyzed in xylem saps collected in different phases of the yearly growth cycle and from different heights up the trunks (up to 14 m). The xylem saps contained two major peroxidase isozymes with acidic isoelectric points of 4.1 and 4.6, respectively. Mean peroxidase activity was low during the emergence of the new leaves and high in summer and in winter. In the cold season, peroxidase activity decreased from the stem base to the top, whereas significant gradients were not observed during the vegetative period.     

Radial distribution of sap flux density in trunks of a mature beech stand

In a mature beech stand located in north-eastern Germany, xylem sap flux measurements were continuously performed during the 2002–2004 growing seasons. Ten representative trunks were studied using heated thermal dissipation probes. The measurements aimed at identifying principles governing radial profiles of xylem flux in beech trunks. The measurements were taken up to a trunk depth of 132 mm. The sap flow density in the pericambial xylem was found to vary among trees of different diameters, but was not considerably smaller in suppressed trees. A model for the radial distribution of sap flux density was formulated relating trunk radius and sap flow density. The model takes into account different trunk diameter. About 90% of the sap flux was found to occur in the outer two fifths of the trunk. Using this model, an adequate estimate of transpiration can be achieved at tree and stand level, even when the sap flux measurements are restricted to the outer trunk sectors.     

Element concentrations in the xylem sap of Picea abies (L.) Karst. seedlings extracted by various methods under different environmental conditions

We used a Scholander pressure chamber to assess the effects of various extraction methods under different environmental conditions on element concentrations in xylem sap of 3-year-old Picea abies (L.) Karst. seedlings. Sap from excised shoots contained higher element concentrations when extracted at low than at high over-pressures. When comparing plants differing in water status, we found that a high extraction over-pressure introduced a systematic error into the data. For example, in well-watered non-transpiring plants relative to unwatered transpiring plants, potassium concentrations were 70% higher in sap extracted at 0.1 MPa over-pressure, but only 10% higher in sap extracted at 1.0 MPa over-pressure. Moreover, treatment effects depended on the time of day when the sap was extracted. Increased water flux in transpiring plants relative to non-transpiring plants resulted in reduced xylem sap element concentrations when samples were collected after 9 h of transpiration, but not after 4 to 6 h of transpiration. Drought had little effect on xylem sap element concentrations, indicating that rates of element release into xylem conduits, element depletion by growing tissues, and water flow maintained a balance that may prevent nutrient stress during short-term drought.     

Characterization of nitrogenous solutes in tissues and xylem sap of Leucaena leucocephala

Amino acid profiles of leaf, stem, and root tissues from nodulated and nonnodulated Leucaena leucocephala (Lam.) de Wit plants were determined by gas chromatography-mass spectrometry. High concentrations of mimosine and several other potentially toxic nonprotein amino acids, including pipecolic acid and two isomers of hydroxypipecolic acid, were identified in the tissues. Five metabolites remain unidentified. Of the foliar free amino acid nitrogen, 57-66% was associated with the potentially toxic amino acids. Major constituents in the leaf tissues of nonnodulated plants were mimosine and hydroxypipecolic acid (isomer 1). Mimosine was recovered in both the neutral plus basic and acidic amino acid fractions. Major differences between amino acid profiles of nodulated and nonnodulated roots were the low percentages of asparagine + aspartate (3.6% of the total pool compared to 33% in nodulated plants) and pipecolic acid in nonnodulated roots (1% of the total compared to 12.5% in nodulated plants). A novel plant betaine (dihydroxypipecolic acid betaine) was identified by fast-atom-bombardment mass spectrometry in leaf tissues, albeit at relatively low concentrations (< 1 micro mol per gram fresh weight). Analyses of the xylem sap collected from nodulated plants confirmed that Leucaena is an asparagine transporter, as suggested by the high concentrations of asparagine and the low concentrations of ureides in its root nodules. Amino acid profiles of xylem sap from nonnodulated plants showed extremely low concentrations of asparagine + aspartate (0.12 micro mol ml(-1)), whereas asparagine + aspartate was the major constituent (4.38 micro mol ml(-1)) in the xylem sap of nodulated plants. Two nonprotein amino acids, pipecolic acid and hydroxypipecolic acid, were major constituents of the xylem sap of nodulated and nonnodulated plants, respectively. Three unidentified compounds detected in xylem sap samples from both nodulated and nonnodulated plants did not correspond with any of the peaks characterized from tissue samples.     

Spatial and seasonal variation in amino compounds in the xylem sap of a mistletoe (Viscum album) and its hosts (Populus spp. and Abies alba)

In a field study, the composition and concentrations of amino compounds in the xylem sap of the mistletoe, Viscum album L., and in the xylem sap of two host species, an evergreen conifer (Abies alba Mill.) and a deciduous broad-leaved tree (Populus x euramericana), were analyzed. The xylem sap of both hosts and mistletoe contained large, but similar amounts of total organic nitrogen in low molecular weight amino compounds (TONLW). Nevertheless, individual amino compounds accumulated in the xylem sap of mistletoe relative to the host xylem sap, indicating selective uptake. In the xylem sap of Populus, major amino compounds (asparagine (Asn) and glutamine (Gln)) and the bulk parameters, TONLW and proteinogenic amino acids, showed significant seasonal variation. In Abies and in mistletoe on either host, variation of amino compounds in xylem sap was largely explained by inter-annual differences, not by seasonal variation. In both hosts, TONLW in the xylem sap was dominated by Gln. There was a steady decrease in relative abundance of Gln from the host xylem sap to the mistletoe xylem sap and to the stems and leaves of mistletoe. Simultaneously, the abundance of arginine (Arg) increased. Arginine was the predominant amino compound in the stems and leaves of mistletoe, occurring at concentrations previously observed only in leaves of trees exposed to excess nitrogen. We conclude that Gln (2 mol N mol(-1)) delivered by the host xylem sap is converted, in mistletoe, to Arg (4 mol N mol(-1)) and that the organic carbon liberated from Gln contributes significantly to the parasite's heterotrophic carbon gain. Statistical analyses of the data support this conclusion. Accumulation of Arg in mistletoe is an indication of excess N supply as a result of the uptake of amino compounds from the host xylem sap and a lack of phloem uploading.     

Organic and inorganic sulfur transport in the xylem sap and the sulfur budget of Picea abies trees

Temporal changes in inorganic and organic sulfur compounds (sulfate, glutathione, cysteine, methionine) were analyzed in xylem sap of 40-year-old Norway spruce (Picea abies (L.) Karst.) trees growing on acidic soils at a healthy and a declining stand in the Fichtelgebirge (North Bavaria, Germany). Studies were carried out (1) to quantify glutathione (GSH) transport in the xylem of spruce, (2) to study the significance of reduced sulfur versus sulfate (SO(4) (2-)) transport in the xylem, and (3) to compare total sulfur (S) transport in the xylem with the amount of foliar uptake of SO(2) in an air-polluted environment. Glutathione was the main reduced S compound in the xylem ranging in concentration from 0.5 to 5 &mgr;mol l(-1). Concentrations of inorganic SO(4) (2-) in the xylem sap were up to 50 times higher than those of GSH ranging from 60 to 230 &mgr;mol l(-1). During the growing season, concentrations of all S compounds in the xylem were highest in May (up to 246 &mgr;mol l(-1)) and decreased during summer and fall (up to 21 &mgr;mol l(-1)). On average, SO(4) (2-) concentrations in xylem sap were 30% higher at the declining site compared with the healthy site. Diurnal changes in organic S compounds were significant for GSH and cysteine with high concentrations during the night and low concentrations during the day. Diurnal changes in inorganic concentrations were not significant. Xylem sap concentrations of SO(4) (2-) and cysteine were twice as high and GSH concentrations were tenfold higher in surface roots than in branches. At both sites, transport of organic S was low (up to 3% of total S) compared to transport of SO(4) (2-). Annual transport of total S in the xylem (SO(4) (2-) was the main component) ranged from 60 to 197 mmol tree(-1) year(-1) at the healthy site and from 123 to 239 mmol tree(-1) year(-1) at the declining site. Although gaseous uptake of SO(2) was estimated to be similar at both sites (38 mmol tree(-1) year(-1); Horn et al. 1989), the ratio between annual gaseous uptake of SO(2) and transport of S in the xylem was 1:4 and 1:5 at the healthy and declining sites, respectively.     

Winter stem xylem pressure in walnut trees: effects of carbohydrates, cooling and freezing

Pressure transducers were attached to twigs of orchard trees and potted trees of walnut (Juglans regia L.) to measure winter stem xylem pressures. Experimental potted trees were partially defoliated in the late summer and early autumn to lower the amount of stored carbohydrates. Potted trees were placed in cooling chambers and subjected to various temperature regimes, including freeze-thaw cycles. Xylem pressures were inversely proportional to the previous 48-h air temperature, but positively correlated with the osmolarity of the xylem sap. Defoliated trees had significantly lower concentrations of stored carbohydrates and significantly lower xylem sap osmolarities than controls. Plants kept at 1.5 degrees C developed xylem pressures up to 40 kPa, just 7% of the theoretical osmotic pressure of the xylem sap. However, exposure to low, nonfreezing temperatures followed by freeze-thaw cycles resulted in pressures over 210 kPa, which was 39% of the theoretical osmotic pressure. A simple osmotic model could account for the modest positive winter pressures at low, nonfreezing temperatures, but not for the synergistic effects of freeze-thaw cycles.     

Influences of environmental factors on the radial profile of sap flux density in Fagus crenata growing at different elevations in the Naeba Mountains, Japan

Sap flux density was measured continuously during the 1999 and 2000 growing seasons by the heat dissipation method in natural Fagus crenata Blume (Japanese beech) forests growing between 550 and 1600 m on the northern slope of the Kagura Peak of the Naeba Mountains, Japan. Sap flux density decreased radially toward the inner xylem and the decrease was best expressed in relation to the number of annual rings from the cambium, or in relation to the relative depth between the cambium and the trunk center, rather than as a function of absolute depth. The relative influences of radiation, vapor pressure deficit and soil water on sap flux density during the growing season were similar for the outer and inner xylem, and at all sites. Measurements of soil water content and water potential at a depth of 0.25 m demonstrated that sap flux density responded similarly and sensitively to water potential changes in this soil layer, despite large differences in rooting depth at different elevations, localizing one important control point in the functioning of this forest ecosystem. Identification of the relative influences of radiation, vapor pressure deficit and drying of the upper soil layer on sap flux density provides a framework for in-depth analysis of the control of transpiration in Japanese beech forests. In addition, the finding that the same general controls are operating on sap flux density despite climate gradients and large differences in overall forest stand structure will enhance understanding of water use by forests along elevation gradients.     

Stomatal conductance, growth and root signaling in young oak seedlings subjected to partial soil drying

Leaf conductance, water relations, growth, and abscisic acid (ABA) concentrations in xylem sap, root apices and leaves were assessed in oak seedlings (Quercus robur L.) grown with a root system divided between two compartments and subjected to one of four treatments: (a) well watered, WW; (b) half of root system exposed to soil drying and half kept well watered, WD; (c) whole root system exposed to drought, DD; and (d) half of root system severed, RE. Sharp decreases in plant stomatal conductance, leaf water potential, hydraulic conductance and leaf growth were observed during DD treatment. No significant differences in plant leaf water potential and stomatal conductance were detected between the WW and WD treatments. Nevertheless, the WD treatment resulted in inhibition of leaf expansion and stimulation of root elongation only in the well-watered compartment. Abscisic acid concentrations did not change in leaves, root tips, or xylem sap of WD- compared to WW-treated plants. Increased concentrations of ABA were observed in xylem sap from DD-treated plant roots, but the total flux of ABA to shoots was reduced compared to that in WW-treated plants, because of decreases in transpiration flux. Similar plant responses to the WD and RE treatments indicate that the responses observed in the WD-treated plants were probably not triggered by a positive signal originating from drying roots.     

Biochemical responses to iron deficiency in kiwifruit (Actinidia deliciosa)

A comparative study of two kiwifruit genotypes (Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa) with different tolerance to iron (Fe) deficiency was conducted to identify biochemical features associated with tolerance to Fe deficiency. After 14 days of growth in hydroponic culture under Fe-deficient and Fe-sufficient conditions, leaf chlorophyll concentration, activities of ferric chelate reductase (FCR), phosphoenolpyruvate carboxylase (PEPC) and citrate synthase in root extracts, concentrations of organic acids in roots, leaves and xylem sap, and xylem sap pH were measured. In response to Fe deficiency, the tolerant genotype D1 showed: (i) higher FCR activity associated with a longer lasting induction of FCR; (ii) higher PEPC activity; (iii) higher concentrations of citric acid in roots; and (iv) lower xylem sap pH compared with the susceptible genotype Hayward. These findings imply that induction of FCR and PEPC activities in roots in response to Fe deficiency are important physiological adaptations enabling Fe-efficient kiwifruit plants to tolerate Fe deficiency.     

Environmental and physiological controls over oxygen and carbon isotope composition of Tasmanian blue gum, Eucalyptus globulus

We measured oxygen isotope ratios (delta18O) of xylem sap, phloem sap, leaves, wood and bark of Eucalyptus globulus Labill. growing in southwestern Australia. Carbon isotope ratios (delta13C) were measured in the dry matter of phloem sap, leaves and wood. Results were used to test several aspects of a mechanistic model of 18O enrichment and provided insights into post-photosynthetic variations in dry matter delta13C. Xylem water delta18O varied little within the tree crown, whereas variation at the landscape-level was more pronounced, with plantations near the coast being enriched by up to 3 per thousand compared with plantations less than 100 km inland. Phloem water was significantly enriched in 18O compared with xylem water in two of three sampling campaigns; mean enrichments were 0.5 and 0.8 per thousand. Phloem sap sugars exported from E. globulus leaves closely reflected observed leaf water enrichment when diurnal variation in photosynthesis was taken into account. Photosynthetic rates were higher in the morning than in the afternoon, whereas leaf water 18O enrichment increased to maximum values in the afternoon. A non-steady-state model of leaf water 18O enrichment accurately predicted observed values through a full diel cycle. Mean estimates of the proportion of organic oxygen effectively exchanging with xylem water during cellulose synthesis were close to 0.40 for both leaves and wood. Carbon isotope ratios of nascent xylem tissues did not differ from those of phloem sap sugars collected concurrently, whereas nascent leaf tissues were depleted in 13C by 2 per thousand compared with phloem sap sugars, suggesting that, in E. globulus, 13C enrichment of sink tissues compared with source leaves does not result from an enriching process within the sink tissue.     

Winter variation in xylem sap pH of walnut trees: involvement of plasma membrane H+-ATPase of vessel-associated cells

We studied seasonal variation in xylem sap pH of Juglans regia L. Our main objectives were to (1) test the effect of temperature on seasonal changes in xylem sap pH and (2) study the involvement of plasma membrane H+-ATPase of vessel-associated cells in the control of sap pH. For this purpose, orchard-grown trees were compared with trees grown in a heated (> or = 15 degrees C) greenhouse. During autumn, sap pH was not directly influenced by temperature. A seasonal change in H+-ATPase activity resulting from seasonal variation in the amount of protein was measured in orchard-grown trees, whereas no significant seasonal changes were recorded in greenhouse-grown trees. Our data suggest that H+-ATPase does not regulate xylem sap pH directly by donating protons to the xylem, but by facilitating secondary active H+/sugar transport, among other mechanisms.     

Root produced DHZR-, ZR- and IPA-like cytokinins in xylem sap in relation to coppice shoot initiation and growth in cloned trees of Betula pubescens

Six-year-old cloned Betula pubescens Ehrh. trees, grown outdoors at 65 degrees 01' N, were cut on six dates during the growing season to study coppice shoot development in relation to root-produced cytokinin-like compounds. Bleeding sap was collected over timed intervals for two days after cutting, and endogenous cytokinin-like compounds were measured by ELISA assay in HPLC-purified fractions of xylem sap. Initiation and development of coppice shoots on the clonally propagated plants were comparable to those in seedlings. Coppice shoot initiation was affected by the time of cutting, diminishing significantly after June. Of the cytokinin-like compounds detected in the xylem sap, zeatin riboside-like (ZR) compounds were present in the highest concentrations, and the concentrations of dihydrozeatin riboside-like (DHZR) and isopentenyladenoside-like (IPA) compounds were approximately one third and one eighth of the ZR concentrations, respectively. The concentration of cytokinin-like compounds was positively correlated with xylem sap flow rate. The export of cytokinin-like compounds, especially DHZR- and ZR-types, was positively correlated with the initiation and elongation rate of coppice shoots, the number of lateral branches, and the radial growth of the more slowly growing coppice shoots. The export of cytokinin-like compounds collected immediately after cutting may represent the basal value for each tree. This value is probably affected by the size and activity of the root system and may be a relevant estimate for predicting the success of coppicing.